CVE-2026-93186: cxl/mbox: Clamp mailbox output allocation to the payload size

CVE-2026-93186: cxl/mbox: Clamp mailbox output allocation to the payload size

[Greg Kroah-Hartman]

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

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

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

cxl/mbox: Clamp mailbox output allocation to the payload size

CXL_MEM_SEND_COMMAND bounds the user's in.size to the mailbox payload
size but leaves out.size unbounded, then cxl_mbox_cmd_ctor() calls
kvzalloc(out.size). A large out.size drives a huge allocation, above
INT_MAX it WARNs and taints, and with panic_on_warn=1 it panics.

The transport __cxl_pci_mbox_send_cmd() already clamps the response copy
to min(out.size, payload_size, device len), so the output buffer is
never written beyond payload_size. Clamp the allocation to payload_size
too, matching the RAW path.

The Linux kernel CVE team has assigned CVE-2026-93186 to this issue.


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

	Issue introduced in 5.12 with commit 583fa5e71caeb79e04e477e9837e2f7fa53b71e4 and fixed in 6.12.110 with commit f5d2bbf0300f46307948864fbb97bce5097f4fe2
	Issue introduced in 5.12 with commit 583fa5e71caeb79e04e477e9837e2f7fa53b71e4 and fixed in 6.18.52 with commit 31d4841eca7c4b75751ca96d24339e19303337f2
	Issue introduced in 5.12 with commit 583fa5e71caeb79e04e477e9837e2f7fa53b71e4 and fixed in 7.2.6 with commit b4e11c731d6bee3b87315e055a1ca417c92dc1fc
	Issue introduced in 5.12 with commit 583fa5e71caeb79e04e477e9837e2f7fa53b71e4 and fixed in 7.3-rc1 with commit 8a13db9f899d149c3aab24abcb668121cfda5a4f

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-2026-93186
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/mbox.c


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/f5d2bbf0300f46307948864fbb97bce5097f4fe2
	https://git.kernel.org/stable/c/31d4841eca7c4b75751ca96d24339e19303337f2
	https://git.kernel.org/stable/c/b4e11c731d6bee3b87315e055a1ca417c92dc1fc
	https://git.kernel.org/stable/c/8a13db9f899d149c3aab24abcb668121cfda5a4f