Search Results: "orv"

24 July 2020

Raphaël Hertzog: The Debian Handbook has been updated for Debian 10

Better late than never as we say thanks to the work of Daniel Leidert and Jorge Maldonado Ventura, we managed to complete the update of my book for Debian 10 Buster. You can get the electronic version on debian-handbook.info or the paperback version on lulu.com. Or you can just read it online. Translators are busy updating their translations, with German and Norvegian Bokmal leading the way

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1 May 2020

Utkarsh Gupta: FOSS Activites in April 2020

Here s my (seventh) monthly update about the activities I ve done in the F/L/OSS world.

Debian
It s been 14 months since I ve started contributing to Debian. And 4 months since I ve been a Debian Developer. And in this beautiful time, I had this opprotunity to do and learn lots of new and interesting things. And most importantly, meet and interact with lots of lovely people!
Debian is $home.

Uploads:

Other $things:
  • Attended Ruby team meeting. Logs here.
  • Attended Perl team LHF. Report here.
  • Sponsored a lot of uploads for William Desportes and Adam Cecile.
  • Mentoring for newcomers.
  • FTP Trainee reviewing.
  • Moderation of -project mailing list.
  • Applied for DUCI project for Google Summer of Code 2020.

Ruby2.7 Migration:
Ruby2.7 was recently released on 25th December, 2019. Santa s gift. Believe it or not. We, the Debian Ruby team, have been trying hard to make it migrate to testing. And it finally happened. The default version in testing is ruby2.7. Here s the news! \o/
Here s what I worked on this month for this transition.

Upstream: Opened several issues and proposed patches (in the form of PRs):
  • Issue #35 against encryptor for Ruby2.7 test failures.
  • Issue #28 against image_science for removing relative paths.
  • Issue #106 against ffi-yajl for Ruby2.7 test failures.
  • PR #5 against aggregate for simply using require.
  • PR #6 against aggregate for modernizing CI and adding Ruby 2.5 and 2.7 support.
  • Issue #13 against espeak-ruby for Ruby2.7 test failures.
  • Issue #4 against tty-which for test failures in general.
  • Issue #11 against packable for Ruby2.7 test failures. PR #12 has been proposed.
  • Issue #10 against growl for test failures and proposed an initial patch.

Downstream: I fixed and uploaded the following packages in Debian:

Debian LTS
Debian Long Term Support (LTS) is a project to extend the lifetime of all Debian stable releases to (at least) 5 years. Debian LTS is not handled by the Debian security team, but by a separate group of volunteers and companies interested in making it a success.
This was my seventh month as a Debian LTS paid contributor. I was assigned 24.00 hours and worked on the following things:

CVE Fixes and Announcements:

Other LTS Work:

Other(s)
Sometimes it gets hard to categorize work/things into a particular category.
That s why I am writing all of those things inside this category.
This includes two sub-categories and they are as follows.

Personal: This month I could get the following things done:
  • Most importantly, I finally migrated to a new website. Huge UI imporvement! \o/
    From Jekyll to Hugo, it was not easy. But it was worth it! Many thanks to Luiz for writing hugo-coder, Clement, and Samyak!
    If you find any flaws, issues and pull requests are welcomed at utkarsh2102/utkarsh2102.com
  • Wrote battery-alert, a mini-project of my own to show battery alerts at <10% and >90%.
    Written in shell, it brings me all the satisfaction as it has saved my life on many occasions.
    And guess what? It has more users than just myself!
    Reviews and patches are welcomed \o/
  • Mentored in HackOn Hackathon. Thanks to Manvi for reaching out!
    It was fun to see people developing some really nice projects.
  • Thanks to Ray and John, I became a GitLab Hero!
    (I am yet to figure out my role and responibility though)
  • Atteneded Intro Sec Con and had the most fun!
    Heard Ian s keynote and attended other talks and learned how to use WireShark!

Open Source: Again, this contains all the things that I couldn t categorize earlier.
Opened several issues and pull requests:
  • Issue #297 against hugo-coder, asking to enable RSS feed for blogs.
  • PR #316 for hugo-coder for fixing the above issue myself.
  • Issue #173 against arbre for requesting a release.
  • Issue #104 against combustion, asking to relax dependency on rubocop. Fixed in this commit.
  • Issue #16 against ffi-compiler for requesting to fix homepage and license.
  • Issue #57 against gographviz for requesting a release.
  • Issue #14 against crb-blast, suggesting compatability with bio 2.0.x.
  • Issue #58 against uniform_notifier for asking to drop the use of ruby-growl.
  • PR #2072 for polybar, adding installation instructions on Debian systems.

Until next time.
:wq for today.

10 April 2020

Norbert Preining: TeX Live 2020 released

Get the Champagne ready, we have released the final images of TeX Live 2020.
Due to COVID-19, DVD production will be delayed, but we have decided to release the current image and update the net installer. The .iso image is available on CTAN, and the net installer will pull all the newest stuff. Currently we are working on getting those packages updated during the freeze to the newest level in TeX Live. Before providing the full list of changes, here a few things I would like to pick out: Most of the above features have been available already either via tlpretest or via regular updates, but are now fully released on the DVD version. Thanks goes to all the developers, builders, the great CTAN team, and everyone who has contributed to this release! Finally, here are the changes as listed in the master TeX Live documentation: General: epTeX, eupTeX: New primitives \Uchar, \Ucharcat, \current(x)spacingmode, \ifincsname; revise \fontchar?? and \iffontchar. For eupTeX only: \currentcjktoken. LuaTeX: Integration with HarfBuzz library, available as new engines luahbtex (used for lualatex) and luajithbtex. New primitives: \eTeXgluestretchorder, \eTeXglueshrinkorder. pdfTeX: New primitive \pdfmajorversion; this merely changes the version number in the PDF output; it has no e ect on any PDF content. \pdfximage and similar now search for image les in the same way as \openin. pTeX: New primitives \ifjfont, \iftfont. Also in epTeX, upTeX, eupTeX. XeTeX: Fixes for \Umathchardef, \XeTeXinterchartoks, \pdfsavepos. Dvips: Output encodings for bitmap fonts, for better copy/paste capabilities (https://tug.org/TUGboat/tb40-2/tb125rokicki-type3search.pdf). MacTeX: MacTeX and x86_64-darwin now require 10.13 or higher (High Sierra, Mojave, and Catalina); x86_64-darwinlegacy supports 10.6 and newer. MacTeX is notarized and command line programs have hardened runtimes, as now required by Apple for install packages. BibDesk and TeX Live Utility are not in MacTeX because they are not notarized, but a README le lists urls where they can be obtained. tlmgr and infrastructure:

18 March 2020

Antoine Beaupr : How can I trust this git repository?

Join me in the rabbit hole of git repository verification, and how we could improve it.

Problem statement As part of my work on automating install procedures at Tor, I ended up doing things like:
git clone REPO
./REPO/bootstrap.sh
... something eerily similar to the infamous curl pipe bash method which I often decry. As a short-term workaround, I relied on the SHA-1 checksum of the repository to make sure I have the right code, by running this both on a "trusted" (ie. "local") repository and the remote, then visually comparing the output:
$ git show-ref master
9f9a9d70dd1f1e84dec69a12ebc536c1f05aed1c refs/heads/master
One problem with this approach is that SHA-1 is now considered as flawed as MD5 so it can't be used as an authentication mechanism anymore. It's also fundamentally difficult to compare hashes for humans. The other flaw with comparing local and remote checksums is that we assume we trust the local repository. But how can I trust that repository? I can either:
  1. audit all the code present and all the changes done to it after
  2. or trust someone else to do so
The first option here is not practical in most cases. In this specific use case, I have audited the source code -- I'm the author, even -- what I need is to transfer that code over to another server. (Note that I am replacing those procedures with Fabric, which makes this use case moot for now as the trust path narrows to "trust the SSH server" which I already had anyways. But it's still important for my fellow Tor developers who worry about trusting the git server, especially now that we're moving to GitLab.) But anyways, in most cases, I do need to trust some other fellow developer I collaborate with. To do this, I would need to trust the entire chain between me and them:
  1. the git client
  2. the operating system
  3. the hardware
  4. the network (HTTPS and the CA cartel, specifically)
  5. then the hosting provider (and that hardware/software stack)
  6. and then backwards all the way back to that other person's computer
I want to shorten that chain as much as possible, make it "peer to peer", so to speak. Concretely, it would eliminate the hosting provider and the network, as attackers.

OpenPGP verification My first reaction is (perhaps perversely) to "use OpenPGP" for this. I figured that if I sign every commit, then I can just check the latest commit and see if the signature is good. The first problem here is that this is surprisingly hard. Let's pick some arbitrary commit I did recently:
commit b3c538898b0ed4e31da27fc9ca22cb55e1de0000
Author: Antoine Beaupr  <anarcat@debian.org>
Date:   Mon Mar 16 14:37:28 2020 -0400
    fix test autoloading
    pytest only looks for file names matching  test  by default. We inline
    tests inside the source code directly, so hijack that.
diff --git a/fabric_tpa/pytest.ini b/fabric_tpa/pytest.ini
new file mode 100644
index 0000000..71004ea
--- /dev/null
+++ b/fabric_tpa/pytest.ini
@@ -0,0 +1,3 @@
+[pytest]
+# we inline tests directly in the source code
+python_files = *.py
That's the output of git log -p in my local repository. I signed that commit, yet git log is not telling me anything special. To check the signature, I need something special: --show-signature, which looks like this:
commit b3c538898b0ed4e31da27fc9ca22cb55e1de0000
gpg: Signature faite le lun 16 mar 2020 14:37:53 EDT
gpg:                avec la clef RSA 7B164204D096723B019635AB3EA1DDDDB261D97B
gpg: Bonne signature de  Antoine Beaupr  <anarcat@orangeseeds.org>  [ultime]
gpg:                 alias  Antoine Beaupr  <anarcat@torproject.org>  [ultime]
gpg:                 alias  Antoine Beaupr  <anarcat@anarc.at>  [ultime]
gpg:                 alias  Antoine Beaupr  <anarcat@koumbit.org>  [ultime]
gpg:                 alias  Antoine Beaupr  <anarcat@debian.org>  [ultime]
Author: Antoine Beaupr  <anarcat@debian.org>
Date:   Mon Mar 16 14:37:28 2020 -0400
    fix test autoloading
    pytest only looks for file names matching  test  by default. We inline
    tests inside the source code directly, so hijack that.
Can you tell if this is a valid signature? If you speak a little french, maybe you can! But even if you would, you are unlikely to see that output on your own computer. What you would see instead is:
commit b3c538898b0ed4e31da27fc9ca22cb55e1de0000
gpg: Signature made Mon Mar 16 14:37:53 2020 EDT
gpg:                using RSA key 7B164204D096723B019635AB3EA1DDDDB261D97B
gpg: Can't check signature: No public key
Author: Antoine Beaupr  <anarcat@debian.org>
Date:   Mon Mar 16 14:37:28 2020 -0400
    fix test autoloading
    pytest only looks for file names matching  test  by default. We inline
    tests inside the source code directly, so hijack that.
Important part: Can't check signature: No public key. No public key. Because of course you would see that. Why would you have my key lying around, unless you're me. Or, to put it another way, why would that server I'm installing from scratch have a copy of my OpenPGP certificate? Because I'm a Debian developer, my key is actually part of the 800 keys in the debian-keyring package, signed by the APT repositories. So I have a trust path. But that won't work for someone who is not a Debian developer. It will also stop working when my key expires in that repository, as it already has on Debian buster (current stable). So I can't assume I have a trust path there either. One could work with a trusted keyring like we do in the Tor and Debian project, and only work inside that project, that said. But I still feel uncomfortable with those commands. Both git log and git show will happily succeed (return code 0 in the shell) even though the signature verification failed on the commits. Same with git pull and git merge, which will happily push your branch ahead even if the remote has unsigned or badly signed commits. To actually verify commits (or tags), you need the git verify-commit (or git verify-tag) command, which seems to do the right thing:
$ LANG=C.UTF-8 git verify-commit b3c538898b0ed4e31da27fc9ca22cb55e1de0000
gpg: Signature made Mon Mar 16 14:37:53 2020 EDT
gpg:                using RSA key 7B164204D096723B019635AB3EA1DDDDB261D97B
gpg: Can't check signature: No public key
[1]$
At least it fails with some error code (1, above). But it's not flexible: I can't use it to verify that a "trusted" developer (say one that is in a trusted keyring) signed a given commit. Also, it is not clear what a failure means. Is a signature by an expired certificate okay? What if the key is signed by some random key in my personal keyring? Why should that be trusted?

