[PATCH] tcp: tcp_synack_options() fix

Eric Dumazet
2010-05-17T21:04:42Z

Le lundi 17 mai 2010 à 13:42 -0700, Stephen Hemminger a écrit :

> Since you are doing away with flag variable, why not this instead?
>

Sure, we can eliminate this doing_ts variable and save few bytes

Thanks

[PATCH] 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>
---
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 0dda86e..44e98d9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -667,7 +667,6 @@ 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);
@@ -680,7 +679,7 @@ 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;
@@ -695,7 +694,7 @@ 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;
@@ -703,7 +702,7 @@ 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;
}

@@ -711,7 +710,7 @@ 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 */