Search Results: "cd"

28 April 2024

Evgeni Golov: Running Ansible Molecule tests in parallel

Or "How I've halved the execution time of our tests by removing ten lines". Catchy, huh? Also not exactly true, but quite close. Enjoy! Molecule?! "Molecule project is designed to aid in the development and testing of Ansible roles." No idea about the development part (I have vim and mkdir), but it's really good for integration testing. You can write different test scenarios where you define an environment (usually a container), a playbook for the execution and a playbook for verification. (And a lot more, but that's quite unimportant for now, so go read the docs if you want more details.) If you ever used Beaker for Puppet integration testing, you'll feel right at home (once you've thrown away Ruby and DSLs and embraced YAML for everything). I'd like to point out one thing, before we continue. Have another look at the quote above. "Molecule project is designed to aid in the development and testing of Ansible roles." That's right. The project was started in 2015 and was always about roles. There is nothing wrong about that, but given the Ansible world has moved on to collections (which can contain roles), you start facing challenges. Challenges using Ansible Molecule in the Collections world The biggest challenge didn't change since the last time I looked at the topic in 2020: running tests for multiple roles in a single repository ("monorepo") is tedious. Well, guess what a collection is? Yepp, a repository with multiple roles in it. It did get a bit better though. There is pytest-ansible now, which has integration for Molecule. This allows the execution of Molecule and even provides reasonable logging with something as short as:
% pytest --molecule roles/
That's much better than the shell script I used in 2020! However, being able to execute tests is one thing. Being able to execute them fast is another one. Given Molecule was initially designed with single roles in mind, it has switches to run all scenarios of a role (--all), but it has no way to run these in parallel. That's fine if you have one or two scenarios in your role repository. But what if you have 10 in your collection? "No way?!" you say after quickly running molecule test --help, "But there is "
% molecule test --help
Usage: molecule test [OPTIONS] [ANSIBLE_ARGS]...
 
  --parallel / --no-parallel      Enable or disable parallel mode. Default is disabled.
 
Yeah, that switch exists, but it only tells Molecule to place things in separate folders, you still need to parallelize yourself with GNU parallel or pytest. And here our actual journey starts! Running Ansible Molecule tests in parallel To run Molecule via pytest in parallel, we can use pytest-xdist, which allows pytest to run the tests in multiple processes. With that, our pytest call becomes something like this:
% MOLECULE_OPTS="--parallel" pytest --numprocesses auto --molecule roles/
What does that mean? However, once we actually execute it, we see:
% MOLECULE_OPTS="--parallel" pytest --numprocesses auto --molecule roles/
 
WARNING  Driver podman does not provide a schema.
INFO     debian scenario test matrix: dependency, cleanup, destroy, syntax, create, prepare, converge, idempotence, side_effect, verify, cleanup, destroy
INFO     Performing prerun with role_name_check=0...
WARNING  Retrying execution failure 250 of: ansible-galaxy collection install -vvv --force ../..
ERROR    Command returned 250 code:
 
OSError: [Errno 39] Directory not empty: 'roles'
 
FileExistsError: [Errno 17] File exists: b'/home/user/namespace.collection/collections/ansible_collections/namespace/collection'
 
FileNotFoundError: [Errno 2] No such file or directory: b'/home/user/namespace.collection//collections/ansible_collections/namespace/collection/roles/my_role/molecule/debian/molecule.yml'
You might see other errors, other paths, etc, but they all will have one in common: they indicate that either files or directories are present, while the tool expects them not to be, or vice versa. Ah yes, that fine smell of race conditions. I'll spare you the wild-goose chase I went on when trying to find out what the heck was calling ansible-galaxy collection install here. Instead, I'll just point at the following line:
INFO     Performing prerun with role_name_check=0...
What is this "prerun" you ask? Well "To help Ansible find used modules and roles, molecule will perform a prerun set of actions. These involve installing dependencies from requirements.yml specified at the project level, installing a standalone role or a collection." Turns out, this step is not --parallel-safe (yet?). Luckily, it can easily be disabled, for all our roles in the collection:
% mkdir -p .config/molecule
% echo 'prerun: false' >> .config/molecule/config.yml
This works perfectly, as long as you don't have any dependencies. And we don't have any, right? We didn't define any in a molecule/collections.yml, our collection has none. So let's push a PR with that and see what our CI thinks.
OSError: [Errno 39] Directory not empty: 'tests'
Huh?
FileExistsError: [Errno 17] File exists: b'remote.sh' -> b'/home/runner/work/namespace.collection/namespace.collection/collections/ansible_collections/ansible/posix/tests/utils/shippable/aix.sh'
What?
ansible_compat.errors.InvalidPrerequisiteError: Found collection at '/home/runner/work/namespace.collection/namespace.collection/collections/ansible_collections/ansible/posix' but missing MANIFEST.json, cannot get info.
Okay, okay, I get the idea But why? Well, our collection might not have any dependencies, BUT MOLECULE HAS! When using Docker containers, it uses community.docker, when using Podman containers.podman, etc So we have to install those before running Molecule, and everything should be fine. We even can use Molecule to do this!
$ molecule dependency --scenario <scenario>
And with that knowledge, the patch to enable parallel Molecule execution on GitHub Actions using pytest-xdist becomes:
diff --git a/.config/molecule/config.yml b/.config/molecule/config.yml
new file mode 100644
index 0000000..32ed66d
--- /dev/null
+++ b/.config/molecule/config.yml
@@ -0,0 +1 @@
+prerun: false
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 0f9da0d..df55a15 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -58,9 +58,13 @@ jobs:
       - name: Install Ansible
         run: pip install --upgrade https://github.com/ansible/ansible/archive/$  matrix.ansible  .tar.gz
       - name: Install dependencies
-        run: pip install molecule molecule-plugins pytest pytest-ansible
+        run: pip install molecule molecule-plugins pytest pytest-ansible pytest-xdist
+      - name: Install collection dependencies
+        run: cd roles/repository && molecule dependency -s suse
       - name: Run tests
-        run: pytest -vv --molecule roles/
+        run: pytest -vv --numprocesses auto --molecule roles/
+        env:
+          MOLECULE_OPTS: --parallel
   ansible-lint:
     runs-on: ubuntu-latest
But you promised us to delete ten lines, that's just a +7-2 patch! Oh yeah, sorry, the +10-20 (so a net -10) is the foreman-operations-collection version of the patch, that also migrates from an ugly bash script to pytest-ansible. And yes, that cuts down the execution from ~26 minutes to ~13 minutes. In the collection I originally tested this with, it's a more moderate "from 8-9 minutes to 5-6 minutes", which is still good though :)

25 April 2024

Petter Reinholdtsen: 45 orphaned Debian packages moved to git, 391 to go

Nine days ago, I started migrating orphaned Debian packages with no version control system listed in debian/control of the source to git. At the time there were 438 such packages. Now there are 391, according to the UDD. In reality it is slightly less, as there is a delay between uploads and UDD updates. In the nine days since, I have thus been able to work my way through ten percent of the packages. I am starting to run out of steam, and hope someone else will also help brushing some dust of these packages. Here is a recipe how to do it. I start by picking a random package by querying the UDD for a list of 10 random packages from the set of remaining packages:
PGPASSWORD="udd-mirror" psql --port=5432 --host=udd-mirror.debian.net \
  --username=udd-mirror udd -c "select source from sources \
   where release = 'sid' and (vcs_url ilike '%anonscm.debian.org%' \
   OR vcs_browser ilike '%anonscm.debian.org%' or vcs_url IS NULL \
   OR vcs_browser IS NULL) AND maintainer ilike '%packages@qa.debian.org%' \
   order by random() limit 10;"
Next, I visit http://salsa.debian.org/debian and search for the package name, to ensure no git repository already exist. If it does, I clone it and try to get it to an uploadable state, and add the Vcs-* entries in d/control to make the repository more widely known. These packages are a minority, so I will not cover that use case here. For packages without an existing git repository, I run the following script debian-snap-to-salsa to prepare a git repository with the existing packaging.
#!/bin/sh
#
# See also https://bugs.debian.org/804722#31
set -e
# Move to this Standards-Version.
SV_LATEST=4.7.0
PKG="$1"
if [ -z "$PKG" ]; then
    echo "usage: $0 "
    exit 1
fi
if [ -e "$ PKG -salsa" ]; then
    echo "error: $ PKG -salsa already exist, aborting."
    exit 1
fi
if [ -z "ALLOWFAILURE" ] ; then
    ALLOWFAILURE=false
fi
# Fetch every snapshotted source package.  Manually loop until all
# transfers succeed, as 'gbp import-dscs --debsnap' do not fail on
# download failures.
until debsnap --force -v $PKG   $ALLOWFAILURE ; do sleep 1; done
mkdir $ PKG -salsa; cd $ PKG -salsa
git init
# Specify branches to override any debian/gbp.conf file present in the
# source package.
gbp import-dscs  --debian-branch=master --upstream-branch=upstream \
    --pristine-tar ../source-$PKG/*.dsc
# Add Vcs pointing to Salsa Debian project (must be manually created
# and pushed to).
if ! grep -q ^Vcs- debian/control ; then
    awk "BEGIN   s=1   /^\$/   if (s==1)   print \"Vcs-Browser: https://salsa.debian.org/debian/$PKG\"; print \"Vcs-Git: https://salsa.debian.org/debian/$PKG.git\"  ; s=0     print  " < debian/control > debian/control.new && mv debian/control.new debian/control
    git commit -m "Updated vcs in d/control to Salsa." debian/control
fi
# Tell gbp to enforce the use of pristine-tar.
inifile +inifile debian/gbp.conf +create +section DEFAULT +key pristine-tar +value True
git add debian/gbp.conf
git commit -m "Added d/gbp.conf to enforce the use of pristine-tar." debian/gbp.conf
# Update to latest Standards-Version.
SV="$(grep ^Standards-Version: debian/control awk ' print $2 ')"
if [ $SV_LATEST != $SV ]; then
    sed -i "s/\(Standards-Version: \)\(.*\)/\1$SV_LATEST/" debian/control
    git commit -m "Updated Standards-Version from $SV to $SV_LATEST." debian/control
fi
if grep -q pkg-config debian/control; then
    sed -i s/pkg-config/pkgconf/ debian/control
    git commit -m "Replaced obsolete pkg-config build dependency with pkgconf." debian/control
fi
if grep -q libncurses5-dev debian/control; then
    sed -i s/libncurses5-dev/libncurses-dev/ debian/control
    git commit -m "Replaced obsolete libncurses5-dev build dependency with libncurses-dev." debian/control
fi
Some times the debsnap script fail to download some of the versions. In those cases I investigate, and if I decide the failing versions will not be missed, I call it using ALLOWFAILURE=true to ignore the problem and create the git repository anyway. With the git repository in place, I do a test build (gbp buildpackage) to ensure the build is actually working. If it does not I pick a different package, or if the build failure is trivial to fix, I fix it before continuing. At this stage I revisit http://salsa.debian.org/debian and create the project under this group for the package. I then follow the instructions to publish the local git repository. Here is from a recent example:
git remote add origin git@salsa.debian.org:debian/perl-byacc.git
git push --set-upstream origin master upstream pristine-tar
git push --tags
With a working build, I have a look at the build rules if I want to remove some more dust. I normally try to move to debhelper compat level 13, which involves removing debian/compat and modifying debian/control to build depend on debhelper-compat (=13). I also test with 'Rules-Requires-Root: no' in debian/control and verify in debian/rules that hardening is enabled, and include all of these if the package still build. If it fail to build with level 13, I try with 12, 11, 10 and so on until I find a level where it build, as I do not want to spend a lot of time fixing build issues. Some times, when I feel inspired, I make sure debian/copyright is converted to the machine readable format, often by starting with 'debhelper -cc' and then cleaning up the autogenerated content until it matches realities. If I feel like it, I might also clean up non-dh-based debian/rules files to use the short style dh build rules. Once I have removed all the dust I care to process for the package, I run 'gbp dch' to generate a debian/changelog entry based on the commits done so far, run 'dch -r' to switch from 'UNRELEASED' to 'unstable' and get an editor to make sure the 'QA upload' marker is in place and that all long commit descriptions are wrapped into sensible lengths, run 'debcommit --release -a' to commit and tag the new debian/changelog entry, run 'debuild -S' to build a source only package, and 'dput ../perl-byacc_2.0-10_source.changes' to do the upload. During the entire process, and many times per step, I run 'debuild' to verify the changes done still work. I also some times verify the set of built files using 'find debian' to see if I can spot any problems (like no file in usr/bin any more or empty package). I also try to fix all lintian issues reported at the end of each 'debuild' run. If I find Debian specific patches, I try to ensure their metadata is fairly up to date and some times I even try to reach out to upstream, to make the upstream project aware of the patches. Most of my emails bounce, so the success rate is low. For projects with no Homepage entry in debian/control I try to track down one, and for packages with no debian/watch file I try to create one. But at least for some of the packages I have been unable to find a functioning upstream, and must skip both of these. If I could handle ten percent in nine days, twenty people could complete the rest in less then five days. I use approximately twenty minutes per package, when I have twenty minutes spare time to spend. Perhaps you got twenty minutes to spare too? As usual, if you use Bitcoin and want to show your support of my activities, please send Bitcoin donations to my address 15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b.

Jonathan McDowell: Sorting out backup internet #3: failover

With local recursive DNS and a 5G modem in place the next thing was to work on some sort of automatic failover when the primary FTTP connection failed. My wife works from home too and I sometimes travel so I wanted to make sure things didn t require me to be around to kick them into switch the link in use. First, let s talk about what I didn t do. One choice to try and ensure as seamless a failover as possible would be to get a VM somewhere out there. I d then run Wireguard tunnels over both the FTTP + 5G links to the VM, and run some sort of routing protocol (RIP, OSPF?) over the links. Set preferences such that the FTTP is preferred, NAT v4 to the VM IP, and choose somewhere that gave me a v6 range I could just use directly. This has the advantage that I m actively checking link quality to the outside work, rather than just to the next hop. It also means, if the failover detection is fast enough, that existing sessions stay up rather than needing re-established. The downsides are increased complexity, adding another point of potential failure (the VM + provider), the impact on connection quality (even with a decent endpoint it s an extra hop and latency), and finally the increased cost involved. I can cope with having to reconnect my SSH sessions in the event of a failure, and I d rather be sure I can make full use of the FTTP connection, so I didn t go this route. I chose to rely on local link failure detection to provide the signal for failover, and a set of policy routing on top of that to make things a bit more seamless. Local link failure turns out to be fairly easy. My FTTP is a PPPoE configuration, so in /etc/ppp/peers/aquiss I have:
lcp-echo-interval 1
lcp-echo-failure 5
lcp-echo-adaptive
Which gives me a failover of ~ 5s if the link goes down. I m operating the 5G modem in bridge rather than router mode, which means I get the actual IP from the 5G network via DHCP. The DHCP lease the modem hands out is under a minute, and in the event of a network failure it only hands out a 192.168.254.x IP to talk to its web interface. As the 5G modem is the last resort path I choose not to do anything special with this, but the information is at least there if I need it. To allow both interfaces to be up and the FTTP to be preferred I m simply using route metrics. For the PPP configuration that s:
defaultroute-metric 100
and for the 5G modem I have:
iface sfp.31 inet dhcp
    metric 1000
    vlan-raw-device sfp
There s a wrinkle in that pppd will not replace an existing default route, so I ve created /etc/ppp/ip-up.d/default-route to ensure it s added:
#!/bin/bash
[ "$PPP_IFACE" = "pppoe-wan" ]   exit 0
# Ensure we add a default route; pppd will not do so if we have
# a lower pref route out the 5G modem
ip route add default dev pppoe-wan metric 100   true
Additionally, in /etc/dhcp/dhclient.conf I ve disabled asking for any server details (DNS, NTP, etc) - I have internal setups for the servers I want, and don t want to be trying to select things over the 5G link by default. However, what I do want is to be able to access the 5G modem web interface and explicitly route some traffic out that link (e.g. so I can add it to my smokeping tests). For that I need some source based routing. First step, add a 5g table to /etc/iproute2/rt_tables:
16  5g
Then I ended up with the following in /etc/dhcp/dhclient-exit-hooks.d/modem-interface-route, which is more complex than I d like but seems to do what I want:
#!/bin/sh
case "$reason" in
    BOUND RENEW REBIND REBOOT)
        # Check if we've actually changed IP address
        if [ -z "$old_ip_address" ]  
           [ "$old_ip_address" != "$new_ip_address" ]  
           [ "$reason" = "BOUND" ]   [ "$reason" = "REBOOT" ]; then
            if [ ! -z "$old_ip_address" ]; then
                ip rule del from $old_ip_address lookup 5g
            fi
            ip rule add from $new_ip_address lookup 5g
            ip route add default dev sfp.31 table 5g   true
            ip route add 192.168.254.1 dev sfp.31 2>/dev/null   true
        fi
    ;;
    EXPIRE)
        if [ ! -z "$old_ip_address" ]; then
            ip rule del from $old_ip_address lookup 5g
        fi
    ;;
    *)
    ;;
esac
What does all that aim to do? We want to ensure traffic directed to the 5G WAN address goes out the 5G modem, so I can SSH into it even when the main link is up. So we add a rule directing traffic from that IP to hit the 5g routing table, and a default route in that table which uses the 5G link. There s no configuration for the FTTP connection in that table, so if the 5G link is down the traffic gets dropped, which is what we want. We also configure 192.168.254.1 to go out the link to the modem, as that s where the web interface lives. I also have a curl callout (curl --interface sfp.31 to ensure it goes out the 5G link) after the routes are configured to set dynamic DNS with Mythic Beasts, which helps with knowing where to connect back to. I seem to see IP address changes on the 5G link every couple of days at least. Additionally, I have an entry in the interfaces configuration carving out the top set of the netblock my smokeping server is in:
    up ip rule add from 192.0.2.224/27 lookup 5g
My smokeping /etc/smokeping/config.d/Probes file then looks like:
*** Probes ***
+ FPing
binary = /usr/bin/fping
++ FPingNormal
++ FPing5G
sourceaddress = 192.0.2.225
+ FPing6
binary = /usr/bin/fping
which allows me to use probe = FPing5G for targets to test them over the 5G link. That mostly covers the functionality I want for a backup link. There s one piece that isn t quite solved, however, IPv6, which can wait for another post.

