CVE-2024-56568: Concurrent Execution using Shared Resource with Improper Synchronization

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

iommu/arm-smmu: Defer probe of clients after smmu device bound

Null pointer dereference occurs due to a race between smmu driver probe and client driver probe, when of_dma_configure() for client is called after the iommu_device_register() for smmu driver probe has executed but before the driver_bound() for smmu driver has been called.

Following is how the race occurs:

T1:Smmu device probe T2: Client device probe

really_probe() arm_smmu_device_probe() iommu_device_register() really_probe() platform_dma_configure() of_dma_configure() of_dma_configure_id() of_iommu_configure() iommu_probe_device() iommu_init_device() arm_smmu_probe_device() arm_smmu_get_by_fwnode() driver_find_device_by_fwnode() driver_find_device() next_device() klist_next() /* null ptr assigned to smmu */ /* null ptr dereference while smmu->streamid_mask */ driver_bound() klist_add_tail()

When this null smmu pointer is dereferenced later in arm_smmu_probe_device, the device crashes.

Fix this by deferring the probe of the client device until the smmu device has bound to the arm smmu driver.

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