From: Peilin Ye <yepeilin.cs@gmail.com>
To: Stephen Hemminger <stephen@networkplumber.org>,
Jamal Hadi Salim <jhs@mojatatu.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
Jiri Pirko <jiri@resnulli.us>
Cc: Peilin Ye <peilin.ye@bytedance.com>,
Yuming Chen <chenyuming.junnan@bytedance.com>,
Ted Lin <ted@mostlyuseful.tech>, Dave Taht <dave.taht@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Cong Wang <cong.wang@bytedance.com>,
Peilin Ye <yepeilin.cs@gmail.com>
Subject: [PATCH net] net/sched: sch_netem: Fix arithmetic in netem_dump() for 32-bit platforms
Date: Thu, 16 Jun 2022 16:43:36 -0700 [thread overview]
Message-ID: <20220616234336.2443-1-yepeilin.cs@gmail.com> (raw)
From: Peilin Ye <peilin.ye@bytedance.com>
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@bytedance.com>
Fixes: 112f9cb65643 ("netem: convert to qdisc_watchdog_schedule_ns")
Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
---
net/sched/sch_netem.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index ed4ccef5d6a8..5449ed114e40 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;
--
2.20.1
next reply other threads:[~2022-06-16 23:44 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-16 23:43 Peilin Ye [this message]
2022-06-17 3:08 ` [PATCH net] net/sched: sch_netem: Fix arithmetic in netem_dump() for 32-bit platforms Stephen Hemminger
2022-06-18 3:40 ` patchwork-bot+netdevbpf
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