[PATCH 3.14 32/77] KEYS: close race between key lookup and freeing

From: Greg Kroah-Hartman
Date: Tue Jan 27 2015 - 20:42:38 EST


3.14-stable review patch. If anyone has any objections, please let me know.

------------------

From: Sasha Levin <sasha.levin@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
security/keys/gc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -157,12 +157,12 @@ static noinline void key_gc_unused_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


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