Re: [PATCH] Fix reproducible SMP crash in security/keys/key.c

[Andrew Morton <akpm@osdl.org>]

Jani Jaakkola <jjaakkol@cs.Helsinki.FI> wrote:
>
> SMP race handling is broken in key_user_lookup() in security/keys/key.c

This was fixed post-2.6.11.  Can you confirm that 2.6.12-rc2 works OK?

This is the patch we used.  It should go into -stable if it's not already
there.


From: Alexander Nyberg <alexn@dsv.su.se>

I looked at some of the oops reports against keyrings, I think the problem
is that the search isn't restarted after dropping the key_user_lock, *p
will still be NULL when we get back to try_again and look through the tree.

It looks like the intention was that the search start over from scratch.

Signed-off-by: Alexander Nyberg <alexn@dsv.su.se>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 25-akpm/security/keys/key.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletion(-)

diff -puN security/keys/key.c~race-against-parent-deletion-in-key_user_lookup security/keys/key.c
--- 25/security/keys/key.c~race-against-parent-deletion-in-key_user_lookup	2005-03-10 00:38:38.000000000 -0800
+++ 25-akpm/security/keys/key.c	2005-03-10 00:38:38.000000000 -0800
@@ -57,9 +57,10 @@ struct key_user *key_user_lookup(uid_t u
 {
 	struct key_user *candidate = NULL, *user;
 	struct rb_node *parent = NULL;
-	struct rb_node **p = &key_user_tree.rb_node;
+	struct rb_node **p;
 
  try_again:
+	p = &key_user_tree.rb_node;
 	spin_lock(&key_user_lock);
 
 	/* search the tree for a user record with a matching UID */
_