Lukas M rdian: Creating a Netplan enabled system through Debian-Installer

With the work that has been done in the debian-installer/netcfg merge-proposal !9 it is possible to install a standard Debian system, using the normal Debian-Installer (d-i) mini.iso images, that will come pre-installed with Netplan and all network configuration structured in /etc/netplan/. In this write-up I d like to run you through a list of commands for experiencing the Netplan enabled installation process first-hand. For now, we ll be using a custom ISO image, while waiting for the above-mentioned merge-proposal to be landed. Furthermore, as the Debian archive is going through major transitions builds of the unstable branch of d-i don t currently work. So I implemented a small backport, producing updated netcfg and netcfg-static for Bookworm, which can be used as localudebs/ during the d-i build. Let s start with preparing a working directory and installing the software dependencies for our virtualized Debian system:
$ mkdir d-i_bookworm && cd d-i_bookworm
$ apt install ovmf qemu-utils qemu-system-x86
Now let s download the custom mini.iso, linux kernel image and initrd.gz containing the Netplan enablement changes, as mentioned above. TODO: localudebs/
$ wget https://people.ubuntu.com/~slyon/d-i/bookworm/mini.iso
$ wget https://people.ubuntu.com/~slyon/d-i/bookworm/linux
$ wget https://people.ubuntu.com/~slyon/d-i/bookworm/initrd.gz
Next we ll prepare a VM, by copying the EFI firmware files, preparing some persistent EFIVARs file, to boot from FS0:\EFI\debian\grubx64.efi, and create a virtual disk for our machine:
$ cp /usr/share/OVMF/OVMF_CODE_4M.fd .
$ cp /usr/share/OVMF/OVMF_VARS_4M.fd .
$ qemu-img create -f qcow2 ./data.qcow2 5G
Finally, let s launch the installer using a custom preseed.cfg file, that will automatically install Netplan for us in the target system. A minimal preseed file could look like this:
# Install minimal Netplan generator binary
d-i preseed/late_command string in-target apt-get -y install netplan-generator
For this demo, we re installing the full netplan.io package (incl. Python CLI), as the netplan-generator package was not yet split out as an independent binary in the Bookworm cycle. You can choose the preseed file from a set of different variants to test the different configurations: We re using the custom linux kernel and initrd.gz here to be able to pass the PRESEED_URL as a parameter to the kernel s cmdline directly. Launching this VM should bring up the normal debian-installer in its netboot/gtk form:
$ export U=https://people.ubuntu.com/~slyon/d-i/bookworm/netplan-preseed+networkd.cfg
$ qemu-system-x86_64 \
	-M q35 -enable-kvm -cpu host -smp 4 -m 2G \
	-drive if=pflash,format=raw,unit=0,file=OVMF_CODE_4M.fd,readonly=on \
	-drive if=pflash,format=raw,unit=1,file=OVMF_VARS_4M.fd,readonly=off \
	-device qemu-xhci -device usb-kbd -device usb-mouse \
	-vga none -device virtio-gpu-pci \
	-net nic,model=virtio -net user \
	-kernel ./linux -initrd ./initrd.gz -append "url=$U" \
	-hda ./data.qcow2 -cdrom ./mini.iso;
Now you can click through the normal Debian-Installer process, using mostly default settings. Optionally, you could play around with the networking settings, to see how those get translated to /etc/netplan/ in the target system.
After you confirmed your partitioning changes, the base system gets installed. I suggest not to select any additional components, like desktop environments, to speed up the process.
During the final step of the installation (finish-install.d/55netcfg-copy-config) d-i will detect that Netplan was installed in the target system (due to the preseed file provided) and opt to write its network configuration to /etc/netplan/ instead of /etc/network/interfaces or /etc/NetworkManager/system-connections/.
Done! After the installation finished you can reboot into your virgin Debian Bookworm system. To do that, quit the current Qemu process, by pressing Ctrl+C and make sure to copy over the EFIVARS.fd file that was written by grub during the installation, so Qemu can find the new system. Then reboot into the new system, not using the mini.iso image any more:
$ cp ./OVMF_VARS_4M.fd ./EFIVARS.fd
$ qemu-system-x86_64 \
        -M q35 -enable-kvm -cpu host -smp 4 -m 2G \
        -drive if=pflash,format=raw,unit=0,file=OVMF_CODE_4M.fd,readonly=on \
        -drive if=pflash,format=raw,unit=1,file=EFIVARS.fd,readonly=off \
        -device qemu-xhci -device usb-kbd -device usb-mouse \
        -vga none -device virtio-gpu-pci \
        -net nic,model=virtio -net user \
        -drive file=./data.qcow2,if=none,format=qcow2,id=disk0 \
        -device virtio-blk-pci,drive=disk0,bootindex=1
        -serial mon:stdio
Finally, you can play around with your Netplan enabled Debian system! As you will find, /etc/network/interfaces exists but is empty, it could still be used (optionally/additionally). Netplan was configured in /etc/netplan/ according to the settings given during the d-i installation process.
In our case we also installed the Netplan CLI, so we can play around with some of its features, like netplan status:
Thank you for following along the Netplan enabled Debian installation process and happy hacking! If you want to learn more join the discussion at Salsa:installer-team/netcfg and find us at GitHub:netplan.

24 April 2024

Russell Coker: Source Code With Emoji

The XKCD comic Code Quality [1] inspired me to test out emoji in source. I really should have done this years ago when that XKCD was first published. The following code compiles in gcc and runs in the way that anyone who wants to write such code would want it to run. The hover text in the XKCD comic is correct. You could have a style guide for such programming, store error messages in the doctor and nurse emoji for example.
#include <stdio.h>
int main()
 
  int   = 1,   = 2;
  printf(" =%d,  =%d\n",  ,  );
  return 0;
 
To get this to display correctly in Debian you need to install the fonts-noto-color-emoji package (used by the KDE emoji picker that runs when you press Windows-. among other things) and restart programs that use emoji. The Konsole terminal emulator will probably need it s profile settings changed to work with this if you ran Konsole before installing fonts-noto-color-emoji. The Kitty terminal emulator works if you restart it after installing fonts-noto-color-emoji. This web page gives a list of HTML codes for emoji [2]. If I start writing real code with emoji variable names then I ll have to update my source to HTML conversion script (which handles <>" and repeated spaces) to convert emoji. I spent a couple of hours on this and I think it s worth it. I have filed several Debian bug reports about improvements needed to issues related to emoji.

18 April 2024

Jonathan McDowell: Sorting out backup internet #2: 5G modem

Having setup recursive DNS it was time to actually sort out a backup internet connection. I live in a Virgin Media area, but I still haven t forgiven them for my terrible Virgin experiences when moving here. Plus it involves a bigger contractual commitment. There are no altnets locally (though I m watching youfibre who have already rolled out in a few Belfast exchanges), so I decided to go for a 5G modem. That gives some flexibility, and is a bit easier to get up and running. I started by purchasing a ZTE MC7010. This had the advantage of being reasonably cheap off eBay, not having any wifi functionality I would just have to disable (it s going to plug it into the same router the FTTP connection terminates on), being outdoor mountable should I decide to go that way, and, finally, being powered via PoE. For now this device sits on the window sill in my study, which is at the top of the house. I printed a table stand for it which mostly does the job (though not as well with a normal, rather than flat, network cable). The router lives downstairs, so I ve extended a dedicated VLAN through the study switch, down to the core switch and out to the router. The PoE study switch can only do GigE, not 2.5Gb/s, but at present that s far from the limiting factor on the speed of the connection. The device is 3 branded, and, as it happens, I ve ended up with a 3 SIM in it. Up until recently my personal phone was with them, but they ve kicked me off Go Roam, so I ve moved. Going with 3 for the backup connection provides some slight extra measure of resiliency; we now have devices on all 4 major UK networks in the house. The SIM is a preloaded data only SIM good for a year; I don t expect to use all of the data allowance, but I didn t want to have to worry about unexpected excess charges. Performance turns out to be disappointing; I end up locking the device to 4G as the 5G signal is marginal - leaving it enabled results in constantly switching between 4G + 5G and a significant extra latency. The smokeping graph below shows a brief period where I removed the 4G lock and allowed 5G: Smokeping 4G vs 5G graph (There s a handy zte.js script to allow doing this from the device web interface.) I get about 10Mb/s sustained downloads out of it. EE/Vodafone did not lead to significantly better results, so for now I m accepting it is what it is. I tried relocating the device to another part of the house (a little tricky while still providing switch-based PoE, but I have an injector), without much improvement. Equally pinning the 4G to certain bands provided a short term improvement (I got up to 40-50Mb/s sustained), but not reliably so. speedtest.net results This is disappointing, but if it turns out to be a problem I can look at mounting it externally. I also assume as 5G is gradually rolled out further things will naturally improve, but that might be wishful thinking on my part. Rather than wait until my main link had a problem I decided to try a day working over the 5G connection. I spend a lot of my time either in browser based apps or accessing remote systems via SSH, so I m reasonably sensitive to a jittery or otherwise flaky connection. I picked a day that I did not have any meetings planned, but as it happened I ended up with an adhoc video call arranged. I m pleased to say that it all worked just fine; definitely noticeable as slower than the FTTP connection (to be expected), but all workable and even the video call was fine (at least from my end). Looking at the traffic graph shows the expected ~ 10Mb/s peak (actually a little higher, and looking at the FTTP stats for previous days not out of keeping with what we see there), and you can just about see the ~ 3Mb/s symmetric use by the video call at 2pm: 4G traffic during the work day The test run also helped iron out the fact that the content filter was still enabled on the SIM, but that was easily resolved. Up next, vaguely automatic failover.

