ah: Read nexthdr value before overwriting it in ahash input callback.

The AH4/6 ahash input callbacks read out the nexthdr field from the AH
header *after* they overwrite that header.  This is obviously not going
to end well.  Fix it up.
Signed-off-by: NNick Bowler <nbowler@elliptictech.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ah4.c

@@ -262,12 +262,12 @@ static void ah_input_done(struct crypto_async_request *base, int err)
 	if (err)
 		goto out;
 
+	err = ah->nexthdr;
+
 	skb->network_header += ah_hlen;
 	memcpy(skb_network_header(skb), work_iph, ihl);
 	__skb_pull(skb, ah_hlen + ihl);
 	skb_set_transport_header(skb, -ihl);
-
-	err = ah->nexthdr;
 out:
 	kfree(AH_SKB_CB(skb)->tmp);
 	xfrm_input_resume(skb, err);

net/ipv6/ah6.c

@@ -464,12 +464,12 @@ static void ah6_input_done(struct crypto_async_request *base, int err)
 	if (err)
 		goto out;
 
+	err = ah->nexthdr;
+
 	skb->network_header += ah_hlen;
 	memcpy(skb_network_header(skb), work_iph, hdr_len);
 	__skb_pull(skb, ah_hlen + hdr_len);
 	skb_set_transport_header(skb, -hdr_len);
-
-	err = ah->nexthdr;
 out:
 	kfree(AH_SKB_CB(skb)->tmp);
 	xfrm_input_resume(skb, err);