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From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
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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 net v2] net/sched: cake: reject overhead values that
 underflow length
In-Reply-To: <20260609232935.1602659.8545fdb04fbe.cake-overhead-underflow@trailofbits.com>
References: <20260609232935.1602659.8545fdb04fbe.cake-overhead-underflow@trailofbits.com>
Date: Wed, 10 Jun 2026 10:06:04 +0200
X-Clacks-Overhead: GNU Terry Pratchett
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Samuel Moelius <sam.moelius@trailofbits.com> writes:

> CAKE accepts overhead values that can make adjusted packet length
> arithmetic underflow.  A negative effective length can wrap through
> unsigned arithmetic and become a large value.
>
> Such configurations make rate accounting depend on integer wraparound
> rather than on the packet size userspace intended to model.
>
> Validate overhead settings before using them in adjusted length
> calculations.
>
> 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 H=C3=B8iland-J=C3=B8rgensen <toke@toke.dk>