netdev - [PATCH net-next] net: loopback: clear skb->tstamp before netif

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Date:   Fri, 19 Oct 2018 19:11:26 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: [PATCH net-next] net: loopback: clear skb->tstamp before netif_rx()

At least UDP / TCP stacks can now cook skbs with a tstamp using
MONOTONIC base (or arbitrary values with SCM_TXTIME)

Since loopback driver does not call (directly or indirectly)
skb_scrub_packet(), we need to clear skb->tstamp so that
net_timestamp_check() can eventually resample the time,
using ktime_get_real().

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@...gle.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Cc: Soheil Hassas Yeganeh <soheil@...gle.com>
---
 drivers/net/loopback.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index a7207fa7e451311aed13cdeb100e0ea7922931bf..2df7f60fe05220c19896a251b6b15239f4b95112 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -69,6 +69,10 @@ static netdev_tx_t loopback_xmit(struct sk_buff *skb,
 	int len;
 
 	skb_tx_timestamp(skb);
+
+	/* do not fool net_timestamp_check() with various clock bases */
+	skb->tstamp = 0;
+
 	skb_orphan(skb);
 
 	/* Before queueing this packet to netif_rx(),
-- 
2.19.1.568.g152ad8e336-goog