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    Subject[PATCH 3.16.y-ckt 045/126] tcp: initialize tp->copied_seq in case of cross SYN connection
    Date
    3.16.7-ckt22 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Eric Dumazet <edumazet@google.com>

    commit 142a2e7ece8d8ac0e818eb2c91f99ca894730e2a upstream.

    Dmitry provided a syzkaller (http://github.com/google/syzkaller)
    generated program that triggers the WARNING at
    net/ipv4/tcp.c:1729 in tcp_recvmsg() :

    WARN_ON(tp->copied_seq != tp->rcv_nxt &&
    !(flags & (MSG_PEEK | MSG_TRUNC)));

    His program is specifically attempting a Cross SYN TCP exchange,
    that we support (for the pleasure of hackers ?), but it looks we
    lack proper tcp->copied_seq initialization.

    Thanks again Dmitry for your report and testings.

    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: Dmitry Vyukov <dvyukov@google.com>
    Tested-by: Dmitry Vyukov <dvyukov@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    net/ipv4/tcp_input.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
    index e3d40a303b8f..43404d3f9da8 100644
    --- a/net/ipv4/tcp_input.c
    +++ b/net/ipv4/tcp_input.c
    @@ -5549,6 +5549,7 @@ discard:
    }

    tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
    + tp->copied_seq = tp->rcv_nxt;
    tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;

    /* RFC1323: The window in SYN & SYN/ACK segments is

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