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audit: Fix use after free in audit_remove_watch_rule()

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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@vger.kernel.org
Reported-by: Tony Jones <tonyj@suse.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: Tony Jones <tonyj@suse.de>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Jan Kara 2017-08-15 13:00:36 +02:00 committed by Paul Moore
parent b0659ae5e3
commit d76036ab47
1 changed files with 7 additions and 5 deletions
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12
kernel/audit_watch.c
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@ -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);
}
}