KEYS: Fix race between key destruction and finding a keyring by name

commit 94c4554ba07adbdde396748ee7ae01e86cf2d8d7 upstream.

There appears to be a race between:

 (1) key_gc_unused_keys() which frees key->security and then calls
     keyring_destroy() to unlink the name from the name list

 (2) find_keyring_by_name() which calls key_permission(), thus accessing
     key->security, on a key before checking to see whether the key usage is 0
     (ie. the key is dead and might be cleaned up).

Fix this by calling ->destroy() before cleaning up the core key data -
including key->security.

Reported-by: Petr Matousek <pmatouse@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[sw0312.kim: cherry-pick from linux-3.10.y to fix issue before applying CVE-2015-7872]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I857d740596bf886d02fe149055df3191cad9e9db

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 7978186..483ebdf 100644 (file)
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -187,6 +187,10 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
                kdebug("- %u", key->serial);
                key_check(key);
 
+               /* Throw away the key data */
+               if (key->type->destroy)
+                       key->type->destroy(key);
+
                security_key_free(key);
 
                /* deal with the user's key tracking and quota */
@@ -201,10 +205,6 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
                if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
                        atomic_dec(&key->user->nikeys);
 
-               /* now throw away the key memory */
-               if (key->type->destroy)
-                       key->type->destroy(key);
-
                key_user_put(key->user);
 
                kfree(key->description);