[PATCH 3.16.y-ckt 216/216] KEYS: close race between key lookup and freeing

Luis Henriques
2015-01-12T18:31:38Z

From: Sasha Levin <sasha.levin@oracle.com>

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@oracle.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Moritz Muehlenhoff <jmm@inutil.org>
Signed-off-by: Luis Henriques <luis.henriques@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 d3222b6d7d59..009d9370c8fd 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
--
2.1.4