Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6:
KEYS: call_sbin_request_key() must write lock keyrings before modifying them
KEYS: Use RCU dereference wrappers in keyring key type code
KEYS: find_keyring_by_name() can gain access to a freed keyring

security/keys/keyring.c

···
 #include <asm/uaccess.h>
 #include "internal.h"
 
+#define rcu_dereference_locked_keyring(keyring)				\
+	(rcu_dereference_protected(					\
+		(keyring)->payload.subscriptions,			\
+		rwsem_is_locked((struct rw_semaphore *)&(keyring)->sem)))
+
 /*
  * when plumbing the depths of the key tree, this sets a hard limit set on how
  * deep we're willing to go
···
 	int loop, ret;
 
 	ret = 0;
-	klist = keyring->payload.subscriptions;
-
+	klist = rcu_dereference_locked_keyring(keyring);
 	if (klist) {
 		/* calculate how much data we could return */
 		qty = klist->nkeys * sizeof(key_serial_t);
···
 	struct key *keyring;
 	int bucket;
 
-	keyring = ERR_PTR(-EINVAL);
 	if (!name)
-		goto error;
+		return ERR_PTR(-EINVAL);
 
 	bucket = keyring_hash(name);
 
···
 					   KEY_SEARCH) < 0)
 				continue;
 
-			/* we've got a match */
-			atomic_inc(&keyring->usage);
-			read_unlock(&keyring_name_lock);
-			goto error;
+			/* we've got a match but we might end up racing with
+			 * key_cleanup() if the keyring is currently 'dead'
+			 * (ie. it has a zero usage count) */
+			if (!atomic_inc_not_zero(&keyring->usage))
+				continue;
+			goto out;
 		}
 	}
 
-	read_unlock(&keyring_name_lock);
 	keyring = ERR_PTR(-ENOKEY);
-
- error:
+out:
+	read_unlock(&keyring_name_lock);
 	return keyring;
 
 } /* end find_keyring_by_name() */
···
 	}
 
 	/* see if there's a matching key we can displace */
-	klist = keyring->payload.subscriptions;
-
+	klist = rcu_dereference_locked_keyring(keyring);
 	if (klist && klist->nkeys > 0) {
 		struct key_type *type = key->type;
 
···
 				  keyring->datalen + KEYQUOTA_LINK_BYTES);
 	if (ret < 0)
 		goto error2;
-
-	klist = keyring->payload.subscriptions;
 
 	if (klist && klist->nkeys < klist->maxkeys) {
 		/* there's sufficient slack space to add directly */
···
 
 	down_write(&keyring->sem);
 
-	klist = keyring->payload.subscriptions;
+	klist = rcu_dereference_locked_keyring(keyring);
 	if (klist) {
 		/* search the keyring for the key */
 		for (loop = 0; loop < klist->nkeys; loop++)
···
 		/* detach the pointer block with the locks held */
 		down_write(&keyring->sem);
 
-		klist = keyring->payload.subscriptions;
+		klist = rcu_dereference_locked_keyring(keyring);
 		if (klist) {
 			/* adjust the quota */
 			key_payload_reserve(keyring,
···
  */
 static void keyring_revoke(struct key *keyring)
 {
-	struct keyring_list *klist = keyring->payload.subscriptions;
+	struct keyring_list *klist;
+
+	klist = rcu_dereference_locked_keyring(keyring);
 
 	/* adjust the quota */
 	key_payload_reserve(keyring, 0);
···
 
 	down_write(&keyring->sem);
 
-	klist = keyring->payload.subscriptions;
+	klist = rcu_dereference_locked_keyring(keyring);
 	if (!klist)
 		goto no_klist;
 

security/keys/request_key.c

···
 	}
 
 	/* attach the auth key to the session keyring */
-	ret = __key_link(keyring, authkey);
+	ret = key_link(keyring, authkey);
 	if (ret < 0)
 		goto error_link;