Worrying about git and GnuPG In general, I'm worried about git's implementation of OpenPGP signatures. There has been numerous cases of interoperability problems with GnuPG specifically that led to security, like EFAIL or SigSpoof. It would be surprising if such a vulnerability did not exist in git. Even if git did everything "just right" (which I have myself found impossible to do when writing code that talks with GnuPG), what does it actually verify? The commit's SHA-1 checksum? The tree's checksum? The entire archive as a zip file? I would bet it signs the commit's SHA-1 sum, but I just don't know, on the top of my head, and neither do git-commit or git-verify-commit say exactly what is happening. I had an interesting conversation with a fellow Debian developer (dkg) about this and we had to admit those limitations:
<anarcat> i'd like to integrate pgp signing into tor's coding practices more, but so far, my approach has been "sign commits" and the verify step was "TBD" <dkg> that's the main reason i've been reluctant to sign git commits. i haven't heard anyone offer a better subsequent step. if torproject could outline something useful, then i'd be less averse to the practice. i'm also pretty sad that git remains stuck on sha1, esp. given the recent demonstrations. all the fancy strong signatures you can make in git won't matter if the underlying git repo gets changed out from under the signature due to sha1's weakness
In other words, even if git implements the arcane GnuPG dialect just so, and would allow us to setup the trust chain just right, and would give us meaningful and workable error messages, it still would fail because it's still stuck in SHA-1. There is work underway to fix that, but in February 2020, Jonathan Corbet described that work as being in a "relatively unstable state", which is hardly something I would like to trust to verify code. Also, when you clone a fresh new repository, you might get an entirely different repository, with a different root and set of commits. The concept of "validity" of a commit, in itself, is hard to establish in this case, because an hostile server could put you backwards in time, on a different branch, or even on an entirely different repository. Git will warn you about a different repository root with warning: no common commits but that's easy to miss. And complete branch switches, rebases and resets from upstream are hardly more noticeable: only a tiny plus sign (+) instead of a star (*) will tell you that a reset happened, along with a warning (forced update) on the same line. Miss those and your git history can be compromised.

Possible ways forward I don't consider the current implementation of OpenPGP signatures in git to be sufficient. Maybe, eventually, it will mature away from SHA-1 and the interface will be more reasonable, but I don't see that happening in the short term. So what do we do?

git evtag The git-evtag extension is a replacement for git tag -s. It's not designed to sign commits (it only verifies tags) but at least it uses a stronger algorithm (SHA-512) to checksum the tree, and will include everything in that tree, including blobs. If that sounds expensive to you, don't worry too much: it takes about 5 seconds to tag the Linux kernel, according to the author. Unfortunately, that checksum is then signed with GnuPG, in a manner similar to git itself, in that it exposes GnuPG output (which can be confusing) and is likely similarly vulnerable to mis-implementation of the GnuPG dialect as git itself. It also does not allow you to specify a keyring to verify against, so you need to trust GnuPG to make sense of the garbage that lives in your personal keyring (and, trust me, it doesn't). And besides, git-evtag is fundamentally the same as signed git tags: checksum everything and sign with GnuPG. The difference is it uses SHA-512 instead of SHA-1, but that's something git will eventually fix itself anyways.

kernel patch attestations The kernel also faces this problem. Linus Torvalds signs the releases with GnuPG, but patches fly all over mailing list without any form of verification apart from clear-text email. So Konstantin Ryabitsev has proposed a new protocol to sign git patches which uses SHA256 to checksum the patch metadata, commit message and the patch itself, and then sign that with GnuPG. It's unclear to me what this solves, if anything, at all. As dkg argues, it would seem better to add OpenPGP support to git-send-email and teach git tools to recognize that (e.g. git-am) at least if you're going to keep using OpenPGP anyways. And furthermore, it doesn't resolve the problems associated with verifying a full archive either, as it only attests "patches".

jcat Unhappy with the current state of affairs, the author of fwupd (Richard Hughes) wrote his own protocol as well, called jcat, which provides signed "catalog files" similar to the ones provided in Microsoft windows. It consists of a "gzip-compressed JSON catalog files, which can be used to store GPG, PKCS-7 and SHA-256 checksums for each file". So yes, it is yet again another wrapper to GnuPG, probably with all the flaws detailed above, on top of being a niche implementation, disconnected from git.

The Update Framework One more thing dkg correctly identified is:
<dkg> anarcat: even if you could do exactly what you describe, there are still some interesting wrinkles that i think would be problems for you. the big one: "git repo's latest commits" is a loophole big enough to drive a truck through. if your adversary controls that repo, then they get to decide which commits to include in the repo. (since every git repo is a view into the same git repo, just some have more commits than others)
In other words, unless you have a repository that has frequent commits (either because of activity or by a bot generating fake commits), you have to rely on the central server to decide what "the latest version" is. This is the kind of problems that binary package distribution systems like APT and TUF solve correctly. Unfortunately, those don't apply to source code distribution, at least not in git form: TUF only deals with "repositories" and binary packages, and APT only deals with binary packages and source tarballs. That said, there's actually no reason why git could not support the TUF specification. Maybe TUF could be the solution to ensure end-to-end cryptographic integrity of the source code itself. OpenPGP-signed tarballs are nice, and signed git tags can be useful, but from my experience, a lot of OpenPGP (or, more accurately, GnuPG) derived tools are brittle and do not offer clear guarantees, and definitely not to the level that TUF tries to address. This would require changes on the git servers and clients, but I think it would be worth it.

Other Projects

OpenBSD There are other tools trying to do parts of what GnuPG is doing, for example minisign and OpenBSD's signify. But they do not integrate with git at all right now. Although I did find a hack] to use signify with git, it's kind of gross...

Golang Unsurprisingly, this is a problem everyone is trying to solve. Golang is planning on hosting a notary which would leverage a "certificate-transparency-style tamper-proof log" which would be ran by Google (see the spec for details). But that doesn't resolve the "evil server" attack, if we treat Google as an adversary (and we should).

Python Python had OpenPGP going for a while on PyPI, but it's unclear if it ever did anything at all. Now the plan seems to be to use TUF but my hunch is that the complexity of the specification is keeping that from moving ahead.

Docker Docker and the container ecosystem has, in theory, moved to TUF in the form of Notary, "a project that allows anyone to have trust over arbitrary collections of data". In practice however, in my somewhat limited experience, setting up TUF and image verification in Docker is far from trivial.

Android and iOS Even in what is possibly one of the strongest models (at least in terms of user friendliness), mobile phones are surprisingly unclear about those kind of questions. I had to ask if Android had end-to-end authentication and I am still not clear on the answer. I have no idea of what iOS does.

Conclusion One of the core problems with everything here is the common usability aspect of cryptography, and specifically the usability of verification procedures. We have become pretty good at encryption. The harder part (and a requirement for proper encryption) is verification. It seems that problem still remains unsolved, in terms of usability. Even Signal, widely considered to be a success in terms of adoption and usability, doesn't properly solve that problem, as users regularly ignore "The security number has changed" warnings... So, even though they deserve a lot of credit in other areas, it seems unlikely that hardcore C hackers (e.g. git and kernel developers) will be able to resolve that problem without at least a little bit of help. And TUF seems like the state of the art specification around here, it would seem wise to start adopting it in the git community as well. Update: git 2.26 introduced a new gpg.minTrustLevel to "tell various signature verification codepaths the required minimum trust level", presumably to control how Git will treat keys in your keyrings, assuming the "trust database" is valid and up to date. For an interesting narrative of how "normal" (without PGP) git verification can fail, see also A Git Horror Story: Repository Integrity With Signed Commits.

6 November 2017

Jonathan Dowland: Coil

Peter Christopherson and Jhonn Balance, from [Santa Sangre](https://santasangremagazine.wordpress.com/2014/11/16/the-angelic-conversation-in-remembrance-of-coil/) Peter Christopherson and Jhonn Balance, from Santa Sangre
A friend asked me to suggest five tracks by Coil that gave an introduction to their work. Trying to summarize Coil in 5 tracks is tough. I think it's probably impossible to fairly summarize Coil with any subset of their music, for two reasons. Firstly, their music was the output of their work but I don't think is really the whole of the work itself. There's a real mystique around them. They were deeply interested in arcania, old magic, Aleister Crowley, scatology; they were both openly and happily gay and their work sometimes explored their experiences in various related underground scenes and sub-cultures; they lost friends to HIV/AIDS and that had a profound impact on them. They had a big influence on some people who discovered them who were exploring their own sexualities at the time and might have felt excluded from mainstream society. They frequently explored drugs, meditation and other ways to try to expand and open their minds; occultism. They were also fiercely anti-commercial, their stuff was released in limited quantities across a multitude of different music labels, often under different names, and often paired with odd physical objects, runes, vials of blood, etc. Later fascinations included paganism and moon worship. I read somewhere that they literally cursed one of their albums. Secondly, part of their "signature" was the lack of any consistency in their work, or to put it another way, their style over time varied enormously. I'm also not necessarily well-versed in all their stuff, I'm part way on this journey myself... but these are tracks which stand out at least from the subset I've listened to. Both original/core members of Coil have passed away and the legal status of their catalogue is in a state of limbo. Some of these songs are available on currently-in-print releases, but all such releases are under dispute by some associate or other.

1. Heaven's Blade Like (probably) a lot of Coil songs, this one exists in multiple forms, with some dispute about which are canonical, which are officially sanctioned, etc. the video linked above actually contains 5 different versions, but I've linked to a time offset to the 4th: "Heaven's Blade (Backwards)". This version was the last to come to light with the recent release of "Backwards", an album originally prepared in the 90s at Trent Reznor's Nothing Studios in New Orleans, but not finished or released. The circumstances around its present-day release, as well as who did what to it and what manipulation may have been performed to the audio a long time after the two core members had passed, is a current topic in fan circles. Despite that, this is my preferred version. You can choose to investigate the others, or not, at your own discretion.

2. how to destroy angels (ritual music for the accumulation of male sexual energy) A few years ago, "guidopaparazzi", a user at the Echoing the Sound music message board attempted to listen to every Coil release ever made and document the process. He didn't do it chronologically, leaving the EPs until near the end, which is when he tackled this one (which was the first release by Coil, and was the inspiration behind the naming of Trent Reznor's one-time side project "How To Destroy Angels"). Guido seemed to think this was some kind of elaborate joke. Personally I think it's a serious piece and there's something to it but this just goes to show, different people can take things in entirely different ways. Here's Guido's review, and you can find the rest of his reviews linked from that one if you wish. https://archive.org/details/Coil-HowToDestroyAngels1984

3. Red Birds Will Fly Out Of The East And Destroy Paris In A Night Both "Musick To Play In The Dark" volumes (one and two) are generally regarded as amongst the most accessible entry points to the Coil discography. This is my choice of cut from volume 1. For some reason this reminds me a little of some of the background music from the game "Unreal Tournament". I haven't played that in at least 15 years. I should go back and see if I can figure out why it does. The whole EP is worth a listen, especially at night. https://archive.org/details/CoilMusickToPlayInTheDarkVol1/Coil+-+Musick+To+Play+In+The+Dark+Vol+1+-+2+Red+Birds+Will+Fly+Out+Of+The+East+And+Destroy+Paris+In+A+Night.flac

4. Things Happen It's tricky to pick a track from either "Love's Secret Domain" or "Horse Rotorvator"; there are other choices which I think are better known and loved than this one but it's one that haunted me after I first heard it for one reason or another, so here it is.

