Debian Long Term Support (LTS) This is my monthly Debian LTS report. My time this month was spent working on various hairy security issues, most notably XBMC (now known as Kodi) and yaml-cpp.

Kodi directory transversal I started by looking in CVE-2017-5982, a "directory traversal" vulnerability in XBMC (now known as Kodi) which is a technical term for "allow attackers to read any world-readable file on your computer from the network". It's a serious vulnerability which has no known fix. When you enable the "remote control" interface in Kodi, it allows anyone with the password (which is disabled by default) to download any files Kodi has read access to on the machine it's running. Considering Kodi is often connected to multiple services, this may mean elevated compromise and more nasty stuff. I furthered the investigation done with my own analysis which showed the problem is difficult to solve: Kodi internally uses the facility to show thumbnails and media to the user, and there are no clear way of restricting which paths Kodi should have access to. Indeed, Kodi is designed to access mounted file systems and paths in arbitrary locations. In Debian bug #855225, I further confirmed confirmed wheezy and jessie-backports as vulnerable and therefore showed with good certainty that stretch and sid are vulnerable as well. I also suggested possible workaround, but at this point, it's in upstream's hands, as the changes will be intrusive. The file transfer mechanism need to be revamped all over Kodi, or authentication (with a proper password policy), need to be enforced.

Squirrelmail Next I looked at that old webmail software, Squirrelmail, which suffers from a remote code execution vulnerability (CVE-2017-7692) when sending mails with sendmail on the commandline. This is arguably an edge case, but considering the patch was simple, I figured I would provide an update to the LTS community. I tried to get a coordinated release for jessie, since the code is the same, but this wasn't completed at the time of writing. A patch is available and will hopefully be picked up by another LTS worker soon.

Fop and Batik Those issues (CVE-2017-5661 and CVE-2017-5662) were more difficult. The patches weren't clearly documented and there were no upstream references other than security advisories for the first release in years (in the case of batik) or months (in the case of fop), which made it hard to track down the issues. Fortunately, I was able to track down the upstream issues (FOP-2668 and BATIK-1139) where I got confirmation on what the proper fixes were. I could then release DLA-927-1 and DLA-926-1 with the backported patches. I do not use fop or batik. In fact, even after reading the homepage of both products, I couldn't quite figure out what use people could possibly have for that thing. Before uploading the packages, I therefore made packages available for testing for fop and batik.

libsndfile Next up was libsndfile which a bunch of overflows when parsing various audio files. I backported a patch for CVE-2017-7585 CVE-2017-7586 and CVE-2017-7741 which all seemed to be fixed by a single patch usptream. CVE-2017-7742 was also fixed, although with a separate patch. In all of those, i could only test CVE-2017-7741 and CVE-2017-7742, as the others were missing test cases. I provided a test package for a few days then I also figured it would be best to incorporate the security fixes done in stable, which brought in fixes for CVE-2015-7805, CVE-2014-9756 and CVE-2014-9496. So in the end, I ported patches from wheezy to jessie and uploaded the jessie version (reverting certain build changes) into wheezy and uploaded DLA-928-1 with the results.

yaml-cpp I then turned to yaml-cpp, a C++ parser for YAML. This one didn't have a known upstream fix, but I figured I would give it a shot anyways. I ended up writing my first C++ code in years which is still pending review and merge upstream. It's not an easy problem to fix: this is basically an excessive recursion problem that can be used to smash the stack. I figured I could introduce a recursion limit, but as the discussion showed, this is a limited approach: stack size varies on different platforms and it's not easy to find the right limit. The real solution is to rewrite the code to avoid recursion but that's a major code refactoring I didn't feel belong in a LTS update. Besides, this could be better handled by upstream, so I will leave things at that for now. It does make you wonder how much code out there is recursing on untrusted data structures...

kedpm Finally, a friend over at Koumbit.org reported Debian bug #860817, as information leak in kedpm, a password manager I previously maintained. I requested and got assigned CVE-2017-8296 and provided a fix for wheezy and jessie. For unstable and the coming stretch release, I have requested kedpm to be completely removed from Debian (Debian bug #860817) which involved a release notes update (Debian bug #861277). It's unfortunate to see software go, but kedpm wasn't maintained. I wasn't the original author: I just gave a few patches and ended up maintaining that software and not using it. It's a bad situation to be in, as you don't really know what's working and not with the tools you are supposed to be responsible for. There are more modern alternatives available now and I encourage everyone to switch.

