tcp: do not leak non zero tstamp in output packets

Usage of skb->tstamp should remain private to TCP stack
(only set on packets on write queue, not on cloned ones)

Otherwise, packets given to loopback interface with a non null tstamp
can confuse netif_rx() / net_timestamp_check()

Other possibility would be to clear tstamp in loopback_xmit(),
as done in skb_scrub_packet()

Fixes: 740b0f1841f6 ("tcp: switch rtt estimations to usec resolution")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a02c884d43216beda5ca7f8cb38494b11eedc3ed..bc0fb0fc755253d55366d915bea8dc0621114fef 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -882,6 +882,8 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
                        skb = skb_clone(skb, gfp_mask);
                if (unlikely(!skb))
                        return -ENOBUFS;
+               /* Our usage of tstamp should remain private */
+               skb->tstamp.tv64 = 0;
        }
 
        inet = inet_sk(sk);