5. The Anal Staircase Track 1 from Horse Rotorvator. What the heck is a Horse Rotorvator anyway? I think it was supposed to have been a lucid nightmare experienced by the vocalist Jhonn Balance. So here they wrote a song about anal sex. No messing about, no allusion particularly, but why should there be? https://archive.org/details/CoilHorseRotorvator2001Remaster/Coil+-+Horse+Rotorvator+%5B2001+remaster%5D+-+01+The+Anal+Staircase.flac

Bonus 6th: 7-Methoxy-B-Carboline (Telepathine) From the drone album "Time Machines", which has just been re-issued by DIAS records, who describe it as "authorized". Each track is titled by the specific combination of compounds that inspired its composition, supposedly. Or, perhaps it's a "recommended dosing" for listening along. https://archive.org/details/TimeMachines-TimeMachines

Post-script If those piqued your interest, there's some decent words and a list of album suggestions in this Vinyl Factory article. Finally, if you can track them down, Stuart Maconie had two radio shows about Coil on his "Freak Zone" programme. The main show discusses the release of "Backwards", including an interview with collaborator Danny Hyde, who was the main person behind the recent re-issue. The shorter show is entitled John Doran uncoils Coil. Guest John Doran from The Quietus discusses the group and their history interspersed with Coil tracks and tracks from their contemporaries. Interestingly they chose a completely different set of 5 tracks to me.

18 September 2017

Carl Chenet: The Github threat

Many voices arise now and then against risks linked to the Github use by Free Software projects. Yet the infatuation for the collaborative forge of the Octocat Californian start-ups doesn t seem to fade away.

These recent years, Github and its services take an important role in software engineering as they are seen as easy to use, efficient for a daily workload with interesting functions in enterprise collaborative workflow or amid a Free Software project. What are the arguments against using its services and are they valid? We will list them first, then we ll examine their validity.

1. Critical points

1.1 Centralization

The Github application belongs to a single entity, Github Inc, a US company which manage it alone. So, a unique company under US legislation manages the access to most of Free Software application code sources, which may be a problem with groups using it when a code source is no longer available, for political or technical reason.

The Octocat, the Github mascot

This centralization leads to another trouble: as it obtained critical mass, it becomes more and more difficult not having a Github account. People who don t use Github, by choice or not, are becoming a silent minority. It is now fashionable to use Github, and not doing so is seen as out of date . The same phenomenon is a classic, and even the norm, for proprietary social networks (Facebook, Twitter, Instagram).

1.2 A Proprietary Software

When you interact with Github, you are using a proprietary software, with no access to its source code and which may not work the way you think it is. It is a problem at different levels. First, ideologically, but foremost in practice. In the Github case, we send them code we can control outside of their interface. We also send them personal information (profile, Github interactions). And mostly, Github forces any project which goes through the US platform to use a crucial proprietary tools: its bug tracking system.

Windows, the epitome of proprietary software, even if others took the same path

1.3 The Uniformization

Working with Github interface seems easy and intuitive to most. Lots of companies now use it as a source repository, and many developers leaving a company find the same Github working environment in the next one. This pervasive presence of Github in free software development environment is a part of the uniformization of said developers working space.

Uniforms always bring Army in my mind, here the Clone army

2 Critical points cross-examination

2.1 Regarding the centralization

2.1.1 Service availability rate

As said above, nowadays, Github is the main repository of Free Software source code. As such it is a favorite target for cyberattacks. DDOS hit it in March and August 2015. On December 15, 2015, an outage led to the inaccessibility of 5% of the repositories. The same occurred on November 15. And these are only the incident reported by Github itself. One can imagine that the mean outage rate of the platform is underestimated.

2.1.2 Chain reaction could block Free Software development

Today many dependency maintenance tools, as npm for javascript, Bundler for Ruby or even pip for Python can access an application source code directly from Github. Free Software projects getting more and more linked and codependents, if one component is down, all the developing process stop.

One of the best examples is the npmgate. Any company could legally demand that Github take down some source code from its repository, which could create a chain reaction and blocking the development of many Free Software projects, as suffered the Node.js community from the decisions of Npm, Inc, the company managing npm.

2.2 A historical precedent: SourceForge

Github didn t appear out of the blue. In his time, its predecessor, SourceForge, was also extremely popular.

Heavily centralized, based on strong interaction with the community, SourceForge is now seen as an aging SAAS (Software As A Service) and sees most of its customers fleeing to Github. Which creates lots of hurdles for those who stayed. The Gimp project suffered from spams and terrible advertising, which led to the departure of the VLC project, then from installers corrupted with adwares instead of the official Gimp installer for Windows. And finally, the Project Gimp s SourceForge account was hacked by SourceForge team itself!

These are very recent examples of what can do a commercial entity when it is under its stakeholders pressure. It is vital to really understand what it means to trust them with data and exchange centralization, where it could have tremendous repercussion on the day-to-day life and the habits of the Free Software and open source community.

2.3. Regarding proprietary software

2.3.1 One community, several opinions on proprietary software

Mostly based on ideology, this point deals with the definition every member of the community gives to Free Software and open source. Mostly about one thing: is it viral or not? Or GPL vs MIT/BSD.

Those on the side of the viral Free Software will have trouble to use a proprietary software as this last one shouldn t even exist. It must be assimilated, to quote Star Trek, as it is a connected black box, endangering privacy, corrupting for profit our uses and restrain our freedom to use as we re pleased what we own, etc.

Those on the side of complete freedom have no qualms using proprietary software as their very existence is a consequence of freedom without restriction. They even agree that code they developed may be a part of proprietary software, which is quite a common occurrence. This part of the Free Software community has no qualm using Github, which is well within their ideology parameters. Just take a look at the Janson amphitheater during Fosdem and check how many Apple laptops running on macOS are around.

FreeBSD, the main BSD project under the BSD license

2.3.2 Data loss and data restrictions linked to proprietary software use

Even without ideological consideration, and just focusing on Github infrastructure, the bug tracking system is a major problem by itself.

Bug report builds the memory of Free Software projects. It is the entrance point for new contributors, the place to find bug reporting, requests for new functions, etc. The project history can t be limited only to the code. It s very common to find bug reports when you copy and paste an error message in a search engine. Not their historical importance is precious for the project itself, but also for its present and future users.

Github gives the ability to extract bug reports through its API. What would happen if Github is down or if the platform doesn t support this feature anymore? In my opinion, not that many projects ever thought of this outcome. How could they move all the data generated by Github into a new bug tracking system? One old example now is Astrid, a TODO list bought by Yahoo a few years ago. Very popular, it grew fast until it was closed overnight, with only a few weeks for its users to extract their data. It was only a to-do list. The same situation with Github would be tremendously difficult to manage for several projects if they even have the ability to deal with it. Code would still be available and could still live somewhere else, but the project memory would be lost. A project like Debian has today more than 800,000 bug reports, which are a data treasure trove about problems solved, function requests and where the development stand on each. The developers of the Cpython project have anticipated the problem and decided not to use Github bug tracking systems.

Issues, the Github proprietary bug tracking system

Another thing we could lose if Github suddenly disappear: all the work currently done regarding the push requests (aka PRs). This Github function gives the ability to clone one project s Github repository, to modify it to fit your needs, then to offer your own modification to the original repository. The original repository s owner will then review said modification, and if he or she agrees with them will fuse them into the original repository. As such, it s one of the main advantages of Github, since it can be done easily through its graphic interface.

However reviewing all the PRs may be quite long, and most of the successful projects have several ongoing PRs. And this PRs and/or the proprietary bug tracking system are commonly used as a platform for comment and discussion between developers.

Code itself is not lost if Github is down (except one specific situation as seen below), but the peer review works materialized in the PRs and the bug tracking system is lost. Let s remember than the PR mechanism let you clone and modify projects and then generate PRs directly from its proprietary web interface without downloading a single code line on your computer. In this particular case, if Github is down, all the code and the work in progress is lost. Some also use Github as a bookmark place. They follow their favorite projects activity through the Watch function. This technological watch style of data collection would also be lost if Github is down.

Debian, one of the main Free Software projects with at least a thousand official contributors

2.4 Uniformization

The Free Software community is walking a thigh rope between normalization needed for an easier interoperability between its products and an attraction for novelty led by a strong need for differentiation from what is already there.

Github popularized the use of Git, a great tool now used through various sectors far away from its original programming field. Step by step, Git is now so prominent it s almost impossible to even think to another source control manager, even if awesome alternate solutions, unfortunately not as popular, exist as Mercurial.

A new Free Software project is now a Git repository on Github with README.md added as a quick description. All the other solutions are ostracized? How? None or very few potential contributors would notice said projects. It seems very difficult now to encourage potential contributors into learning a new source control manager AND a new forge for every project they want to contribute. Which was a basic requirement a few years ago. It s quite sad because Github, offering an original experience to its users, cut them out of a whole possibility realm. Maybe Github is one of the best web versioning control systems. But being the main one doesn t let room for a new competitor to grow. And it let Github initiate development newcomers into a narrow function set, totally unrelated to the strength of the Git tool itself.

3. Centralization, uniformization, proprietary software What s next? Laziness?

Fight against centralization is a main part of the Free Software ideology as centralization strengthens the power of those who manage it and who through it control those who are managed by it. Uniformization allergies born against main software companies and their wishes to impose a closed commercial software world was for a long time the main fuel for innovation thirst and intelligent alternative development. As we said above, part of the Free Software community was built as a reaction to proprietary software and their threat. The other part, without hoping for their disappearance, still chose a development model opposite to proprietary software, at least in the beginning, as now there s more and more bridges between the two.

The Github effect is a morbid one because of its consequences: at least centralization, uniformization, proprietary software usage as their bug tracking system. But some years ago the Dear Github buzz showed one more side effect, one I ve never thought about: laziness. For those who don t know what it is about, this letter is a complaint from several spokespersons from several Free Software projects which demand to Github team to finally implement, after years of polite asking, new functions. Since when Free Software project facing a roadblock request for clemency and don t build themselves the path they need? When Torvalds was involved in the Bitkeeper problem and the Linux kernel development team couldn t use anymore their revision control software, he developed Git. The mere fact of not being able to use one tool or functions lacking is the main motivation to seek alternative solutions and, as such, of the Free Software movement. Every Free Software community member able to code should have this reflex. You don t like what Github offers? Switch to Gitlab. You don t like it Gitlab? Improve it or make your own solution.

The Gitlab logo

Let s be crystal clear. I ve never said that every Free Software developers blocked should code his or her own alternative. We all have our own priorities, and some of us even like their beauty sleep, including me. But, to see that this open letter to Github has 1340 names attached to it, among them some spokespersons for major Free Software project showed me that need, willpower and strength to code a replacement are here. Maybe said replacement will be born from this letter, it would be the best outcome of this buzz.

In the end, Github usage is just another example of Internet usage massification. As Internet users are bound to go to massively centralized social network as Facebook or Twitter, developers are following the same path with Github. Even if a large fraction of developers realize the threat linked this centralized and proprietary organization, the whole community is following this centralization and uniformization trend. Github service is useful, free or with a reasonable price (depending on the functions you need) easy to use and up most of the time. Why would we try something else? Maybe because others are using us while we are savoring the convenience? The Free Software community seems to be quite sleepy to me.

The lion enjoying the hearth warm

About Me Carl Chenet, Free Software Indie Hacker, founder of the French-speaking Hacker News-like Journal du hacker. Follow me on social networks Translated from French by St phanie Chaptal. Original article written in 2015.