Triage Looking for more work, I peeked a bit in the secretary tasks to triage some pending issues. I found that trafficserver could be crashed with simple requests (CVE-2017-5659) so I looked into that issue. My analysis showed that the patch is long and complex and could be difficult to backport to the old version available in wheezy. I also couldn't reproduce the issue in wheezy, so it may be a bug introduced only later, although I couldn't confirm that directly. I also triaged wireshark, where I just noted the maintainer expressed concern that we were taking up issues too fast and will probably take care of this one. I also postponed various issues in GnuTLS (marked "no-dsa") as they affect only a (unfortunately) rarely used part of GnuTLS that has been removed in later version: OpenPGP support.

Other free software work

Debiman I finally got around contributing to the debiman project. I worked on ensuring that there is a dman compatibility in debiman, by shipping dman in the debian-goodies package (Debian bug #860920). I also submitted a pull request to fix the fix about page title, document the custom assets repository, fix a stray bracket and link to the link to venerable man7.org project After a discussion on IRC, I also filed a few more issues:

• redirect bpf to bpf.2, not bpf.4freebsd
• redirect to unstable by default
• arrows missing in table of contents
• automatically collapse long links
• old ?query= parameter ignored/failing

I'm happy to be able to contribute to this important service and I hope the new FAQ I created will be online soon!

XMonad and Emacs I started using writeroom-mode again as part of my work on LWN. As it turns out, my setup was not exactly working: I had to port my config to the new version and windows weren't "sticky" as they should be, a known issue with Xmonad. Indeed, Xmonad doesn't obey the "static" or "all desktops" standard directives. Writeroom is a "distraction-free writing" mode for Emacs, so the irony of working on such a deep distraction in establishing a distraction free environment is not lost on me. Needing to scratch that particular itch, and with the help of clever people from the IRC channel, I was able to make Emacs tell Xmonad to show its window (or "frame" as Emacs likes to call it) on all desktops. This involved creating a new function which I think could be useful in the CopyWindow library:

--   Toggle between "copyToAll" or "killAllOtherCopies". Copies to all
-- workspaces, or remove from all other workspaces, depending on
-- previous state (checked with "wsContainingCopies").
copyToAllToggle :: X ()
copyToAllToggle = do
    -- check which workspaces have copies
    copies <- wsContainingCopies
    if null copies
      then windows copyToAll -- no workspaces, make sticky
      else killAllOtherCopies -- already other workspaces, unstick

There are probably better ways of implementing this directly in the CopyWindow code - wsContainingCopies, in particular, is probably overkill. But it's all I can use directly from my xmonad.hs, so that's what I did. The other bit I needed was something to trigger that function from the outside. I rejected the ServerMode hook because it looked a bit too complicated and there is a built-in facility within X that works without this, which, from Emacs' point of view, is the x-send-client-message function. So I made up a new message identifier and wrote a event hook handler to process it:

--   handle X client messages that tell Xmonad to make a window appear
-- on all workspaces
--
-- this should really be using _NET_WM_STATE and
-- _NET_WM_STATE_STICKY. but that's more complicated: then we'd need
-- to inspect a window and figure out the current state and act
-- accordingly. I am not good enough with Xmonad to figure out that
-- part yet.
--
-- Instead, just check for the relevant message and check if the
-- focused window is already on all workspaces and toggle based on
-- that.
--
-- this is designed to interoperate with Emacs's writeroom-mode module
-- and called be called from elisp with:
--
-- (x-send-client-message nil 0 nil "XMONAD_COPY_ALL_SELF" 8 '(0))
myClientMessageEventHook :: Event -> X All
myClientMessageEventHook (ClientMessageEvent  ev_message_type = mt, ev_data = dt ) = do
  dpy <- asks display
  -- the client message we're expecting
  copyAllMsg <- io $ internAtom dpy "XMONAD_COPY_ALL_SELF" False
  -- if the event matches the message we expect, toggle sticky state
  when (mt == copyAllMsg && dt /= []) $ do
    copyToAllToggle
  -- we processed the event completely
  return $ All True

All that was left was to hook that into Emacs, and I was done! Whoohoo! Full screen total domination, distraction free work! I would love to hear from others what they think of that approach, if they have improvements or if the above copyToAllToggle function could be merged in. Ideally, Xmonad would just parse the STICKY client messages and do the right thing - maybe even directly in CopyWindow - but I have found this enough Haskell for one day. You can see the diff on my home directory to see exactly the changes involved to make this configuration work.