13 April 2024

Simon Josefsson: Reproducible and minimal source-only tarballs

With the release of Libntlm version 1.8 the release tarball can be reproduced on several distributions. We also publish a signed minimal source-only tarball, produced by git-archive which is the same format used by Savannah, Codeberg, GitLab, GitHub and others. Reproducibility of both tarballs are tested continuously for regressions on GitLab through a CI/CD pipeline. If that wasn t enough to excite you, the Debian packages of Libntlm are now built from the reproducible minimal source-only tarball. The resulting binaries are reproducible on several architectures. What does that even mean? Why should you care? How you can do the same for your project? What are the open issues? Read on, dear reader This article describes my practical experiments with reproducible release artifacts, following up on my earlier thoughts that lead to discussion on Fosstodon and a patch by Janneke Nieuwenhuizen to make Guix tarballs reproducible that inspired me to some practical work. Let s look at how a maintainer release some software, and how a user can reproduce the released artifacts from the source code. Libntlm provides a shared library written in C and uses GNU Make, GNU Autoconf, GNU Automake, GNU Libtool and gnulib for build management, but these ideas should apply to most project and build system. The following illustrate the steps a maintainer would take to prepare a release:
git clone https://gitlab.com/gsasl/libntlm.git
cd libntlm
git checkout v1.8
./bootstrap
./configure
make distcheck
gpg -b libntlm-1.8.tar.gz
The generated files libntlm-1.8.tar.gz and libntlm-1.8.tar.gz.sig are published, and users download and use them. This is how the GNU project have been doing releases since the late 1980 s. That is a testament to how successful this pattern has been! These tarballs contain source code and some generated files, typically shell scripts generated by autoconf, makefile templates generated by automake, documentation in formats like Info, HTML, or PDF. Rarely do they contain binary object code, but historically that happened. The XZUtils incident illustrate that tarballs with files that are not included in the git archive offer an opportunity to disguise malicious backdoors. I blogged earlier how to mitigate this risk by using signed minimal source-only tarballs. The risk of hiding malware is not the only motivation to publish signed minimal source-only tarballs. With pre-generated content in tarballs, there is a risk that GNU/Linux distributions such as Trisquel, Guix, Debian/Ubuntu or Fedora ship generated files coming from the tarball into the binary *.deb or *.rpm package file. Typically the person packaging the upstream project never realized that some installed artifacts was not re-built through a typical autoconf -fi && ./configure && make install sequence, and never wrote the code to rebuild everything. This can also happen if the build rules are written but are buggy, shipping the old artifact. When a security problem is found, this can lead to time-consuming situations, as it may be that patching the relevant source code and rebuilding the package is not sufficient: the vulnerable generated object from the tarball would be shipped into the binary package instead of a rebuilt artifact. For architecture-specific binaries this rarely happens, since object code is usually not included in tarballs although for 10+ years I shipped the binary Java JAR file in the GNU Libidn release tarball, until I stopped shipping it. For interpreted languages and especially for generated content such as HTML, PDF, shell scripts this happens more than you would like. Publishing minimal source-only tarballs enable easier auditing of a project s code, to avoid the need to read through all generated files looking for malicious content. I have taken care to generate the source-only minimal tarball using git-archive. This is the same format that GitLab, GitHub etc offer for the automated download links on git tags. The minimal source-only tarballs can thus serve as a way to audit GitLab and GitHub download material! Consider if/when hosting sites like GitLab or GitHub has a security incident that cause generated tarballs to include a backdoor that is not present in the git repository. If people rely on the tag download artifact without verifying the maintainer PGP signature using GnuPG, this can lead to similar backdoor scenarios that we had for XZUtils but originated with the hosting provider instead of the release manager. This is even more concerning, since this attack can be mounted for some selected IP address that you want to target and not on everyone, thereby making it harder to discover. With all that discussion and rationale out of the way, let s return to the release process. I have added another step here:
make srcdist
gpg -b libntlm-1.8-src.tar.gz
Now the release is ready. I publish these four files in the Libntlm s Savannah Download area, but they can be uploaded to a GitLab/GitHub release area as well. These are the SHA256 checksums I got after building the tarballs on my Trisquel 11 aramo laptop:
91de864224913b9493c7a6cec2890e6eded3610d34c3d983132823de348ec2ca  libntlm-1.8-src.tar.gz
ce6569a47a21173ba69c990965f73eb82d9a093eb871f935ab64ee13df47fda1  libntlm-1.8.tar.gz
So how can you reproduce my artifacts? Here is how to reproduce them in a Ubuntu 22.04 container:
podman run -it --rm ubuntu:22.04
apt-get update
apt-get install -y --no-install-recommends autoconf automake libtool make git ca-certificates
git clone https://gitlab.com/gsasl/libntlm.git
cd libntlm
git checkout v1.8
./bootstrap
./configure
make dist srcdist
sha256sum libntlm-*.tar.gz
You should see the exact same SHA256 checksum values. Hooray! This works because Trisquel 11 and Ubuntu 22.04 uses the same version of git, autoconf, automake, and libtool. These tools do not guarantee the same output content for all versions, similar to how GNU GCC does not generate the same binary output for all versions. So there is still some delicate version pairing needed. Ideally, the artifacts should be possible to reproduce from the release artifacts themselves, and not only directly from git. It is possible to reproduce the full tarball in a AlmaLinux 8 container replace almalinux:8 with rockylinux:8 if you prefer RockyLinux:
podman run -it --rm almalinux:8
dnf update -y
dnf install -y make wget gcc
wget https://download.savannah.nongnu.org/releases/libntlm/libntlm-1.8.tar.gz
tar xfa libntlm-1.8.tar.gz
cd libntlm-1.8
./configure
make dist
sha256sum libntlm-1.8.tar.gz
The source-only minimal tarball can be regenerated on Debian 11:
podman run -it --rm debian:11
apt-get update
apt-get install -y --no-install-recommends make git ca-certificates
git clone https://gitlab.com/gsasl/libntlm.git
cd libntlm
git checkout v1.8
make -f cfg.mk srcdist
sha256sum libntlm-1.8-src.tar.gz 
As the Magnus Opus or chef-d uvre, let s recreate the full tarball directly from the minimal source-only tarball on Trisquel 11 replace docker.io/kpengboy/trisquel:11.0 with ubuntu:22.04 if you prefer.
podman run -it --rm docker.io/kpengboy/trisquel:11.0
apt-get update
apt-get install -y --no-install-recommends autoconf automake libtool make wget git ca-certificates
wget https://download.savannah.nongnu.org/releases/libntlm/libntlm-1.8-src.tar.gz
tar xfa libntlm-1.8-src.tar.gz
cd libntlm-v1.8
./bootstrap
./configure
make dist
sha256sum libntlm-1.8.tar.gz
Yay! You should now have great confidence in that the release artifacts correspond to what s in version control and also to what the maintainer intended to release. Your remaining job is to audit the source code for vulnerabilities, including the source code of the dependencies used in the build. You no longer have to worry about auditing the release artifacts. I find it somewhat amusing that the build infrastructure for Libntlm is now in a significantly better place than the code itself. Libntlm is written in old C style with plenty of string manipulation and uses broken cryptographic algorithms such as MD4 and single-DES. Remember folks: solving supply chain security issues has no bearing on what kind of code you eventually run. A clean gun can still shoot you in the foot. Side note on naming: GitLab exports tarballs with pathnames libntlm-v1.8/ (i.e.., PROJECT-TAG/) and I ve adopted the same pathnames, which means my libntlm-1.8-src.tar.gz tarballs are bit-by-bit identical to GitLab s exports and you can verify this with tools like diffoscope. GitLab name the tarball libntlm-v1.8.tar.gz (i.e., PROJECT-TAG.ARCHIVE) which I find too similar to the libntlm-1.8.tar.gz that we also publish. GitHub uses the same git archive style, but unfortunately they have logic that removes the v in the pathname so you will get a tarball with pathname libntlm-1.8/ instead of libntlm-v1.8/ that GitLab and I use. The content of the tarball is bit-by-bit identical, but the pathname and archive differs. Codeberg (running Forgejo) uses another approach: the tarball is called libntlm-v1.8.tar.gz (after the tag) just like GitLab, but the pathname inside the archive is libntlm/, otherwise the produced archive is bit-by-bit identical including timestamps. Savannah s CGIT interface uses archive name libntlm-1.8.tar.gz with pathname libntlm-1.8/, but otherwise file content is identical. Savannah s GitWeb interface provides snapshot links that are named after the git commit (e.g., libntlm-a812c2ca.tar.gz with libntlm-a812c2ca/) and I cannot find any tag-based download links at all. Overall, we are so close to get SHA256 checksum to match, but fail on pathname within the archive. I ve chosen to be compatible with GitLab regarding the content of tarballs but not on archive naming. From a simplicity point of view, it would be nice if everyone used PROJECT-TAG.ARCHIVE for the archive filename and PROJECT-TAG/ for the pathname within the archive. This aspect will probably need more discussion. Side note on git archive output: It seems different versions of git archive produce different results for the same repository. The version of git in Debian 11, Trisquel 11 and Ubuntu 22.04 behave the same. The version of git in Debian 12, AlmaLinux/RockyLinux 8/9, Alpine, ArchLinux, macOS homebrew, and upcoming Ubuntu 24.04 behave in another way. Hopefully this will not change that often, but this would invalidate reproducibility of these tarballs in the future, forcing you to use an old git release to reproduce the source-only tarball. Alas, GitLab and most other sites appears to be using modern git so the download tarballs from them would not match my tarballs even though the content would. Side note on ChangeLog: ChangeLog files were traditionally manually curated files with version history for a package. In recent years, several projects moved to dynamically generate them from git history (using tools like git2cl or gitlog-to-changelog). This has consequences for reproducibility of tarballs: you need to have the entire git history available! The gitlog-to-changelog tool also output different outputs depending on the time zone of the person using it, which arguable is a simple bug that can be fixed. However this entire approach is incompatible with rebuilding the full tarball from the minimal source-only tarball. It seems Libntlm s ChangeLog file died on the surgery table here. So how would a distribution build these minimal source-only tarballs? I happen to help on the libntlm package in Debian. It has historically used the generated tarballs as the source code to build from. This means that code coming from gnulib is vendored in the tarball. When a security problem is discovered in gnulib code, the security team needs to patch all packages that include that vendored code and rebuild them, instead of merely patching the gnulib package and rebuild all packages that rely on that particular code. To change this, the Debian libntlm package needs to Build-Depends on Debian s gnulib package. But there was one problem: similar to most projects that use gnulib, Libntlm depend on a particular git commit of gnulib, and Debian only ship one commit. There is no coordination about which commit to use. I have adopted gnulib in Debian, and add a git bundle to the *_all.deb binary package so that projects that rely on gnulib can pick whatever commit they need. This allow an no-network GNULIB_URL and GNULIB_REVISION approach when running Libntlm s ./bootstrap with the Debian gnulib package installed. Otherwise libntlm would pick up whatever latest version of gnulib that Debian happened to have in the gnulib package, which is not what the Libntlm maintainer intended to be used, and can lead to all sorts of version mismatches (and consequently security problems) over time. Libntlm in Debian is developed and tested on Salsa and there is continuous integration testing of it as well, thanks to the Salsa CI team. Side note on git bundles: unfortunately there appears to be no reproducible way to export a git repository into one or more files. So one unfortunate consequence of all this work is that the gnulib *.orig.tar.gz tarball in Debian is not reproducible any more. I have tried to get Git bundles to be reproducible but I never got it to work see my notes in gnulib s debian/README.source on this aspect. Of course, source tarball reproducibility has nothing to do with binary reproducibility of gnulib in Debian itself, fortunately. One open question is how to deal with the increased build dependencies that is triggered by this approach. Some people are surprised by this but I don t see how to get around it: if you depend on source code for tools in another package to build your package, it is a bad idea to hide that dependency. We ve done it for a long time through vendored code in non-minimal tarballs. Libntlm isn t the most critical project from a bootstrapping perspective, so adding git and gnulib as Build-Depends to it will probably be fine. However, consider if this pattern was used for other packages that uses gnulib such as coreutils, gzip, tar, bison etc (all are using gnulib) then they would all Build-Depends on git and gnulib. Cross-building those packages for a new architecture will therefor require git on that architecture first, which gets circular quick. The dependency on gnulib is real so I don t see that going away, and gnulib is a Architecture:all package. However, the dependency on git is merely a consequence of how the Debian gnulib package chose to make all gnulib git commits available to projects: through a git bundle. There are other ways to do this that doesn t require the git tool to extract the necessary files, but none that I found practical ideas welcome! Finally some brief notes on how this was implemented. Enabling bootstrappable source-only minimal tarballs via gnulib s ./bootstrap is achieved by using the GNULIB_REVISION mechanism, locking down the gnulib commit used. I have always disliked git submodules because they add extra steps and has complicated interaction with CI/CD. The reason why I gave up git submodules now is because the particular commit to use is not recorded in the git archive output when git submodules is used. So the particular gnulib commit has to be mentioned explicitly in some source code that goes into the git archive tarball. Colin Watson added the GNULIB_REVISION approach to ./bootstrap back in 2018, and now it no longer made sense to continue to use a gnulib git submodule. One alternative is to use ./bootstrap with --gnulib-srcdir or --gnulib-refdir if there is some practical problem with the GNULIB_URL towards a git bundle the GNULIB_REVISION in bootstrap.conf. The srcdist make rule is simple:
git archive --prefix=libntlm-v1.8/ -o libntlm-v1.8.tar.gz HEAD
Making the make dist generated tarball reproducible can be more complicated, however for Libntlm it was sufficient to make sure the modification times of all files were set deterministically to the timestamp of the last commit in the git repository. Interestingly there seems to be a couple of different ways to accomplish this, Guix doesn t support minimal source-only tarballs but rely on a .tarball-timestamp file inside the tarball. Paul Eggert explained what TZDB is using some time ago. The approach I m using now is fairly similar to the one I suggested over a year ago. If there are problems because all files in the tarball now use the same modification time, there is a solution by Bruno Haible that could be implemented. Side note on git tags: Some people may wonder why not verify a signed git tag instead of verifying a signed tarball of the git archive. Currently most git repositories uses SHA-1 for git commit identities, but SHA-1 is not a secure hash function. While current SHA-1 attacks can be detected and mitigated, there are fundamental doubts that a git SHA-1 commit identity uniquely refers to the same content that was intended. Verifying a git tag will never offer the same assurance, since a git tag can be moved or re-signed at any time. Verifying a git commit is better but then we need to trust SHA-1. Migrating git to SHA-256 would resolve this aspect, but most hosting sites such as GitLab and GitHub does not support this yet. There are other advantages to using signed tarballs instead of signed git commits or git tags as well, e.g., tar.gz can be a deterministically reproducible persistent stable offline storage format but .git sub-directory trees or git bundles do not offer this property. Doing continous testing of all this is critical to make sure things don t regress. Libntlm s pipeline definition now produce the generated libntlm-*.tar.gz tarballs and a checksum as a build artifact. Then I added the 000-reproducability job which compares the checksums and fails on mismatches. You can read its delicate output in the job for the v1.8 release. Right now we insists that builds on Trisquel 11 match Ubuntu 22.04, that PureOS 10 builds match Debian 11 builds, that AlmaLinux 8 builds match RockyLinux 8 builds, and AlmaLinux 9 builds match RockyLinux 9 builds. As you can see in pipeline job output, not all platforms lead to the same tarballs, but hopefully this state can be improved over time. There is also partial reproducibility, where the full tarball is reproducible across two distributions but not the minimal tarball, or vice versa. If this way of working plays out well, I hope to implement it in other projects too. What do you think? Happy Hacking!

Paul Tagliamonte: Domo Arigato, Mr. debugfs

Years ago, at what I think I remember was DebConf 15, I hacked for a while on debhelper to write build-ids to debian binary control files, so that the build-id (more specifically, the ELF note .note.gnu.build-id) wound up in the Debian apt archive metadata. I ve always thought this was super cool, and seeing as how Michael Stapelberg blogged some great pointers around the ecosystem, including the fancy new debuginfod service, and the find-dbgsym-packages helper, which uses these same headers, I don t think I m the only one. At work I ve been using a lot of rust, specifically, async rust using tokio. To try and work on my style, and to dig deeper into the how and why of the decisions made in these frameworks, I ve decided to hack up a project that I ve wanted to do ever since 2015 write a debug filesystem. Let s get to it.

Back to the Future Time to admit something. I really love Plan 9. It s just so good. So many ideas from Plan 9 are just so prescient, and everything just feels right. Not just right like, feels good like, correct. The bit that I ve always liked the most is 9p, the network protocol for serving a filesystem over a network. This leads to all sorts of fun programs, like the Plan 9 ftp client being a 9p server you mount the ftp server and access files like any other files. It s kinda like if fuse were more fully a part of how the operating system worked, but fuse is all running client-side. With 9p there s a single client, and different servers that you can connect to, which may be backed by a hard drive, remote resources over something like SFTP, FTP, HTTP or even purely synthetic. The interesting (maybe sad?) part here is that 9p wound up outliving Plan 9 in terms of adoption 9p is in all sorts of places folks don t usually expect. For instance, the Windows Subsystem for Linux uses the 9p protocol to share files between Windows and Linux. ChromeOS uses it to share files with Crostini, and qemu uses 9p (virtio-p9) to share files between guest and host. If you re noticing a pattern here, you d be right; for some reason 9p is the go-to protocol to exchange files between hypervisor and guest. Why? I have no idea, except maybe due to being designed well, simple to implement, and it s a lot easier to validate the data being shared and validate security boundaries. Simplicity has its value. As a result, there s a lot of lingering 9p support kicking around. Turns out Linux can even handle mounting 9p filesystems out of the box. This means that I can deploy a filesystem to my LAN or my localhost by running a process on top of a computer that needs nothing special, and mount it over the network on an unmodified machine unlike fuse, where you d need client-specific software to run in order to mount the directory. For instance, let s mount a 9p filesystem running on my localhost machine, serving requests on 127.0.0.1:564 (tcp) that goes by the name mountpointname to /mnt.
$ mount -t 9p \
-o trans=tcp,port=564,version=9p2000.u,aname=mountpointname \
127.0.0.1 \
/mnt
Linux will mount away, and attach to the filesystem as the root user, and by default, attach to that mountpoint again for each local user that attempts to use it. Nifty, right? I think so. The server is able to keep track of per-user access and authorization along with the host OS.

WHEREIN I STYX WITH IT Since I wanted to push myself a bit more with rust and tokio specifically, I opted to implement the whole stack myself, without third party libraries on the critical path where I could avoid it. The 9p protocol (sometimes called Styx, the original name for it) is incredibly simple. It s a series of client to server requests, which receive a server to client response. These are, respectively, T messages, which transmit a request to the server, which trigger an R message in response (Reply messages). These messages are TLV payload with a very straight forward structure so straight forward, in fact, that I was able to implement a working server off nothing more than a handful of man pages. Later on after the basics worked, I found a more complete spec page that contains more information about the unix specific variant that I opted to use (9P2000.u rather than 9P2000) due to the level of Linux specific support for the 9P2000.u variant over the 9P2000 protocol.

