Message-ID: <2025041656-CVE-2025-22031-b941@gregkh>
Date: Wed, 16 Apr 2025 16:12:02 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-22031: PCI/bwctrl: Fix NULL pointer dereference on bus number exhaustion

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

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

PCI/bwctrl: Fix NULL pointer dereference on bus number exhaustion

When BIOS neglects to assign bus numbers to PCI bridges, the kernel
attempts to correct that during PCI device enumeration.  If it runs out
of bus numbers, no pci_bus is allocated and the "subordinate" pointer in
the bridge's pci_dev remains NULL.

The PCIe bandwidth controller erroneously does not check for a NULL
subordinate pointer and dereferences it on probe.

Bandwidth control of unusable devices below the bridge is of questionable
utility, so simply error out instead.  This mirrors what PCIe hotplug does
since commit 62e4492c3063 ("PCI: Prevent NULL dereference during pciehp
probe").

The PCI core emits a message with KERN_INFO severity if it has run out of
bus numbers.  PCIe hotplug emits an additional message with KERN_ERR
severity to inform the user that hotplug functionality is disabled at the
bridge.  A similar message for bandwidth control does not seem merited,
given that its only purpose so far is to expose an up-to-date link speed
in sysfs and throttle the link speed on certain laptops with limited
Thermal Design Power.  So error out silently.

User-visible messages:

  pci 0000:16:02.0: bridge configuration invalid ([bus 00-00]), reconfiguring
  [...]
  pci_bus 0000:45: busn_res: [bus 45-74] end is updated to 74
  pci 0000:16:02.0: devices behind bridge are unusable because [bus 45-74] cannot be assigned for them
  [...]
  pcieport 0000:16:02.0: pciehp: Hotplug bridge without secondary bus, ignoring
  [...]
  BUG: kernel NULL pointer dereference
  RIP: pcie_update_link_speed
  pcie_bwnotif_enable
  pcie_bwnotif_probe
  pcie_port_probe_service
  really_probe

The Linux kernel CVE team has assigned CVE-2025-22031 to this issue.


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

	Issue introduced in 6.13 with commit 665745f274870c921020f610e2c99a3b1613519b and fixed in 6.13.11 with commit d93d309013e89631630a12b1770d27e4be78362a
	Issue introduced in 6.13 with commit 665745f274870c921020f610e2c99a3b1613519b and fixed in 6.14.2 with commit 1181924af78e5299ddec6e457789c02dd5966559
	Issue introduced in 6.13 with commit 665745f274870c921020f610e2c99a3b1613519b and fixed in 6.15-rc1 with commit 667f053b05f00a007738cd7ed6fa1901de19dc7e

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-2025-22031
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/pcie/bwctrl.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/d93d309013e89631630a12b1770d27e4be78362a
	https://git.kernel.org/stable/c/1181924af78e5299ddec6e457789c02dd5966559
	https://git.kernel.org/stable/c/667f053b05f00a007738cd7ed6fa1901de19dc7e

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