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Date:   Thu, 16 Jan 2020 12:03:30 -0500
From:   Sasha Levin <>
Cc:     Vladimir Oltean <>,
        Vinicius Costa Gomes <>,
        "David S . Miller" <>,
        Sasha Levin <>,
Subject: [PATCH AUTOSEL 4.19 572/671] net: sched: cbs: Avoid division by zero when calculating the port rate

From: Vladimir Oltean <>

[ Upstream commit 83c8c3cf45163f0c823db37be6ab04dfcf8ac751 ]

As explained in the "net: sched: taprio: Avoid division by zero on
invalid link speed" commit, it is legal for the ethtool API to return
zero as a link speed. So guard against it to ensure we don't perform a
division by zero in kernel.

Fixes: e0a7683d30e9 ("net/sched: cbs: fix port_rate miscalculation")
Signed-off-by: Vladimir Oltean <>
Acked-by: Vinicius Costa Gomes <>
Signed-off-by: David S. Miller <>
Signed-off-by: Sasha Levin <>
 net/sched/sch_cbs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/sch_cbs.c b/net/sched/sch_cbs.c
index 289f66b9238d..940e72d6db18 100644
--- a/net/sched/sch_cbs.c
+++ b/net/sched/sch_cbs.c
@@ -310,7 +310,7 @@ static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q)
 	if (err < 0)
 		goto skip;
-	if (ecmd.base.speed != SPEED_UNKNOWN)
+	if (ecmd.base.speed && ecmd.base.speed != SPEED_UNKNOWN)
 		speed = ecmd.base.speed;

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