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@emc.com>
Signed-off-by: Adam Langley <agl@imperialviolet.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a00532de2a8..8165f5aa8c7 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;