MR ROBOTO The backend stack over at zoo is rust and tokio running i/o for an HTTP and WebRTC server. I figured I d pick something fairly similar to write my filesystem with, since 9P can be implemented on basically anything with I/O. That means tokio tcp server bits, which construct and use a 9p server, which has an idiomatic Rusty API that partially abstracts the raw R and T messages, but not so much as to cause issues with hiding implementation possibilities. At each abstraction level, there s an escape hatch allowing someone to implement any of the layers if required. I called this framework arigato which can be found over on docs.rs and crates.io.
/// Simplified version of the arigato File trait; this isn't actually
/// the same trait; there's some small cosmetic differences. The
/// actual trait can be found at:
///
/// https://docs.rs/arigato/latest/arigato/server/trait.File.html
trait File  
/// OpenFile is the type returned by this File via an Open call.
 type OpenFile: OpenFile;
/// Return the 9p Qid for this file. A file is the same if the Qid is
 /// the same. A Qid contains information about the mode of the file,
 /// version of the file, and a unique 64 bit identifier.
 fn qid(&self) -> Qid;
/// Construct the 9p Stat struct with metadata about a file.
 async fn stat(&self) -> FileResult<Stat>;
/// Attempt to update the file metadata.
 async fn wstat(&mut self, s: &Stat) -> FileResult<()>;
/// Traverse the filesystem tree.
 async fn walk(&self, path: &[&str]) -> FileResult<(Option<Self>, Vec<Self>)>;
/// Request that a file's reference be removed from the file tree.
 async fn unlink(&mut self) -> FileResult<()>;
/// Create a file at a specific location in the file tree.
 async fn create(
&mut self,
name: &str,
perm: u16,
ty: FileType,
mode: OpenMode,
extension: &str,
) -> FileResult<Self>;
/// Open the File, returning a handle to the open file, which handles
 /// file i/o. This is split into a second type since it is genuinely
 /// unrelated -- and the fact that a file is Open or Closed can be
 /// handled by the  arigato  server for us.
 async fn open(&mut self, mode: OpenMode) -> FileResult<Self::OpenFile>;
 
/// Simplified version of the arigato OpenFile trait; this isn't actually
/// the same trait; there's some small cosmetic differences. The
/// actual trait can be found at:
///
/// https://docs.rs/arigato/latest/arigato/server/trait.OpenFile.html
trait OpenFile  
/// iounit to report for this file. The iounit reported is used for Read
 /// or Write operations to signal, if non-zero, the maximum size that is
 /// guaranteed to be transferred atomically.
 fn iounit(&self) -> u32;
/// Read some number of bytes up to  buf.len()  from the provided
 ///  offset  of the underlying file. The number of bytes read is
 /// returned.
 async fn read_at(
&mut self,
buf: &mut [u8],
offset: u64,
) -> FileResult<u32>;
/// Write some number of bytes up to  buf.len()  from the provided
 ///  offset  of the underlying file. The number of bytes written
 /// is returned.
 fn write_at(
&mut self,
buf: &mut [u8],
offset: u64,
) -> FileResult<u32>;
 

Thanks, decade ago paultag! Let s do it! Let s use arigato to implement a 9p filesystem we ll call debugfs that will serve all the debug files shipped according to the Packages metadata from the apt archive. We ll fetch the Packages file and construct a filesystem based on the reported Build-Id entries. For those who don t know much about how an apt repo works, here s the 2-second crash course on what we re doing. The first is to fetch the Packages file, which is specific to a binary architecture (such as amd64, arm64 or riscv64). That architecture is specific to a component (such as main, contrib or non-free). That component is specific to a suite, such as stable, unstable or any of its aliases (bullseye, bookworm, etc). Let s take a look at the Packages.xz file for the unstable-debug suite, main component, for all amd64 binaries.
$ curl \
https://deb.debian.org/debian-debug/dists/unstable-debug/main/binary-amd64/Packages.xz \
  unxz
This will return the Debian-style rfc2822-like headers, which is an export of the metadata contained inside each .deb file which apt (or other tools that can use the apt repo format) use to fetch information about debs. Let s take a look at the debug headers for the netlabel-tools package in unstable which is a package named netlabel-tools-dbgsym in unstable-debug.
Package: netlabel-tools-dbgsym
Source: netlabel-tools (0.30.0-1)
Version: 0.30.0-1+b1
Installed-Size: 79
Maintainer: Paul Tagliamonte <paultag@debian.org>
Architecture: amd64
Depends: netlabel-tools (= 0.30.0-1+b1)
Description: debug symbols for netlabel-tools
Auto-Built-Package: debug-symbols
Build-Ids: e59f81f6573dadd5d95a6e4474d9388ab2777e2a
Description-md5: a0e587a0cf730c88a4010f78562e6db7
Section: debug
Priority: optional
Filename: pool/main/n/netlabel-tools/netlabel-tools-dbgsym_0.30.0-1+b1_amd64.deb
Size: 62776
SHA256: 0e9bdb087617f0350995a84fb9aa84541bc4df45c6cd717f2157aa83711d0c60
So here, we can parse the package headers in the Packages.xz file, and store, for each Build-Id, the Filename where we can fetch the .deb at. Each .deb contains a number of files but we re only really interested in the files inside the .deb located at or under /usr/lib/debug/.build-id/, which you can find in debugfs under rfc822.rs. It s crude, and very single-purpose, but I m feeling a bit lazy.

Who needs dpkg?! For folks who haven t seen it yet, a .deb file is a special type of .ar file, that contains (usually) three files inside debian-binary, control.tar.xz and data.tar.xz. The core of an .ar file is a fixed size (60 byte) entry header, followed by the specified size number of bytes.
[8 byte .ar file magic]
[60 byte entry header]
[N bytes of data]
[60 byte entry header]
[N bytes of data]
[60 byte entry header]
[N bytes of data]
...
First up was to implement a basic ar parser in ar.rs. Before we get into using it to parse a deb, as a quick diversion, let s break apart a .deb file by hand something that is a bit of a rite of passage (or at least it used to be? I m getting old) during the Debian nm (new member) process, to take a look at where exactly the .debug file lives inside the .deb file.
$ ar x netlabel-tools-dbgsym_0.30.0-1+b1_amd64.deb
$ ls
control.tar.xz debian-binary
data.tar.xz netlabel-tools-dbgsym_0.30.0-1+b1_amd64.deb
$ tar --list -f data.tar.xz   grep '.debug$'
./usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
Since we know quite a bit about the structure of a .deb file, and I had to implement support from scratch anyway, I opted to implement a (very!) basic debfile parser using HTTP Range requests. HTTP Range requests, if supported by the server (denoted by a accept-ranges: bytes HTTP header in response to an HTTP HEAD request to that file) means that we can add a header such as range: bytes=8-68 to specifically request that the returned GET body be the byte range provided (in the above case, the bytes starting from byte offset 8 until byte offset 68). This means we can fetch just the ar file entry from the .deb file until we get to the file inside the .deb we are interested in (in our case, the data.tar.xz file) at which point we can request the body of that file with a final range request. I wound up writing a struct to handle a read_at-style API surface in hrange.rs, which we can pair with ar.rs above and start to find our data in the .deb remotely without downloading and unpacking the .deb at all. After we have the body of the data.tar.xz coming back through the HTTP response, we get to pipe it through an xz decompressor (this kinda sucked in Rust, since a tokio AsyncRead is not the same as an http Body response is not the same as std::io::Read, is not the same as an async (or sync) Iterator is not the same as what the xz2 crate expects; leading me to read blocks of data to a buffer and stuff them through the decoder by looping over the buffer for each lzma2 packet in a loop), and tarfile parser (similarly troublesome). From there we get to iterate over all entries in the tarfile, stopping when we reach our file of interest. Since we can t seek, but gdb needs to, we ll pull it out of the stream into a Cursor<Vec<u8>> in-memory and pass a handle to it back to the user. From here on out its a matter of gluing together a File traited struct in debugfs, and serving the filesystem over TCP using arigato. Done deal!

A quick diversion about compression I was originally hoping to avoid transferring the whole tar file over the network (and therefore also reading the whole debug file into ram, which objectively sucks), but quickly hit issues with figuring out a way around seeking around an xz file. What s interesting is xz has a great primitive to solve this specific problem (specifically, use a block size that allows you to seek to the block as close to your desired seek position just before it, only discarding at most block size - 1 bytes), but data.tar.xz files generated by dpkg appear to have a single mega-huge block for the whole file. I don t know why I would have expected any different, in retrospect. That means that this now devolves into the base case of How do I seek around an lzma2 compressed data stream ; which is a lot more complex of a question. Thankfully, notoriously brilliant tianon was nice enough to introduce me to Jon Johnson who did something super similar adapted a technique to seek inside a compressed gzip file, which lets his service oci.dag.dev seek through Docker container images super fast based on some prior work such as soci-snapshotter, gztool, and zran.c. He also pulled this party trick off for apk based distros over at apk.dag.dev, which seems apropos. Jon was nice enough to publish a lot of his work on this specifically in a central place under the name targz on his GitHub, which has been a ton of fun to read through. The gist is that, by dumping the decompressor s state (window of previous bytes, in-memory data derived from the last N-1 bytes) at specific checkpoints along with the compressed data stream offset in bytes and decompressed offset in bytes, one can seek to that checkpoint in the compressed stream and pick up where you left off creating a similar block mechanism against the wishes of gzip. It means you d need to do an O(n) run over the file, but every request after that will be sped up according to the number of checkpoints you ve taken. Given the complexity of xz and lzma2, I don t think this is possible for me at the moment especially given most of the files I ll be requesting will not be loaded from again especially when I can just cache the debug header by Build-Id. I want to implement this (because I m generally curious and Jon has a way of getting someone excited about compression schemes, which is not a sentence I thought I d ever say out loud), but for now I m going to move on without this optimization. Such a shame, since it kills a lot of the work that went into seeking around the .deb file in the first place, given the debian-binary and control.tar.gz members are so small.

The Good First, the good news right? It works! That s pretty cool. I m positive my younger self would be amused and happy to see this working; as is current day paultag. Let s take debugfs out for a spin! First, we need to mount the filesystem. It even works on an entirely unmodified, stock Debian box on my LAN, which is huge. Let s take it for a spin:
$ mount \
-t 9p \
-o trans=tcp,version=9p2000.u,aname=unstable-debug \
192.168.0.2 \
/usr/lib/debug/.build-id/
And, let s prove to ourselves that this actually mounted before we go trying to use it:
$ mount   grep build-id
192.168.0.2 on /usr/lib/debug/.build-id type 9p (rw,relatime,aname=unstable-debug,access=user,trans=tcp,version=9p2000.u,port=564)
Slick. We ve got an open connection to the server, where our host will keep a connection alive as root, attached to the filesystem provided in aname. Let s take a look at it.
$ ls /usr/lib/debug/.build-id/
00 0d 1a 27 34 41 4e 5b 68 75 82 8E 9b a8 b5 c2 CE db e7 f3
01 0e 1b 28 35 42 4f 5c 69 76 83 8f 9c a9 b6 c3 cf dc E7 f4
02 0f 1c 29 36 43 50 5d 6a 77 84 90 9d aa b7 c4 d0 dd e8 f5
03 10 1d 2a 37 44 51 5e 6b 78 85 91 9e ab b8 c5 d1 de e9 f6
04 11 1e 2b 38 45 52 5f 6c 79 86 92 9f ac b9 c6 d2 df ea f7
05 12 1f 2c 39 46 53 60 6d 7a 87 93 a0 ad ba c7 d3 e0 eb f8
06 13 20 2d 3a 47 54 61 6e 7b 88 94 a1 ae bb c8 d4 e1 ec f9
07 14 21 2e 3b 48 55 62 6f 7c 89 95 a2 af bc c9 d5 e2 ed fa
08 15 22 2f 3c 49 56 63 70 7d 8a 96 a3 b0 bd ca d6 e3 ee fb
09 16 23 30 3d 4a 57 64 71 7e 8b 97 a4 b1 be cb d7 e4 ef fc
0a 17 24 31 3e 4b 58 65 72 7f 8c 98 a5 b2 bf cc d8 E4 f0 fd
0b 18 25 32 3f 4c 59 66 73 80 8d 99 a6 b3 c0 cd d9 e5 f1 fe
0c 19 26 33 40 4d 5a 67 74 81 8e 9a a7 b4 c1 ce da e6 f2 ff
Outstanding. Let s try using gdb to debug a binary that was provided by the Debian archive, and see if it ll load the ELF by build-id from the right .deb in the unstable-debug suite:
$ gdb -q /usr/sbin/netlabelctl
Reading symbols from /usr/sbin/netlabelctl...
Reading symbols from /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug...
(gdb)
Yes! Yes it will!
$ file /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
/usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter *empty*, BuildID[sha1]=e59f81f6573dadd5d95a6e4474d9388ab2777e2a, for GNU/Linux 3.2.0, with debug_info, not stripped

The Bad Linux s support for 9p is mainline, which is great, but it s not robust. Network issues or server restarts will wedge the mountpoint (Linux can t reconnect when the tcp connection breaks), and things that work fine on local filesystems get translated in a way that causes a lot of network chatter for instance, just due to the way the syscalls are translated, doing an ls, will result in a stat call for each file in the directory, even though linux had just got a stat entry for every file while it was resolving directory names. On top of that, Linux will serialize all I/O with the server, so there s no concurrent requests for file information, writes, or reads pending at the same time to the server; and read and write throughput will degrade as latency increases due to increasing round-trip time, even though there are offsets included in the read and write calls. It works well enough, but is frustrating to run up against, since there s not a lot you can do server-side to help with this beyond implementing the 9P2000.L variant (which, maybe is worth it).

The Ugly Unfortunately, we don t know the file size(s) until we ve actually opened the underlying tar file and found the correct member, so for most files, we don t know the real size to report when getting a stat. We can t parse the tarfiles for every stat call, since that d make ls even slower (bummer). Only hiccup is that when I report a filesize of zero, gdb throws a bit of a fit; let s try with a size of 0 to start:
$ ls -lah /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
-r--r--r-- 1 root root 0 Dec 31 1969 /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
$ gdb -q /usr/sbin/netlabelctl
Reading symbols from /usr/sbin/netlabelctl...
Reading symbols from /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug...
warning: Discarding section .note.gnu.build-id which has a section size (24) larger than the file size [in module /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug]
[...]
This obviously won t work since gdb will throw away all our hard work because of stat s output, and neither will loading the real size of the underlying file. That only leaves us with hardcoding a file size and hope nothing else breaks significantly as a result. Let s try it again:
$ ls -lah /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
-r--r--r-- 1 root root 954M Dec 31 1969 /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
$ gdb -q /usr/sbin/netlabelctl
Reading symbols from /usr/sbin/netlabelctl...
Reading symbols from /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug...
(gdb)
Much better. I mean, terrible but better. Better for now, anyway.

Kilroy was here Do I think this is a particularly good idea? I mean; kinda. I m probably going to make some fun 9p arigato-based filesystems for use around my LAN, but I don t think I ll be moving to use debugfs until I can figure out how to ensure the connection is more resilient to changing networks, server restarts and fixes on i/o performance. I think it was a useful exercise and is a pretty great hack, but I don t think this ll be shipping anywhere anytime soon. Along with me publishing this post, I ve pushed up all my repos; so you should be able to play along at home! There s a lot more work to be done on arigato; but it does handshake and successfully export a working 9P2000.u filesystem. Check it out on on my github at arigato, debugfs and also on crates.io and docs.rs. At least I can say I was here and I got it working after all these years.

11 April 2024

Jonathan McDowell: Sorting out backup internet #1: recursive DNS

I work from home these days, and my nearest office is over 100 miles away, 3 hours door to door if I travel by train (and, to be honest, probably not a lot faster given rush hour traffic if I drive). So I m reliant on a functional internet connection in order to be able to work. I m lucky to have access to Openreach FTTP, provided by Aquiss, but I worry about what happens if there s a cable cut somewhere or some other long lasting problem. Worst case I could tether to my work phone, or try to find some local coworking space to use while things get sorted, but I felt like arranging a backup option was a wise move. Step 1 turned out to be sorting out recursive DNS. It s been many moons since I had to deal with running DNS in a production setting, and I ve mostly done my best to avoid doing it at home too. dnsmasq has done a decent job at providing for my needs over the years, covering DHCP, DNS (+ tftp for my test device network). However I just let it forward to my ISP s nameservers, which means if that link goes down it ll no longer be able to resolve anything outside the house. One option would have been to either point to a different recursive DNS server (Cloudfare s 1.1.1.1 or Google s Public DNS being the common choices), but I ve no desire to share my lookup information with them. As another approach I could have done some sort of failover of resolv.conf when the primary network went down, but then I would have to get into moving files around based on networking status and that felt a bit clunky. So I decided to finally setup a proper local recursive DNS server, which is something I ve kinda meant to do for a while but never had sufficient reason to look into. Last time I did this I did it with BIND 9 but there are more options these days, and I decided to go with unbound, which is primarily focused on recursive DNS. One extra wrinkle, pointed out by Lars, is that having dynamic name information from DHCP hosts is exceptionally convenient. I ve kept dnsmasq as the local DHCP server, so I wanted to be able to forward local queries there. I m doing all of this on my RB5009, running Debian. Installing unbound was a simple matter of apt install unbound. I needed 2 pieces of configuration over the default, one to enable recursive serving for the house networks, and one to enable forwarding of queries for the local domain to dnsmasq. I originally had specified the wildcard address for listening, but this caused problems with the fact my router has many interfaces and would sometimes respond from a different address than the request had come in on.
/etc/unbound/unbound.conf.d/network-resolver.conf
server:
  interface: 192.0.2.1
  interface: 2001::db8:f00d::1
  access-control: 192.0.2.0/24 allow
  access-control: 2001::db8:f00d::/56 allow

/etc/unbound/unbound.conf.d/local-to-dnsmasq.conf
server:
  domain-insecure: "example.org"
  do-not-query-localhost: no
forward-zone:
  name: "example.org"
  forward-addr: 127.0.0.1@5353

I then had to configure dnsmasq to not listen on port 53 (so unbound could), respond to requests on the loopback interface (I have dnsmasq restricted to only explicitly listed interfaces), and to hand out unbound as the appropriate nameserver in DHCP requests - once dnsmasq is not listening on port 53 it no longer does this by default.
/etc/dnsmasq.d/behind-unbound
interface=lo
port=5353
dhcp-option=option6:dns-server,[2001::db8:f00d::1]
dhcp-option=option:dns-server,192.0.2.1

With these minor changes in place I now have local recursive DNS being handled by unbound, without losing dynamic local DNS for DHCP hosts. As an added bonus I now get 10/10 on Test IPv6 - previously I was getting dinged on the ability for my DNS server to resolve purely IPv6 reachable addresses. Next step, actually sorting out a backup link.

