xfrm: Move the test on replay window size into the replay check functions

As it is, the replay check is just performed if the replay window of the
legacy implementation is nonzero. So we move the test on a nonzero replay
window inside the replay check functions to be sure we are testing for the
right implementation.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/xfrm/xfrm_input.c

@@ -173,7 +173,7 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type)
 			goto drop_unlock;
 		}
 
-		if (x->props.replay_window && x->repl->check(x, skb, seq)) {
+		if (x->repl->check(x, skb, seq)) {
 			XFRM_INC_STATS(net, LINUX_MIB_XFRMINSTATESEQERROR);
 			goto drop_unlock;
 		}

net/xfrm/xfrm_replay.c

@@ -118,6 +118,9 @@ static int xfrm_replay_check(struct xfrm_state *x,
 	u32 diff;
 	u32 seq = ntohl(net_seq);
 
+	if (!x->props.replay_window)
+		return 0;
+
 	if (unlikely(seq == 0))
 		goto err;
 
@@ -193,9 +196,14 @@ static int xfrm_replay_check_bmp(struct xfrm_state *x,
 {
 	unsigned int bitnr, nr;
 	struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
+	u32 pos;
 	u32 seq = ntohl(net_seq);
 	u32 diff =  replay_esn->seq - seq;
-	u32 pos = (replay_esn->seq - 1) % replay_esn->replay_window;
+
+	if (!replay_esn->replay_window)
+		return 0;
+
+	pos = (replay_esn->seq - 1) % replay_esn->replay_window;
 
 	if (unlikely(seq == 0))
 		goto err;
@@ -373,12 +381,17 @@ static int xfrm_replay_check_esn(struct xfrm_state *x,
 	unsigned int bitnr, nr;
 	u32 diff;
 	struct xfrm_replay_state_esn *replay_esn = x->replay_esn;
+	u32 pos;
 	u32 seq = ntohl(net_seq);
-	u32 pos = (replay_esn->seq - 1) % replay_esn->replay_window;
 	u32 wsize = replay_esn->replay_window;
 	u32 top = replay_esn->seq;
 	u32 bottom = top - wsize + 1;
 
+	if (!wsize)
+		return 0;
+
+	pos = (replay_esn->seq - 1) % replay_esn->replay_window;
+
 	if (unlikely(seq == 0 && replay_esn->seq_hi == 0 &&
 		     (replay_esn->seq < replay_esn->replay_window - 1)))
 		goto err;