On 2020-07-01 01:40, Qian Cai wrote:
Looks like this patchset introduced an use-after-free on arm-smmu-v3.

Reproduced using mlx5,

# echo 1 > /sys/class/net/enp11s0f1np1/device/sriov_numvfs
# echo 0 > /sys/class/net/enp11s0f1np1/device/sriov_numvfs

The .config,
https://github.com/cailca/linux-mm/blob/master/arm64.config

Looking at the free stack,

iommu_release_device->iommu_group_remove_device

was introduced in 07/34 ("iommu: Add probe_device() and release_device()
call-backs").

Right, iommu_group_remove_device can tear down the group and call ->domain_free before the driver has any knowledge of the last device going away via the ->release_device call.

I guess the question is do we simply flip the call order in iommu_release_device() so drivers can easily clean up their internal per-device state first, or do we now want them to be robust against freeing domains with devices still nominally attached?

Robin.
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