tcp: early_demux fixes

1) Remove a non needed pskb_may_pull() in tcp_v4_early_demux()
   and fix a potential bug if skb->head was reallocated
   (iph & th pointers were not reloaded)

TCP stack will pull/check headers anyway.

2) must reload iph in ip_rcv_finish() after early_demux()
 call since skb->head might have changed.

3) skb->dev->ifindex can be now replaced by skb->skb_iif
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ip_input.c

@@ -326,8 +326,11 @@ static int ip_rcv_finish(struct sk_buff *skb)
 
 		rcu_read_lock();
 		ipprot = rcu_dereference(inet_protos[protocol]);
-		if (ipprot && ipprot->early_demux)
+		if (ipprot && ipprot->early_demux) {
 			ipprot->early_demux(skb);
+			/* must reload iph, skb->head might have changed */
+			iph = ip_hdr(skb);
+		}
 		rcu_read_unlock();
 	}
 

net/ipv4/tcp_ipv4.c

@@ -1686,7 +1686,6 @@ void tcp_v4_early_demux(struct sk_buff *skb)
 	struct net *net = dev_net(skb->dev);
 	const struct iphdr *iph;
 	const struct tcphdr *th;
-	struct net_device *dev;
 	struct sock *sk;
 
 	if (skb->pkt_type != PACKET_HOST)
@@ -1701,14 +1700,10 @@ void tcp_v4_early_demux(struct sk_buff *skb)
 	if (th->doff < sizeof(struct tcphdr) / 4)
 		return;
 
-	if (!pskb_may_pull(skb, ip_hdrlen(skb) + th->doff * 4))
-		return;
-
-	dev = skb->dev;
 	sk = __inet_lookup_established(net, &tcp_hashinfo,
 				       iph->saddr, th->source,
 				       iph->daddr, ntohs(th->dest),
-				       dev->ifindex);
+				       skb->skb_iif);
 	if (sk) {
 		skb->sk = sk;
 		skb->destructor = sock_edemux;
@@ -1718,7 +1713,7 @@ void tcp_v4_early_demux(struct sk_buff *skb)
 			if (dst)
 				dst = dst_check(dst, 0);
 			if (dst &&
-			    icsk->rx_dst_ifindex == dev->ifindex)
+			    icsk->rx_dst_ifindex == skb->skb_iif)
 				skb_dst_set_noref(skb, dst);
 		}
 	}