crypto: algif_skcipher - Add key check exception for cipher_null

commit 6e8d8ecf upstream.

This patch adds an exception to the key check so that cipher_null
users may continue to use algif_skcipher without setting a key.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[bwh: Backported to 3.2: use crypto_ablkcipher_has_setkey()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

crypto/algif_skcipher.c

@@ -760,7 +760,7 @@ static int skcipher_accept_parent(void *private, struct sock *sk)
 {
 	struct skcipher_tfm *tfm = private;
 
-	if (!tfm->has_key)
+	if (!tfm->has_key && crypto_ablkcipher_has_setkey(tfm->skcipher))
 		return -ENOKEY;
 
 	return skcipher_accept_parent_common(private, sk);