[Cake] [PATCH] sch_cake: avoid possible divide by zero in cake_enqueue()

[Wen Yang]

The variables 'window_interval' is u64 and do_div()
truncates it to 32 bits, which means it can test
non-zero and be truncated to zero for division.
The unit of window_interval is nanoseconds,
so its lower 32-bit is relatively easy to exceed.
Fix this issue by using div64_u64() instead.

Fixes: 7298de9cd725 ("sch_cake: Add ingress mode")
Signed-off-by: Wen Yang <wenyang at linux.alibaba.com>
Cc: Kevin Darbyshire-Bryant <ldir at darbyshire-bryant.me.uk>
Cc: Toke Høiland-Jørgensen <toke at redhat.com>
Cc: David S. Miller <davem at davemloft.net>
Cc: Cong Wang <xiyou.wangcong at gmail.com>
Cc: cake at lists.bufferbloat.net
Cc: netdev at vger.kernel.org
Cc: linux-kernel at vger.kernel.org
---
 net/sched/sch_cake.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 6cc3ab1..90ef7cc 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1768,7 +1768,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 						      q->avg_window_begin));
 			u64 b = q->avg_window_bytes * (u64)NSEC_PER_SEC;
 
-			do_div(b, window_interval);
+			b = div64_u64(b, window_interval);
 			q->avg_peak_bandwidth =
 				cake_ewma(q->avg_peak_bandwidth, b,
 					  b > q->avg_peak_bandwidth ? 2 : 8);
-- 
1.8.3.1