CVE-2022-49434

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

PCI: Avoid pci_dev_lock() AB/BA deadlock with sriov_numvfs_store()

The sysfs sriov_numvfs_store() path acquires the device lock before the config space access lock:

sriov_numvfs_store device_lock # A (1) acquire device lock sriov_configure vfio_pci_sriov_configure # (for example) vfio_pci_core_sriov_configure pci_disable_sriov sriov_disable pci_cfg_access_lock pci_wait_cfg # B (4) wait for dev->block_cfg_access == 0

Previously, pci_dev_lock() acquired the config space access lock before the device lock:

pci_dev_lock pci_cfg_access_lock dev->block_cfg_access = 1 # B (2) set dev->block_cfg_access = 1 device_lock # A (3) wait for device lock

Any path that uses pci_dev_lock(), e.g., pci_reset_function(), may deadlock with sriov_numvfs_store() if the operations occur in the sequence (1) (2) (3) (4).

Avoid the deadlock by reversing the order in pci_dev_lock() so it acquires the device lock before the config space access lock, the same as the sriov_numvfs_store() path.

[bhelgaas: combined and adapted commit log from Jay Zhous independent subsequent posting: https://lore.kernel.org/r/20220404062539.1710-1-jianjay.zhou@huawei.com]

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/2cdd5284035322795b0964f899eefba254cfe483
• https://git.kernel.org/stable/c/59ea6b3ae51df7cd6bfd84c9c0030609b9315622
• https://git.kernel.org/stable/c/a91ee0e9fca9d7501286cfbced9b30a33e52740a
• https://git.kernel.org/stable/c/aed6d4d519210c28817948f34c53b6e058e0456c
• https://git.kernel.org/stable/c/c3c6dc1853b8bf3c718f96fd8480a6eb09ba4831
• https://git.kernel.org/stable/c/c9a81f9ed6ae3554621d6a50220b1bc74b67d81e
• https://git.kernel.org/stable/c/da9792920ab525b8a932aa9aeee34529ad7b83f7
• https://git.kernel.org/stable/c/ea047f51172aa68841adef7f52d375002438b8f0
• https://git.kernel.org/stable/c/eff3587b9c01439b738298475e555c028ac9f55e