On Tue, Aug 15, 2017 at 7:00 AM, Jan Kara <jack@xxxxxxx> wrote:
> 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@xxxxxxxxxxxxxxx
> Reported-by: Tony Jones <tonyj@xxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> kernel/audit_watch.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
This looks good to me, thanks for the fix. I'm going to merge this
into the audit/stable-4.13 branch and assuming it passes the audit
tests I'll send it up to Linus later this week.
> 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
--
paul moore
www.paul-moore.com