sch_cake: avoid possible divide by zero in cake_enqueue()

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>

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index e0f40400f679c2ae40aecd43c2a4118fab515505..2277369feae58bfb9c70b449e7e096ae5f61dae1 100644 (file)
--- 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);