5 September 2017

Kees Cook: security things in Linux v4.13

Previously: v4.12. Here s a short summary of some of interesting security things in Sunday s v4.13 release of the Linux kernel: security documentation ReSTification
The kernel has been switching to formatting documentation with ReST, and I noticed that none of the Documentation/security/ tree had been converted yet. I took the opportunity to take a few passes at formatting the existing documentation and, at Jon Corbet s recommendation, split it up between end-user documentation (which is mainly how to use LSMs) and developer documentation (which is mainly how to use various internal APIs). A bunch of these docs need some updating, so maybe with the improved visibility, they ll get some extra attention. CONFIG_REFCOUNT_FULL
Since Peter Zijlstra implemented the refcount_t API in v4.11, Elena Reshetova (with Hans Liljestrand and David Windsor) has been systematically replacing atomic_t reference counters with refcount_t. As of v4.13, there are now close to 125 conversions with many more to come. However, there were concerns over the performance characteristics of the refcount_t implementation from the maintainers of the net, mm, and block subsystems. In order to assuage these concerns and help the conversion progress continue, I added an unchecked refcount_t implementation (identical to the earlier atomic_t implementation) as the default, with the fully checked implementation now available under CONFIG_REFCOUNT_FULL. The plan is that for v4.14 and beyond, the kernel can grow per-architecture implementations of refcount_t that have performance characteristics on par with atomic_t (as done in grsecurity s PAX_REFCOUNT). CONFIG_FORTIFY_SOURCE
Daniel Micay created a version of glibc s FORTIFY_SOURCE compile-time and run-time protection for finding overflows in the common string (e.g. strcpy, strcmp) and memory (e.g. memcpy, memcmp) functions. The idea is that since the compiler already knows the size of many of the buffer arguments used by these functions, it can already build in checks for buffer overflows. When all the sizes are known at compile time, this can actually allow the compiler to fail the build instead of continuing with a proven overflow. When only some of the sizes are known (e.g. destination size is known at compile-time, but source size is only known at run-time) run-time checks are added to catch any cases where an overflow might happen. Adding this found several places where minor leaks were happening, and Daniel and I chased down fixes for them. One interesting note about this protection is that is only examines the size of the whole object for its size (via __builtin_object_size(..., 0)). If you have a string within a structure, CONFIG_FORTIFY_SOURCE as currently implemented will make sure only that you can t copy beyond the structure (but therefore, you can still overflow the string within the structure). The next step in enhancing this protection is to switch from 0 (above) to 1, which will use the closest surrounding subobject (e.g. the string). However, there are a lot of cases where the kernel intentionally copies across multiple structure fields, which means more fixes before this higher level can be enabled. NULL-prefixed stack canary
Rik van Riel and Daniel Micay changed how the stack canary is defined on 64-bit systems to always make sure that the leading byte is zero. This provides a deterministic defense against overflowing string functions (e.g. strcpy), since they will either stop an overflowing read at the NULL byte, or be unable to write a NULL byte, thereby always triggering the canary check. This does reduce the entropy from 64 bits to 56 bits for overflow cases where NULL bytes can be written (e.g. memcpy), but the trade-off is worth it. (Besdies, x86_64 s canary was 32-bits until recently.) IPC refactoring
Partially in support of allowing IPC structure layouts to be randomized by the randstruct plugin, Manfred Spraul and I reorganized the internal layout of how IPC is tracked in the kernel. The resulting allocations are smaller and much easier to deal with, even if I initially missed a few needed container_of() uses. randstruct gcc plugin
I ported grsecurity s clever randstruct gcc plugin to upstream. This plugin allows structure layouts to be randomized on a per-build basis, providing a probabilistic defense against attacks that need to know the location of sensitive structure fields in kernel memory (which is most attacks). By moving things around in this fashion, attackers need to perform much more work to determine the resulting layout before they can mount a reliable attack. Unfortunately, due to the timing of the development cycle, only the manual mode of randstruct landed in upstream (i.e. marking structures with __randomize_layout). v4.14 will also have the automatic mode enabled, which randomizes all structures that contain only function pointers. A large number of fixes to support randstruct have been landing from v4.10 through v4.13, most of which were already identified and fixed by grsecurity, but many were novel, either in newly added drivers, as whitelisted cross-structure casts, refactorings (like IPC noted above), or in a corner case on ARM found during upstream testing. lower ELF_ET_DYN_BASE
One of the issues identified from the Stack Clash set of vulnerabilities was that it was possible to collide stack memory with the highest portion of a PIE program s text memory since the default ELF_ET_DYN_BASE (the lowest possible random position of a PIE executable in memory) was already so high in the memory layout (specifically, 2/3rds of the way through the address space). Fixing this required teaching the ELF loader how to load interpreters as shared objects in the mmap region instead of as a PIE executable (to avoid potentially colliding with the binary it was loading). As a result, the PIE default could be moved down to ET_EXEC (0x400000) on 32-bit, entirely avoiding the subset of Stack Clash attacks. 64-bit could be moved to just above the 32-bit address space (0x100000000), leaving the entire 32-bit region open for VMs to do 32-bit addressing, but late in the cycle it was discovered that Address Sanitizer couldn t handle it moving. With most of the Stack Clash risk only applicable to 32-bit, fixing 64-bit has been deferred until there is a way to teach Address Sanitizer how to load itself as a shared object instead of as a PIE binary. early device randomness
I noticed that early device randomness wasn t actually getting added to the kernel entropy pools, so I fixed that to improve the effectiveness of the latent_entropy gcc plugin. That s it for now; please let me know if I missed anything. As a side note, I was rather alarmed to discover that due to all my trivial ReSTification formatting, and tiny FORTIFY_SOURCE and randstruct fixes, I made it into the most active 4.13 developers list (by patch count) at LWN with 76 patches: a whopping 0.6% of the cycle s patches. ;) Anyway, the v4.14 merge window is open!

2017, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

20 August 2017

Vincent Bernat: IPv6 route lookup on Linux

TL;DR: With its implementation of IPv6 routing tables using radix trees, Linux offers subpar performance (450 ns for a full view 40,000 routes) compared to IPv4 (50 ns for a full view 500,000 routes) but fair memory usage (20 MiB for a full view).
In a previous article, we had a look at IPv4 route lookup on Linux. Let s see how different IPv6 is.

Lookup trie implementation Looking up a prefix in a routing table comes down to find the most specific entry matching the requested destination. A common structure for this task is the trie, a tree structure where each node has its parent as prefix. With IPv4, Linux uses a level-compressed trie (or LPC-trie), providing good performances with low memory usage. For IPv6, Linux uses a more classic radix tree (or Patricia trie). There are three reasons for not sharing:
  • The IPv6 implementation (introduced in Linux 2.1.8, 1996) predates the IPv4 implementation based on LPC-tries (in Linux 2.6.13, commit 19baf839ff4a).
  • The feature set is different. Notably, IPv6 supports source-specific routing1 (since Linux 2.1.120, 1998).
  • The IPv4 address space is denser than the IPv6 address space. Level-compression is therefore quite efficient with IPv4. This may not be the case with IPv6.
The trie in the below illustration encodes 6 prefixes: Radix tree For more in-depth explanation on the different ways to encode a routing table into a trie and a better understanding of radix trees, see the explanations for IPv4. The following figure shows the in-memory representation of the previous radix tree. Each node corresponds to a struct fib6_node. When a node has the RTN_RTINFO flag set, it embeds a pointer to a struct rt6_info containing information about the next-hop. Memory representation of a routing table The fib6_lookup_1() function walks the radix tree in two steps:
  1. walking down the tree to locate the potential candidate, and
  2. checking the candidate and, if needed, backtracking until a match.
Here is a slightly simplified version without source-specific routing:
static struct fib6_node *fib6_lookup_1(struct fib6_node *root,
                                       struct in6_addr  *addr)
 
    struct fib6_node *fn;
    __be32 dir;
    /* Step 1: locate potential candidate */
    fn = root;
    for (;;)  
        struct fib6_node *next;
        dir = addr_bit_set(addr, fn->fn_bit);
        next = dir ? fn->right : fn->left;
        if (next)  
            fn = next;
            continue;
         
        break;
     
    /* Step 2: check prefix and backtrack if needed */
    while (fn)  
        if (fn->fn_flags & RTN_RTINFO)  
            struct rt6key *key;
            key = fn->leaf->rt6i_dst;
            if (ipv6_prefix_equal(&key->addr, addr, key->plen))  
                if (fn->fn_flags & RTN_RTINFO)
                    return fn;
             
         
        if (fn->fn_flags & RTN_ROOT)
            break;
        fn = fn->parent;
     
    return NULL;
 

Caching While IPv4 lost its route cache in Linux 3.6 (commit 5e9965c15ba8), IPv6 still has a caching mechanism. However cache entries are directly put in the radix tree instead of a distinct structure. Since Linux 2.1.30 (1997) and until Linux 4.2 (commit 45e4fd26683c), almost any successful route lookup inserts a cache entry in the radix tree. For example, a router forwarding a ping between 2001:db8:1::1 and 2001:db8:3::1 would get those two cache entries:
$ ip -6 route show cache
2001:db8:1::1 dev r2-r1  metric 0
    cache
2001:db8:3::1 via 2001:db8:2::2 dev r2-r3  metric 0
    cache
These entries are cleaned up by the ip6_dst_gc() function controlled by the following parameters:
$ sysctl -a   grep -F net.ipv6.route
net.ipv6.route.gc_elasticity = 9
net.ipv6.route.gc_interval = 30
net.ipv6.route.gc_min_interval = 0
net.ipv6.route.gc_min_interval_ms = 500
net.ipv6.route.gc_thresh = 1024
net.ipv6.route.gc_timeout = 60
net.ipv6.route.max_size = 4096
net.ipv6.route.mtu_expires = 600
The garbage collector is triggered at most every 500 ms when there are more than 1024 entries or at least every 30 seconds. The garbage collection won t run for more than 60 seconds, except if there are more than 4096 routes. When running, it will first delete entries older than 30 seconds. If the number of cache entries is still greater than 4096, it will continue to delete more recent entries (but no more recent than 512 jiffies, which is the value of gc_elasticity) after a 500 ms pause. Starting from Linux 4.2 (commit 45e4fd26683c), only a PMTU exception would create a cache entry. A router doesn t have to handle those exceptions, so only hosts would get cache entries. And they should be pretty rare. Martin KaFai Lau explains:
Out of all IPv6 RTF_CACHE routes that are created, the percentage that has a different MTU is very small. In one of our end-user facing proxy server, only 1k out of 80k RTF_CACHE routes have a smaller MTU. For our DC traffic, there is no MTU exception.
Here is how a cache entry with a PMTU exception looks like:
$ ip -6 route show cache
2001:db8:1::50 via 2001:db8:1::13 dev out6  metric 0
    cache  expires 573sec mtu 1400 pref medium

Performance We consider three distinct scenarios:
Excerpt of an Internet full view
In this scenario, Linux acts as an edge router attached to the default-free zone. Currently, the size of such a routing table is a little bit above 40,000 routes.
/48 prefixes spread linearly with different densities
Linux acts as a core router inside a datacenter. Each customer or rack gets one or several /48 networks, which need to be routed around. With a density of 1, /48 subnets are contiguous.
/128 prefixes spread randomly in a fixed /108 subnet
Linux acts as a leaf router for a /64 subnet with hosts getting their IP using autoconfiguration. It is assumed all hosts share the same OUI and therefore, the first 40 bits are fixed. In this scenario, neighbor reachability information for the /64 subnet are converted into routes by some external process and redistributed among other routers sharing the same subnet2.

