tcp: tcp_synack_options() fix

Commit 33ad798c924b4a (tcp: options clean up) introduced a problem
if MD5+SACK+timestamps were used in initial SYN message.

Some stacks (old linux for example) try to negotiate MD5+SACK+TSTAMP
sessions, but since 40 bytes of tcp options space are not enough to
store all the bits needed, we chose to disable timestamps in this case.

We send a SYN-ACK _without_ timestamp option, but socket has timestamps
enabled and all further outgoing messages contain a TS block, all with
the initial timestamp of the remote peer.

Fix is to really disable timestamps option for the whole session.

Reported-by: Bijay Singh <Bijay.Singh@guavus.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 5 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 18a3302480c..b4ed957f201 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -668,7 +668,6 @@ static unsigned tcp_synack_options(struct sock *sk,
         u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
                          xvp->cookie_plus :
                          0;
-        bool doing_ts = ireq->tstamp_ok;
 
 #ifdef CONFIG_TCP_MD5SIG
         *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
@@ -681,7 +680,7 @@ static unsigned tcp_synack_options(struct sock *sk,
                  * rather than TS in order to fit in better with old,
                  * buggy kernels, but that was deemed to be unnecessary.
                  */
-                doing_ts &= !ireq->sack_ok;
+                ireq->tstamp_ok &= !ireq->sack_ok;
         }
 #else
         *md5 = NULL;
@@ -696,7 +695,7 @@ static unsigned tcp_synack_options(struct sock *sk,
                 opts->options |= OPTION_WSCALE;
                 remaining -= TCPOLEN_WSCALE_ALIGNED;
         }
-        if (likely(doing_ts)) {
+        if (likely(ireq->tstamp_ok)) {
                 opts->options |= OPTION_TS;
                 opts->tsval = TCP_SKB_CB(skb)->when;
                 opts->tsecr = req->ts_recent;
@@ -704,7 +703,7 @@ static unsigned tcp_synack_options(struct sock *sk,
         }
         if (likely(ireq->sack_ok)) {
                 opts->options |= OPTION_SACK_ADVERTISE;
-                if (unlikely(!doing_ts))
+                if (unlikely(!ireq->tstamp_ok))
                         remaining -= TCPOLEN_SACKPERM_ALIGNED;
         }
 
@@ -712,7 +711,7 @@ static unsigned tcp_synack_options(struct sock *sk,
          * If the <SYN> options fit, the same options should fit now!
          */
         if (*md5 == NULL &&
-            doing_ts &&
+            ireq->tstamp_ok &&
             cookie_plus > TCPOLEN_COOKIE_BASE) {
                 int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */