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    Subject[PATCH 3.16 239/346] tcp: fastopen: fix rcv_wup initialization for TFO server on SYN/data
    3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Neal Cardwell <ncardwell@google.com>

    commit 28b346cbc0715ae45b2814d857f1d8a7e6817ed8 upstream.

    Yuchung noticed that on the first TFO server data packet sent after
    the (TFO) handshake, the server echoed the TCP timestamp value in the
    SYN/data instead of the timestamp value in the final ACK of the
    handshake. This problem did not happen on regular opens.

    The tcp_replace_ts_recent() logic that decides whether to remember an
    incoming TS value needs tp->rcv_wup to hold the latest receive
    sequence number that we have ACKed (latest tp->rcv_nxt we have
    ACKed). This commit fixes this issue by ensuring that a TFO server
    properly updates tp->rcv_wup to match tp->rcv_nxt at the time it sends
    a SYN/ACK for the SYN/data.

    Reported-by: Yuchung Cheng <ycheng@google.com>
    Signed-off-by: Neal Cardwell <ncardwell@google.com>
    Signed-off-by: Yuchung Cheng <ycheng@google.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
    Fixes: 168a8f58059a ("tcp: TCP Fast Open Server - main code path")
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    net/ipv4/tcp_fastopen.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/net/ipv4/tcp_fastopen.c
    +++ b/net/ipv4/tcp_fastopen.c
    @@ -213,6 +213,7 @@ static bool tcp_fastopen_create_child(st
    }
    }
    tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = end_seq;
    + tp->rcv_wup = tp->rcv_nxt;
    sk->sk_data_ready(sk);
    bh_unlock_sock(child);
    sock_put(child);
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