tree 6f6f8ef6cd887530f5eb4d083cbaceaa8f0512c8
parent 3e1a3ce2f19a8a74fe6771f6dcd642d61ae050dc
author Eric Dumazet <dada1@cosmosbay.com> 1236788637 -0700
committer David S. Miller <davem@davemloft.net> 1236788637 -0700

tcp: allow timestamps even if SYN packet has tsval=0

Some systems send SYN packets with apparently wrong RFC1323 timestamp
option values [timestamp tsval=0 tsecr=0].
It might be for security reasons (http://www.secuobs.com/plugs/25220.shtml )

Linux TCP stack ignores this option and sends back a SYN+ACK packet
without timestamp option, thus many TCP flows cannot use timestamps
and lose some benefit of RFC1323.

Other operating systems seem to not care about initial tsval value, and let
tcp flows to negotiate timestamp option.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>