PCI: of_property: Omit bus properties without a subordinate bus

Overview

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

PCI: of_property: Omit bus properties without a subordinate bus

A bridge (a device with a Type 1 header) may not have a secondary bus allocated (pdev->subordinate), e.g., if there are no available bus numbers or the bridge secondary/subordinate bus numbers are not writable.

The dynamic OF helpers of_pci_prop_bus_range() and of_pci_prop_intr_map() dereference pdev->subordinate without checking it. When CONFIG_PCI_DYNAMIC_OF_NODES is enabled, this can cause a NULL pointer dereference and early boot hang.

Generate 'bus-range' and 'interrupt-map' properties only when a subordinate bus exists. Keep the node and its remaining properties for bridges without one.

The problem was latent since 407d1a51921e ("PCI: Create device tree node for bridge"), but wasn't reachable until 1f340724419e ("PCI: of: Create device tree PCI host bridge node"), which appeared in v6.15. Before 1f340724419e, of_pci_make_dev_node() returned early because the parent OF node was missing.

[bhelgaas: move pdev->subordinate test to callees, commit log]

Affected

• Linux >= 407d1a51921e9f28c1bcec647c2205925bd1fdab < ccd32fa3489cbe86a0b281da4447b4c7eadb3518
• Linux >= 407d1a51921e9f28c1bcec647c2205925bd1fdab < a6d97d10e49ae49026ae13af6c41634fce470a37
• Linux >= 407d1a51921e9f28c1bcec647c2205925bd1fdab < 879c911f77b8a7862aa16079b04efc3fdc5d32ec
• Linux >= 407d1a51921e9f28c1bcec647c2205925bd1fdab < aee774588abd78f75952fd34c3fa461bc46b62c2
• Linux >= 407d1a51921e9f28c1bcec647c2205925bd1fdab < 8805840aad73df7146778be243a196d48b4f6430
• Linux 6.6

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.