audit: fix use-after-free in audit_add_watch
authorRonny Chevalier <ronny.chevalier@hp.com>
Wed, 11 Jul 2018 12:39:37 +0000 (14:39 +0200)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 26 Sep 2018 06:38:09 +0000 (08:38 +0200)
commit67e522a76d99a0035150b4640295aab2c573d455
tree5e6b25bf37a7e7a18173c977076ea409a563676c
parenta41ab6fe169943cfef516ee5230ba8ce55118112
audit: fix use-after-free in audit_add_watch

[ Upstream commit baa2a4fdd525c8c4b0f704d20457195b29437839 ]

audit_add_watch stores locally krule->watch without taking a reference
on watch. Then, it calls audit_add_to_parent, and uses the watch stored
locally.

Unfortunately, it is possible that audit_add_to_parent updates
krule->watch.
When it happens, it also drops a reference of watch which
could free the watch.

How to reproduce (with KASAN enabled):

    auditctl -w /etc/passwd -F success=0 -k test_passwd
    auditctl -w /etc/passwd -F success=1 -k test_passwd2

The second call to auditctl triggers the use-after-free, because
audit_to_parent updates krule->watch to use a previous existing watch
and drops the reference to the newly created watch.

To fix the issue, we grab a reference of watch and we release it at the
end of the function.

Signed-off-by: Ronny Chevalier <ronny.chevalier@hp.com>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kernel/audit_watch.c