Emacs packaging Speaking of Emacs, after complaining in the noisy #emacs IRC channel about the poor TLS configuration of marmelade.org -- and filing a bug (Debian bug #861106) regarding the use of SHA-1 in certificate pinning -- I was told we shouldn't expect trust from third-party ELPA repositories. Marmelade seems to be dead, as the maintainer is "behind the great firewall of China" and MELPA still hasn't figured out how to sign packages. In the end, it seems like there are tons of elpa packages in Debian and that if your favorite one is missing, that's a bug that can be filed and fixed. I first discovered that 6 of the packages I used were already packaged:

• elpa-notmuch
• elpa-ledger
• elpa-use-package
• elpa-markdown-mode
• elpa-go-mode
• elpa-anzu

And so I went ahead and filed a ton more bugs for the packages I am using but that aren't in Debian just yet:

• company-go: Debian bug #861177
• elpy: Debian bug #861174
• markdown-toc: Debian bug #861128
• multiple-cursors: Debian bug #861127
• writegood-mode: Debian bug #861125
• writeroom-mode: Debian bug #861124

Of those, I can't recommend multiple-cursors (MC) enough: I used it at least 4 times just writing this text. It's just awesome. The other ones are also all great in their own right of course, but I feel they are more specific to my workflow whereas MC is just amazing.

ikiwiki I did some more work on ikiwiki the software driving this blog. I created a new plugin to, at least, fix anchors in the table of contents to be human readable. This is something I had done on the MoinMoin wiki almost a decade ago -- which I called then NicerHeadingIds and that I have always found frustrating with Ikiwiki. It turns out the problem was both easier and hairier than I thought. Right from the start, something weird was happening: something was already adding nice headings, but they were somewhat broken. It turns out that multimarkdown already inserts those headers, but I wasn't satisfied with the way they were generated. But even worse, I had the headinganchors plugin enabled, but that plugin wasn't taking effect, because of multimarkdown. And even if it would take effect, it doesn't behave well with non-ASCII characters, which gets turned in their numeric presentation. So I also wrote the i18nheadinganchors plugin that creates better headings and patched the toc plugin so that it can reuse existing anchors if they exist, while keeping backwards compatibility. I hope this gets merged in a future ikiwiki release so I do not have to carry this patch locally too long... In other news, I have upgraded the ikiwiki-hosting package to the latest version and sent a patch upstream to provide HSTS support.

Other stuff I have migrated all my public repos hosted on my home server to either Gitlab.com or Github. I also have repositories on 0xacab and it seemed ludicrous to have 4 different, canonical, places where my code was hosted. I have now about 40 different projects on Gitlab and about 60 on Github, although most of the latter are forks of existing projects. I also made a manpage for stressant and moved the documentation to RTFD which makes it neatly accessible. I also made small incremental improvements (like --directory support). I installed Rainloop on this server to give a nice, mobile-friendly webmail. Instructions to replicate this setup are in mail. In the constant git-annex documentation effort, I tried to draft a user guide that could be a basis for restructuring the documentation to be more easily accessible. I also helped a friend put his documentation on the wiki in splitting a repository. Finally, I also looked into Android stuff a little more. I wrote a usability review of the F-Droid privileged extension that will bring good changes, I hope. I also opened the discussion regarding reproducible builds to try and clarify exactly how those worked to help the Wallabag people ship consistently signed alphas. So far, it seems that it will remain a standard practice on F-Droid to ship packages that are not signed by the official upstream signature, unfortunately, unless upstream provides a reproducible build that is publicly available... Switching to such build is also a hairy issue, as, obviously, the signature changes, which raises the alarm we are trying to avoid in the first place.

Over 80% of the :latest versions of official images contained at least on high severity vulnerability!

• WordPress itself
• All plugins, themes, customizations
• All PHP libraries it uses (MySQL, image-processing, etc.)
• MySQL
• Apache
• All libraries MySQL or Apache use: OpenSSL, libc, PHP itself, etc.
• The kernel
• All containerization tools

1. No built-in way to know when a base needs to be updated, or to automatically update it
2. Diverse and complicated vendor security picture
3. No way to detect when intermediate libraries need to be updated
4. Complicated final application security picture

• nginx: debian:stretch-slim (stretch is pre-release at this date!)
• mysql: debian:jessie
• mongo: debian:wheezy-slim (previous release)
• apache httpd: debian:jessie-backports
• postgres: debian:jessie
• node: buildpack-deps:jessie, eventually depends on debian:jessie
• wordpress: php:5.6-apache, eventually depends on debian:jessie

• oracle/openjdk: oraclelinux:latest
• robotamer/citadel: debian:testing (dangerous, because testing is an alias for different distros at different times)
• docker.elastic.co/kibana: ubuntu of some sort

She shimmers, my city, she shimmers. She is said to be the most beautiful of all the cities of the Civilized Worlds, more beautiful even than Parpallaix or the cathedral cities of Vesper. To the west, pushing into the green sea like a huge, jewel-studded sleeve of city, the fragile obsidian cloisters and hospices of the Farsider's Quarter gleamed like black glass mirrors. Straight ahead as we skated, I saw the frothy churn of the Sound and their whitecaps of breakers crashing against the cliffs of North Beach and above the entire city, veined with purple and glazed with snow and ice, Waaskel and Attakel rose up like vast pyramids against the sky. Beneath the half-ring of extinct volcanoes (Urkel, I should mention, is the southernmost peak, and though less magnificent than the others, it has a conical symmetry that some find pleasing) the towers and spires of the Academy scattered the dazzling false winter light so that the whole of the Old City sparkled.

