[PATCH net] net: clear skb->tstamp in forwarding paths

Sergey reported that forwarding was no longer working
if fq packet scheduler was used.

This is caused by the recent switch to EDT model, since incoming
packets might have been timestamped by __net_timestamp()

__net_timestamp() uses ktime_get_real(), while fq expects packets
using CLOCK_MONOTONIC base.

The fix is to clear skb->tstamp in forwarding paths.

Fixes: 80b14dee2bea ("net: Add a new socket option for a future transmit time.")
Fixes: fb420d5d91c1 ("tcp/fq: move back to CLOCK_MONOTONIC")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Sergey Matyukevich <geomatsi@gmail.com>
Tested-by: Sergey Matyukevich <geomatsi@gmail.com>
---
 net/ipv4/ip_forward.c | 1 +
 net/ipv6/ip6_output.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c
index 32662e9e5d218868341169bba1dc3ab430952c58..d5984d31ab931487fdea844aa4a240df00d2b64e 100644
--- a/net/ipv4/ip_forward.c
+++ b/net/ipv4/ip_forward.c

@@ -72,6 +72,7 @@ static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *s
 	if (unlikely(opt->optlen))
 		ip_forward_options(skb);
 
+	skb->tstamp = 0;
 	return dst_output(net, sk, skb);
 }
 

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index fcd3c66ded1620d0d320fd7b1753f2734d1dfa46..4591ca4bdbe8831f8183c4df0d4237d023b5bb68 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c

@@ -378,6 +378,7 @@ static inline int ip6_forward_finish(struct net *net, struct sock *sk,
 	__IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTFORWDATAGRAMS);
 	__IP6_ADD_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTOCTETS, skb->len);
 
+	skb->tstamp = 0;
 	return dst_output(net, sk, skb);
 }
 

-- 
2.20.0.405.gbc1bbc6f85-goog

From: Eric Dumazet <edumazet@google.com>
Date: Fri, 14 Dec 2018 06:46:49 -0800

Sergey reported that forwarding was no longer working
if fq packet scheduler was used.

This is caused by the recent switch to EDT model, since incoming
packets might have been timestamped by __net_timestamp()

__net_timestamp() uses ktime_get_real(), while fq expects packets
using CLOCK_MONOTONIC base.

The fix is to clear skb->tstamp in forwarding paths.

Fixes: 80b14dee2bea ("net: Add a new socket option for a future transmit time.")
Fixes: fb420d5d91c1 ("tcp/fq: move back to CLOCK_MONOTONIC")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Sergey Matyukevich <geomatsi@gmail.com>
Tested-by: Sergey Matyukevich <geomatsi@gmail.com>

Applied and queued up for -stable, thanks Eric.