tree 304b0c9cfa48189f716d4c9eafa135a8416351a4
parent cfa9ed48d7b41bec72216c864a9e47e36fdc73c4
author Lukas Wunner <lukas@wunner.de> 1718708095 +0200
committer Shuo Yang <gshuoy@google.com> 1725904910 +0000

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

commit 11a1f4bc47362700fcbde717292158873fb847ed upstream.

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()

BUG=b/362700943
TEST=presubmit
RELEASE_NOTE=Fixes CVE-2024-42302 in the Linux kernel

cos-patch: security-high
Fixes: 53b54ad074de ("PCI/DPC: Await readiness of secondary bus after reset")
Closes: https://lore.kernel.org/r/20240612181625.3604512-3-kbusch@meta.com/
Link: https://lore.kernel.org/linux-pci/8e4bcd4116fd94f592f2bf2749f168099c480ddf.1718707743.git.lukas@wunner.de
Reported-by: Keith Busch <kbusch@kernel.org>
Tested-by: Keith Busch <kbusch@kernel.org>
Change-Id: I5906d1bf2d2c88e7c5c62d6de8c0f22e4590b687
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Shuo Yang <gshuoy@google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/80359
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Anil Altinay <aaltinay@google.com>