Although I knew I had never seen her before, I felt as if I had known her all my life. I was instantly in love with her, not, of course, as one loves another human being, but as a wanderer might love a new ocean or a gorgeous snowy peak he has glimpsed for the first time. I was practically struck dumb by her calmness and her beauty, so I said the first stupid thing which came to mind. "Welcome to Neverness," I told her.

• On April 26th Chris Lamb will give a talk at foss-north 2017 in Gothenburg, Sweden on Reproducible Builds.
• Between May 5th-7th the Reproducible Builds Hackathon 2017 will take place in Hamburg, Germany.
• On May 13th Chris Lamb will give a talk at OSCAL'17 in Tirana, Albania on Reproducible Builds.

• It is now possible to upload .buildinfo files to Launchpad.
• There has been more progress on rustc reproducible debugging symbols.

• #860470 filed against libccrtp.
• #860731 filed against viruskiller.
• #860770 filed against qjackctl.
• #860848 filed against osinfo-db.
• #860972 filed against cyclades-serial-client.

• #860418 filed against sugar-memorize-activity. (Patch by Chris Lamb)

• randomness_in_r_rdb_rds_databases: add hint to code line number

• new portable_executable_strong_name_varies
• captures_build_path_in_python_sugar3_symlinks

• Chris Lamb (2)

• Ximin Luo:
  • Add support for R rds and rdb object files
  • rdata: don't break if the .rdx isn't present
• Chris Lamb:
  • Ensure r-base-core is available when testing.
  • Misc cleanups

• Use RPATH in nxagent now for finding libNX_X11 (our fake libX11 with nxcomp support added).
• Drop support for various archaic platforms.
• Fix valgrind issue in new Xinerama code.
• Regression: Fix crash due to incompletely backported code in 3.5.99.3.
• RPM packaging review by nx-libs's official Fedora maintainer (thanks, Orion!).
• Update roll-tarball.sh script.

• Support building against libXfont2 API (using Xfont2, if available in build environment, otherwise falling back to Xfont(1) API)
• Support built-in fonts, no requirement anymore to have the misc fonts installed.
• Various Xserver os/ and dix/ backports from X.org.
• ABI backports: CreatePixmap allocation hints, no index in CloseScreen() destructors propagated anymore, SetNotifyFd ABI, GetClientCmd et al. ABI.
• Add quilt based patch system for bundled Mesa.
• Fix upstream ChangeLog creation in roll-tarball.sh.
• Keystroke.c code fully revisited by Ulrich Sibiller (Thanks!!!).
• nxcomp now builds again on Cygwin. Thanks to Mike DePaulo for providing the patch!
• Bump libNX_X11 to a status that resembles latest X.org libX11 HEAD. (Again, thanks Ulrich!!!).
• Various changes to make valgrind more happy (esp. uninitialized memory issues).
• Hard-code RGB color values, drop previously shipped rgb.txt config file.

• Regression fix for 3.5.99.5: Now fonts are display correctly again after session resumption.
• Prefer source tree's nxcomp to system-wide installed nxcomp headers.
• Provide nxagent specific auto-detection code for available display numbers (see nxagent man page for details, under -displayfd).
• Man page updates for nxagent (thanks, Ulrich!).
• Make sure that xkbcomp is available to nxagent (thanks, Mihai!).
• Switch on building nxagent with MIT-SCREEN-SAVER extension.
• Fix FTBFS on SPARC64, arm64 and m86k Linux platforms.
• Avoid duplicate runs of 'make build' due to flaw in main Makefile.