Route lookup performance With the help of a small kernel module, we can accurately benchmark3 the ip6_route_output_flags() function and correlate the results with the radix tree size: Maximum depth and lookup time Getting meaningful results is challenging due to the size of the address space. None of the scenarios have a fallback route and we only measure time for successful hits4. For the full view scenario, only the range from 2400::/16 to 2a06::/16 is scanned (it contains more than half of the routes). For the /128 scenario, the whole /108 subnet is scanned. For the /48 scenario, the range from the first /48 to the last one is scanned. For each range, 5000 addresses are picked semi-randomly. This operation is repeated until we get 5000 hits or until 1 million tests have been executed. The relation between the maximum depth and the lookup time is incomplete and I can t explain the difference of performance between the different densities of the /48 scenario. We can extract two important performance points:
  • With a full view, the lookup time is 450 ns. This is almost ten times the budget for forwarding at 10 Gbps which is about 50 ns.
  • With an almost empty routing table, the lookup time is 150 ns. This is still over the time budget for forwarding at 10 Gbps.
With IPv4, the lookup time for an almost empty table was 20 ns while the lookup time for a full view (500,000 routes) was a bit above 50 ns. How to explain such a difference? First, the maximum depth of the IPv4 LPC-trie with 500,000 routes was 6, while the maximum depth of the IPv6 radix tree for 40,000 routes is 40. Second, while both IPv4 s fib_lookup() and IPv6 s ip6_route_output_flags() functions have a fixed cost implied by the evaluation of routing rules, IPv4 has several optimizations when the rules are left unmodified5. Those optimizations are removed on the first modification. If we cancel those optimizations, the lookup time for IPv4 is impacted by about 30 ns. This still leaves a 100 ns difference with IPv6 to be explained. Let s compare how time is spent in each lookup function. Here is a CPU flamegraph for IPv4 s fib_lookup(): IPv4 route lookup flamegraph Only 50% of the time is spent in the actual route lookup. The remaining time is spent evaluating the routing rules (about 30 ns). This ratio is dependent on the number of routes we inserted (only 1000 in this example). It should be noted the fib_table_lookup() function is executed twice: once with the local routing table and once with the main routing table. The equivalent flamegraph for IPv6 s ip6_route_output_flags() is depicted below: IPv6 route lookup flamegraph Here is an approximate breakdown on the time spent:
  • 50% is spent in the route lookup in the main table,
  • 15% is spent in handling locking (IPv4 is using the more efficient RCU mechanism),
  • 5% is spent in the route lookup of the local table,
  • most of the remaining is spent in routing rule evaluation (about 100 ns)6.
Why does the evaluation of routing rules is less efficient with IPv6? Again, I don t have a definitive answer.

History The following graph shows the performance progression of route lookups through Linux history: IPv6 route lookup performance progression All kernels are compiled with GCC 4.9 (from Debian Jessie). This version is able to compile older kernels as well as current ones. The kernel configuration is the default one with CONFIG_SMP, CONFIG_IPV6, CONFIG_IPV6_MULTIPLE_TABLES and CONFIG_IPV6_SUBTREES options enabled. Some other unrelated options are enabled to be able to boot them in a virtual machine and run the benchmark. There are three notable performance changes:
  • In Linux 3.1, Eric Dumazet delays a bit the copy of route metrics to fix the undesirable sharing of route-specific metrics by all cache entries (commit 21efcfa0ff27). Each cache entry now gets its own metrics, which explains the performance hit for the non-/128 scenarios.
  • In Linux 3.9, Yoshifuji Hideaki removes the reference to the neighbor entry in struct rt6_info (commit 887c95cc1da5). This should have lead to a performance increase. The small regression may be due to cache-related issues.
  • In Linux 4.2, Martin KaFai Lau prevents the creation of cache entries for most route lookups. The most sensible performance improvement comes with commit 4b32b5ad31a6. The second one is from commit 45e4fd26683c, which effectively removes creation of cache entries, except for PMTU exceptions.

Insertion performance Another interesting performance-related metric is the insertion time. Linux is able to insert a full view in less than two seconds. For some reason, the insertion time is not linear above 50,000 routes and climbs very fast to 60 seconds for 500,000 routes. Insertion time Despite its more complex insertion logic, the IPv4 subsystem is able to insert 2 million routes in less than 10 seconds.

Memory usage Radix tree nodes (struct fib6_node) and routing information (struct rt6_info) are allocated with the slab allocator7. It is therefore possible to extract the information from /proc/slabinfo when the kernel is booted with the slab_nomerge flag:
# sed -ne 2p -e '/^ip6_dst/p' -e '/^fib6_nodes/p' /proc/slabinfo   cut -f1 -d:
   name            <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab>
fib6_nodes         76101  76104     64   63    1
ip6_dst_cache      40090  40090    384   10    1
In the above example, the used memory is 76104 64+40090 384 bytes (about 20 MiB). The number of struct rt6_info matches the number of routes while the number of nodes is roughly twice the number of routes: Nodes The memory usage is therefore quite predictable and reasonable, as even a small single-board computer can support several full views (20 MiB for each): Memory usage The LPC-trie used for IPv4 is more efficient: when 512 MiB of memory is needed for IPv6 to store 1 million routes, only 128 MiB are needed for IPv4. The difference is mainly due to the size of struct rt6_info (336 bytes) compared to the size of IPv4 s struct fib_alias (48 bytes): IPv4 puts most information about next-hops in struct fib_info structures that are shared with many entries.

Conclusion The takeaways from this article are:
  • upgrade to Linux 4.2 or more recent to avoid excessive caching,
  • route lookups are noticeably slower compared to IPv4 (by an order of magnitude),
  • CONFIG_IPV6_MULTIPLE_TABLES option incurs a fixed penalty of 100 ns by lookup,
  • memory usage is fair (20 MiB for 40,000 routes).
Compared to IPv4, IPv6 in Linux doesn t foster the same interest, notably in term of optimizations. Hopefully, things are changing as its adoption and use at scale are increasing.

  1. For a given destination prefix, it s possible to attach source-specific prefixes:
    ip -6 route add 2001:db8:1::/64 \
      from 2001:db8:3::/64 \
      via fe80::1 \
      dev eth0
    
    Lookup is first done on the destination address, then on the source address.
  2. This is quite different of the classic scenario where Linux acts as a gateway for a /64 subnet. In this case, the neighbor subsystem stores the reachability information for each host and the routing table only contains a single /64 prefix.
  3. The measurements are done in a virtual machine with one vCPU and no neighbors. The host is an Intel Core i5-4670K running at 3.7 GHz during the experiment (CPU governor set to performance). The benchmark is single-threaded. Many lookups are performed and the result reported is the median value. Timings of individual runs are computed from the TSC.
  4. Most of the packets in the network are expected to be routed to a destination. However, this also means the backtracking code path is not used in the /128 and /48 scenarios. Having a fallback route gives far different results and make it difficult to ensure we explore the address space correctly.
  5. The exact same optimizations could be applied for IPv6. Nobody did it yet.
  6. Compiling out table support effectively removes those last 100 ns.
  7. There is also per-CPU pointers allocated directly (4 bytes per entry per CPU on a 64-bit architecture). We ignore this detail.

3 July 2017

Vincent Bernat: Performance progression of IPv4 route lookup on Linux

TL;DR: Each of Linux 2.6.39, 3.6 and 4.0 brings notable performance improvements for the IPv4 route lookup process.
In a previous article, I explained how Linux implements an IPv4 routing table with compressed tries to offer excellent lookup times. The following graph shows the performance progression of Linux through history: IPv4 route lookup performance Two scenarios are tested: All kernels are compiled with GCC 4.9 (from Debian Jessie). This version is able to compile older kernels1 as well as current ones. The kernel configuration used is the default one with CONFIG_SMP and CONFIG_IP_MULTIPLE_TABLES options enabled (however, no IP rules are used). Some other unrelated options are enabled to be able to boot them in a virtual machine and run the benchmark. The measurements are done in a virtual machine with one vCPU2. The host is an Intel Core i5-4670K and the CPU governor was set to performance . The benchmark is single-threaded. Implemented as a kernel module, it calls fib_lookup() with various destinations in 100,000 timed iterations and keeps the median. Timings of individual runs are computed from the TSC (and converted to nanoseconds by assuming a constant clock). The following kernel versions bring a notable performance improvement:

  1. Compiling old kernels with an updated userland may still require some small patches.
  2. The kernels are compiled with the CONFIG_SMP option to use the hierarchical RCU and activate more of the same code paths as actual routers. However, progress on parallelism are left unnoticed.

21 June 2017

Vincent Bernat: IPv4 route lookup on Linux

TL;DR: With its implementation of IPv4 routing tables using LPC-tries, Linux offers good lookup performance (50 ns for a full view) and low memory usage (64 MiB for a full view).
During the lifetime of an IPv4 datagram inside the Linux kernel, one important step is the route lookup for the destination address through the fib_lookup() function. From essential information about the datagram (source and destination IP addresses, interfaces, firewall mark, ), this function should quickly provide a decision. Some possible options are: Since 2.6.39, Linux stores routes into a compressed prefix tree (commit 3630b7c050d9). In the past, a route cache was maintained but it has been removed1 in Linux 3.6.

Route lookup in a trie Looking up a route in a routing table is to find the most specific prefix matching the requested destination. Let s assume the following routing table:
$ ip route show scope global table 100
default via 203.0.113.5 dev out2
192.0.2.0/25
        nexthop via 203.0.113.7  dev out3 weight 1
        nexthop via 203.0.113.9  dev out4 weight 1
192.0.2.47 via 203.0.113.3 dev out1
192.0.2.48 via 203.0.113.3 dev out1
192.0.2.49 via 203.0.113.3 dev out1
192.0.2.50 via 203.0.113.3 dev out1
Here are some examples of lookups and the associated results:
Destination IP Next hop
192.0.2.49 203.0.113.3 via out1
192.0.2.50 203.0.113.3 via out1
192.0.2.51 203.0.113.7 via out3 or 203.0.113.9 via out4 (ECMP)
192.0.2.200 203.0.113.5 via out2
A common structure for route lookup is the trie, a tree structure where each node has its parent as prefix.

Lookup with a simple trie The following trie encodes the previous routing table: Simple routing trie For each node, the prefix is known by its path from the root node and the prefix length is the current depth. A lookup in such a trie is quite simple: at each step, fetch the nth bit of the IP address, where n is the current depth. If it is 0, continue with the first child. Otherwise, continue with the second. If a child is missing, backtrack until a routing entry is found. For example, when looking for 192.0.2.50, we will find the result in the corresponding leaf (at depth 32). However for 192.0.2.51, we will reach 192.0.2.50/31 but there is no second child. Therefore, we backtrack until the 192.0.2.0/25 routing entry. Adding and removing routes is quite easy. From a performance point of view, the lookup is done in constant time relative to the number of routes (due to maximum depth being capped to 32). Quagga is an example of routing software still using this simple approach.

Lookup with a path-compressed trie In the previous example, most nodes only have one child. This leads to a lot of unneeded bitwise comparisons and memory is also wasted on many nodes. To overcome this problem, we can use path compression: each node with only one child is removed (except if it also contains a routing entry). Each remaining node gets a new property telling how many input bits should be skipped. Such a trie is also known as a Patricia trie or a radix tree. Here is the path-compressed version of the previous trie: Patricia trie Since some bits have been ignored, on a match, a final check is executed to ensure all bits from the found entry are matching the input IP address. If not, we must act as if the entry wasn t found (and backtrack to find a matching prefix). The following figure shows two IP addresses matching the same leaf: Lookup in a Patricia trie The reduction on the average depth of the tree compensates the necessity to handle those false positives. The insertion and deletion of a routing entry is still easy enough. Many routing systems are using Patricia trees:

Lookup with a level-compressed trie In addition to path compression, level compression2 detects parts of the trie that are densily populated and replace them with a single node and an associated vector of 2k children. This node will handle k input bits instead of just one. For example, here is a level-compressed version our previous trie: Level-compressed trie Such a trie is called LC-trie or LPC-trie and offers higher lookup performances compared to a radix tree. An heuristic is used to decide how many bits a node should handle. On Linux, if the ratio of non-empty children to all children would be above 50% when the node handles an additional bit, the node gets this additional bit. On the other hand, if the current ratio is below 25%, the node loses the responsibility of one bit. Those values are not tunable. Insertion and deletion becomes more complex but lookup times are also improved.