Reproducible Builds: Reproducible Builds in March 2024

Welcome to the March 2024 report from the Reproducible Builds project! In our reports, we attempt to outline what we have been up to over the past month, as well as mentioning some of the important things happening more generally in software supply-chain security. As ever, if you are interested in contributing to the project, please visit our Contribute page on our website. Table of contents:
  1. Arch Linux minimal container userland now 100% reproducible
  2. Validating Debian s build infrastructure after the XZ backdoor
  3. Making Fedora Linux (more) reproducible
  4. Increasing Trust in the Open Source Supply Chain with Reproducible Builds and Functional Package Management
  5. Software and source code identification with GNU Guix and reproducible builds
  6. Two new Rust-based tools for post-processing determinism
  7. Distribution work
  8. Mailing list highlights
  9. Website updates
  10. Delta chat clients now reproducible
  11. diffoscope updates
  12. Upstream patches
  13. Reproducibility testing framework

Arch Linux minimal container userland now 100% reproducible In remarkable news, Reproducible builds developer kpcyrd reported that that the Arch Linux minimal container userland is now 100% reproducible after work by developers dvzv and Foxboron on the one remaining package. This represents a real world , widely-used Linux distribution being reproducible. Their post, which kpcyrd suffixed with the question now what? , continues on to outline some potential next steps, including validating whether the container image itself could be reproduced bit-for-bit. The post, which was itself a followup for an Arch Linux update earlier in the month, generated a significant number of replies.

Validating Debian s build infrastructure after the XZ backdoor From our mailing list this month, Vagrant Cascadian wrote about being asked about trying to perform concrete reproducibility checks for recent Debian security updates, in an attempt to gain some confidence about Debian s build infrastructure given that they performed builds in environments running the high-profile XZ vulnerability. Vagrant reports (with some caveats):
So far, I have not found any reproducibility issues; everything I tested I was able to get to build bit-for-bit identical with what is in the Debian archive.
That is to say, reproducibility testing permitted Vagrant and Debian to claim with some confidence that builds performed when this vulnerable version of XZ was installed were not interfered with.

Making Fedora Linux (more) reproducible In March, Davide Cavalca gave a talk at the 2024 Southern California Linux Expo (aka SCALE 21x) about the ongoing effort to make the Fedora Linux distribution reproducible. Documented in more detail on Fedora s website, the talk touched on topics such as the specifics of implementing reproducible builds in Fedora, the challenges encountered, the current status and what s coming next. (YouTube video)

Increasing Trust in the Open Source Supply Chain with Reproducible Builds and Functional Package Management Julien Malka published a brief but interesting paper in the HAL open archive on Increasing Trust in the Open Source Supply Chain with Reproducible Builds and Functional Package Management:
Functional package managers (FPMs) and reproducible builds (R-B) are technologies and methodologies that are conceptually very different from the traditional software deployment model, and that have promising properties for software supply chain security. This thesis aims to evaluate the impact of FPMs and R-B on the security of the software supply chain and propose improvements to the FPM model to further improve trust in the open source supply chain. PDF
Julien s paper poses a number of research questions on how the model of distributions such as GNU Guix and NixOS can be leveraged to further improve the safety of the software supply chain , etc.

Software and source code identification with GNU Guix and reproducible builds In a long line of commendably detailed blog posts, Ludovic Court s, Maxim Cournoyer, Jan Nieuwenhuizen and Simon Tournier have together published two interesting posts on the GNU Guix blog this month. In early March, Ludovic Court s, Maxim Cournoyer, Jan Nieuwenhuizen and Simon Tournier wrote about software and source code identification and how that might be performed using Guix, rhetorically posing the questions: What does it take to identify software ? How can we tell what software is running on a machine to determine, for example, what security vulnerabilities might affect it? Later in the month, Ludovic Court s wrote a solo post describing adventures on the quest for long-term reproducible deployment. Ludovic s post touches on GNU Guix s aim to support time travel , the ability to reliably (and reproducibly) revert to an earlier point in time, employing the iconic image of Harold Lloyd hanging off the clock in Safety Last! (1925) to poetically illustrate both the slapstick nature of current modern technology and the gymnastics required to navigate hazards of our own making.

Two new Rust-based tools for post-processing determinism Zbigniew J drzejewski-Szmek announced add-determinism, a work-in-progress reimplementation of the Reproducible Builds project s own strip-nondeterminism tool in the Rust programming language, intended to be used as a post-processor in RPM-based distributions such as Fedora In addition, Yossi Kreinin published a blog post titled refix: fast, debuggable, reproducible builds that describes a tool that post-processes binaries in such a way that they are still debuggable with gdb, etc.. Yossi post details the motivation and techniques behind the (fast) performance of the tool.

Distribution work In Debian this month, since the testing framework no longer varies the build path, James Addison performed a bulk downgrade of the bug severity for issues filed with a level of normal to a new level of wishlist. In addition, 28 reviews of Debian packages were added, 38 were updated and 23 were removed this month adding to ever-growing knowledge about identified issues. As part of this effort, a number of issue types were updated, including Chris Lamb adding a new ocaml_include_directories toolchain issue [ ] and James Addison adding a new filesystem_order_in_java_jar_manifest_mf_include_resource issue [ ] and updating the random_uuid_in_notebooks_generated_by_nbsphinx to reference a relevant discussion thread [ ]. In addition, Roland Clobus posted his 24th status update of reproducible Debian ISO images. Roland highlights that the images for Debian unstable often cannot be generated due to changes in that distribution related to the 64-bit time_t transition. Lastly, Bernhard M. Wiedemann posted another monthly update for his reproducibility work in openSUSE.

Mailing list highlights Elsewhere on our mailing list this month:

Website updates There were made a number of improvements to our website this month, including:
  • Pol Dellaiera noticed the frequent need to correctly cite the website itself in academic work. To facilitate easier citation across multiple formats, Pol contributed a Citation File Format (CIF) file. As a result, an export in BibTeX format is now available in the Academic Publications section. Pol encourages community contributions to further refine the CITATION.cff file. Pol also added an substantial new section to the buy in page documenting the role of Software Bill of Materials (SBOMs) and ephemeral development environments. [ ][ ]
  • Bernhard M. Wiedemann added a new commandments page to the documentation [ ][ ] and fixed some incorrect YAML elsewhere on the site [ ].
  • Chris Lamb add three recent academic papers to the publications page of the website. [ ]
  • Mattia Rizzolo and Holger Levsen collaborated to add Infomaniak as a sponsor of amd64 virtual machines. [ ][ ][ ]
  • Roland Clobus updated the stable outputs page, dropping version numbers from Python documentation pages [ ] and noting that Python s set data structure is also affected by the PYTHONHASHSEED functionality. [ ]

Delta chat clients now reproducible Delta Chat, an open source messaging application that can work over email, announced this month that the Rust-based core library underlying Delta chat application is now reproducible.

diffoscope diffoscope is our in-depth and content-aware diff utility that can locate and diagnose reproducibility issues. This month, Chris Lamb made a number of changes such as uploading versions 259, 260 and 261 to Debian and made the following additional changes:
  • New features:
    • Add support for the zipdetails tool from the Perl distribution. Thanks to Fay Stegerman and Larry Doolittle et al. for the pointer and thread about this tool. [ ]
  • Bug fixes:
    • Don t identify Redis database dumps as GNU R database files based simply on their filename. [ ]
    • Add a missing call to File.recognizes so we actually perform the filename check for GNU R data files. [ ]
    • Don t crash if we encounter an .rdb file without an equivalent .rdx file. (#1066991)
    • Correctly check for 7z being available and not lz4 when testing 7z. [ ]
    • Prevent a traceback when comparing a contentful .pyc file with an empty one. [ ]
  • Testsuite improvements:
    • Fix .epub tests after supporting the new zipdetails tool. [ ]
    • Don t use parenthesis within test skipping messages, as PyTest adds its own parenthesis. [ ]
    • Factor out Python version checking in test_zip.py. [ ]
    • Skip some Zip-related tests under Python 3.10.14, as a potential regression may have been backported to the 3.10.x series. [ ]
    • Actually test 7z support in the test_7z set of tests, not the lz4 functionality. (Closes: reproducible-builds/diffoscope#359). [ ]
In addition, Fay Stegerman updated diffoscope s monkey patch for supporting the unusual Mozilla ZIP file format after Python s zipfile module changed to detect potentially insecure overlapping entries within .zip files. (#362) Chris Lamb also updated the trydiffoscope command line client, dropping a build-dependency on the deprecated python3-distutils package to fix Debian bug #1065988 [ ], taking a moment to also refresh the packaging to the latest Debian standards [ ]. Finally, Vagrant Cascadian submitted an update for diffoscope version 260 in GNU Guix. [ ]

Upstream patches This month, we wrote a large number of patches, including: Bernhard M. Wiedemann used reproducibility-tooling to detect and fix packages that added changes in their %check section, thus failing when built with the --no-checks option. Only half of all openSUSE packages were tested so far, but a large number of bugs were filed, including ones against caddy, exiv2, gnome-disk-utility, grisbi, gsl, itinerary, kosmindoormap, libQuotient, med-tools, plasma6-disks, pspp, python-pypuppetdb, python-urlextract, rsync, vagrant-libvirt and xsimd. Similarly, Jean-Pierre De Jesus DIAZ employed reproducible builds techniques in order to test a proposed refactor of the ath9k-htc-firmware package. As the change produced bit-for-bit identical binaries to the previously shipped pre-built binaries:
I don t have the hardware to test this firmware, but the build produces the same hashes for the firmware so it s safe to say that the firmware should keep working.

Reproducibility testing framework The Reproducible Builds project operates a comprehensive testing framework running primarily at tests.reproducible-builds.org in order to check packages and other artifacts for reproducibility. In March, an enormous number of changes were made by Holger Levsen:
  • Debian-related changes:
    • Sleep less after a so-called 404 package state has occurred. [ ]
    • Schedule package builds more often. [ ][ ]
    • Regenerate all our HTML indexes every hour, but only every 12h for the released suites. [ ]
    • Create and update unstable and experimental base systems on armhf again. [ ][ ]
    • Don t reschedule so many depwait packages due to the current size of the i386 architecture queue. [ ]
    • Redefine our scheduling thresholds and amounts. [ ]
    • Schedule untested packages with a higher priority, otherwise slow architectures cannot keep up with the experimental distribution growing. [ ]
    • Only create the stats_buildinfo.png graph once per day. [ ][ ]
    • Reproducible Debian dashboard: refactoring, update several more static stats only every 12h. [ ]
    • Document how to use systemctl with new systemd-based services. [ ]
    • Temporarily disable armhf and i386 continuous integration tests in order to get some stability back. [ ]
    • Use the deb.debian.org CDN everywhere. [ ]
    • Remove the rsyslog logging facility on bookworm systems. [ ]
    • Add zst to the list of packages which are false-positive diskspace issues. [ ]
    • Detect failures to bootstrap Debian base systems. [ ]
  • Arch Linux-related changes:
    • Temporarily disable builds because the pacman package manager is broken. [ ][ ]
    • Split reproducible_html_live_status and split the scheduling timing . [ ][ ][ ]
    • Improve handling when database is locked. [ ][ ]
  • Misc changes:
    • Show failed services that require manual cleanup. [ ][ ]
    • Integrate two new Infomaniak nodes. [ ][ ][ ][ ]
    • Improve IRC notifications for artifacts. [ ]
    • Run diffoscope in different systemd slices. [ ]
    • Run the node health check more often, as it can now repair some issues. [ ][ ]
    • Also include the string Bot in the userAgent for Git. (Re: #929013). [ ]
    • Document increased tmpfs size on our OUSL nodes. [ ]
    • Disable memory account for the reproducible_build service. [ ][ ]
    • Allow 10 times as many open files for the Jenkins service. [ ]
    • Set OOMPolicy=continue and OOMScoreAdjust=-1000 for both the Jenkins and the reproducible_build service. [ ]
Mattia Rizzolo also made the following changes:
  • Debian-related changes:
    • Define a systemd slice to group all relevant services. [ ][ ]
    • Add a bunch of quotes in scripts to assuage the shellcheck tool. [ ]
    • Add stats on how many packages have been built today so far. [ ]
    • Instruct systemd-run to handle diffoscope s exit codes specially. [ ]
    • Prefer the pgrep tool over grepping the output of ps. [ ]
    • Re-enable a couple of i386 and armhf architecture builders. [ ][ ]
    • Fix some stylistic issues flagged by the Python flake8 tool. [ ]
    • Cease scheduling Debian unstable and experimental on the armhf architecture due to the time_t transition. [ ]
    • Start a few more i386 & armhf workers. [ ][ ][ ]
    • Temporarly skip pbuilder updates in the unstable distribution, but only on the armhf architecture. [ ]
  • Other changes:
    • Perform some large-scale refactoring on how the systemd service operates. [ ][ ]
    • Move the list of workers into a separate file so it s accessible to a number of scripts. [ ]
    • Refactor the powercycle_x86_nodes.py script to use the new IONOS API and its new Python bindings. [ ]
    • Also fix nph-logwatch after the worker changes. [ ]
    • Do not install the stunnel tool anymore, it shouldn t be needed by anything anymore. [ ]
    • Move temporary directories related to Arch Linux into a single directory for clarity. [ ]
    • Update the arm64 architecture host keys. [ ]
    • Use a common Postfix configuration. [ ]
The following changes were also made by:
  • Jan-Benedict Glaw:
    • Initial work to clean up a messy NetBSD-related script. [ ][ ]
  • Roland Clobus:
    • Show the installer log if the installer fails to build. [ ]
    • Avoid the minus character (i.e. -) in a variable in order to allow for tags in openQA. [ ]
    • Update the schedule of Debian live image builds. [ ]
  • Vagrant Cascadian:
    • Maintenance on the virt* nodes is completed so bring them back online. [ ]
    • Use the fully qualified domain name in configuration. [ ]
Node maintenance was also performed by Holger Levsen, Mattia Rizzolo [ ][ ] and Vagrant Cascadian [ ][ ][ ][ ]

If you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:

5 April 2024

Emanuele Rocca: PGP keys on Yubikey, with a side of Mutt

Here are my notes about copying PGP keys to external hardware devices such as Yubikeys. Let me begin by saying that the gpg tools are pretty bad at this.
MAKE A COUPLE OF BACKUPS OF ~/.gnupg/ TO DIFFERENT ENCRYPTED USB STICKS BEFORE YOU START. GPG WILL MESS UP YOUR KEYS. SERIOUSLY.
For example, would you believe me if I said that saving changes results in the removal of your private key? Well check this out.
Now that you have multiple safe, offline backups of your keys, here are my notes.
apt install yubikey-manager scdaemon
Plug the Yubikey in, see if it s recognized properly:
ykman list
gpg --card-status
Change the default PIN (123456) and Admin PIN (12345678):
gpg --card-edit
gpg/card> admin
gpg/card> passwd
Look at the openpgp information and change the maximum number of retries, if you like. I have seen this failing a couple of times, unplugging the Yubikey and putting it back in worked.
ykman openpgp info
ykman openpgp access set-retries 7 7 7
Copy your keys. MAKE A BACKUP OF ~/.gnupg/ BEFORE YOU DO THIS.
gpg --edit-key $KEY_ID
gpg> keytocard # follow the prompts to copy the first key
Now choose the next key and copy that one too. Repeat till all subkeys are copied.
gpg> key 1
gpg> keytocard
Typing gpg --card-status you should be able to see all your keys on the Yubikey now.

