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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,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        Vinicius Costa Gomes <vinicius.gomes@intel.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.3 135/166] net: sched: taprio: Fix potential integer overflow in taprio_set_picos_per_byte
Date:   Sun,  6 Oct 2019 19:21:41 +0200
Message-Id: <20191006171224.523399591@linuxfoundation.org>
In-Reply-To: <20191006171212.850660298@linuxfoundation.org>
References: <20191006171212.850660298@linuxfoundation.org>
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From: Vladimir Oltean <olteanv@gmail.com>

[ Upstream commit 68ce6688a5baefde30914fc07fc27292dbbe8320 ]

The speed divisor is used in a context expecting an s64, but it is
evaluated using 32-bit arithmetic.

To avoid that happening, instead of multiplying by 1,000,000 in the
first place, simplify the fraction and do a standard 32 bit division
instead.

Fixes: f04b514c0ce2 ("taprio: Set default link speed to 10 Mbps in taprio_set_picos_per_byte")
Reported-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/sched/sch_taprio.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -965,8 +965,7 @@ static void taprio_set_picos_per_byte(st
 		speed = ecmd.base.speed;
 
 skip:
-	picos_per_byte = div64_s64(NSEC_PER_SEC * 1000LL * 8,
-				   speed * 1000 * 1000);
+	picos_per_byte = (USEC_PER_SEC * 8) / speed;
 
 	atomic64_set(&q->picos_per_byte, picos_per_byte);
 	netdev_dbg(dev, "taprio: set %s's picos_per_byte to: %lld, linkspeed: %d\n",