Re: [PATCH] netfilter: nf_conntrack: fix tcp_in_window for Fast Open

[Eric Dumazet <eric.dumazet@gmail.com>]

On Fri, 2013-08-09 at 17:21 -0700, Yuchung Cheng wrote:
> Currently the conntrack checks if the ending sequence of a packet
> falls within the observed receive window. However it does so even
> if it has not observe any packet from the remote yet and uses an
> uninitialized receive window (td_maxwin).
> 
> If a connection uses Fast Open to send a SYN-data packet which is
> dropped afterward in the network. The subsequent SYNs retransmits
> will all fail this check and be discarded, leading to a connection
> timeout. This is because the SYN retransmit does not contain data
> payload so
> 
> end == initial sequence number (isn) + 1
> sender->td_end == isn + syn_data_len
> receiver->td_maxwin == 0
> 
> The fix is to only apply this check after td_maxwin is initialized.
> 
> Reported-by: Michael Chan <mcfchan@stanford.edu>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> ---

Acked-by: Eric Dumazet <edumazet@google.com>