From: Simon Horman <horms@kernel.org>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: netdev@vger.kernel.org, Jamal Hadi Salim <jhs@mojatatu.com>,
Jiri Pirko <jiri@resnulli.us>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Neal Cardwell <ncardwell@google.com>,
Yousuk Seung <ysseung@google.com>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net v3 7/7] net/sched: netem: fix slot delay calculation overflow
Date: Sat, 4 Apr 2026 10:51:28 +0100 [thread overview]
Message-ID: <20260404095128.GA113102@horms.kernel.org> (raw)
In-Reply-To: <20260402202037.176299-8-stephen@networkplumber.org>
On Thu, Apr 02, 2026 at 01:19:35PM -0700, Stephen Hemminger wrote:
> get_slot_next() computes a random delay between min_delay and
> max_delay using:
>
> get_random_u32() * (max_delay - min_delay) >> 32
>
> This overflows signed 64-bit arithmetic when the delay range exceeds
> approximately 2.1 seconds (2^31 nanoseconds), producing a negative
> result that effectively disables slot-based pacing. This is a
> realistic configuration for WAN emulation (e.g., slot 1s 5s).
>
> Use mul_u64_u32_shr() which handles the widening multiply without
> overflow.
>
> Fixes: 0a9fe5c375b5 ("netem: slotting with non-uniform distribution")
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Simon Horman <horms@kernel.org>
prev parent reply other threads:[~2026-04-04 9:51 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-02 20:19 [PATCH net v3 0/7] net/sched: netem: bug fixes Stephen Hemminger
2026-04-02 20:19 ` [PATCH net v3 1/7] net/sched: netem: fix probability gaps in 4-state loss model Stephen Hemminger
2026-04-04 9:50 ` Simon Horman
2026-04-02 20:19 ` [PATCH net v3 2/7] net/sched: netem: fix queue limit check to include reordered packets Stephen Hemminger
2026-04-04 9:50 ` Simon Horman
2026-04-02 20:19 ` [PATCH net v3 3/7] net/sched: netem: only reseed PRNG when seed is explicitly provided Stephen Hemminger
2026-04-04 9:50 ` Simon Horman
2026-04-02 20:19 ` [PATCH net v3 4/7] net/sched: netem: restructure dequeue to avoid re-entrancy with child qdisc Stephen Hemminger
2026-04-04 9:49 ` Simon Horman
2026-04-06 15:41 ` Jakub Kicinski
2026-04-06 17:12 ` Stephen Hemminger
2026-04-08 16:21 ` Simon Horman
2026-04-02 20:19 ` [PATCH net v3 5/7] net/sched: netem: null-terminate tfifo linear queue tail Stephen Hemminger
2026-04-04 9:50 ` Simon Horman
2026-04-02 20:19 ` [PATCH net v3 6/7] net/sched: netem: check for invalid slot range Stephen Hemminger
2026-04-04 9:51 ` Simon Horman
2026-04-02 20:19 ` [PATCH net v3 7/7] net/sched: netem: fix slot delay calculation overflow Stephen Hemminger
2026-04-04 9:51 ` Simon Horman [this message]
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