linux-cve-announce - CVE-2025-37843: PCI: pciehp: Avoid unnecessary device replacement check

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Message-ID: <2025050916-CVE-2025-37843-6b22@gregkh>
Date: Fri,  9 May 2025 08:42:21 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-37843: PCI: pciehp: Avoid unnecessary device replacement check

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

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

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

PCI: pciehp: Avoid unnecessary device replacement check

Hot-removal of nested PCI hotplug ports suffers from a long-standing race
condition which can lead to a deadlock:  A parent hotplug port acquires
pci_lock_rescan_remove(), then waits for pciehp to unbind from a child
hotplug port.  Meanwhile that child hotplug port tries to acquire
pci_lock_rescan_remove() as well in order to remove its own children.

The deadlock only occurs if the parent acquires pci_lock_rescan_remove()
first, not if the child happens to acquire it first.

Several workarounds to avoid the issue have been proposed and discarded
over the years, e.g.:

https://lore.kernel.org/r/4c882e25194ba8282b78fe963fec8faae7cf23eb.1529173804.git.lukas@wunner.de/

A proper fix is being worked on, but needs more time as it is nontrivial
and necessarily intrusive.

Recent commit 9d573d19547b ("PCI: pciehp: Detect device replacement during
system sleep") provokes more frequent occurrence of the deadlock when
removing more than one Thunderbolt device during system sleep.  The commit
sought to detect device replacement, but also triggered on device removal.
Differentiating reliably between replacement and removal is impossible
because pci_get_dsn() returns 0 both if the device was removed, as well as
if it was replaced with one lacking a Device Serial Number.

Avoid the more frequent occurrence of the deadlock by checking whether the
hotplug port itself was hot-removed.  If so, there's no sense in checking
whether its child device was replaced.

This works because the ->resume_noirq() callback is invoked in top-down
order for the entire hierarchy:  A parent hotplug port detecting device
replacement (or removal) marks all children as removed using
pci_dev_set_disconnected() and a child hotplug port can then reliably
detect being removed.

The Linux kernel CVE team has assigned CVE-2025-37843 to this issue.

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

	Issue introduced in 6.11 with commit 9d573d19547b3fae0c1d4e5fce52bdad3fda3664 and fixed in 6.12.24 with commit e4a1d7defbc2d806540720a5adebe24ec3488683
	Issue introduced in 6.11 with commit 9d573d19547b3fae0c1d4e5fce52bdad3fda3664 and fixed in 6.13.12 with commit 0d0bbd01f7c0ac7d1be9f85aaf2cd0baec34655f
	Issue introduced in 6.11 with commit 9d573d19547b3fae0c1d4e5fce52bdad3fda3664 and fixed in 6.14.3 with commit 7535d10a2c61baeff493300070cf04d9ddda216b
	Issue introduced in 6.11 with commit 9d573d19547b3fae0c1d4e5fce52bdad3fda3664 and fixed in 6.15-rc1 with commit e3260237aaadc9799107ccb940c6688195c4518d

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-2025-37843
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/pci/hotplug/pciehp_core.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/e4a1d7defbc2d806540720a5adebe24ec3488683
	https://git.kernel.org/stable/c/0d0bbd01f7c0ac7d1be9f85aaf2cd0baec34655f
	https://git.kernel.org/stable/c/7535d10a2c61baeff493300070cf04d9ddda216b
	https://git.kernel.org/stable/c/e3260237aaadc9799107ccb940c6688195c4518d