CVE-2024-42302

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()