Implementation in Linux The implementation for IPv4 in Linux exists since 2.6.13 (commit 19baf839ff4a) and is enabled by default since 2.6.39 (commit 3630b7c050d9). Here is the representation of our example routing table in memory3: Memory representation of a trie There are several structures involved: The trie can be retrieved through /proc/net/fib_trie:
$ cat /proc/net/fib_trie
Id 100:
  +-- 0.0.0.0/0 2 0 2
      -- 0.0.0.0
        /0 universe UNICAST
     +-- 192.0.2.0/26 2 0 1
         -- 192.0.2.0
           /25 universe UNICAST
         -- 192.0.2.47
           /32 universe UNICAST
        +-- 192.0.2.48/30 2 0 1
            -- 192.0.2.48
              /32 universe UNICAST
            -- 192.0.2.49
              /32 universe UNICAST
            -- 192.0.2.50
              /32 universe UNICAST
[...]
For internal nodes, the numbers after the prefix are:
  1. the number of bits handled by the node,
  2. the number of full children (they only handle one bit),
  3. the number of empty children.
Moreover, if the kernel was compiled with CONFIG_IP_FIB_TRIE_STATS, some interesting statistics are available in /proc/net/fib_triestat4:
$ cat /proc/net/fib_triestat
Basic info: size of leaf: 48 bytes, size of tnode: 40 bytes.
Id 100:
        Aver depth:     2.33
        Max depth:      3
        Leaves:         6
        Prefixes:       6
        Internal nodes: 3
          2: 3
        Pointers: 12
Null ptrs: 4
Total size: 1  kB
[...]
When a routing table is very dense, a node can handle many bits. For example, a densily populated routing table with 1 million entries packed in a /12 can have one internal node handling 20 bits. In this case, route lookup is essentially reduced to a lookup in a vector. The following graph shows the number of internal nodes used relative to the number of routes for different scenarios (routes extracted from an Internet full view, /32 routes spreaded over 4 different subnets with various densities). When routes are densily packed, the number of internal nodes are quite limited. Internal nodes and null pointers

Performance So how performant is a route lookup? The maximum depth stays low (about 6 for a full view), so a lookup should be quite fast. With the help of a small kernel module, we can accurately benchmark5 the fib_lookup() function: Maximum depth and lookup time The lookup time is loosely tied to the maximum depth. When the routing table is densily populated, the maximum depth is low and the lookup times are fast. When forwarding at 10 Gbps, the time budget for a packet would be about 50 ns. Since this is also the time needed for the route lookup alone in some cases, we wouldn t be able to forward at line rate with only one core. Nonetheless, the results are pretty good and they are expected to scale linearly with the number of cores. The measurements are done with a Linux kernel 4.11 from Debian unstable. I have gathered performance metrics accross kernel versions in Performance progression of IPv4 route lookup on Linux . Another interesting figure is the time it takes to insert all those routes into the kernel. Linux is also quite efficient in this area since you can insert 2 million routes in less than 10 seconds: Insertion time

Memory usage The memory usage is available directly in /proc/net/fib_triestat. The statistic provided doesn t account for the fib_info structures, but you should only have a handful of them (one for each possible next-hop). As you can see on the graph below, the memory use is linear with the number of routes inserted, whatever the shape of the routes is. Memory usage The results are quite good. With only 256 MiB, about 2 million routes can be stored!

Routing rules Unless configured without CONFIG_IP_MULTIPLE_TABLES, Linux supports several routing tables and has a system of configurable rules to select the table to use. These rules can be configured with ip rule. By default, there are three of them:
$ ip rule show
0:      from all lookup local
32766:  from all lookup main
32767:  from all lookup default
Linux will first lookup for a match in the local table. If it doesn t find one, it will lookup in the main table and at last resort, the default table.

Builtin tables The local table contains routes for local delivery:
$ ip route show table local
broadcast 127.0.0.0 dev lo proto kernel scope link src 127.0.0.1
local 127.0.0.0/8 dev lo proto kernel scope host src 127.0.0.1
local 127.0.0.1 dev lo proto kernel scope host src 127.0.0.1
broadcast 127.255.255.255 dev lo proto kernel scope link src 127.0.0.1
broadcast 192.168.117.0 dev eno1 proto kernel scope link src 192.168.117.55
local 192.168.117.55 dev eno1 proto kernel scope host src 192.168.117.55
broadcast 192.168.117.63 dev eno1 proto kernel scope link src 192.168.117.55
This table is populated automatically by the kernel when addresses are configured. Let s look at the three last lines. When the IP address 192.168.117.55 was configured on the eno1 interface, the kernel automatically added the appropriate routes:
  • a route for 192.168.117.55 for local unicast delivery to the IP address,
  • a route for 192.168.117.255 for broadcast delivery to the broadcast address,
  • a route for 192.168.117.0 for broadcast delivery to the network address.
When 127.0.0.1 was configured on the loopback interface, the same kind of routes were added to the local table. However, a loopback address receives a special treatment and the kernel also adds the whole subnet to the local table. As a result, you can ping any IP in 127.0.0.0/8:
$ ping -c1 127.42.42.42
PING 127.42.42.42 (127.42.42.42) 56(84) bytes of data.
64 bytes from 127.42.42.42: icmp_seq=1 ttl=64 time=0.039 ms
--- 127.42.42.42 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.039/0.039/0.039/0.000 ms
The main table usually contains all the other routes:
$ ip route show table main
default via 192.168.117.1 dev eno1 proto static metric 100
192.168.117.0/26 dev eno1 proto kernel scope link src 192.168.117.55 metric 100
The default route has been configured by some DHCP daemon. The connected route (scope link) has been automatically added by the kernel (proto kernel) when configuring an IP address on the eno1 interface. The default table is empty and has little use. It has been kept when the current incarnation of advanced routing has been introduced in Linux 2.1.68 after a first tentative using classes in Linux 2.1.156.

Performance Since Linux 4.1 (commit 0ddcf43d5d4a), when the set of rules is left unmodified, the main and local tables are merged and the lookup is done with this single table (and the default table if not empty). Moreover, since Linux 3.0 (commit f4530fa574df), without specific rules, there is no performance hit when enabling the support for multiple routing tables. However, as soon as you add new rules, some CPU cycles will be spent for each datagram to evaluate them. Here is a couple of graphs demonstrating the impact of routing rules on lookup times: Routing rules impact on performance For some reason, the relation is linear when the number of rules is between 1 and 100 but the slope increases noticeably past this threshold. The second graph highlights the negative impact of the first rule (about 30 ns). A common use of rules is to create virtual routers: interfaces are segregated into domains and when a datagram enters through an interface from domain A, it should use routing table A:
# ip rule add iif vlan457 table 10
# ip rule add iif vlan457 blackhole
# ip rule add iif vlan458 table 20
# ip rule add iif vlan458 blackhole
The blackhole rules may be removed if you are sure there is a default route in each routing table. For example, we add a blackhole default with a high metric to not override a regular default route:
# ip route add blackhole default metric 9999 table 10
# ip route add blackhole default metric 9999 table 20
# ip rule add iif vlan457 table 10
# ip rule add iif vlan458 table 20
To reduce the impact on performance when many interface-specific rules are used, interfaces can be attached to VRF instances and a single rule can be used to select the appropriate table:
# ip link add vrf-A type vrf table 10
# ip link set dev vrf-A up
# ip link add vrf-B type vrf table 20
# ip link set dev vrf-B up
# ip link set dev vlan457 master vrf-A
# ip link set dev vlan458 master vrf-B
# ip rule show
0:      from all lookup local
1000:   from all lookup [l3mdev-table]
32766:  from all lookup main
32767:  from all lookup default
The special l3mdev-table rule was automatically added when configuring the first VRF interface. This rule will select the routing table associated to the VRF owning the input (or output) interface. VRF was introduced in Linux 4.3 (commit 193125dbd8eb), the performance was greatly enhanced in Linux 4.8 (commit 7889681f4a6c) and the special routing rule was also introduced in Linux 4.8 (commit 96c63fa7393d, commit 1aa6c4f6b8cd). You can find more details about it in the kernel documentation.

Conclusion The takeaways from this article are:
  • route lookup times hardly increase with the number of routes,
  • densily packed /32 routes lead to amazingly fast route lookups,
  • memory use is low (128 MiB par million routes),
  • no optimization is done on routing rules.

  1. The routing cache was subject to reasonably easy to launch denial of service attacks. It was also believed to not be efficient for high volume sites like Google but I have first-hand experience it was not the case for moderately high volume sites.
  2. IP-address lookup using LC-tries , IEEE Journal on Selected Areas in Communications, 17(6):1083-1092, June 1999.
  3. For internal nodes, the key_vector structure is embedded into a tnode structure. This structure contains information rarely used during lookup, notably the reference to the parent that is usually not needed for backtracking as Linux keeps the nearest candidate in a variable.
  4. One leaf can contain several routes (struct fib_alias is a list). The number of prefixes can therefore be greater than the number of leaves. The system also keeps statistics about the distribution of the internal nodes relative to the number of bits they handle. In our example, all the three internal nodes are handling 2 bits.
  5. The measurements are done in a virtual machine with one vCPU. The host is an Intel Core i5-4670K running at 3.7 GHz during the experiment (CPU governor was set to performance). The benchmark is single-threaded. It runs a warm-up phase, then executes about 100,000 timed iterations and keeps the median. Timings of individual runs are computed from the TSC.
  6. Fun fact: the documentation of this first tentative of more flexible routing is still available in today s kernel tree and explains the usage of the default class .

7 June 2017

Petter Reinholdtsen: Idea for storing trusted timestamps in a Noark 5 archive

This is a copy of an email I posted to the nikita-noark mailing list. Please follow up there if you would like to discuss this topic. The background is that we are making a free software archive system based on the Norwegian Noark 5 standard for government archives. I've been wondering a bit lately how trusted timestamps could be stored in Noark 5. Trusted timestamps can be used to verify that some information (document/file/checksum/metadata) have not been changed since a specific time in the past. This is useful to verify the integrity of the documents in the archive. Then it occured to me, perhaps the trusted timestamps could be stored as dokument variants (ie dokumentobjekt referered to from dokumentbeskrivelse) with the filename set to the hash it is stamping? Given a "dokumentbeskrivelse" with an associated "dokumentobjekt", a new dokumentobjekt is associated with "dokumentbeskrivelse" with the same attributes as the stamped dokumentobjekt except these attributes: This assume a service following IETF RFC 3161 is used, which specifiy the given MIME type for replies and the .tsr file ending for the content of such trusted timestamp. As far as I can tell from the Noark 5 specifications, it is OK to have several variants/renderings of a dokument attached to a given dokumentbeskrivelse objekt. It might be stretching it a bit to make some of these variants represent crypto-signatures useful for verifying the document integrity instead of representing the dokument itself. Using the source of the service in formatDetaljer allow several timestamping services to be used. This is useful to spread the risk of key compromise over several organisations. It would only be a problem to trust the timestamps if all of the organisations are compromised. The following oneliner on Linux can be used to generate the tsr file. $input is the path to the file to checksum, and $sha256 is the SHA-256 checksum of the file (ie the ".tsr" value mentioned above).
openssl ts -query -data "$inputfile" -cert -sha256 -no_nonce \
    curl -s -H "Content-Type: application/timestamp-query" \
      --data-binary "@-" http://zeitstempel.dfn.de > $sha256.tsr
To verify the timestamp, you first need to download the public key of the trusted timestamp service, for example using this command:
wget -O ca-cert.txt \
  https://pki.pca.dfn.de/global-services-ca/pub/cacert/chain.txt
Note, the public key should be stored alongside the timestamps in the archive to make sure it is also available 100 years from now. It is probably a good idea to standardise how and were to store such public keys, to make it easier to find for those trying to verify documents 100 or 1000 years from now. :) The verification itself is a simple openssl command:
openssl ts -verify -data $inputfile -in $sha256.tsr \
  -CAfile ca-cert.txt -text
Is there any reason this approach would not work? Is it somehow against the Noark 5 specification?