• Debian: deb http://packages.arctica-project.org/debian jessie,stretch,sid main
• Ubuntu: deb http://packages.arctica-project.org/ubuntu trusty,xenial main

 wget -qO - http://packages.arctica-project.org/archive.key   sudo apt-key add -

• [1] https://github.com/ArcticaProject/nx-libs/releases/tag/3.5.99.6
• [issues] https://github.com/ArcticaProject/nx-libs/issues

[~] tlmgr shell
protocol 1
tlmgr> load local
OK
tlmgr> load remote
tlmgr: package repository /home/norbert/public_html/tlpretest (verified)
OK
tlmgr> update --list
tlmgr: saving backups to /home/norbert/tl/2017/tlpkg/backups
update:   bchart             [147k]: local:    27496, source:    43928
...
update:   xindy              [535k]: local:    43873, source:    43934
OK
tlmgr> update --all
tlmgr: saving backups to /home/norbert/tl/2017/tlpkg/backups
[ 1/22, ??:??/??:??] update: bchart [147k] (27496 -> 43928) ... done
[ 2/22, 00:00/00:00] update: biber [1041k] (43873 -> 43910) ... done
...
[22/22, 00:50/00:50] update: xindy [535k] (43873 -> 43934) ... done
running mktexlsr ...
done running mktexlsr.
...
OK
tlmgr> quit
tlmgr: package log updated: /home/norbert/tl/2017/texmf-var/web2c/tlmgr.log 
[~] 

Linux as the standard interface During his keynote at Netdev, Jesse Brandeburg explained that traffic is exploding on the Internet: "From 2006 to 2016 the compound annual growth rate was 78% of network traffic. So the network traffic is growing like crazy. In 2010 to 2023, it's going to grow by a thousand times." He also mentioned Intel was working on devices that could do up to 400 Gbps. In his talk, he argued that Linux has a critical place in the modern world by repeating the mantra that "everything is on the network, and the network runs Linux", but does it really? Through Android, Linux has become the most popular end-user device operating system and is also dominant on the server but what about the actual fabric of the network: the routers and switches that interconnect all those machines? Mukherjee, in his own keynote, argued that even though Linux has achieved dominance in the server and virtualization markets, there is a "discontinuity [...] at the boundary where the host and the network meet" and argued "that the host without the network will not survive". In other words, proprietary hardware and software in the network threaten free software in the server. Even though some manufacturers are already providing a "Linux interface" in their hardware, it is often only some sort of compatibility shell which might be compared with the Ubuntu compatibility layer in Windows: it's not a real Linux. Mukherjee pushed this idea further by saying that those companies are limiting themselves by not using the full Linux stack. He presented Linux as the "top vehicle for innovation" that provides a featureful network stack, citing VXLAN, eBPF, and Quagga as prime features used on switches. Mukherjee also praised the diversity of the user-space Linux ecosystem as something that commercial alternatives can't rival; he compared the faster Linux development to the commercial sector where similar top features stay in the beta stage for up to 3 years. Because of its dominance in the server market, consumers are expecting a Linux-like interface on their networking gear now, which means Linux could be the standard interface all providers strive toward. As a Debian developer, I can't help but smile at the thought; if there's one thing we have not been able to do among Linux distributions, it's pretty much standardize user space in a consistent interface. POSIX is old and incomplete, the FHS is showing its age, and most distributions have abandoned LSB. Yet, the idea is certainly enticing: there is a base set of tools and applications, especially for the Linux kernel, that are standardized: iproute2, ethtool, and iptables are generally consistent across distributions, even though each distribution has its own way of using them. Yet Linux is not dominant, why? Mukherjee identified the problem as "packaging issues" and listed a set of features he would like Linux to improve:

• Standardization of the ethtool interface. The idea is to make ethtool a de-facto standard to manage switches and ports. Mukherjee gave the example that data centers spend more money on cables than any other hardware and explained that making it easier to identify cables is therefore a key functionality. Getting consistent interface naming was also a key problem identified by numerous participants at the conference. While systemd tried to fix this with the predictable network interface names specification, the interface names are not necessarily predictable across virtual machines or on special hardware; in fact, this was the topic of the first talk of the conference. ethtool also needs to support interfaces that run faster than 1 Gbps, something that still has limited support in Linux at the moment.
• Scaling of the Linux bridge. Through the rise of "software defined networking", we are likely to see multi-switch virtual environments that need to scale to hundreds of interfaces and devices easily. This is something the Linux bridge was never designed to do and it's showing scalability issues. During the conference, there was hope that the new XDP and eBPF developments could help, but also concerns this would create yet another bridge layer inside the kernel.

Cumulus's goal seems to be to establish Linux as the industry standard for this new era of networking and it is not alone. Through its Open Compute project, Facebook is sharing open designs of data center products and, while we have yet to see commercial off-the-shelf (COTS) 24 and 48-port gigabit switches trickle down to the consumer market, the company is definitely deploying new hardware based on those specifications in its own data centers, and those devices are often based on Linux.

