[3.13.y-ckt stable] Patch "KEYS: close race between key lookup and freeing" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    KEYS: close race between key lookup and freeing

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 55036ae4a8fef4a678598cb30eee84a0fe766380 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sasha.levin at oracle.com>
Date: Mon, 29 Dec 2014 09:39:01 -0500
Subject: KEYS: close race between key lookup and freeing

commit a3a8784454692dd72e5d5d34dcdab17b4420e74c upstream.

When a key is being garbage collected, it's key->user would get put before
the ->destroy() callback is called, where the key is removed from it's
respective tracking structures.

This leaves a key hanging in a semi-invalid state which leaves a window open
for a different task to try an access key->user. An example is
find_keyring_by_name() which would dereference key->user for a key that is
in the process of being garbage collected (where key->user was freed but
->destroy() wasn't called yet - so it's still present in the linked list).

This would cause either a panic, or corrupt memory.

Fixes CVE-2014-9529.

Signed-off-by: Sasha Levin <sasha.levin at oracle.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 security/keys/gc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index d3222b6..009d937 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -157,12 +157,12 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
 		if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 			atomic_dec(&key->user->nikeys);

-		key_user_put(key->user);
-
 		/* now throw away the key memory */
 		if (key->type->destroy)
 			key->type->destroy(key);

+		key_user_put(key->user);
+
 		kfree(key->description);

 #ifdef KEY_DEBUGGING
--
1.9.1