linux-cve-announce - CVE-2025-68209: mlx5: Fix default values in create CQ

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Message-ID: <2025121633-CVE-2025-68209-2e49@gregkh>
Date: Tue, 16 Dec 2025 14:54:38 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68209: mlx5: Fix default values in create CQ

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

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

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

mlx5: Fix default values in create CQ

Currently, CQs without a completion function are assigned the
mlx5_add_cq_to_tasklet function by default. This is problematic since
only user CQs created through the mlx5_ib driver are intended to use
this function.

Additionally, all CQs that will use doorbells instead of polling for
completions must call mlx5_cq_arm. However, the default CQ creation flow
leaves a valid value in the CQ's arm_db field, allowing FW to send
interrupts to polling-only CQs in certain corner cases.

These two factors would allow a polling-only kernel CQ to be triggered
by an EQ interrupt and call a completion function intended only for user
CQs, causing a null pointer exception.

Some areas in the driver have prevented this issue with one-off fixes
but did not address the root cause.

This patch fixes the described issue by adding defaults to the create CQ
flow. It adds a default dummy completion function to protect against
null pointer exceptions, and it sets an invalid command sequence number
by default in kernel CQs to prevent the FW from sending an interrupt to
the CQ until it is armed. User CQs are responsible for their own
initialization values.

Callers of mlx5_core_create_cq are responsible for changing the
completion function and arming the CQ per their needs.

The Linux kernel CVE team has assigned CVE-2025-68209 to this issue.

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

	Issue introduced in 6.0 with commit cdd04f4d4d71cbf93d0d9abe63bc838f47c467fa and fixed in 6.17.9 with commit 08469f5393a1a39f26a6e2eb2e8c33187665c1f4
	Issue introduced in 6.0 with commit cdd04f4d4d71cbf93d0d9abe63bc838f47c467fa and fixed in 6.18 with commit e5eba42f01340f73888dfe560be2806057c25913

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-2025-68209
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/infiniband/hw/mlx5/cq.c
	drivers/net/ethernet/mellanox/mlx5/core/cq.c
	drivers/net/ethernet/mellanox/mlx5/core/en_main.c
	drivers/net/ethernet/mellanox/mlx5/core/fpga/conn.c
	drivers/net/ethernet/mellanox/mlx5/core/steering/hws/send.c
	drivers/net/ethernet/mellanox/mlx5/core/steering/sws/dr_send.c
	drivers/vdpa/mlx5/net/mlx5_vnet.c
	include/linux/mlx5/cq.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/08469f5393a1a39f26a6e2eb2e8c33187665c1f4
	https://git.kernel.org/stable/c/e5eba42f01340f73888dfe560be2806057c25913