crypto: algif_hash - Fix race condition in hash_check_key

commit ad46d7e3 upstream.

We need to lock the child socket in hash_check_key as otherwise
two simultaneous calls can cause the parent socket to be freed.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

crypto/algif_hash.c

@@ -255,22 +255,23 @@ static struct proto_ops algif_hash_ops = {
 
 static int hash_check_key(struct socket *sock)
 {
-	int err;
+	int err = 0;
 	struct sock *psk;
 	struct alg_sock *pask;
 	struct algif_hash_tfm *tfm;
 	struct sock *sk = sock->sk;
 	struct alg_sock *ask = alg_sk(sk);
 
+	lock_sock(sk);
 	if (ask->refcnt)
-		return 0;
+		goto unlock_child;
 
 	psk = ask->parent;
 	pask = alg_sk(ask->parent);
 	tfm = pask->private;
 
 	err = -ENOKEY;
-	lock_sock(psk);
+	lock_sock_nested(psk, SINGLE_DEPTH_NESTING);
 	if (!tfm->has_key)
 		goto unlock;
 
@@ -284,6 +285,8 @@ static int hash_check_key(struct socket *sock)
 
 unlock:
 	release_sock(psk);
+unlock_child:
+	release_sock(sk);
 
 	return err;
 }