[PATCH 5.3 135/166] net: sched: taprio: Fix potential integer overflow in taprio_set_picos_per_byte

Greg Kroah-Hartman
2019-10-06T17:55:00Z

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",