netdev - Re: [PATCH] tcp: fix tcp header size miscalculation when window scale is unused

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Date:	Sun, 24 Aug 2008 10:40:23 -0700
From:	"Adam Langley" <agl@...erialviolet.org>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, love_phil@....com
Subject: Re: [PATCH] tcp: fix tcp header size miscalculation when window scale is unused

From: Philip Love <love_phil@....com>

tcp: fix tcp header size miscalculation when window scale is unused

The size of the TCP header is miscalculated when the window scale ends up being
0. Additionally, this can be induced by sending a SYN to a passive open port
with a window scale option with value 0.

Signed-off-by: Philip Love <love_phil@....com>
Signed-off-by: Adam Langley <agl@...erialviolet.org>

---

 net/ipv4/tcp_output.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a00532d..71eea00 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -468,7 +468,8 @@ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
 	}
 	if (likely(sysctl_tcp_window_scaling)) {
 		opts->ws = tp->rx_opt.rcv_wscale;
-		size += TCPOLEN_WSCALE_ALIGNED;
+		if (likely(opts->ws))
+			size += TCPOLEN_WSCALE_ALIGNED;
 	}
 	if (likely(sysctl_tcp_sack)) {
 		opts->options |= OPTION_SACK_ADVERTISE;
@@ -509,7 +510,8 @@ static unsigned tcp_synack_options(struct sock *sk,
 
 	if (likely(ireq->wscale_ok)) {
 		opts->ws = ireq->rcv_wscale;
-		size += TCPOLEN_WSCALE_ALIGNED;
+		if (likely(opts->ws))
+			size += TCPOLEN_WSCALE_ALIGNED;
 	}
 	if (likely(doing_ts)) {
 		opts->options |= OPTION_TS;
--
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