Using the key on another machine
How do you use your PGP keys on the Yubikey on other systems?
Go to another system, if it does have a ~/.gnupg directory already move it somewhere else.
apt install scdaemon
Import your public key:
gpg -k
gpg --keyserver pgp.mit.edu --recv-keys $KEY_ID
Check the fingerprint and if it is indeed your key say you trust it:
gpg --edit-key $KEY_ID
> trust
> 5
> y
> save
Now try gpg --card-status and gpg --list-secret-keys, you should be able to see your keys. Try signing something, it should work.
gpg --output /tmp/x.out --sign /etc/motd
gpg --verify /tmp/x.out

Using the Yubikey with Mutt
If you re using mutt with IMAP, there is a very simple trick to safely store your password on disk. Create an encrypted file with your IMAP password:
echo SUPERSECRET   gpg --encrypt > ~/.mutt_password.gpg
Add the following to ~/.muttrc:
set imap_pass= gpg --decrypt ~/.mutt_password.gpg 
With the above, mutt now prompts you to insert the Yubikey and type your PIN in order to connect to the IMAP server.

26 March 2024

Emmanuel Kasper: Adding a private / custom Certificate Authority to the firefox trust store

Today at $WORK I needed to add the private company Certificate Authority (CA) to Firefox, and I found the steps were unnecessarily complex. Time to blog about that, and I also made a Debian wiki article of that post, so that future generations can update the information, when Firefox 742 is released on Debian 17. The cacert certificate authority is not included in Debian and Firefox, and is thus a good example of adding a private CA. Note that this does not mean I specifically endorse that CA.
  • Test that SSL connections to a site signed by the private CA is failing
$ gnutls-cli wiki.cacert.org:443
...
- Status: The certificate is NOT trusted. The certificate issuer is unknown. 
*** PKI verification of server certificate failed...
*** Fatal error: Error in the certificate.
  • Download the private CA
$ wget http://www.cacert.org/certs/root_X0F.crt
  • test that a connection works with the private CA
$ gnutls-cli --x509cafile root_X0F.crt wiki.cacert.org:443
...
- Status: The certificate is trusted. 
- Description: (TLS1.2-X.509)-(ECDHE-SECP256R1)-(RSA-SHA256)-(AES-256-GCM)
- Session ID: 37:56:7A:89:EA:5F:13:E8:67:E4:07:94:4B:52:23:63:1E:54:31:69:5D:70:17:3C:D0:A4:80:B0:3A:E5:22:B3
- Options: safe renegotiation,
- Handshake was completed
...
  • add the private CA to the Debian trust store located in /etc/ssl/certs/ca-certificates.crt
$ sudo cp root_X0F.crt /usr/local/share/ca-certificates/cacert-org-root-ca.crt
$ sudo update-ca-certificates --verbose
...
Adding debian:cacert-org-root-ca.pem
...
  • verify that we can connect without passing the private CA on the command line
$ gnutls-cli wiki.cacert.org:443
... 
 - Status: The certificate is trusted.
  • At that point most applications are able to connect to systems with a certificate signed by the private CA (curl, Gnome builtin Browser ). However Firefox is using its own trust store and will still display a security error if connecting to https://wiki.cacert.org. To make Firefox trust the Debian trust store, we need to add a so called security device, in fact an extra library wrapping the Debian trust store. The library will wrap the Debian trust store in the PKCS#11 industry format that Firefox supports.
  • install the pkcs#11 wrapping library and command line tools
$ sudo apt install p11-kit p11-kit-modules
  • verify that the private CA is accessible via PKCS#11
$ trust list   grep --context 2 'CA Cert'
pkcs11:id=%16%B5%32%1B%D4%C7%F3%E0%E6%8E%F3%BD%D2%B0%3A%EE%B2%39%18%D1;type=cert
    type: certificate
    label: CA Cert Signing Authority
    trust: anchor
    category: authority
  • now we need to add a new security device in Firefox pointing to the pkcs11 trust store. The pkcs11 trust store is located in /usr/lib/x86_64-linux-gnu/pkcs11/p11-kit-trust.so
$ dpkg --listfiles p11-kit-modules   grep trust
/usr/lib/x86_64-linux-gnu/pkcs11/p11-kit-trust.so
  • in Firefox (tested in version 115 esr), go to Settings -> Privacy & Security -> Security -> Security Devices.
    Then click Load , in the popup window use My local trust as a module name, and /usr/lib/x86_64-linux-gnu/pkcs11/p11-kit-trust.so as a module filename. After adding the module, you should see it in the list of Security Devices, having /etc/ssl/certs/ca-certificates.crt as a description.
  • now restart Firefox and you should be able to browse https://wiki.cacert.org without security errors

24 March 2024

Jacob Adams: Regular Reboots

Uptime is often considered a measure of system reliability, an indication that the running software is stable and can be counted on. However, this hides the insidious build-up of state throughout the system as it runs, the slow drift from the expected to the strange. As Nolan Lawson highlights in an excellent post entitled Programmers are bad at managing state, state is the most challenging part of programming. It s why did you try turning it off and on again is a classic tech support response to any problem. In addition to the problem of state, installing regular updates periodically requires a reboot, even if the rest of the process is automated through a tool like unattended-upgrades. For my personal homelab, I manage a handful of different machines running various services. I used to just schedule a day to update and reboot all of them, but that got very tedious very quickly. I then moved the reboot to a cronjob, and then recently to a systemd timer and service. I figure that laying out my path to better management of this might help others, and will almost certainly lead to someone telling me a better way to do this. UPDATE: Turns out there s another option for better systemd cron integration. See systemd-cron below.

Stage One: Reboot Cron The first, and easiest approach, is a simple cron job. Just adding the following line to /var/spool/cron/crontabs/root1 is enough to get your machine to reboot once a month2 on the 6th at 8:00 AM3:
0 8 6 * * reboot
I had this configured for many years and it works well. But you have no indication as to whether it succeeds except for checking your uptime regularly yourself.

Stage Two: Reboot systemd Timer The next evolution of this approach for me was to use a systemd timer. I created a regular-reboot.timer with the following contents:
[Unit]
Description=Reboot on a Regular Basis
[Timer]
Unit=regular-reboot.service
OnBootSec=1month
[Install]
WantedBy=timers.target
This timer will trigger the regular-reboot.service systemd unit when the system reaches one month of uptime. I ve seen some guides to creating timer units recommend adding a Wants=regular-reboot.service to the [Unit] section, but this has the consequence of running that service every time it starts the timer. In this case that will just reboot your system on startup which is not what you want. Care needs to be taken to use the OnBootSec directive instead of OnCalendar or any of the other time specifications, as your system could reboot, discover its still within the expected window and reboot again. With OnBootSec your system will not have that problem. Technically, this same problem could have occurred with the cronjob approach, but in practice it never did, as the systems took long enough to come back up that they were no longer within the expected window for the job. I then added the regular-reboot.service:
[Unit]
Description=Reboot on a Regular Basis
Wants=regular-reboot.timer
[Service]
Type=oneshot
ExecStart=shutdown -r 02:45
You ll note that this service is actually scheduling a specific reboot time via the shutdown command instead of just immediately rebooting. This is a bit of a hack needed because I can t control when the timer runs exactly when using OnBootSec. This way different systems have different reboot times so that everything doesn t just reboot and fail all at once. Were something to fail to come back up I would have some time to fix it, as each machine has a few hours between scheduled reboots. One you have both files in place, you ll simply need to reload configuration and then enable and start the timer unit:
systemctl daemon-reload
systemctl enable --now regular-reboot.timer
You can then check when it will fire next:
# systemctl status regular-reboot.timer
  regular-reboot.timer - Reboot on a Regular Basis
     Loaded: loaded (/etc/systemd/system/regular-reboot.timer; enabled; preset: enabled)
     Active: active (waiting) since Wed 2024-03-13 01:54:52 EDT; 1 week 4 days ago
    Trigger: Fri 2024-04-12 12:24:42 EDT; 2 weeks 4 days left
   Triggers:   regular-reboot.service
Mar 13 01:54:52 dorfl systemd[1]: Started regular-reboot.timer - Reboot on a Regular Basis.

Sidenote: Replacing all Cron Jobs with systemd Timers More generally, I ve now replaced all cronjobs on my personal systems with systemd timer units, mostly because I can now actually track failures via prometheus-node-exporter. There are plenty of ways to hack in cron support to the node exporter, but just moving to systemd units provides both support for tracking failure and logging, both of which make system administration much easier when things inevitably go wrong.

systemd-cron An alternative to converting everything by hand, if you happen to have a lot of cronjobs is systemd-cron. It will make each crontab and /etc/cron.* directory into automatic service and timer units. Thanks to Alexandre Detiste for letting me know about this project. I have few enough cron jobs that I ve already converted, but for anyone looking at a large number of jobs to convert you ll want to check it out!

Stage Three: Monitor that it s working The final step here is confirm that these units actually work, beyond just firing regularly. I now have the following rule in my prometheus-alertmanager rules:
  - alert: UptimeTooHigh
    expr: (time() - node_boot_time_seconds job="node" ) / 86400 > 35
    annotations:
      summary: "Instance  Has Been Up Too Long!"
      description: "Instance  Has Been Up Too Long!"
This will trigger an alert anytime that I have a machine up for more than 35 days. This actually helped me track down one machine that I had forgotten to set up this new unit on4.

Not everything needs to scale Is It Worth The Time One of the most common fallacies programmers fall into is that we will jump to automating a solution before we stop and figure out how much time it would even save. In taking a slow improvement route to solve this problem for myself, I ve managed not to invest too much time5 in worrying about this but also achieved a meaningful improvement beyond my first approach of doing it all by hand.
  1. You could also add a line to /etc/crontab or drop a script into /etc/cron.monthly depending on your system.
  2. Why once a month? Mostly to avoid regular disruptions, but still be reasonably timely on updates.
  3. If you re looking to understand the cron time format I recommend crontab guru.
  4. In the long term I really should set up something like ansible to automatically push fleetwide changes like this but with fewer machines than fingers this seems like overkill.
  5. Of course by now writing about it, I ve probably doubled the amount of time I ve spent thinking about this topic but oh well

23 March 2024

Kentaro Hayashi: How about allocating more buildd resource for armel and armhf?

This article is cross-posting from grow-your-ideas. This is just an idea. salsa.debian.org

The problem According to Developer Machines [1], current buildd machines are like this:
  • armel: 4 buildd (4 for arm64/armhf/armel)
  • armhf: 7 buildd (4 for arm64/armhf/armel and 3 for armhf only)
[1] https://db.debian.org/machines.cgi In contrast to other buildd architectures, these instances are quite a few and it seems that it causes a shortage of buildd resourses. (e.g. during mass transition, give-back turn around time becomes longer and longer.)

Actual situation As you know, during 64bit time_t transition, many packages should be built, but it seems that +b1 or +bN build becomes slower. (I've hit BD-Uninstalled some times because of missing dependency rebuild) ref. https://qa.debian.org/dose/debcheck/unstable_main/index.html

Expected situation Allocate more buildd resources for armel and armhf. It is just an idea, but how about assigning some buildd as armel/armhf buildd? Above buildd is used only for arm64 buildd currently. Maybe there is some technical reason not suitable for armel/armhf buildd, but I don't know yet.
2024/03/24 UPDATE: arm-arm01,arm-arm03,arm-arm-04 has already assigned to armel/armhf buildd, so it is an invalid proposal. See https://buildd.debian.org/status/architecture.php?a=armhf&suite=sid&buildd=buildd_arm64-arm-arm-01, https://buildd.debian.org/status/architecture.php?a=armhf&suite=sid&buildd=buildd_arm64-arm-arm-03, https://buildd.debian.org/status/architecture.php?a=armhf&suite=sid&buildd=buildd_arm64-arm-arm-04

Additional information
  • arm64: 10 buildd (4 for arm64/armhf/armel, 6 for arm64 only)
  • amd64: 7 buildd (5 for amd64/i386 buildd)
  • riscv64: 9 buildd

