apparmor aa_change_onexec doesn't work

libapparmor provides an aa_change_onexec(3) function which writes into /proc/self/attr/exec file, which is managed by a loaded security module. aa_change_onexec(3) requires the AppArmor module be loaded. (Source for this routine is in package libapparmor, src/change_hat.c.)

The provided program and profile will demonstrate the problem.

Save the profile into /etc/apparmor.d/test_onexec

Load the profile with: sudo apparmor_parser --replace /etc/apparmor.d/test_onexec

Compile the program with: gcc -o aa-change aa-change.c -lapparmor

Run the program as follows:

$ ./aa-change profile test_onexec 'head -1 /etc/passwd ; cat /proc/self/attr/current'
Currently running in domain 'test_onexec (enforce)'
sh: head: Permission denied
test_onexec (enforce)
$ ./aa-change exec test_onexec 'head -1 /etc/passwd ; cat /proc/self/attr/current'
Will transition to 'test_onexec (enforce)' domain on exec()
root:x:0:0:root:/root:/bin/bash
unconfined

'profile' uses aa_change_profile(3) to immediate change into the test_onexec profile. 'head' cannot execute, and 'cat' is confined with the test_onexec profile.

'exec' uses aa_change_onexec(3) to change into the test_onexec profile at the next exec(2) call. 'head' runs (it should fail) and reads /etc/passwd (which should also fail). The 'cat' process is unconfined. Thus the aa_change_onexec(3) has failed. Output should be very similar to 'profile' case.

$ uname -a
Linux haig 2.6.32-26-generic #47-Ubuntu SMP Wed Nov 17 15:58:05 UTC 2010 x86_64 GNU/Linux
$ cat /proc/version_signature
Ubuntu 2.6.32-26.47-generic 2.6.32.24+drm33.11
$

dmesg will include lines like the following:
type=1505 audit(1292894196.363:299): operation="profile_load" pid=5543 name="test_onexec"
type=1503 audit(1292894419.381:301): operation="exec" pid=5592 parent=5590 profile="test_onexec" requested_mask="::x" denied_mask="::x" fsuid=1000 ouid=0 name="/usr/bin/head"

While watching dmesg output you can confirm that the 'exec' mode of the test program doesn't reject execution of /usr/bin/head, while the 'profile' mode of the test program does reject execution of /usr/bin/head.

Feel free to close WONTFIX if fixing this is beyond the scope of LTS. (I want to save others time in the future when this issue is discovered by someone else.)