The Linux switch implementation So how exactly do switches work in Linux? The Linux kernel manipulates switches with three different operation structures: switchdev_ops, which we previously covered, ethtool_ops, and netdev_ops. Certain switches, however, also need distributed switch architecture (DSA) features to be properly handled. DSA is a more obscure part of the network stack that allows Linux to represent hardware switches or chains of switches using regular Linux tools like bridge, ifconfig, and so on. While switchdev is a new layer, DSA has been in the kernel since 2.6.28 in 2008. Originally developed to support Marvell switches, DSA is now a generic layer deployed in WiFi access points, set-top boxes, on-board flight entertainment systems, trains, and other industrial equipment. Switches that have an Ethernet controller need DSA, whereas the kernel can support switches without Ethernet controllers directly with switchdev drivers. The first years of DSA's development consisted only of basic maintenance but, in the last three years, DSA has seen a resurgence of contributions, as part of Linux networking push to support hardware offloading and network switches. Between 2014 and 2015, DSA added support for Broadcom hardware, wake on LAN, and hardware port bridging, among other features. DSA's development was parallel to swconfig, written by the OpenWrt project to support the small office and home office (SOHO) routers that the project is targeting. The main difference between swconfig and DSA is that DSA-supported switches show one network interface per port, whereas swconfig-configured switches show up as a single port, which limits the amount of information that can be extracted from the switch. For example, you cannot have per-port traffic statistics with swconfig. That limitation is what led to the creation of the switchdev framework, when swconfig was proposed (then refused) for inclusion in mainline. Another goal of switchdev was to support bridge hardware offloading and network interface card (NIC) virtualization. Also, whereas swconfig uses virtual LAN (VLAN) tagging to address ports, DSA enables the use of device-specific tagging headers to address different ports, which enables DSA to have better control over the switches. This allows, for example, DSA to do internet group management protocol (IGMP) snooping or implement the spanning tree protocol, whereas swconfig doesn't have those features. Some switches are actually connected to the host CPU through an Ethernet interface instead of regular PCI-Express interface, and DSA supports this as well. One advantage that remains in the swconfig approach is that it treats the internal switch as a simple external switch, and addresses ports with standard VLAN tags. This is something DSA could do, as well, but no one has bothered implementing this just yet. For now, DSA drivers use device-specific tagging mechanisms that limit the number of supported devices. Other areas of future improvement for DSA are better multi-chip support, IGMP snooping, and bonding, as well as firewall, NAT, and TC offloading.

Where is the freedom? Given all those technical improvements, you might rightfully wonder if your own wireless router or data center switch runs Linux. In recent years, we have seen more and more networking devices shipped with Linux and sometimes even OpenWrt (e.g. in the case of the Turris Omnia, which we previously covered), and especially on SOHO routers, but it sometimes means a crippled operating system that only offers you a proprietary web interface. But at least those efforts make it easier to deploy free operating systems on those devices. Based on my experience running OpenWrt on wireless routers to build the Montreal mesh network, deploying Linux on routers and switches has always been a manual process. The Ubiquiti hardware being used in the mesh network comes with an OpenWrt derivative, but it includes proprietary drivers and a proprietary web interface. To use the mesh networking protocol that was chosen, it was necessary to deploy custom OpenWrt images by hand. For years, it was a continuous struggle for OpenWrt developers to liberate generation after generation of proprietary hardware with companies like Cisco locking down the venerable WRT platform in 2006 and the US Federal Communications Commission (FCC) rules that forced TP-Link to block free software on its routers, a change that was later reverted. Most hardware providers are obviously not dedicated to software freedom: deploying Linux on their hardware is for them an economic, not political choice. As you might expect, a "Linux router" these days often means a closed device and operating system, using Linux as the only free component. I had the privilege of doing some reverse engineering on the SmartRG SR603n VDSL modem, which also doubles as a WiFi router and VoIP phone adapter. I was able to get a shell on that machine, and what I found was a custom operating system built on top of the Linux kernel. I wrote a detailed report about this two years ago and the situation then was pretty grim. Another experience I had was working over a decade in data centers, which tells an even worse story: most switches and routers there are not running free software at all. We have deployed HP ProCurve switches that provide free (as in beer) software updates and have struggled for years to find free (as in speech) software alternatives for those. We built our own routers using COTS server hardware, at a significant performance cost over the dedicated application-specific integrated circuits (ASICs) built into commercial routers, which do not offer us the trust and flexibility we were looking for. But Linux is definitely making some headway, and has been for a while. When we covered switchdev in February 2016, it was just getting started, but now vendors like Mellanox, Broadcom, Cumulus, and Intel are writing and shipping code using the framework. Cumulus, in particular, is developing a Debian-based distribution (Cumulus Linux) that it deploys for clients on targeted hardware. Most of the hardware in that list, however, is not actually open in the more radical sense: they are devices that can run free software but are not generally open-source hardware. There are some exceptions, but they sit at the higher end of the spectrum: most organizations probably don't need a 100 Gbps ports, let alone the 128 ports in the Backpack switch that Cumulus is shipping. How much this translates to actual freedom for the end-user is therefore questionable. While I have seen encouraging progress on the high end of the hardware spectrum at Netdev, I'm not sure this will translate into immediate wins in the data center or even for home users in the short term. In the long term, however, we will hopefully see some progress in Linux's rise in general-purpose networking hardware following its dominance in general-purpose computing.

