Samuel Moelius 336c1e414f net/sched: cake: reject overhead values that underflow length
[ Upstream commit b7f97cae7e ]

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: a729b7f0bd ("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>
Link: https://patch.msgid.link/20260702000758.297407.e5c888d9d99d.cake-overhead-underflow@trailofbits.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2026-07-24 16:03:28 +02:00
2026-07-24 16:03:06 +02:00
2026-05-23 13:03:09 +02:00
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2026-05-23 13:03:09 +02:00
2026-07-04 13:42:28 +02:00
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Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
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