19 March 2017

Petter Reinholdtsen: Free software archive system Nikita now able to store documents

The Nikita Noark 5 core project is implementing the Norwegian standard for keeping an electronic archive of government documents. The Noark 5 standard document the requirement for data systems used by the archives in the Norwegian government, and the Noark 5 web interface specification document a REST web service for storing, searching and retrieving documents and metadata in such archive. I've been involved in the project since a few weeks before Christmas, when the Norwegian Unix User Group announced it supported the project. I believe this is an important project, and hope it can make it possible for the government archives in the future to use free software to keep the archives we citizens depend on. But as I do not hold such archive myself, personally my first use case is to store and analyse public mail journal metadata published from the government. I find it useful to have a clear use case in mind when developing, to make sure the system scratches one of my itches. If you would like to help make sure there is a free software alternatives for the archives, please join our IRC channel (#nikita on irc.freenode.net) and the project mailing list. When I got involved, the web service could store metadata about documents. But a few weeks ago, a new milestone was reached when it became possible to store full text documents too. Yesterday, I completed an implementation of a command line tool archive-pdf to upload a PDF file to the archive using this API. The tool is very simple at the moment, and find existing fonds, series and files while asking the user to select which one to use if more than one exist. Once a file is identified, the PDF is associated with the file and uploaded, using the title extracted from the PDF itself. The process is fairly similar to visiting the archive, opening a cabinet, locating a file and storing a piece of paper in the archive. Here is a test run directly after populating the database with test data using our API tester:
~/src//noark5-tester$ ./archive-pdf mangelmelding/mangler.pdf
using arkiv: Title of the test fonds created 2017-03-18T23:49:32.103446
using arkivdel: Title of the test series created 2017-03-18T23:49:32.103446
 0 - Title of the test case file created 2017-03-18T23:49:32.103446
 1 - Title of the test file created 2017-03-18T23:49:32.103446
Select which mappe you want (or search term): 0
Uploading mangelmelding/mangler.pdf
  PDF title: Mangler i spesifikasjonsdokumentet for NOARK 5 Tjenestegrensesnitt
  File 2017/1: Title of the test case file created 2017-03-18T23:49:32.103446
~/src//noark5-tester$
You can see here how the fonds (arkiv) and serie (arkivdel) only had one option, while the user need to choose which file (mappe) to use among the two created by the API tester. The archive-pdf tool can be found in the git repository for the API tester. In the project, I have been mostly working on the API tester so far, while getting to know the code base. The API tester currently use the HATEOAS links to traverse the entire exposed service API and verify that the exposed operations and objects match the specification, as well as trying to create objects holding metadata and uploading a simple XML file to store. The tester has proved very useful for finding flaws in our implementation, as well as flaws in the reference site and the specification. The test document I uploaded is a summary of all the specification defects we have collected so far while implementing the web service. There are several unclear and conflicting parts of the specification, and we have started writing down the questions we get from implementing it. We use a format inspired by how The Austin Group collect defect reports for the POSIX standard with their instructions for the MANTIS defect tracker system, in lack of an official way to structure defect reports for Noark 5 (our first submitted defect report was a request for a procedure for submitting defect reports :). The Nikita project is implemented using Java and Spring, and is fairly easy to get up and running using Docker containers for those that want to test the current code base. The API tester is implemented in Python.

17 February 2017

Joey Hess: Presenting at LibrePlanet 2017

I've gotten in the habit of going to the FSF's LibrePlanet conference in Boston. It's a very special conference, much wider ranging than a typical technology conference, solidly grounded in software freedom, and full of extraordinary people. (And the only conference I've ever taken my Mom to!) After attending for four years, I finally thought it was time to perhaps speak at it.
Four keynote speakers will anchor the event. Kade Crockford, director of the Technology for Liberty program of the American Civil Liberties Union of Massachusetts, will kick things off on Saturday morning by sharing how technologists can enlist in the growing fight for civil liberties. On Saturday night, Free Software Foundation president Richard Stallman will present the Free Software Awards and discuss pressing threats and important opportunities for software freedom. Day two will begin with Cory Doctorow, science fiction author and special consultant to the Electronic Frontier Foundation, revealing how to eradicate all Digital Restrictions Management (DRM) in a decade. The conference will draw to a close with Sumana Harihareswara, leader, speaker, and advocate for free software and communities, giving a talk entitled "Lessons, Myths, and Lenses: What I Wish I'd Known in 1998." That's not all. We'll hear about the GNU philosophy from Marianne Corvellec of the French free software organization April, Joey Hess will touch on encryption with a talk about backing up your GPG keys, and Denver Gingerich will update us on a crucial free software need: the mobile phone. Others will look at ways to grow the free software movement: through cross-pollination with other activist movements, removal of barriers to free software use and contribution, and new ideas for free software as paid work.
-- Here's a sneak peek at LibrePlanet 2017: Register today! I'll be giving some varient of the keysafe talk from Linux.Conf.Au. By the way, videos of my keysafe and propellor talks at Linux.Conf.Au are now available, see the talks page.

26 December 2016

Lucas Nussbaum: The Linux 2.5, Ruby 1.9 and Python 3 release management anti-pattern

There s a pattern that comes up from time to time in the release management of free software projects. To allow for big, disruptive changes, a new development branch is created. Most of the developers focus moves to the development branch. However at the same time, the users focus stays on the stable branch. As a result: This situation can grow up to a quasi-deadlock, with people questioning whether it was a good idea to do such a massive fork in the first place, and if it is a good idea to even spend time switching to the new branch. To make things more unclear, the development branch is often declared stable by its developers, before most of the libraries or applications have been ported to it. This has happened at least three times. First, in the Linux 2.4 / 2.5 era. Wikipedia describes the situation like this:

Before the 2.6 series, there was a stable branch (2.4) where only relatively minor and safe changes were merged, and an unstable branch (2.5), where bigger changes and cleanups were allowed. Both of these branches had been maintained by the same set of people, led by Torvalds. This meant that users would always have a well-tested 2.4 version with the latest security and bug fixes to use, though they would have to wait for the features which went into the 2.5 branch. The downside of this was that the stable kernel ended up so far behind that it no longer supported recent hardware and lacked needed features. In the late 2.5 kernel series, some maintainers elected to try backporting of their changes to the stable kernel series, which resulted in bugs being introduced into the 2.4 kernel series. The 2.5 branch was then eventually declared stable and renamed to 2.6. But instead of opening an unstable 2.7 branch, the kernel developers decided to continue putting major changes into the 2.6 branch, which would then be released at a pace faster than 2.4.x but slower than 2.5.x. This had the desirable effect of making new features more quickly available and getting more testing of the new code, which was added in smaller batches and easier to test. Then, in the Ruby community. In 2007, Ruby 1.8.6 was the stable version of Ruby. Ruby 1.9.0 was released on 2007-12-26, without being declared stable, as a snapshot from Ruby s trunk branch, and most of the development s attention moved to 1.9.x. On 2009-01-31, Ruby 1.9.1 was the first release of the 1.9 branch to be declared stable. But at the same time, the disruptive changes introduced in Ruby 1.9 made users stay with Ruby 1.8, as many libraries (gems) remained incompatible with Ruby 1.9.x. Debian provided packages for both branches of Ruby in Squeeze (2011) but only changed the default to 1.9 in 2012 (in a stable release with Wheezy 2013). Finally, in the Python community. Similarly to what happened with Ruby 1.9, Python 3.0 was released in December 2008. Releases from the 3.x branch have been shipped in Debian Squeeze (3.1), Wheezy (3.2), Jessie (3.4). But the python command still points to 2.7 (I don t think that there are plans to make it point to 3.x, making python 3.x essentially a different language), and there are talks about really getting rid of Python 2.7 in Buster (Stretch+1, Jessie+2). In retrospect, and looking at what those projects have been doing in recent years, it is probably a better idea to break early, break often, and fix a constant stream of breakages, on a regular basis, even if that means temporarily exposing breakage to users, and spending more time seeking strategies to limit the damage caused by introducing breakage. What also changed since the time those branches were introduced is the increased popularity of automated testing and continuous integration, which makes it easier to measure breakage caused by disruptive changes. Distributions are in a good position to help here, by being able to provide early feedback to upstream projects about potentially disruptive changes. And distributions also have good motivations to help here, because it is usually not a great solution to ship two incompatible branches of the same project. (I wonder if there are other occurrences of the same pattern?) Update: There s a discussion about this post on HN

12 December 2016

Kees Cook: security things in Linux v4.9

Previously: v4.8. Here are a bunch of security things I m excited about in the newly released Linux v4.9: Latent Entropy GCC plugin Building on her earlier work to bring GCC plugin support to the Linux kernel, Emese Revfy ported PaX s Latent Entropy GCC plugin to upstream. This plugin is significantly more complex than the others that have already been ported, and performs extensive instrumentation of functions marked with __latent_entropy. These functions have their branches and loops adjusted to mix random values (selected at build time) into a global entropy gathering variable. Since the branch and loop ordering is very specific to boot conditions, CPU quirks, memory layout, etc, this provides some additional uncertainty to the kernel s entropy pool. Since the entropy actually gathered is hard to measure, no entropy is credited , but rather used to mix the existing pool further. Probably the best place to enable this plugin is on small devices without other strong sources of entropy. vmapped kernel stack and thread_info relocation on x86 Normally, kernel stacks are mapped together in memory. This meant that attackers could use forms of stack exhaustion (or stack buffer overflows) to reach past the end of a stack and start writing over another process s stack. This is bad, and one way to stop it is to provide guard pages between stacks, which is provided by vmalloced memory. Andy Lutomirski did a bunch of work to move to vmapped kernel stack via CONFIG_VMAP_STACK on x86_64. Now when writing past the end of the stack, the kernel will immediately fault instead of just continuing to blindly write. Related to this, the kernel was storing thread_info (which contained sensitive values like addr_limit) at the bottom of the kernel stack, which was an easy target for attackers to hit. Between a combination of explicitly moving targets out of thread_info, removing needless fields, and entirely moving thread_info off the stack, Andy Lutomirski and Linus Torvalds created CONFIG_THREAD_INFO_IN_TASK for x86. CONFIG_DEBUG_RODATA mandatory on arm64 As recently done for x86, Mark Rutland made CONFIG_DEBUG_RODATA mandatory on arm64. This feature controls whether the kernel enforces proper memory protections on its own memory regions (code memory is executable and read-only, read-only data is actually read-only and non-executable, and writable data is non-executable). This protection is a fundamental security primitive for kernel self-protection, so there s no reason to make the protection optional. random_page() cleanup Cleaning up the code around the userspace ASLR implementations makes them easier to reason about. This has been happening for things like the recent consolidation on arch_mmap_rnd() for ET_DYN and during the addition of the entropy sysctl. Both uncovered some awkward uses of get_random_int() (or similar) in and around arch_mmap_rnd() (which is used for mmap (and therefore shared library) and PIE ASLR), as well as in randomize_stack_top() (which is used for stack ASLR). Jason Cooper cleaned things up further by doing away with randomize_range() entirely and replacing it with the saner random_page(), making the per-architecture arch_randomize_brk() (responsible for brk ASLR) much easier to understand. That s it for now! Let me know if there are other fun things to call attention to in v4.9.

2016, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

15 November 2016

Antoine Beaupr : The Turris Omnia router: help for the IoT mess?

The Turris Omnia router is not the first FLOSS router out there, but it could well be one of the first open hardware routers to be available. As the crowdfunding campaign is coming to a close, it is worth reflecting on the place of the project in the ecosystem. Beyond that, I got my hardware recently, so I was able to give it a try.

