From: "Toke Høiland-Jørgensen" <toke@toke.dk>
To: Samuel Moelius <sam.moelius@trailofbits.com>
Cc: Samuel Moelius <sam.moelius@trailofbits.com>,
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>,
Simon Horman <horms@kernel.org>,
"moderated list:CAKE QDISC" <cake@lists.bufferbloat.net>,
"open list:TC subsystem" <netdev@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] net/sched: cake: reject overhead values that underflow length
Date: Thu, 02 Jul 2026 11:40:27 +0200 [thread overview]
Message-ID: <87pl1520hg.fsf@toke.dk> (raw)
In-Reply-To: <20260702000758.297407.e5c888d9d99d.cake-overhead-underflow@trailofbits.com>
Samuel Moelius <sam.moelius@trailofbits.com> writes:
> CAKE accepts signed overhead values and stores them in an s16, but the
> adjusted packet length calculation uses unsigned arithmetic. A negative
> effective length can therefore wrap to a large value.
>
> Such configurations make rate accounting depend on integer wraparound
> rather than on the packet size userspace intended to model. A static
> netlink lower bound is not enough because packets reaching CAKE can be
> smaller than any reasonable manual-overhead allowance.
>
> Fold the signed overhead adjustment into the existing datapath MPU clamp
> so negative adjusted lengths are clamped before link-layer framing
> adjustments.
>
> Fixes: a729b7f0bd5b ("sch_cake: Add overhead compensation support to the rate shaper")
> Assisted-by: Codex:gpt-5.5-cyber-preview
> Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
next prev parent reply other threads:[~2026-07-02 9:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-02 0:07 [PATCH v3] net/sched: cake: reject overhead values that underflow length Samuel Moelius
2026-07-02 9:40 ` Toke Høiland-Jørgensen [this message]
2026-07-08 9:50 ` patchwork-bot+netdevbpf
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