Patch "audit: Fix use after free in audit_remove_watch_rule()" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

audit: Fix use after free in audit_remove_watch_rule()

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
audit-fix-use-after-free-in-audit_remove_watch_rule.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Tue, 15 Aug 2017 13:00:36 +0200
Subject: audit: Fix use after free in audit_remove_watch_rule()

From: Jan Kara <[email protected]>

commit d76036ab47eafa6ce52b69482e91ca3ba337d6d6 upstream.

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.

---
 kernel/audit_watch.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

@@ -455,13 +455,15 @@ void audit_remove_watch_rule(struct audi
 	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);
 	}
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/audit-fix-use-after-free-in-audit_remove_watch_rule.patch