Re: [PATCH 1/2] audit: Fix use after free in audit_remove_watch_rule()

audit_remove_watch_rule() drops watch's reference to parent but then continues to work with it. That is not safe as parent can get freed once we drop our reference. The following is a trivial reproducer: mount -o loop image /mnt touch /mnt/file auditctl -w /mnt/file -p wax umount /mnt auditctl -D <crash in fsnotify_destroy_mark()> Grab our own reference in audit_remove_watch_rule() earlier to make sure mark does not get freed under us. CC: stable(a)vger.kernel.org Reported-by: Tony Jones <tonyj(a)suse.de&gt; Signed-off-by: Jan Kara <jack(a)suse.cz&gt; --- kernel/audit_watch.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c index 62d686d96581..ed748ee40029 100644 --- a/kernel/audit_watch.c +++ b/kernel/audit_watch.c @@ -457,13 +457,15 @@ void audit_remove_watch_rule(struct audit_krule *krule) list_del(&krule->rlist); if (list_empty(&watch->rules)) { + /* + * audit_remove_watch() drops our reference to 'parent' which + * can get freed. Grab our own reference to be safe. + */ + audit_get_parent(parent); audit_remove_watch(watch); - - if (list_empty(&parent->watches)) { - audit_get_parent(parent); + if (list_empty(&parent->watches)) fsnotify_destroy_mark(&parent->mark, audit_watch_group); - audit_put_parent(parent); - } + audit_put_parent(parent); } } -- 2.12.3