A short introduction to the Omnia project The Turris Omnia Router The Omnia router is a followup project on CZ.NIC's original research project, the Turris. The goal of the project was to identify hostile traffic on end-user networks and develop global responses to those attacks across every monitored device. The Omnia is an extension of the original project: more features were added and data collection is now opt-in. Whereas the original Turris was simply a home router, the new Omnia router includes:
  • 1.6GHz ARM CPU
  • 1-2GB RAM
  • 8GB flash storage
  • 6 Gbit Ethernet ports
  • SFP fiber port
  • 2 Mini-PCI express ports
  • mSATA port
  • 3 MIMO 802.11ac and 2 MIMO 802.11bgn radios and antennas
  • SIM card support for backup connectivity
Some models sold had a larger case to accommodate extra hard drives, turning the Omnia router into a NAS device that could actually serve as a multi-purpose home server. Indeed, it is one of the objectives of the project to make "more than just a router". The NAS model is not currently on sale anymore, but there are plans to bring it back along with LTE modem options and new accessories "to expand Omnia towards home automation". Omnia runs a fork of the OpenWRT distribution called TurrisOS that has been customized to support automated live updates, a simpler web interface, and other extra features. The fork also has patches to the Linux kernel, which is based on Linux 4.4.13 (according to uname -a). It is unclear why those patches are necessary since the ARMv7 Armada 385 CPU has been supported in Linux since at least 4.2-rc1, but it is common for OpenWRT ports to ship patches to the kernel, either to backport missing functionality or perform some optimization. There has been some pressure from backers to petition Turris to "speedup the process of upstreaming Omnia support to OpenWrt". It could be that the team is too busy with delivering the devices already ordered to complete that process at this point. The software is available on the CZ-NIC GitHub repository and the actual Linux patches can be found here and here. CZ.NIC also operates a private GitLab instance where more software is available. There is technically no reason why you wouldn't be able to run your own distribution on the Omnia router: OpenWRT development snapshots should be able to run on the Omnia hardware and some people have installed Debian on Omnia. It may require some customization (e.g. the kernel) to make sure the Omnia hardware is correctly supported. Most people seem to prefer to run TurrisOS because of the extra features. The hardware itself is also free and open for the most part. There is a binary blob needed for the 5GHz wireless card, which seems to be the only proprietary component on the board. The schematics of the device are available through the Omnia wiki, but oddly not in the GitHub repository like the rest of the software.

Hands on I received my own router last week, which is about six months late from the original April 2016 delivery date; it allowed me to do some hands-on testing of the device. The first thing I noticed was a known problem with the antenna connectors: I had to open up the case to screw the fittings tight, otherwise the antennas wouldn't screw in correctly. Once that was done, I simply had to go through the usual process of setting up the router, which consisted of connecting the Omnia to my laptop with an Ethernet cable, connecting the Omnia to an uplink (I hooked it into my existing network), and go through a web wizard. I was pleasantly surprised with the interface: it was smooth and easy to use, but at the same time imposed good security practices on the user. Install wizard performing automatic updates For example, the wizard, once connected to the network, goes through a full system upgrade and will, by default, automatically upgrade itself (including reboots) when new updates become available. Users have to opt-in to the automatic updates, and can chose to automate only the downloading and installation of the updates without having the device reboot on its own. Reboots are also performed during user-specified time frames (by default, Omnia applies kernel updates during the night). I also liked the "skip" button that allowed me to completely bypass the wizard and configure the device myself, through the regular OpenWRT systems (like LuCI or SSH) if I needed to. The Omnia router about to rollback to latest snapshot Notwithstanding the antenna connectors themselves, the hardware is nice. I ordered the black metal case, and I must admit I love the many LED lights in the front. It is especially useful to have color changes in the reset procedure: no more guessing what state the device is in or if I pressed the reset button long enough. The LEDs can also be dimmed to reduce the glare that our electronic devices produce. All this comes at a price, however: at \$250 USD, it is a much higher price tag than common home routers, which typically go for around \$50. Furthermore, it may be difficult to actually get the device, because no orders are being accepted on the Indiegogo site after October 31. The Turris team doesn't actually want to deal with retail sales and has now delegated retail sales to other stores, which are currently limited to European deliveries.

A nice device to help fight off the IoT apocalypse It seems there isn't a week that goes by these days without a record-breaking distributed denial-of-service (DDoS) attack. Those attacks are more and more caused by home routers, webcams, and "Internet of Things" (IoT) devices. In that context, the Omnia sets a high bar for how devices should be built but also how they should be operated. Omnia routers are automatically upgraded on a nightly basis and, by default, do not provide telnet or SSH ports to run arbitrary code. There is the password-less wizard that starts up on install, but it forces the user to chose a password in order to complete the configuration. Both the hardware and software of the Omnia are free and open. The automatic update's EULA explicitly states that the software provided by CZ.NIC "will be released under a free software licence" (and it has been, as mentioned earlier). This makes the machine much easier to audit by someone looking for possible flaws, say for example a customs official looking to approve the import in the eventual case where IoT devices end up being regulated. But it also makes the device itself more secure. One of the problems with these kinds of devices is "bit rot": they have known vulnerabilities that are not fixed in a timely manner, if at all. While it would be trivial for an attacker to disable the Omnia's auto-update mechanisms, the point is not to counterattack, but to prevent attacks on known vulnerabilities. The CZ.NIC folks take it a step further and encourage users to actively participate in a monitoring effort to document such attacks. For example, the Omnia can run a honeypot to lure attackers into divulging their presence. The Omnia also runs an elaborate data collection program, where routers report malicious activity to a central server that collects information about traffic flows, blocked packets, bandwidth usage, and activity from a predefined list of malicious addresses. The exact data collected is specified in another EULA that is currently only available to users logged in at the Turris web site. That data can then be turned into tweaked firewall rules to protect the overall network, which the Turris project calls a distributed adaptive firewall. Users need to explicitly opt-in to the monitoring system by registering on a portal using their email address. Turris devices also feature the Majordomo software (not to be confused with the venerable mailing list software) that can also monitor devices in your home and identify hostile traffic, potentially leading users to take responsibility over the actions of their own devices. This, in turn, could lead users to trickle complaints back up to the manufacturers that could change their behavior. It turns out that some companies do care about their reputations and will issue recalls if their devices have significant enough issues. It remains to be seen how effective the latter approach will be, however. In the meantime, the Omnia seems to be an excellent all-around server and router for even the most demanding home or small-office environments that is a great example for future competitors.
Note: this article first appeared in the Linux Weekly News.

13 November 2016

Andrew Cater: Debian MiniConf, ARM, Cambridge 11/11/16 - Day 2 post 2

It's raining cats and dogs in Cambridge.

Just listening to Lars Wirzenius - who shared an office with Linus Torvalds, owned the computer that first ran Linux, founded the Linux Documentation Project. Living history in more than one sense :)

Live streaming is also happening.

Building work is also happening - so there may be random noise happening occasionally.

23 October 2016

Jaldhar Vyas: What I Did During My Summer Vacation

Thats So Raven If I could sum up the past year in one word, that word would be distraction. There have been so many strange, confusing or simply unforseen things going on I have had trouble focusing like never before. For instance, on the opposite side of the street from me is one of Jersey City's old resorvoirs. It's not used for drinking water anymore and the city eventually plans on merging it into the park on the other side. In the meantime it has become something of a wildlife refuge. Which is nice except one of the newly settled critters was a bird of prey -- the consensus is possibly some kind of hawk or raven. Starting your morning commute under the eyes of a harbinger of death is very goth and I even learned to deal with the occasional piece of deconstructed rodent on my doorstep but nighttime was a big problem. For contrary to popular belief, ravens do not quoth "nevermore" but "KRRAAAA". Very loudly. Just as soon as you have drifted of to sleep. Eventually my sleep-deprived neighbors and I appealed to the NJ division of enviromental protection to get it removed but by the time they were ready to swing into action the bird had left for somewhere more congenial like Transylvania or Newark. Or here are some more complete wastes of time: I go the doctor for my annual physical. The insurance company codes it as Adult Onset Diabetes by accident. One day I opened the lid of my laptop and there's a "ping" sound and a piece of the hinge flies off. Apparently that also severed the connection to the screen and naturally the warranty had just expired so I had to spend the next month tethered to an external monitor until I could afford to buy a new one. Mix in all the usual social, political, family and work drama and you can see that it has been a very trying time for me. Dovecot I have managed to get some Debian work done. On Dovecot, my principal package, I have gotten tremendous support from Apollon Oikonomopolous who I belatedly welcome as a member of the Dovecot maintainer team. He has been particularly helpful in fixing our systemd support and cleaning out a lot of the old and invalid bugs. We're in pretty good shape for the freeze. Upstream has released an RC of 2.2.26 and hopefully the final version will be out in the next couple of days so we can include it in Stretch. We can always use more help with the package so let me know if you're interested. Debian-IN Most of the action has been going on without me but I've been lending support and sponsoring whenever I can. We have several new DDs and DMs but still no one north of the Vindhyas I'm afraid. Debian Perl Group gregoa did a ping of inactive maintainers and I regretfully had to admit to myself that I wasn't going to be of use anytime soon so I resigned. Perl remains my favorite language and I've actually been more involved in the meetings of my local Perlmongers group so hopefully I will be back again one day. And I still maintain the Perl modules I wrote myself. Debian-Axe-Murderers* May have gained a recruit. *Stricly speaking it should be called Debian-People-Who-Dont-Think-Faults-in-One-Moral-Domain-Such-As-For-Example-Axe-Murdering-Should-Leak-Into-Another-Moral-Domain-Such-As-For-Example-Debian but come on, that's just silly.

17 September 2016

Norbert Preining: Android 7.0 Nougat Root PokemonGo

Since my switch to Android my Nexus 6p is rooted and I have happily fixed the Android (<7) font errors with Japanese fonts in English environment (see this post). The recently released Android 7 Nougat finally fixes this problem, so it was high time to update. In addition, a recent update to Pokemon Go excluded rooted devices, so I was searching for a solution that allows me to: update to Nougat, keep root, and run PokemonGo (as well as some bank security apps etc). android-nougat-root-poke After some playing around here are the steps I took: Installation of necessary components Warning: The following is for Nexus6p device, you need different image files and TWRP recovery for other devices. Flash Nougat firmware images Get it from the Google Android Nexus images web site, unpack the zip and the included zip one gets a lot of img files.
unzip angler-nrd90u-factory-7c9b6a2b.zip
cd angler-nrd90u/
unzip image-angler-nrd90u.zip
As I don t want my user partition to get flashed, I did not use the included flash script, but did it manually:
fastboot flash bootloader bootloader-angler-angler-03.58.img
fastboot reboot-bootloader
sleep 5
fastboot flash radio radio-angler-angler-03.72.img
fastboot reboot-bootloader
sleep 5
fastboot erase system
fastboot flash system system.img
fastboot erase boot
fastboot flash boot boot.img
fastboot erase cache
fastboot flash cache cache.img
fastboot erase vendor
fastboot flash vendor vendor.img
fastboot erase recovery
fastboot flash recovery recovery.img
fastboot reboot
After that boot into the normal system and let it do all the necessary upgrades. Once this is done, let us prepare for systemless root and possible hiding of it. Get the necessary file Get Magisk, SuperSU-magisk, as well as the Magisk-Manager.apk from this forum thread (direct links as of 2016/9: Magisk-v6.zip, SuperSU-v2.76-magisk.zip, Magisk-Manager.apk). Transfer these two files to your device I am using an external USB stick that can be plugged into the device, or copy it via your computer or via a cloud service. Also we need to get a custom recovery image, I am using TWRP. I used the version 3.0.2-0 of TWRP I had already available, but that version didn t manage to decrypt the file system and hangs. One needs to get at least version 3.0.2-2 from the TWRP web site. Install latest TWRP recorvery Reboot into boot-loader, then use fastboot to flash twrp:
fastboot erase recovery
fastboot flash recovery twrp-3.0.2-2-angler.img
fastboot reboot-bootloader
After that select Recovery with the up-down buttons and start twrp. You will be asked you pin if you have one set. Install Magisk-v6.zip Select Install in TWRP, select the Magisk-v6.zip file, and see you device being prepared for systemless root. Install SuperSU, Magisk version Again, boot into TWRP and use the install tool to install SuperSU-v2.76-magisk.zip. After reboot you should have a SuperSU binary running. Install the Magisk Manager From your device browse to the .apk and install it. How to run safety net programs Those programs that check for safety functions (Pokemon Go, Android Pay, several bank apps) need root disabled. Open the Magisk Manager and switch the root switch to the left (off). After this starting the program should bring you past the special check.

16 August 2016

Lars Wirzenius: 20 years ago I became a Debian developer

Today it is 23 years ago since Ian Murdock published his intention to develop a new Linux distribution, Debian. It also about 20 years since I became a Debian developer and made my first package upload. In the time since: It's been a good twenty years. And the fun ain't over yet.

Next.