[Bug 1815320] Re: Potential data loss in CryFS 0.9.9 (fixed in 0.9.10)

[Simon Quigley]

Hello Sebastian, thanks for your work on this! I appreciate the thorough
and standards-compliant bug description on the first try. :)

I no-change backported 0.9.10-1 to Bionic and uploaded it to the queue.
I didn't backport 0.9.10-2 because it is a mipsel-related change that
really isn't appropriate for an SRU. 0.9.9-2 is equivalent to
0.9.9-1ubuntu1, so it can replace that change.

Unsubscribing the Ubuntu Sponsors Team.

** Changed in: cryfs (Ubuntu Bionic)
       Status: New => In Progress

** Changed in: cryfs (Ubuntu Bionic)
     Assignee: (unassigned) => Simon Quigley (tsimonq2)

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Title:
  Potential data loss in CryFS 0.9.9 (fixed in 0.9.10)

Status in cryfs package in Ubuntu:
  Fix Released
Status in cryfs source package in Bionic:
  In Progress

Bug description:
  CryFS 0.9.10 fixed a dead lock and a race condition, the latter of
  which can cause data loss if the file system is under heavy load and
  accessed concurrently.

  Changelog: https://github.com/cryfs/cryfs/blob/0.9.10/ChangeLog.txt

  Some user reports about the data loss:
  - https://github.com/cryfs/cryfs/issues/243
  - https://github.com/cryfs/cryfs/issues/224
  - https://github.com/cryfs/cryfs/issues/237

  This issue is fixed in 0.9.10 but stable Ubuntu versions (bionic, cosmic) still distribute 0.9.9.
  The package should be updated in the software repositories.

  Versioning notes:
  - 0.9.10 is a new upstream microrelease.
  - A 0.9.10 package is already in Debian and Ubuntu Disco, see https://packages.debian.org/buster/cryfs and https://packages.ubuntu.com/search?keywords=cryfs
  - Debian will soon update to 0.10, and Ubuntu Disco is expected to follow. However, older Ubuntu versions should not update to 0.10.0 but only to 0.9.10 to fix the data loss bug.

  [Test Case]

  Follow the instructions in the linked GitHub issues. Since this is a
  race condition, it doesn't always manifest, but
  https://github.com/cryfs/cryfs/issues/224 was quite stable to me:

  1. Create a file system using CryFS 0.9.9

  $ cryfs -f /tmp/basedir /tmp/mountdir

  Note: the '-f' causes CryFS to run in foreground, i.e. you won't get
  your terminal back. Keep it running and open a new terminal for the
  next commands.

  2. Create a video file in the mounted directory

  $ ffmpeg -i some_video_file.mp4 /tmp/mountdir/video.avi

  3. Open /tmp/mountdir/video.avi VLC and run it

  $ vlc /tmp/mountdir/video.avi

  4. While it is running, re-create it

  $ ffmpeg -i some_video_file.mp4 /tmp/mountdir/video.avi

  5. Observe the crash in the terminal running the CryFS process

  6. Try the same with CryFS 0.9.10 and observe that it doesn't crash.

  [Regression Potential]

  The race condition was fixed in 0.9.10 using additional mutexes, so
  the most likely regression is the introduction of a new deadlock.

  Generally, CryFS has a very extensive test suite and CI that is run on each commit and each release, see https://github.com/cryfs/cryfs/tree/0.9.10/test
  This test suite is also run automatically when the Debian package is created.

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