CVE-2026-52927

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ebtables: fix OOB read in compat_mtw_from_user

Luxiao Xu says:

The function compat_mtw_from_user() converts ebtables extensions from

32-bit user structures to kernel native structures. However, it lacks

proper validation of the user-supplied match_size/target_size.

When certain extensions are processed, the kernel-side translation

logic may perform memory accesses based on the extension's expected

size. If the user provides a size smaller than what the extension

requires, it results in an out-of-bounds read as reported by KASAN.

This fix introduces a check to ensure match_size is at least as large

as the extension's required compatsize. This covers matches, watchers,

and targets, while maintaining compatibility with standard targets.

AFAIU this is relevant for matches that need to go though

match->compat_from_user() call. Those that use plain memcpy with the

user-provided size are ok because the caller checks that size vs the

start of the next rule entry offset (which itself is checked vs. total

size copied from userspace).

The ->compat_from_user() callbacks assume they can read compatsize bytes,

so they need this extra check.

Based on an earlier patch from Luxiao Xu.