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    Subject[PATCH 5.4 147/165] sch_cake: avoid possible divide by zero in cake_enqueue()
    Date
    From: Wen Yang <wenyang@linux.alibaba.com>

    [ 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 <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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    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);

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