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>
[carnil: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 2e2395d..207e968 100644 (file)
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -172,6 +172,10 @@ static noinline void key_gc_unused_key(struct key *key)
 {
        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 */
@@ -186,10 +190,6 @@ static noinline void key_gc_unused_key(struct key *key)
        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);