linux-cve-announce - CVE-2025-40120: net: usb: asix: hold PM usage ref to avoid PM/MDIO + RTNL deadlock

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Message-ID: <2025111252-CVE-2025-40120-8b68@gregkh>
Date: Wed, 12 Nov 2025 19:23:56 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40120: net: usb: asix: hold PM usage ref to avoid PM/MDIO + RTNL deadlock

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

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

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

net: usb: asix: hold PM usage ref to avoid PM/MDIO + RTNL deadlock

Prevent USB runtime PM (autosuspend) for AX88772* in bind.

usbnet enables runtime PM (autosuspend) by default, so disabling it via
the usb_driver flag is ineffective. On AX88772B, autosuspend shows no
measurable power saving with current driver (no link partner, admin
up/down). The ~0.453 W -> ~0.248 W drop on v6.1 comes from phylib powering
the PHY off on admin-down, not from USB autosuspend.

The real hazard is that with runtime PM enabled, ndo_open() (under RTNL)
may synchronously trigger autoresume (usb_autopm_get_interface()) into
asix_resume() while the USB PM lock is held. Resume paths then invoke
phylink/phylib and MDIO, which also expect RTNL, leading to possible
deadlocks or PM lock vs MDIO wake issues.

To avoid this, keep the device runtime-PM active by taking a usage
reference in ax88772_bind() and dropping it in unbind(). A non-zero PM
usage count blocks runtime suspend regardless of userspace policy
(.../power/control - pm_runtime_allow/forbid), making this approach
robust against sysfs overrides.

Holding a runtime-PM usage ref does not affect system-wide suspend;
system sleep/resume callbacks continue to run as before.

The Linux kernel CVE team has assigned CVE-2025-40120 to this issue.

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

	Issue introduced in 5.14 with commit 4a2c7217cd5a87e85ceb761e307b030fe6db4805 and fixed in 5.15.195 with commit 71a0ba7fdaf8d035426912a4ed7bf1738a81010c
	Issue introduced in 5.14 with commit 4a2c7217cd5a87e85ceb761e307b030fe6db4805 and fixed in 6.1.156 with commit 3e96cd27ff1a004d84908c1b6cc68ac60913874e
	Issue introduced in 5.14 with commit 4a2c7217cd5a87e85ceb761e307b030fe6db4805 and fixed in 6.6.112 with commit 724a9db84188f80ef60b1f21cc7b4e9c84e0cb64
	Issue introduced in 5.14 with commit 4a2c7217cd5a87e85ceb761e307b030fe6db4805 and fixed in 6.12.53 with commit 1534517300e12f2930b6ff477b8820ff658afd11
	Issue introduced in 5.14 with commit 4a2c7217cd5a87e85ceb761e307b030fe6db4805 and fixed in 6.17.3 with commit 9d8bcaf6fae1bd82bc27ec09a2694497e6f6c4b4
	Issue introduced in 5.14 with commit 4a2c7217cd5a87e85ceb761e307b030fe6db4805 and fixed in 6.18-rc1 with commit 3d3c4cd5c62f24bb3cb4511b7a95df707635e00a

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-2025-40120
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/net/usb/asix_devices.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/71a0ba7fdaf8d035426912a4ed7bf1738a81010c
	https://git.kernel.org/stable/c/3e96cd27ff1a004d84908c1b6cc68ac60913874e
	https://git.kernel.org/stable/c/724a9db84188f80ef60b1f21cc7b4e9c84e0cb64
	https://git.kernel.org/stable/c/1534517300e12f2930b6ff477b8820ff658afd11
	https://git.kernel.org/stable/c/9d8bcaf6fae1bd82bc27ec09a2694497e6f6c4b4
	https://git.kernel.org/stable/c/3d3c4cd5c62f24bb3cb4511b7a95df707635e00a