thumbnailer should honor TMPDIR to work with apparmor policy

[Bill Filler]

in tracking down gallery-app bug https://bugs.launchpad.net/ubuntu/+source/gallery-app/+bug/1296634, we discovered thumbnailer is not honoring the TMPDIR apparmour policy.

Getting this DENIAL in /var/log/syslog if you have a video file in ~/Videos and you launch gallery-app:

Mar 24 18:27:54 ubuntu-phablet kernel: [ 3401.330077] type=1400 audit(1395700074.636:164): apparmor="DENIED" operation="mknod" parent=7101 profile="com.ubuntu.gallery_gallery_2.9.1.931" name="/tmp/filePdq5SX" pid=7102 comm="vs-thumb" requested_mask="c" denied_mask="c" fsuid=32011 ouid=32011

[Jamie Strandboge (jdstrand)]

Note, TMPDIR is set to an app-specific directory for apps running under confinement as per https://wiki.ubuntu.com/SecurityTeam/Specifications/ApplicationConfinement

[Jussi Pakkanen (jpakkane)]

Thumbnailer is using the tmpnam libc function to generate its temporary file names. If that is not generating valid files then

a) should this be fixed in the platform and
b) if not, what is the correct way to generate a temporary file name that can be used across the process boundary?

[Colin Watson (cjwatson)]

The fix probably isn't any worse, but why not pay attention to the tmpnam manual page ("Never use this function") and use mkstemp or tmpfile instead of rolling your own temporary file creation function?

[Launchpad Janitor (janitor)]

This bug was fixed in the package thumbnailer - 1.0+14.04.20140327-0ubuntu1

---------------
thumbnailer (1.0+14.04.20140327-0ubuntu1) trusty; urgency=low

  [ Jussi Pakkanen ]
  * Obey the TMPDIR. (LP: #1296987)
 -- Ubuntu daily release <email address hidden> Thu, 27 Mar 2014 08:36:59 +0000

[Jussi Pakkanen (jpakkane)]

Tmpfile does not work because I need a visible file name to pass to a helper executable. Mkstemp could work, but I had some uncertainty about it, though I don't remember what the exact issue was. Anyway I put the creation in a separate function just for this reason: that makes it easy to see and easy to change.