From a86a58fb61553fbd9c48727bfa2751f7f557aa6c Mon Sep 17 00:00:00 2001
From: Wen Yang <wenyang@linux.alibaba.com>
Date: Thu, 2 Jan 2020 17:21:43 +0800
Subject: [PATCH] sch_cake: avoid possible divide by zero in cake_enqueue()
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commit 68aab823c223646fab311f8a6581994facee66a0 upstream.

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@linux.alibaba.com>
Cc: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
Cc: Toke Høiland-Jørgensen <toke@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: cake@lists.bufferbloat.net
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index 53a80bc6b13a..dd0e8680b030 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1769,7 +1769,7 @@ 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);
-- 
2.7.4