18 March 2024

Simon Josefsson: Apt archive mirrors in Git-LFS

My effort to improve transparency and confidence of public apt archives continues. I started to work on this in Apt Archive Transparency in which I mention the debdistget project in passing. Debdistget is responsible for mirroring index files for some public apt archives. I ve realized that having a publicly auditable and preserved mirror of the apt repositories is central to being able to do apt transparency work, so the debdistget project has become more central to my project than I thought. Currently I track Trisquel, PureOS, Gnuinos and their upstreams Ubuntu, Debian and Devuan. Debdistget download Release/Package/Sources files and store them in a git repository published on GitLab. Due to size constraints, it uses two repositories: one for the Release/InRelease files (which are small) and one that also include the Package/Sources files (which are large). See for example the repository for Trisquel release files and the Trisquel package/sources files. Repositories for all distributions can be found in debdistutils archives GitLab sub-group. The reason for splitting into two repositories was that the git repository for the combined files become large, and that some of my use-cases only needed the release files. Currently the repositories with packages (which contain a couple of months worth of data now) are 9GB for Ubuntu, 2.5GB for Trisquel/Debian/PureOS, 970MB for Devuan and 450MB for Gnuinos. The repository size is correlated to the size of the archive (for the initial import) plus the frequency and size of updates. Ubuntu s use of Apt Phased Updates (which triggers a higher churn of Packages file modifications) appears to be the primary reason for its larger size. Working with large Git repositories is inefficient and the GitLab CI/CD jobs generate quite some network traffic downloading the git repository over and over again. The most heavy user is the debdistdiff project that download all distribution package repositories to do diff operations on the package lists between distributions. The daily job takes around 80 minutes to run, with the majority of time is spent on downloading the archives. Yes I know I could look into runner-side caching but I dislike complexity caused by caching. Fortunately not all use-cases requires the package files. The debdistcanary project only needs the Release/InRelease files, in order to commit signatures to the Sigstore and Sigsum transparency logs. These jobs still run fairly quickly, but watching the repository size growth worries me. Currently these repositories are at Debian 440MB, PureOS 130MB, Ubuntu/Devuan 90MB, Trisquel 12MB, Gnuinos 2MB. Here I believe the main size correlation is update frequency, and Debian is large because I track the volatile unstable. So I hit a scalability end with my first approach. A couple of months ago I solved this by discarding and resetting these archival repositories. The GitLab CI/CD jobs were fast again and all was well. However this meant discarding precious historic information. A couple of days ago I was reaching the limits of practicality again, and started to explore ways to fix this. I like having data stored in git (it allows easy integration with software integrity tools such as GnuPG and Sigstore, and the git log provides a kind of temporal ordering of data), so it felt like giving up on nice properties to use a traditional database with on-disk approach. So I started to learn about Git-LFS and understanding that it was able to handle multi-GB worth of data that looked promising. Fairly quickly I scripted up a GitLab CI/CD job that incrementally update the Release/Package/Sources files in a git repository that uses Git-LFS to store all the files. The repository size is now at Ubuntu 650kb, Debian 300kb, Trisquel 50kb, Devuan 250kb, PureOS 172kb and Gnuinos 17kb. As can be expected, jobs are quick to clone the git archives: debdistdiff pipelines went from a run-time of 80 minutes down to 10 minutes which more reasonable correlate with the archive size and CPU run-time. The LFS storage size for those repositories are at Ubuntu 15GB, Debian 8GB, Trisquel 1.7GB, Devuan 1.1GB, PureOS/Gnuinos 420MB. This is for a couple of days worth of data. It seems native Git is better at compressing/deduplicating data than Git-LFS is: the combined size for Ubuntu is already 15GB for a couple of days data compared to 8GB for a couple of months worth of data with pure Git. This may be a sub-optimal implementation of Git-LFS in GitLab but it does worry me that this new approach will be difficult to scale too. At some level the difference is understandable, Git-LFS probably store two different Packages files around 90MB each for Trisquel as two 90MB files, but native Git would store it as one compressed version of the 90MB file and one relatively small patch to turn the old files into the next file. So the Git-LFS approach surprisingly scale less well for overall storage-size. Still, the original repository is much smaller, and you usually don t have to pull all LFS files anyway. So it is net win. Throughout this work, I kept thinking about how my approach relates to Debian s snapshot service. Ultimately what I would want is a combination of these two services. To have a good foundation to do transparency work I would want to have a collection of all Release/Packages/Sources files ever published, and ultimately also the source code and binaries. While it makes sense to start on the latest stable releases of distributions, this effort should scale backwards in time as well. For reproducing binaries from source code, I need to be able to securely find earlier versions of binary packages used for rebuilds. So I need to import all the Release/Packages/Sources packages from snapshot into my repositories. The latency to retrieve files from that server is slow so I haven t been able to find an efficient/parallelized way to download the files. If I m able to finish this, I would have confidence that my new Git-LFS based approach to store these files will scale over many years to come. This remains to be seen. Perhaps the repository has to be split up per release or per architecture or similar. Another factor is storage costs. While the git repository size for a Git-LFS based repository with files from several years may be possible to sustain, the Git-LFS storage size surely won t be. It seems GitLab charges the same for files in repositories and in Git-LFS, and it is around $500 per 100GB per year. It may be possible to setup a separate Git-LFS backend not hosted at GitLab to serve the LFS files. Does anyone know of a suitable server implementation for this? I had a quick look at the Git-LFS implementation list and it seems the closest reasonable approach would be to setup the Gitea-clone Forgejo as a self-hosted server. Perhaps a cloud storage approach a la S3 is the way to go? The cost to host this on GitLab will be manageable for up to ~1TB ($5000/year) but scaling it to storing say 500TB of data would mean an yearly fee of $2.5M which seems like poor value for the money. I realized that ultimately I would want a git repository locally with the entire content of all apt archives, including their binary and source packages, ever published. The storage requirements for a service like snapshot (~300TB of data?) is today not prohibitly expensive: 20TB disks are $500 a piece, so a storage enclosure with 36 disks would be around $18.000 for 720TB and using RAID1 means 360TB which is a good start. While I have heard about ~TB-sized Git-LFS repositories, would Git-LFS scale to 1PB? Perhaps the size of a git repository with multi-millions number of Git-LFS pointer files will become unmanageable? To get started on this approach, I decided to import a mirror of Debian s bookworm for amd64 into a Git-LFS repository. That is around 175GB so reasonable cheap to host even on GitLab ($1000/year for 200GB). Having this repository publicly available will make it possible to write software that uses this approach (e.g., porting debdistreproduce), to find out if this is useful and if it could scale. Distributing the apt repository via Git-LFS would also enable other interesting ideas to protecting the data. Consider configuring apt to use a local file:// URL to this git repository, and verifying the git checkout using some method similar to Guix s approach to trusting git content or Sigstore s gitsign. A naive push of the 175GB archive in a single git commit ran into pack size limitations: remote: fatal: pack exceeds maximum allowed size (4.88 GiB) however breaking up the commit into smaller commits for parts of the archive made it possible to push the entire archive. Here are the commands to create this repository: git init
git lfs install
git lfs track 'dists/**' 'pool/**'
git add .gitattributes
git commit -m"Add Git-LFS track attributes." .gitattributes
time debmirror --method=rsync --host ftp.se.debian.org --root :debian --arch=amd64 --source --dist=bookworm,bookworm-updates --section=main --verbose --diff=none --keyring /usr/share/keyrings/debian-archive-keyring.gpg --ignore .git .
git add dists project
git commit -m"Add." -a
git remote add origin git@gitlab.com:debdistutils/archives/debian/mirror.git
git push --set-upstream origin --all
for d in pool//; do
echo $d;
time git add $d;
git commit -m"Add $d." -a
git push
done
The resulting repository size is around 27MB with Git LFS object storage around 174GB. I think this approach would scale to handle all architectures for one release, but working with a single git repository for all releases for all architectures may lead to a too large git repository (>1GB). So maybe one repository per release? These repositories could also be split up on a subset of pool/ files, or there could be one repository per release per architecture or sources. Finally, I have concerns about using SHA1 for identifying objects. It seems both Git and Debian s snapshot service is currently using SHA1. For Git there is SHA-256 transition and it seems GitLab is working on support for SHA256-based repositories. For serious long-term deployment of these concepts, it would be nice to go for SHA256 identifiers directly. Git-LFS already uses SHA256 but Git internally uses SHA1 as does the Debian snapshot service. What do you think? Happy Hacking!

13 March 2024

Russell Coker: The Shape of Computers

Introduction There have been many experiments with the sizes of computers, some of which have stayed around and some have gone away. The trend has been to make computers smaller, the early computers had buildings for them. Recently for come classes computers have started becoming as small as could be reasonably desired. For example phones are thin enough that they can blow away in a strong breeze, smart watches are much the same size as the old fashioned watches they replace, and NUC type computers are as small as they need to be given the size of monitors etc that they connect to. This means that further development in the size and shape of computers will largely be determined by human factors. I think we need to consider how computers might be developed to better suit humans and how to write free software to make such computers usable without being constrained by corporate interests. Those of us who are involved in developing OSs and applications need to consider how to adjust to the changes and ideally anticipate changes. While we can t anticipate the details of future devices we can easily predict general trends such as being smaller, higher resolution, etc. Desktop/Laptop PCs When home computers first came out it was standard to have the keyboard in the main box, the Apple ][ being the most well known example. This has lost popularity due to the demand to have multiple options for a light keyboard that can be moved for convenience combined with multiple options for the box part. But it still pops up occasionally such as the Raspberry Pi 400 [1] which succeeds due to having the computer part being small and light. I think this type of computer will remain a niche product. It could be used in a add a screen to make a laptop as opposed to the add a keyboard to a tablet to make a laptop model but a tablet without a keyboard is more useful than a non-server PC without a display. The PC as box with connections for keyboard, display, etc has a long future ahead of it. But the sizes will probably decrease (they should have stopped making PC cases to fit CD/DVD drives at least 10 years ago). The NUC size is a useful option and I think that DVD drives will stop being used for software soon which will allow a range of smaller form factors. The regular laptop is something that will remain useful, but the tablet with detachable keyboard devices could take a lot of that market. Full functionality for all tasks requires a keyboard because at the moment text editing with a touch screen is an unsolved problem in computer science [2]. The Lenovo Thinkpad X1 Fold [3] and related Lenovo products are very interesting. Advances in materials allow laptops to be thinner and lighter which leaves the screen size as a major limitation to portability. There is a conflict between desiring a large screen to see lots of content and wanting a small size to carry and making a device foldable is an obvious solution that has recently become possible. Making a foldable laptop drives a desire for not having a permanently attached keyboard which then makes a touch screen keyboard a requirement. So this means that user interfaces for PCs have to be adapted to work well on touch screens. The Think line seems to be continuing the history of innovation that it had when owned by IBM. There are also a range of other laptops that have two regular screens so they are essentially the same as the Thinkpad X1 Fold but with two separate screens instead of one folding one, prices are as low as $600US. I think that the typical interfaces for desktop PCs (EG MS-Windows and KDE) don t work well for small devices and touch devices and the Android interface generally isn t a good match for desktop systems. We need to invent more options for this. This is not a criticism of KDE, I use it every day and it works well. But it s designed for use cases that don t match new hardware that is on sale. As an aside it would be nice if Lenovo gave samples of their newest gear to people who make significant contributions to GUIs. Give a few Thinkpad Fold devices to KDE people, a few to GNOME people, and a few others to people involved in Wayland development and see how that promotes software development and future sales. We also need to adopt features from laptops and phones into desktop PCs. When voice recognition software was first released in the 90s it was for desktop PCs, it didn t take off largely because it wasn t very accurate (none of them recognised my voice). Now voice recognition in phones is very accurate and it s very common for desktop PCs to have a webcam or headset with a microphone so it s time for this to be re-visited. GPS support in laptops is obviously useful and can work via Wifi location, via a USB GPS device, or via wwan mobile phone hardware (even if not used for wwan networking). Another possibility is using the same software interfaces as used for GPS on laptops for a static definition of location for a desktop PC or server. The Interesting New Things Watch Like The wrist-watch [4] has been a standard format for easy access to data when on the go since it s military use at the end of the 19th century when the practical benefits beat the supposed femininity of the watch. So it seems most likely that they will continue to be in widespread use in computerised form for the forseeable future. For comparison smart phones have been in widespread use as pocket watches for about 10 years. The question is how will watch computers end up? Will we have Dick Tracy style watch phones that you speak into? Will it be the current smart watch functionality of using the watch to answer a call which goes to a bluetooth headset? Will smart watches end up taking over the functionality of the calculator watch [5] which was popular in the 80 s? With today s technology you could easily have a fully capable PC strapped to your forearm, would that be useful? Phone Like Folding phones (originally popularised as Star Trek Tricorders) seem likely to have a long future ahead of them. Engineering technology has only recently developed to the stage of allowing them to work the way people would hope them to work (a folding screen with no gaps). Phones and tablets with multiple folds are coming out now [6]. This will allow phones to take much of the market share that tablets used to have while tablets and laptops merge at the high end. I ve previously written about Convergence between phones and desktop computers [7], the increased capabilities of phones adds to the case for Convergence. Folding phones also provide new possibilities for the OS. The Oppo OnePlus Open and the Google Pixel Fold both have a UI based around using the two halves of the folding screen for separate data at some times. I think that the current user interfaces for desktop PCs don t properly take advantage of multiple monitors and the possibilities raised by folding phones only adds to the lack. My pet peeve with multiple monitor setups is when they don t make it obvious which monitor has keyboard focus so you send a CTRL-W or ALT-F4 to the wrong screen by mistake, it s a problem that also happens on a single screen but is worse with multiple screens. There are rumours of phones described as three fold (where three means the number of segments with two folds between them), it will be interesting to see how that goes. Will phones go the same way as PCs in terms of having a separation between the compute bit and the input device? It s quite possible to have a compute device in the phone form factor inside a secure pocket which talks via Bluetooth to another device with a display and speakers. Then you could change your phone between a phone-size display and a tablet sized display easily and when using your phone a thief would not be able to easily steal the compute bit (which has passwords etc). Could the watch part of the phone (strapped to your wrist and difficult to steal) be the active part and have a tablet size device as an external display? There are already announcements of smart watches with up to 1GB of RAM (same as the Samsung Galaxy S3), that s enough for a lot of phone functionality. The Rabbit R1 [8] and the Humane AI Pin [9] have some interesting possibilities for AI speech interfaces. Could that take over some of the current phone use? It seems that visually impaired people have been doing badly in the trend towards touch screen phones so an option of a voice interface phone would be a good option for them. As an aside I hope some people are working on AI stuff for FOSS devices. Laptop Like One interesting PC variant I just discovered is the Higole 2 Pro portable battery operated Windows PC with 5.5 touch screen [10]. It looks too thick to fit in the same pockets as current phones but is still very portable. The version with built in battery is $AU423 which is in the usual price range for low end laptops and tablets. I don t think this is the future of computing, but it is something that is usable today while we wait for foldable devices to take over. The recent release of the Apple Vision Pro [11] has driven interest in 3D and head mounted computers. I think this could be a useful peripheral for a laptop or phone but it won t be part of a primary computing environment. In 2011 I wrote about the possibility of using augmented reality technology for providing a desktop computing environment [12]. I wonder how a Vision Pro would work for that on a train or passenger jet. Another interesting thing that s on offer is a laptop with 7 touch screen beside the keyboard [13]. It seems that someone just looked at what parts are available cheaply in China (due to being parts of more popular devices) and what could fit together. I think a keyboard should be central to the monitor for serious typing, but there may be useful corner cases where typing isn t that common and a touch-screen display is of use. Developing a range of strange hardware and then seeing which ones get adopted is a good thing and an advantage of Ali Express and Temu. Useful Hardware for Developing These Things I recently bought a second hand Thinkpad X1 Yoga Gen3 for $359 which has stylus support [14], and it s generally a great little laptop in every other way. There s a common failure case of that model where touch support for fingers breaks but the stylus still works which allows it to be used for testing touch screen functionality while making it cheap. The PineTime is a nice smart watch from Pine64 which is designed to be open [15]. I am quite happy with it but haven t done much with it yet (apart from wearing it every day and getting alerts etc from Android). At $50 when delivered to Australia it s significantly more expensive than most smart watches with similar features but still a lot cheaper than the high end ones. Also the Raspberry Pi Watch [16] is interesting too. The PinePhonePro is an OK phone made to open standards but it s hardware isn t as good as Android phones released in the same year [17]. I ve got some useful stuff done on mine, but the battery life is a major issue and the screen resolution is low. The Librem 5 phone from Purism has a better hardware design for security with switches to disable functionality [18], but it s even slower than the PinePhonePro. These are good devices for test and development but not ones that many people would be excited to use every day. Wwan hardware (for accessing the phone network) in M.2 form factor can be obtained for free if you have access to old/broken laptops. Such devices start at about $35 if you want to buy one. USB GPS devices also start at about $35 so probably not worth getting if you can get a wwan device that does GPS as well. What We Must Do Debian appears to have some voice input software in the pocketsphinx package but no documentation on how it s to be used. This would be a good thing to document, I spent 15 mins looking at it and couldn t get it going. To take advantage of the hardware features in phones we need software support and we ideally don t want free software to lag too far behind proprietary software which IMHO means the typical Android setup for phones/tablets. Support for changing screen resolution is already there as is support for touch screens. Support for adapting the GUI to changed screen size is something that needs to be done even today s hardware of connecting a small laptop to an external monitor doesn t have the ideal functionality for changing the UI. There also seem to be some limitations in touch screen support with multiple screens, I haven t investigated this properly yet, it definitely doesn t work in an expected manner in Ubuntu 22.04 and I haven t yet tested the combinations on Debian/Unstable. ML is becoming a big thing and it has some interesting use cases for small devices where a smart device can compensate for limited input options. There s a lot of work that needs to be done in this area and we are limited by the fact that we can t just rip off the work of other people for use as training data in the way that corporations do. Security is more important for devices that are at high risk of theft. The vast majority of free software installations are way behind Android in terms of security and we need to address that. I have some ideas for improvement but there is always a conflict between security and usability and while Android is usable for it s own special apps it s not usable in a I want to run applications that use any files from any other applicationsin any way I want sense. My post about Sandboxing Phone apps is relevant for people who are interested in this [19]. We also need to extend security models to cope with things like ok google type functionality which has the potential to be a bug and the emerging class of LLM based attacks. I will write more posts about these thing. Please write comments mentioning FOSS hardware and software projects that address these issues and also documentation for such things.

