Commit de213e5e authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: tcp_synack_options() fix 



Commit 33ad798c (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: default avatarBijay Singh <Bijay.Singh@guavus.com>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent eedf042a

net/ipv4/tcp_output.c

+4 −5
Original line number Diff line number Diff line
@@ -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 */

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