Add the no SACK route option feature

Implement querying and acting upon the no sack bit in the features
field.

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>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 2e2eb74ac4cc..b35802af3c4c 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -464,6 +464,7 @@ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
                                 struct tcp_md5sig_key **md5) {
         struct tcp_sock *tp = tcp_sk(sk);
         unsigned size = 0;
+        struct dst_entry *dst = __sk_dst_get(sk);
 
 #ifdef CONFIG_TCP_MD5SIG
         *md5 = tp->af_specific->md5_lookup(sk, sk);
@@ -498,7 +499,8 @@ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
                 opts->options |= OPTION_WSCALE;
                 size += TCPOLEN_WSCALE_ALIGNED;
         }
-        if (likely(sysctl_tcp_sack)) {
+        if (likely(sysctl_tcp_sack &&
+                   !dst_feature(dst, RTAX_FEATURE_NO_SACK))) {
                 opts->options |= OPTION_SACK_ADVERTISE;
                 if (unlikely(!(OPTION_TS & opts->options)))
                         size += TCPOLEN_SACKPERM_ALIGNED;