netdev - [PATCH net-next] tcp: remove redundant checks

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Date:	Wed, 03 Jun 2015 23:49:21 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next] tcp: remove redundant checks

From: Eric Dumazet  <edumazet@...gle.com>

tcp_v4_rcv() checks the following before calling tcp_v4_do_rcv():

if (th->doff < sizeof(struct tcphdr) / 4)
    goto bad_packet;
if (!pskb_may_pull(skb, th->doff * 4))
    goto discard_it;

So following check in tcp_v4_do_rcv() is redundant
and "goto csum_err;" is wrong anyway.

if (skb->len < tcp_hdrlen(skb) || ...)
	goto csum_err;

A second check can be removed after no_tcp_socket label for same reason.

Same tests can be removed in tcp_v6_do_rcv()

Note : short tcp frames are not properly accounted in tcpInErrs MIB,
because pskb_may_pull() failure simply drops incoming skb, we might
fix this in a separate patch.

Signed-off-by: Eric Dumazet  <edumazet@...gle.com>
---
 net/ipv4/tcp_ipv4.c |    4 ++--
 net/ipv6/tcp_ipv6.c |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index feb875769b8d57dcdb85e12b782f3f5e0fb6193a..3130c42240c86545f1037648635a9e7de0876095 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1400,7 +1400,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 		return 0;
 	}
 
-	if (skb->len < tcp_hdrlen(skb) || tcp_checksum_complete(skb))
+	if (tcp_checksum_complete(skb))
 		goto csum_err;
 
 	if (sk->sk_state == TCP_LISTEN) {
@@ -1647,7 +1647,7 @@ no_tcp_socket:
 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
 		goto discard_it;
 
-	if (skb->len < (th->doff << 2) || tcp_checksum_complete(skb)) {
+	if (tcp_checksum_complete(skb)) {
 csum_error:
 		TCP_INC_STATS_BH(net, TCP_MIB_CSUMERRORS);
 bad_packet:
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 7be3d858cbf0a4f5b7f4ecce8788aa8e4136d6fa..b72e1ffc6bb40f486764874e6a167b72d899605b 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1250,7 +1250,7 @@ static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 		return 0;
 	}
 
-	if (skb->len < tcp_hdrlen(skb) || tcp_checksum_complete(skb))
+	if (tcp_checksum_complete(skb))
 		goto csum_err;
 
 	if (sk->sk_state == TCP_LISTEN) {
@@ -1442,7 +1442,7 @@ no_tcp_socket:
 
 	tcp_v6_fill_cb(skb, hdr, th);
 
-	if (skb->len < (th->doff<<2) || tcp_checksum_complete(skb)) {
+	if (tcp_checksum_complete(skb)) {
 csum_error:
 		TCP_INC_STATS_BH(net, TCP_MIB_CSUMERRORS);
 bad_packet:


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