Subject: CVE-2024-42302: PCI/DPC: Fix use-after-free on concurrent DPC and hot-removal

From: Greg Kroah-Hartman <[email-masked]>

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

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

PCI/DPC: Fix use-after-free on concurrent DPC and hot-removal

Keith reports a use-after-free when a DPC event occurs concurrently to
hot-removal of the same portion of the hierarchy:

The dpc_handler() awaits readiness of the secondary bus below the
Downstream Port where the DPC event occurred.  To do so, it polls the
config space of the first child device on the secondary bus.  If that
child device is concurrently removed, accesses to its struct pci_dev
cause the kernel to oops.

That's because pci_bridge_wait_for_secondary_bus() neglects to hold a
reference on the child device.  Before v6.3, the function was only
called on resume from system sleep or on runtime resume.  Holding a
reference wasn't necessary back then because the pciehp IRQ thread
could never run concurrently.  (On resume from system sleep, IRQs are
not enabled until after the resume_noirq phase.  And runtime resume is
always awaited before a PCI device is removed.)

However starting with v6.3, pci_bridge_wait_for_secondary_bus() is also
called on a DPC event.  Commit 53b54ad074de ("PCI/DPC: Await readiness
of secondary bus after reset"), which introduced that, failed to
appreciate that pci_bridge_wait_for_secondary_bus() now needs to hold a
reference on the child device because dpc_handler() and pciehp may
indeed run concurrently.  The commit was backported to v5.10+ stable
kernels, so that's the oldest one affected.

Add the missing reference acquisition.

Abridged stack trace:

  BUG: unable to handle page fault for address: 00000000091400c0
  CPU: 15 PID: 2464 Comm: irq/53-pcie-dpc 6.9.0
  RIP: pci_bus_read_config_dword+0x17/0x50
  pci_dev_wait()
  pci_bridge_wait_for_secondary_bus()
  dpc_reset_link()
  pcie_do_recovery()
  dpc_handler()

The Linux kernel CVE team has assigned CVE-2024-42302 to this issue.

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

	Issue introduced in 5.10.176 with commit d0292124bb57 and fixed in 5.10.224 with commit c52f9e1a9eb4
	Issue introduced in 5.15.104 with commit ffe2318405e6 and fixed in 5.15.165 with commit 2c111413f38c
	Issue introduced in 6.1.16 with commit 189f856e76f5 and fixed in 6.1.103 with commit f63df70b439b
	Issue introduced in 6.3 with commit 53b54ad074de and fixed in 6.6.44 with commit 2cc8973bdc4d
	Issue introduced in 6.3 with commit 53b54ad074de and fixed in 6.10.3 with commit b16f3ea1db47
	Issue introduced in 6.3 with commit 53b54ad074de and fixed in 6.11 with commit 11a1f4bc4736
	Issue introduced in 6.2.3 with commit 0081032082b5

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-2024-42302
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/pci.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/c52f9e1a9eb40f13993142c331a6cfd334d4b91d
	https://git.kernel.org/stable/c/2c111413f38ca5cf87557cab89f6d82b0e3433e7
	https://git.kernel.org/stable/c/f63df70b439bb8331358a306541893bf415bf1da
	https://git.kernel.org/stable/c/2cc8973bdc4d6c928ebe38b88090a2cdfe81f42f
	https://git.kernel.org/stable/c/b16f3ea1db47a6766a9f1169244cf1fc287a7c62
	https://git.kernel.org/stable/c/11a1f4bc47362700fcbde717292158873fb847ed