Merge branch 'for-linus2' of git://git.kernel.org/pub/scm/linux/kerne…

…l/git/jmorris/linux-security

Pull key handling bugfix from James Morris:
 "Fix a race between keyctl_read() and keyctl_revoke()"

* 'for-linus2' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
  KEYS: Fix race between read and revoke

security/keys/keyctl.c

@@ -751,16 +751,16 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 
 	/* the key is probably readable - now try to read it */
 can_read_key:
-	ret = key_validate(key);
-	if (ret == 0) {
-		ret = -EOPNOTSUPP;
-		if (key->type->read) {
-			/* read the data with the semaphore held (since we
-			 * might sleep) */
-			down_read(&key->sem);
+	ret = -EOPNOTSUPP;
+	if (key->type->read) {
+		/* Read the data with the semaphore held (since we might sleep)
+		 * to protect against the key being updated or revoked.
+		 */
+		down_read(&key->sem);
+		ret = key_validate(key);
+		if (ret == 0)
 			ret = key->type->read(key, buffer, buflen);
-			up_read(&key->sem);
-		}
+		up_read(&key->sem);
 	}
 
 error2: