CVE-2026-93096: cxl/features: Serialize multi-part Get/Set Feature transfers

CVE-2026-93096: cxl/features: Serialize multi-part Get/Set Feature transfers

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

cxl/features: Serialize multi-part Get/Set Feature transfers

A Get or Set Feature payload larger than the mailbox payload size is
split into several mailbox commands. mbox_mutex only serializes
individual mailbox commands and is dropped between iterations of these
loops. Nothing serializes the multi-part transfer as a whole.
cxl_get_feature() and cxl_set_feature() are reachable concurrently
from fwctl (per-fd RPCs run under a read-held registration lock) and
from the EDAC scrub/ECS/repair paths, so two transfers to the same
mailbox can interleave their parts and corrupt the device's transfer
context.

Add a per-mailbox feat_mutex and hold it across the whole transfer in
both functions. It nests outside mbox_mutex (which is taken inside
cxl_internal_send_cmd()), and is taken nowhere else, so no lock-ordering
inversion is introduced.

The Linux kernel CVE team has assigned CVE-2026-93096 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.15 with commit 5e5ac21f629de796ab5d598b59c5e468c6fe4f95 and fixed in 7.2.6 with commit 7682b617db1f19bc606b5f1badadcf1e63a87b14
	Issue introduced in 6.15 with commit 5e5ac21f629de796ab5d598b59c5e468c6fe4f95 and fixed in 7.3-rc1 with commit 77b814c1832fde018c30357b4ec3fcdaa91a1c10

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-93096
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/cxl/core/features.c
	drivers/cxl/core/mbox.c
	include/cxl/mailbox.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/7682b617db1f19bc606b5f1badadcf1e63a87b14
	https://git.kernel.org/stable/c/77b814c1832fde018c30357b4ec3fcdaa91a1c10