[Bug 1761585] [NEW] ibus_bus_init does an unconditional call to chmod on $HOME/.config/ibus/bus

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Olivier Tilloy (osomon):

This was spotted by jdstrand when running the chromium snap, which
recently enabled ibus support (https://forum.snapcraft.io/t/cant-use-
input-method-in-snap-apps/4712/12):

audit[16919]: AVC apparmor="DENIED" operation="chmod"
profile="snap.chromium.chromium" name="/home/osomon/.config/ibus/bus/"
pid=16919 comm="chromium-browse" requested_mask="w" denied_mask="w"
fsuid=1000 ouid=1000

The code that calls chmod is in ibus_bus_init:

  static void
  ibus_bus_init (IBusBus *bus)
  {
    gchar *path;
    […]
    path = g_path_get_dirname (ibus_get_socket_path ());
    g_mkdir_with_parents (path, 0700);
    g_chmod (path, 0700);
    […]
  }

This is rather harmless, but it could be avoided by checking first the
file mode bits on that directory, and do the g_chmod call only if ≠
0700.


[Impact]

Snaps that build on a xenial stack against libibus will trigger that apparmor denial, and even if actually harmless this will no doubt be reported as a problem by users who inspect the denials generated by their snaps.
The patch (that is already upstream: https://github.com/ibus/ibus/commit/28d0c1d4bc47beb38995d84cc4bb1d539c08a070) fixes that by calling chmod conditionally, only if the file mode bits on the ibus socket path are ≠ 0700.


[Test Case]

Install the chromium snap from the stable channel (version
65.0.3325.181, revision 274 as of this writing), and monitor the system
journal for apparmor denials while launching it:

    journalctl -f | grep chmod

Observe a denial similar to that one:

    audit[16919]: AVC apparmor="DENIED" operation="chmod"
profile="snap.chromium.chromium" name="/home/osomon/.config/ibus/bus/"
pid=16919 comm="chromium-browse" requested_mask="w" denied_mask="w"
fsuid=1000 ouid=1000

Now rebuild the chromium snap with the patched libibus (this can be done
by downloading the .snap file, unpacking it with  unsquashfs, replacing
the libibus files by unpacking the updated deb, then repacking the snap
with `snapcraft pack`), install it and launch it while monitoring the
system journal.

Observe the denial on chmod is gone.


[Regression Potential]

This is a low-risk, self-contained change. It doesn't change the logic of ibus_bus_init.
ibus input still working in apps (both debs and snaps) should be enough to prove that there are no regressions.



ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ibus 1.5.17-3ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-13.14-generic 4.15.10
Uname: Linux 4.15.0-13-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.9-0ubuntu2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 5 21:55:30 2018
EcryptfsInUse: Yes
InstallationDate: Installed on 2016-07-02 (642 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: ibus
UpgradeStatus: Upgraded to bionic on 2018-01-29 (66 days ago)

** Affects: ibus
     Importance: Unknown
         Status: Unknown

** Affects: ibus (Ubuntu)
     Importance: Low
     Assignee: Olivier Tilloy (osomon)
         Status: Fix Released


** Tags: amd64 apport-bug bionic
-- 
ibus_bus_init does an unconditional call to chmod on $HOME/.config/ibus/bus
https://bugs.launchpad.net/bugs/1761585
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