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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
        Willem de Bruijn <willemb@google.com>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 049/361] net: loopback: clear skb->tstamp before netif_rx()
Date:   Sun, 11 Nov 2018 14:16:36 -0800
Message-Id: <20181111221626.882767669@linuxfoundation.org>
In-Reply-To: <20181111221619.915519183@linuxfoundation.org>
References: <20181111221619.915519183@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@google.com>

[ 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 <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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(),