10 March 2024

Vasudev Kamath: Cloning a laptop over NVME TCP

Recently, I got a new laptop and had to set it up so I could start using it. But I wasn't really in the mood to go through the same old steps which I had explained in this post earlier. I was complaining about this to my colleague, and there came the suggestion of why not copy the entire disk to the new laptop. Though it sounded like an interesting idea to me, I had my doubts, so here is what I told him in return.
  1. I don't have the tools to open my old laptop and connect the new disk over USB to my new laptop.
  2. I use full disk encryption, and my old laptop has a 512GB disk, whereas the new laptop has a 1TB NVME, and I'm not so familiar with resizing LUKS.
He promptly suggested both could be done. For step 1, just expose the disk using NVME over TCP and connect it over the network and do a full disk copy, and the rest is pretty simple to achieve. In short, he suggested the following:
  1. Export the disk using nvmet-tcp from the old laptop.
  2. Do a disk copy to the new laptop.
  3. Resize the partition to use the full 1TB.
  4. Resize LUKS.
  5. Finally, resize the BTRFS root disk.
Exporting Disk over NVME TCP The easiest way suggested by my colleague to do this is using systemd-storagetm.service. This service can be invoked by simply booting into storage-target-mode.target by specifying rd.systemd.unit=storage-target-mode.target. But he suggested not to use this as I need to tweak the dracut initrd image to involve network services as well as configuring WiFi from this mode is a painful thing to do. So alternatively, I simply booted both my laptops with GRML rescue CD. And the following step was done to export the NVME disk on my current laptop using the nvmet-tcp module of Linux:
modprobe nvmet-tcp
cd /sys/kernel/config/nvmet
mkdir ports/0
cd ports/0
echo "ipv4" > addr_adrfam
echo 0.0.0.0 > addr_traaddr
echo 4420 > addr_trsvcid
echo tcp > addr_trtype
cd /sys/kernel/config/nvmet/subsystems
mkdir testnqn
echo 1 >testnqn/allow_any_host
mkdir testnqn/namespaces/1
cd testnqn
# replace the device name with the disk you want to export
echo "/dev/nvme0n1" > namespaces/1/device_path
echo 1 > namespaces/1/enable
ln -s "../../subsystems/testnqn" /sys/kernel/config/nvmet/ports/0/subsystems/testnqn
These steps ensure that the device is now exported using NVME over TCP. The next step is to detect this on the new laptop and connect the device:
nvme discover -t tcp -a <ip> -s 4420
nvme connectl-all -t tcp -a <> -s 4420
Finally, nvme list shows the device which is connected to the new laptop, and we can proceed with the next step, which is to do the disk copy.
Copying the Disk I simply used the dd command to copy the root disk to my new laptop. Since the new laptop didn't have an Ethernet port, I had to rely only on WiFi, and it took about 7 and a half hours to copy the entire 512GB to the new laptop. The speed at which I was copying was about 18-20MB/s. The other option would have been to create an initial partition and file system and do an rsync of the root disk or use BTRFS itself for file system transfer.
dd if=/dev/nvme2n1 of=/dev/nvme0n1 status=progress bs=40M
Resizing Partition and LUKS Container The final part was very easy. When I launched parted, it detected that the partition table does not match the disk size and asked if it can fix it, and I said yes. Next, I had to install cloud-guest-utils to get growpart to fix the second partition, and the following command extended the partition to the full 1TB:
growpart /dev/nvem0n1 p2
Next, I used cryptsetup-resize to increase the LUKS container size.
cryptsetup luksOpen /dev/nvme0n1p2 ENC
cryptsetup resize ENC
Finally, I rebooted into the disk, and everything worked fine. After logging into the system, I resized the BTRFS file system. BTRFS requires the system to be mounted for resize, so I could not attempt it in live boot.
btfs fielsystem resize max /
Conclussion The only benefit of this entire process is that I have a new laptop, but I still feel like I'm using my existing laptop. Typically, setting up a new laptop takes about a week or two to completely get adjusted, but in this case, that entire time is saved. An added benefit is that I learned how to export disks using NVME over TCP, thanks to my colleague. This new knowledge adds to the value of the experience.

25 February 2024

Jacob Adams: AAC and Debian

Currently, in a default installation of Debian with the GNOME desktop, Bluetooth headphones that require the AAC codec1 cannot be used. As the Debian wiki outlines, using the AAC codec over Bluetooth, while technically supported by PipeWire, is explicitly disabled in Debian at this time. This is because the fdk-aac library needed to enable this support is currently in the non-free component of the repository, meaning that PipeWire, which is in the main component, cannot depend on it.

How to Fix it Yourself If what you, like me, need is simply for Bluetooth Audio to work with AAC in Debian s default desktop environment2, then you ll need to rebuild the pipewire package to include the AAC codec. While the current version in Debian main has been built with AAC deliberately disabled, it is trivial to enable if you can install a version of the fdk-aac library. I preface this with the usual caveats when it comes to patent and licensing controversies. I am not a lawyer, building this package and/or using it could get you into legal trouble. These instructions have only been tested on an up-to-date copy of Debian 12.
  1. Install pipewire s build dependencies
    sudo apt install build-essential devscripts
    sudo apt build-dep pipewire
    
  2. Install libfdk-aac-dev
    sudo apt install libfdk-aac-dev
    
    If the above doesn t work you ll likely need to enable non-free and try again
    sudo sed -i 's/main/main non-free/g' /etc/apt/sources.list
    sudo apt update
    
    Alternatively, if you wish to ensure you are maximally license-compliant and patent un-infringing3, you can instead build fdk-aac-free which includes only those components of AAC that are known to be patent-free3. This is what should eventually end up in Debian to resolve this problem (see below).
    sudo apt install git-buildpackage
    mkdir fdk-aac-source
    cd fdk-aac-source
    git clone https://salsa.debian.org/multimedia-team/fdk-aac
    cd fdk-aac
    gbp buildpackage
    sudo dpkg -i ../libfdk-aac2_*deb ../libfdk-aac-dev_*deb
    
  3. Get the pipewire source code
    mkdir pipewire-source
    cd pipewire-source
    apt source pipewire
    
    This will create a bunch of files within the pipewire-source directory, but you ll only need the pipewire-<version> folder, this contains all the files you ll need to build the package, with all the debian-specific patches already applied. Note that you don t want to run the apt source command as root, as it will then create files that your regular user cannot edit.
  4. Fix the dependencies and build options To fix up the build scripts to use the fdk-aac library, you need to save the following as pipewire-source/aac.patch
    --- debian/control.orig
    +++ debian/control
    @@ -40,8 +40,8 @@
                 modemmanager-dev,
                 pkg-config,
                 python3-docutils,
    -               systemd [linux-any]
    -Build-Conflicts: libfdk-aac-dev
    +               systemd [linux-any],
    +               libfdk-aac-dev
     Standards-Version: 4.6.2
     Vcs-Browser: https://salsa.debian.org/utopia-team/pipewire
     Vcs-Git: https://salsa.debian.org/utopia-team/pipewire.git
    --- debian/rules.orig
    +++ debian/rules
    @@ -37,7 +37,7 @@
     		-Dauto_features=enabled \
     		-Davahi=enabled \
     		-Dbluez5-backend-native-mm=enabled \
    -		-Dbluez5-codec-aac=disabled \
    +		-Dbluez5-codec-aac=enabled \
     		-Dbluez5-codec-aptx=enabled \
     		-Dbluez5-codec-lc3=enabled \
     		-Dbluez5-codec-lc3plus=disabled \
    
    Then you ll need to run patch from within the pipewire-<version> folder created by apt source:
    patch -p0 < ../aac.patch
    
  5. Build pipewire
    cd pipewire-*
    debuild
    
    Note that you will likely see an error from debsign at the end of this process, this is harmless, you simply don t have a GPG key set up to sign your newly-built package4. Packages don t need to be signed to be installed, and debsign uses a somewhat non-standard signing process that dpkg does not check anyway.
  1. Install libspa-0.2-bluetooth
    sudo dpkg -i libspa-0.2-bluetooth_*.deb
    
  2. Restart PipeWire and/or Reboot
    sudo reboot
    
    Theoretically there s a set of services to restart here that would get pipewire to pick up the new library, probably just pipewire itself. But it s just as easy to restart and ensure everything is using the correct library.

Why This is a slightly unusual situation, as the fdk-aac library is licensed under what even the GNU project acknowledges is a free software license. However, this license explicitly informs the user that they need to acquire a patent license to use this software5:
3. NO PATENT LICENSE NO EXPRESS OR IMPLIED LICENSES TO ANY PATENT CLAIMS, including without limitation the patents of Fraunhofer, ARE GRANTED BY THIS SOFTWARE LICENSE. Fraunhofer provides no warranty of patent non-infringement with respect to this software. You may use this FDK AAC Codec software or modifications thereto only for purposes that are authorized by appropriate patent licenses.
To quote the GNU project:
Because of this, and because the license author is a known patent aggressor, we encourage you to be careful about using or redistributing software under this license: you should first consider whether the licensor might aim to lure you into patent infringement.
AAC is covered by a number of patents, which expire at some point in the 2030s6. As such the current version of the library is potentially legally dubious to ship with any other software, as it could be considered patent-infringing3.

Fedora s solution Since 2017, Fedora has included a modified version of the library as fdk-aac-free, see the announcement and the bugzilla bug requesting review. This version of the library includes only the AAC LC profile, which is believed to be entirely patent-free3. Based on this, there is an open bug report in Debian requesting that the fdk-aac package be moved to the main component and that the pipwire package be updated to build against it.

The Debian NEW queue To resolve these bugs, a version of fdk-aac-free has been uploaded to Debian by Jeremy Bicha. However, to make it into Debian proper, it must first pass through the ftpmaster s NEW queue. The current version of fdk-aac-free has been in the NEW queue since July 2023. Based on conversations in some of the bugs above, it s been there since at least 20227. I hope this helps anyone stuck with AAC to get their hardware working for them while we wait for the package to eventually make it through the NEW queue. Discuss on Hacker News
  1. Such as, for example, any Apple AirPods, which only support AAC AFAICT.
  2. Which, as of Debian 12 is GNOME 3 under Wayland with PipeWire.
  3. I m not a lawyer, I don t know what kinds of infringement might or might not be possible here, do your own research, etc. 2 3 4
  4. And if you DO have a key setup with debsign you almost certainly don t need these instructions.
  5. This was originally phrased as explicitly does not grant any patent rights. It was pointed out on Hacker News that this is not exactly what it says, as it also includes a specific note that you ll need to acquire your own patent license. I ve now quoted the relevant section of the license for clarity.
  6. Wikipedia claims the base patents expire in 2031, with the extensions expiring in 2038, but its source for these claims is some guy s spreadsheet in a forum. The same discussion also brings up Wikipedia s claim and casts some doubt on it, so I m not entirely sure what s correct here, but I didn t feel like doing a patent deep-dive today. If someone can provide a clear answer that would be much appreciated.
  7. According to Jeremy B cha: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1021370#17

19 February 2024

Matthew Garrett: Debugging an odd inability to stream video

We have a cabin out in the forest, and when I say "out in the forest" I mean "in a national forest subject to regulation by the US Forest Service" which means there's an extremely thick book describing the things we're allowed to do and (somewhat longer) not allowed to do. It's also down in the bottom of a valley surrounded by tall trees (the whole "forest" bit). There used to be AT&T copper but all that infrastructure burned down in a big fire back in 2021 and AT&T no longer supply new copper links, and Starlink isn't viable because of the whole "bottom of a valley surrounded by tall trees" thing along with regulations that prohibit us from putting up a big pole with a dish on top. Thankfully there's LTE towers nearby, so I'm simply using cellular data. Unfortunately my provider rate limits connections to video streaming services in order to push them down to roughly SD resolution. The easy workaround is just to VPN back to somewhere else, which in my case is just a Wireguard link back to San Francisco.

This worked perfectly for most things, but some streaming services simply wouldn't work at all. Attempting to load the video would just spin forever. Running tcpdump at the local end of the VPN endpoint showed a connection being established, some packets being exchanged, and then nothing. The remote service appeared to just stop sending packets. Tcpdumping the remote end of the VPN showed the same thing. It wasn't until I looked at the traffic on the VPN endpoint's external interface that things began to become clear.

This probably needs some background. Most network infrastructure has a maximum allowable packet size, which is referred to as the Maximum Transmission Unit or MTU. For ethernet this defaults to 1500 bytes, and these days most links are able to handle packets of at least this size, so it's pretty typical to just assume that you'll be able to send a 1500 byte packet. But what's important to remember is that that doesn't mean you have 1500 bytes of packet payload - that 1500 bytes includes whatever protocol level headers are on there. For TCP/IP you're typically looking at spending around 40 bytes on the headers, leaving somewhere around 1460 bytes of usable payload. And if you're using a VPN, things get annoying. In this case the original packet becomes the payload of a new packet, which means it needs another set of TCP (or UDP) and IP headers, and probably also some VPN header. This still all needs to fit inside the MTU of the link the VPN packet is being sent over, so if the MTU of that is 1500, the effective MTU of the VPN interface has to be lower. For Wireguard, this works out to an effective MTU of 1420 bytes. That means simply sending a 1500 byte packet over a Wireguard (or any other VPN) link won't work - adding the additional headers gives you a total packet size of over 1500 bytes, and that won't fit into the underlying link's MTU of 1500.

And yet, things work. But how? Faced with a packet that's too big to fit into a link, there are two choices - break the packet up into multiple smaller packets ("fragmentation") or tell whoever's sending the packet to send smaller packets. Fragmentation seems like the obvious answer, so I'd encourage you to read Valerie Aurora's article on how fragmentation is more complicated than you think. tl;dr - if you can avoid fragmentation then you're going to have a better life. You can explicitly indicate that you don't want your packets to be fragmented by setting the Don't Fragment bit in your IP header, and then when your packet hits a link where your packet exceeds the link MTU it'll send back a packet telling the remote that it's too big, what the actual MTU is, and the remote will resend a smaller packet. This avoids all the hassle of handling fragments in exchange for the cost of a retransmit the first time the MTU is exceeded. It also typically works these days, which wasn't always the case - people had a nasty habit of dropping the ICMP packets telling the remote that the packet was too big, which broke everything.

What I saw when I tcpdumped on the remote VPN endpoint's external interface was that the connection was getting established, and then a 1500 byte packet would arrive (this is kind of the behaviour you'd expect for video - the connection handshaking involves a bunch of relatively small packets, and then once you start sending the video stream itself you start sending packets that are as large as possible in order to minimise overhead). This 1500 byte packet wouldn't fit down the Wireguard link, so the endpoint sent back an ICMP packet to the remote telling it to send smaller packets. The remote should then have sent a new, smaller packet - instead, about a second after sending the first 1500 byte packet, it sent that same 1500 byte packet. This is consistent with it ignoring the ICMP notification and just behaving as if the packet had been dropped.

All the services that were failing were failing in identical ways, and all were using Fastly as their CDN. I complained about this on social media and then somehow ended up in contact with the engineering team responsible for this sort of thing - I sent them a packet dump of the failure, they were able to reproduce it, and it got fixed. Hurray!

(Between me identifying the problem and it getting fixed I was able to work around it. The TCP header includes a Maximum Segment Size (MSS) field, which indicates the maximum size of the payload for this connection. iptables allows you to rewrite this, so on the VPN endpoint I simply rewrote the MSS to be small enough that the packets would fit inside the Wireguard MTU. This isn't a complete fix since it's done at the TCP level rather than the IP level - so any large UDP packets would still end up breaking)

I've no idea what the underlying issue was, and at the client end the failure was entirely opaque: the remote simply stopped sending me packets. The only reason I was able to debug this at all was because I controlled the other end of the VPN as well, and even then I wouldn't have been able to do anything about it other than being in the fortuitous situation of someone able to do something about it seeing my post. How many people go through their lives dealing with things just being broken and having no idea why, and how do we fix that?

(Edit: thanks to this comment, it sounds like the underlying issue was a kernel bug that Fastly developed a fix for - under certain configurations, the kernel fails to associate the MTU update with the egress interface and so it continues sending overly large packets)

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16 February 2024

Mike Gabriel: Debian Edu 12 - Call for Testing

This is a call for testing of Debian Edu based on Debian bookworm. With the Debian 12.5 point release all required packages have landed in the Debian Edu ISO images that allow you to install a Debian Edu system based on Debian 12. ISO Image Downloads You can find the Blueray Disc ISO image (use for main server installation) at: http://cdimage.debian.org/cdimage/release/current/amd64/iso-bd/debian-ed... For standalone workstation installations or installations on an already up-and-running Debian Edu site, please use the netinst ISO image: http://cdimage.debian.org/cdimage/release/current/amd64/iso-cd/debian-ed... Quick Start HowTo For testing Debian Edu 12, set up e.g. LXD or libVirt and install (at least) three virtual machines. In your virtualization software prepare an internal network where the VMs can reach one another without needing access to your local network. The three VMs: Happy testing! Further Readings Overall installation profile concept of Debian Edu:
https://wiki.debian.org/DebianEdu/BeforeGettingStarted Debian Edu 12 manual:
https://jenkins.debian.net/userContent/debian-edu-doc/ Debian Edu 12 status page:
https://wiki.debian.org/DebianEdu/Status/Bookworm

Next.