[Bug 1438942] [NEW] Host's /dev/shm is mounted over when entering 14.10 and older sbuild schroots

[Tyler Hicks]

Public bug reported:

Originally reported by Scott Moser:

https://bugs.launchpad.net/ubuntu/+source/click/+bug/1427264/comments/12

On a Vivid system with schroot 1.6.10-1ubuntu1, the host's /dev/shm is
mounted over with a new tmpfs instance when entering a 14.10 and older
schroot. It does not happen when entering a Vivid schroot.

# Create 14.10 and Vivid sbuild schroots
$ arch=amd64
$ for rel in vivid utopic; do mk-sbuild --eatmydata --arch=$arch $rel 2>&1 | tee /tmp/schroot-$rel-$arch.log; done

# Enter vivid-amd64 sbuild schroot and diff /proc/self/mounts
$ mounts=/proc/self/mounts
$ orig=$(mktemp) && cp $mounts $orig && schroot -c vivid-amd64 true; diff -u $orig $mounts

# Enter utopic-amd64 sbuild schroot and diff /proc/self/mounts
$ orig=$(mktemp) && cp $mounts $orig && schroot -c utopic-amd64 true; diff -u $orig $mounts
--- /tmp/tmp.DdnrDnkS2B	2015-03-31 18:19:51.406526006 -0500
+++ /proc/self/mounts	2015-03-31 18:19:51.818526006 -0500
@@ -28,3 +28,4 @@
 tmpfs /run/user/108 tmpfs rw,nosuid,nodev,relatime,size=101688k,mode=700,uid=108,gid=117 0 0
 gvfsd-fuse /run/user/108/gvfs fuse.gvfsd-fuse rw,nosuid,nodev,relatime,user_id=108,group_id=117 0 0
 tmpfs /run/user/1000 tmpfs rw,nosuid,nodev,relatime,size=101688k,mode=700,uid=1000,gid=1000 0 0
+tmpfs /dev/shm tmpfs rw,relatime 0 0

# Verify that /proc/self/mounts now contains two /dev/shm mounts
$ grep /dev/shm $mounts
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
tmpfs /dev/shm tmpfs rw,relatime 0 0

This causes a problem for programs that keep state in /dev/shm. For
example, ecryptfs-utils maintains a per-user session counter in /dev/shm
that is lost when a new tmpfs mount is performed on top of the old tmpfs
mount. This results in encrypted home directories being unmounted when
the schroot is tore down.

** Affects: schroot (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1438942

Title:
  Host's /dev/shm is mounted over when entering 14.10 and older sbuild
  schroots

Status in schroot package in Ubuntu:
  New

Bug description:
  Originally reported by Scott Moser:

  https://bugs.launchpad.net/ubuntu/+source/click/+bug/1427264/comments/12

  On a Vivid system with schroot 1.6.10-1ubuntu1, the host's /dev/shm is
  mounted over with a new tmpfs instance when entering a 14.10 and older
  schroot. It does not happen when entering a Vivid schroot.

  # Create 14.10 and Vivid sbuild schroots
  $ arch=amd64
  $ for rel in vivid utopic; do mk-sbuild --eatmydata --arch=$arch $rel 2>&1 | tee /tmp/schroot-$rel-$arch.log; done

  # Enter vivid-amd64 sbuild schroot and diff /proc/self/mounts
  $ mounts=/proc/self/mounts
  $ orig=$(mktemp) && cp $mounts $orig && schroot -c vivid-amd64 true; diff -u $orig $mounts

  # Enter utopic-amd64 sbuild schroot and diff /proc/self/mounts
  $ orig=$(mktemp) && cp $mounts $orig && schroot -c utopic-amd64 true; diff -u $orig $mounts
  --- /tmp/tmp.DdnrDnkS2B	2015-03-31 18:19:51.406526006 -0500
  +++ /proc/self/mounts	2015-03-31 18:19:51.818526006 -0500
  @@ -28,3 +28,4 @@
   tmpfs /run/user/108 tmpfs rw,nosuid,nodev,relatime,size=101688k,mode=700,uid=108,gid=117 0 0
   gvfsd-fuse /run/user/108/gvfs fuse.gvfsd-fuse rw,nosuid,nodev,relatime,user_id=108,group_id=117 0 0
   tmpfs /run/user/1000 tmpfs rw,nosuid,nodev,relatime,size=101688k,mode=700,uid=1000,gid=1000 0 0
  +tmpfs /dev/shm tmpfs rw,relatime 0 0

  # Verify that /proc/self/mounts now contains two /dev/shm mounts
  $ grep /dev/shm $mounts
  tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
  tmpfs /dev/shm tmpfs rw,relatime 0 0

  This causes a problem for programs that keep state in /dev/shm. For
  example, ecryptfs-utils maintains a per-user session counter in
  /dev/shm that is lost when a new tmpfs mount is performed on top of
  the old tmpfs mount. This results in encrypted home directories being
  unmounted when the schroot is tore down.

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