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    Subject[PATCH 3.10 06/31] tcp: tcp_make_synack() should clear skb->tstamp
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

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

    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit b50edd7812852d989f2ef09dcfc729690f54a42d ]

    I noticed tcpdump was giving funky timestamps for locally
    generated SYNACK messages on loopback interface.

    11:42:46.938990 IP 127.0.0.1.48245 > 127.0.0.2.23850: S
    945476042:945476042(0) win 43690 <mss 65495,nop,nop,sackOK,nop,wscale 7>

    20:28:58.502209 IP 127.0.0.2.23850 > 127.0.0.1.48245: S
    3160535375:3160535375(0) ack 945476043 win 43690 <mss
    65495,nop,nop,sackOK,nop,wscale 7>

    This is because we need to clear skb->tstamp before
    entering lower stack, otherwise net_timestamp_check()
    does not set skb->tstamp.

    Fixes: 7faee5c0d514 ("tcp: remove TCP_SKB_CB(skb)->when")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/tcp_output.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/net/ipv4/tcp_output.c
    +++ b/net/ipv4/tcp_output.c
    @@ -2772,6 +2772,8 @@ struct sk_buff *tcp_make_synack(struct s
    }
    #endif

    + /* Do not fool tcpdump (if any), clean our debris */
    + skb->tstamp.tv64 = 0;
    return skb;
    }
    EXPORT_SYMBOL(tcp_make_synack);



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