crypto: algif_hash - Only export and import on sockets with data

commit 4afa5f96 upstream.

The hash_accept call fails to work on sockets that have not received
any data.  For some algorithm implementations it may cause crashes.

This patch fixes this by ensuring that we only export and import on
sockets that have received data.
Reported-by: Harsh Jain <harshjain.prof@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

crypto/algif_hash.c

@@ -192,9 +192,14 @@ static int hash_accept(struct socket *sock, struct socket *newsock, int flags)
 	struct sock *sk2;
 	struct alg_sock *ask2;
 	struct hash_ctx *ctx2;
+	bool more;
 	int err;
 
-	err = crypto_ahash_export(req, state);
+	lock_sock(sk);
+	more = ctx->more;
+	err = more ? crypto_ahash_export(req, state) : 0;
+	release_sock(sk);
+
 	if (err)
 		return err;
 
@@ -205,7 +210,10 @@ static int hash_accept(struct socket *sock, struct socket *newsock, int flags)
 	sk2 = newsock->sk;
 	ask2 = alg_sk(sk2);
 	ctx2 = ask2->private;
-	ctx2->more = 1;
+	ctx2->more = more;
+
+	if (!more)
+		return err;
 
 	err = crypto_ahash_import(&ctx2->req, state);
 	if (err) {