This is a note to let you know that I've just added the patch titled net/sched: sch_netem: Fix arithmetic in netem_dump() for 32-bit platforms to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-sched-sch_netem-fix-arithmetic-in-netem_dump-for.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 9bc1c69969008a593faf298de1df9ae17c21eedc Author: Peilin Ye <peilin.ye@xxxxxxxxxxxxx> Date: Thu Jun 16 16:43:36 2022 -0700 net/sched: sch_netem: Fix arithmetic in netem_dump() for 32-bit platforms [ Upstream commit a2b1a5d40bd12b44322c2ccd40bb0ec1699708b6 ] As reported by Yuming, currently tc always show a latency of UINT_MAX for netem Qdisc's on 32-bit platforms: $ tc qdisc add dev dummy0 root netem latency 100ms $ tc qdisc show dev dummy0 qdisc netem 8001: root refcnt 2 limit 1000 delay 275s 275s ^^^^^^^^^^^^^^^^ Let us take a closer look at netem_dump(): qopt.latency = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->latency, UINT_MAX); qopt.latency is __u32, psched_tdiff_t is signed long, (psched_tdiff_t)(UINT_MAX) is negative for 32-bit platforms, so qopt.latency is always UINT_MAX. Fix it by using psched_time_t (u64) instead. Note: confusingly, users have two ways to specify 'latency': 1. normally, via '__u32 latency' in struct tc_netem_qopt; 2. via the TCA_NETEM_LATENCY64 attribute, which is s64. For the second case, theoretically 'latency' could be negative. This patch ignores that corner case, since it is broken (i.e. assigning a negative s64 to __u32) anyways, and should be handled separately. Thanks Ted Lin for the analysis [1] . [1] https://github.com/raspberrypi/linux/issues/3512 Reported-by: Yuming Chen <chenyuming.junnan@xxxxxxxxxxxxx> Fixes: 112f9cb65643 ("netem: convert to qdisc_watchdog_schedule_ns") Reviewed-by: Cong Wang <cong.wang@xxxxxxxxxxxxx> Signed-off-by: Peilin Ye <peilin.ye@xxxxxxxxxxxxx> Acked-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220616234336.2443-1-yepeilin.cs@xxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index f4101a920d1f..1802f134aa40 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -1146,9 +1146,9 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb) struct tc_netem_rate rate; struct tc_netem_slot slot; - qopt.latency = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->latency), + qopt.latency = min_t(psched_time_t, PSCHED_NS2TICKS(q->latency), UINT_MAX); - qopt.jitter = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->jitter), + qopt.jitter = min_t(psched_time_t, PSCHED_NS2TICKS(q->jitter), UINT_MAX); qopt.limit = q->limit; qopt.loss = q->loss;