The author would like to thank the Netdev organizers for travel assistance. Also, thanks to Andrew Lunn for a technical review of this article. Note: this article first appeared in the Linux Weekly News.

• For 3G-SDI, they output level A only, with no option for level B. (In fact, there are no options at all.) Level A is the most sane standard, and also what most equipment uses, but there exists certain older equipment that only works with level B.
• They don't have reclocking chips, so their timing accuracy is not superb. I managed to borrow a Phabrix SDI analyzer and measured the jitter; with a very short cable, I got approximately 0.85 0.95 UI (varying a bit), whereas a Blackmagic converter gave me 0.23 0.24 UI (much more stable). This may be a problem at very long cable lengths, although I haven't tried 100m runs and such.
• When converting to and from RGB, they seem to assume Rec. 601 Y'CbCr coefficients even for HD resolutions. This means the colors will be a bit off in some cases, although for most people, it will be hard to notice without looking at it side-by-side. (I believe the HDMI-to-SDI and SDI-to-HDMI converters make the same mistake, so that the errors cancel out if you just want to use a pair as HDMI extenders. Also, if your signal is Y'CbCr already, you don't need to care.)
• They don't insert SMPTE 352M payload ID. (Supposedly, this is because the SDI chip they use, called GV7600, is slightly out-of-standard on purpose in order to avoid paying expensive licensing fees to SMPTE.) Normally, you wouldn't need to care, but 3G-SDI actually requires this, and worse; Blackmagic's equipment (at least the Duo 2, and I've seen reports about the ATEMs as well) enforces that. If you try to run e.g. 1080p50 through them and into a Duo 2, it will be misdetected as 1080p25, no signal . There's no workaround that I know of.

• An introduction to various aspects of the Debian Project
• Talks about Debian and Free Software in art, education and/or research
• A primer on contributing to Free Software projects
• Free software & Privacy/Surveillance
• An introduction to programming and/or hardware tinkering
• A workshop about your favorite piece of Free Software
• A presentation about your favorite Free Software-related project (user group, advocacy group, etc.)

• compiler version needs to be identical and recorded
• build options and their order need to be identical and recorder
• build path needs to be identical and recorded (otherwise debug symbols - and BuildIDs - change)
• diffoscope helps checking for differences in build output

• use -Wl,--no-insert-timestamp for .exe (with old binutils 2.25 caveat)
• no need to set a build path for stripped .exe (no ELF BuildID)
• reprotest helps checking build variations automatically
• MXE stack is apparently deterministic enough for a reproducible static build
• umask needs to be identical and recorded
• file timestamps needs to be set and recorded (more on this in a future episode)

$ reprotest 'i686-w64-mingw32.static-gcc hello.c -I /opt/mxe/usr/i686-w64-mingw32.static/include -I/opt/mxe/usr/i686-w64-mingw32.static/include/SDL2 -L/opt/mxe/usr/i686-w64-mingw32.static/lib -lmingw32 -Dmain=SDL_main -lSDL2main -lSDL2 -lSDL2main -Wl,--no-insert-timestamp -luser32 -lgdi32 -lwinmm -limm32 -lole32 -loleaut32 -lshell32 -lversion -o hello && chmod 700 hello && analysePE.py hello   tee /tmp/hello.log-$(date +%s); sleep 1' 'hello'
$ diff -au /tmp/hello.log-1*
--- /tmp/hello.log-1490950327   2017-03-31 10:52:07.788616930 +0200
+++ /tmp/hello.log-1523203509   2017-03-31 10:52:09.064633539 +0200
@@ -18,7 +18,7 @@
 found PE header (size: 20)
     machine: i386
     number of sections: 17
-    timedatestamp: -1198218512 (Tue Jan 12 05:31:28 1932)
+    timedatestamp: 632430928 (Tue Jan 16 09:15:28 1990)
     pointer to symbol table: 4593152 (0x461600)
     number of symbols: 11581 (0x2d3d)
     size of optional header: 224
@@ -47,7 +47,7 @@
     Win32VersionValue: 0
     size of image (memory): 4640768
     size of headers (offset to first section raw data): 1536
-    checksum (for drivers): 4927867
+    checksum (for drivers): 4922616
     subsystem: 3
         win32 console binary
     DllCharacteristics: 0

