Allow to turn off TCP window scale opt per route

Add and use no window scale bit in the features field.

Note that this is not the same as setting a window scale of 0
as would happen with window limit on route.

Signed-off-by: Gilad Ben-Yossef <gilad@codefidence.com>
Sigend-off-by: Ori Finkelman <ori@comsleep.com>
Sigend-off-by: Yony Amit <yony@comsleep.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 6 insertions, 3 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 6097491aa9fc..393c56921dcb 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3739,7 +3739,8 @@ void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
                                 break;
                         case TCPOPT_WINDOW:
                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
-                                    !estab && sysctl_tcp_window_scaling) {
+                                    !estab && sysctl_tcp_window_scaling &&
+                                    !dst_feature(dst, RTAX_FEATURE_NO_WSCALE)) {
                                         __u8 snd_wscale = *(__u8 *)ptr;
                                         opt_rx->wscale_ok = 1;
                                         if (snd_wscale > 14) {
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8819eba8ebb8..616c686ca253 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -496,7 +496,8 @@ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
                 opts->tsecr = tp->rx_opt.ts_recent;
                 size += TCPOLEN_TSTAMP_ALIGNED;
         }
-        if (likely(sysctl_tcp_window_scaling)) {
+        if (likely(sysctl_tcp_window_scaling &&
+                   !dst_feature(dst, RTAX_FEATURE_NO_WSCALE))) {
                 opts->ws = tp->rx_opt.rcv_wscale;
                 opts->options |= OPTION_WSCALE;
                 size += TCPOLEN_WSCALE_ALIGNED;
@@ -2347,7 +2348,8 @@ static void tcp_connect_init(struct sock *sk)
                                   tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
                                   &tp->rcv_wnd,
                                   &tp->window_clamp,
-                                  sysctl_tcp_window_scaling,
+                                  (sysctl_tcp_window_scaling &&
+                                   !dst_feature(dst, RTAX_FEATURE_NO_WSCALE)),
                                   &rcv_wscale);
 
         tp->rx_opt.rcv_wscale = rcv_wscale;