From: Eric Dumazet <edumazet@google.com>
Date: Thu, 9 Apr 2015 20:31:56 +0000 (-0700)
Subject: tcp: tcp_make_synack() should clear skb->tstamp
X-Git-Tag: v3.19.6~15
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1b6c8d50c051e5cd96701c0c8067024a1046b75b;p=thirdparty%2Fkernel%2Fstable.git

tcp: tcp_make_synack() should clear skb->tstamp

[ 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>
---

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 9790f396ce5ee..9f29453049dc4 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2931,6 +2931,8 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
 	}
 #endif
 
+	/* Do not fool tcpdump (if any), clean our debris */
+	skb->tstamp.tv64 = 0;
 	return skb;
 }
 EXPORT_SYMBOL(tcp_make_synack);