    "Build Date: %s\n", ..., __TDATE__

$ sha256sum *.zip
189d0ca5240374896c6ecc6dfcca00905ae60797ab48abce2162fa36568e7cf1  freedink-109.0-bin-buildsh.zip
e182406b4f4d7c3a4d239eee126134ba5c0304bbaa4af3de15fd4f8bda5634a9  freedink-109.0-bin-docker.zip
e182406b4f4d7c3a4d239eee126134ba5c0304bbaa4af3de15fd4f8bda5634a9  freedink-109.0-bin-reprotest-docker.zip
37007f6ee043d9479d8c48ea0a861ae1d79fb234cd05920a25bb3db704828ece  freedink-109.0-bin-reprotest-null.zip

• existing home: ./configure attempts to run conftest.exe, wine can create ~/.wine, conftest.exe runs with binfmt emulation, configure assumes:

  checking whether we are cross compiling... no

• non-existing home: ./configure attempts to run conftest.exe, wine can't create ~/.wine, conftest.exe fails, configure assumes:

  checking whether we are cross compiling... yes

$ sha256sum *.zip
3545270ef6eaa997640cb62d66dc610a328ce0e7d412f24c8f18fdc7445907fd  freedink-109.0-bin-buildsh.zip
cc50ec1a38598d143650bdff66904438f0f5c1d3e2bea0219b749be2dcd2c3eb  freedink-109.0-bin-docker.zip
3545270ef6eaa997640cb62d66dc610a328ce0e7d412f24c8f18fdc7445907fd  freedink-109.0-bin-reprotest-chroot.zip
cc50ec1a38598d143650bdff66904438f0f5c1d3e2bea0219b749be2dcd2c3eb  freedink-109.0-bin-reprotest-docker.zip
3545270ef6eaa997640cb62d66dc610a328ce0e7d412f24c8f18fdc7445907fd  freedink-109.0-bin-reprotest-null.zip

45f8c5d50a68aa9919ee3602a4e3f5b2bd0333bc8d781d7852b2b6121c8ba27b  /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a  # host
6870b84f8e17aec4b5cf23cfe9c2e87e40d9cf59772a92707152361b6ebc1eb4  /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a  # docker

• First I rsync a copy of my Docker filesystem and run it in a host chroot with a reset environment.

$ sudo env -i /usr/sbin/chroot chroot-docker/
$ exec bash -l
$ cd /opt/mxe
$ touch src/gcc.mk
$ sha256sum /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a 
6870b84f8e17aec4b5cf23cfe9c2e87e40d9cf59772a92707152361b6ebc1eb4  /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a
$ make gcc
[build]     gcc                    i686-w64-mingw32.static
[done]      gcc                    i686-w64-mingw32.static                                 2709464 KiB    7m2.039s
$ sha256sum /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a 
45f8c5d50a68aa9919ee3602a4e3f5b2bd0333bc8d781d7852b2b6121c8ba27b  /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a
# consistent with host builds

• Then I import my previous reprotest chroot (plain debootstrap) in Docker:

$ sudo tar -C chroot -c .   docker import - chroot-debootstrap
$ docker run -ti chroot-debootstrap /bin/bash
$ sha256sum /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a
45f8c5d50a68aa9919ee3602a4e3f5b2bd0333bc8d781d7852b2b6121c8ba27b  /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a
$ touch src/gcc.mk
$ make gcc
[build]     gcc                    i686-w64-mingw32.static
[done]      gcc                    i686-w64-mingw32.static                                 2709412 KiB    7m6.608s
$ sha256sum /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a
6870b84f8e17aec4b5cf23cfe9c2e87e40d9cf59772a92707152361b6ebc1eb4  /opt/mxe/usr/lib/gcc/i686-w64-mingw32.static/5.4.0/libstdc++.a
# consistent with docker builds

• exactly the same kernel
• exactly the same GCC sources
• exactly the same host binaries

I am not sure I d consider this much of a problem. Yeah, it s a UNIX pitfall, but rm -rf /foo/.* will work the exact same way, no?Lennart Poettering, systemd issue 5644

I conclude that there are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies and the other way is to make it so complicated that there are no obvious deficiencies. Antony Hoare, Turing Award Lecture 1980

deb http://www.preining.info/debian/ calibre main
deb-src http://www.preining.info/debian/ calibre main