Subject: [PATCH 5.4 147/165] sch_cake: avoid possible divide by zero in cake_enqueue()

From: Greg Kroah-Hartman <[email-masked]>
Date: Sat, 11 Jan 2020 10:51:06 +0100

From: Wen Yang <[email-masked]>

[ Upstream commit 68aab823c223646fab311f8a6581994facee66a0 ]

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 <[email-masked]>
Cc: Kevin Darbyshire-Bryant <[email-masked]>
Cc: Toke Høiland-Jørgensen <[email-masked]>
Cc: David S. Miller <[email-masked]>
Cc: Cong Wang <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Cc: [email-masked]
Acked-by: Toke Høiland-Jørgensen <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
---
 net/sched/sch_cake.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1769,7 +1769,7 @@ static s32 cake_enqueue(struct sk_buff *
 						      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);