IPsec: do not ignore crypto err in ah6 input

ah6 input processing uses the asynchronous hash crypto API which
supplies an error code as part of the operation completion but
the error code was being ignored.

Treat a crypto API error indication as a verification failure.

While a crypto API reported error would almost certainly result
in a memcpy of the digest failing anyway and thus the security
risk seems minor, performing a memory compare on what might be
uninitialized memory is wrong.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv6/ah6.c

@@ -474,6 +474,9 @@ static void ah6_input_done(struct crypto_async_request *base, int err)
 	int hdr_len = skb_network_header_len(skb);
 	int ah_hlen = (ah->hdrlen + 2) << 2;
 
+	if (err)
+		goto out;
+
 	work_iph = AH_SKB_CB(skb)->tmp;
 	auth_data = ah_tmp_auth(work_iph, hdr_len);
 	icv = ah_tmp_icv(ahp->ahash, auth_data, ahp->icv_trunc_len);