[PATCH v2 net] net: sched: taprio: Fix potential integer overflow in taprio_set_picos_per_byte

[Vladimir Oltean <olteanv@gmail.com>]

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>
---
 net/sched/sch_taprio.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 2f7b34205c82..2aab46ada94f 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1048,8 +1048,7 @@ static void taprio_set_picos_per_byte(struct net_device *dev,
 		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",
-- 
2.17.1