4.19-stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <[email protected]>

[ Upstream commit 4c16128b6271e70c8743178e90cccee147858503 ]

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 <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Cc: Soheil Hassas Yeganeh <[email protected]>
Acked-by: Soheil Hassas Yeganeh <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/loopback.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -75,6 +75,10 @@ static netdev_tx_t loopback_xmit(struct
        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(),


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