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SubjectRe: [RFC PATCH 17/34] iommu/arm-smmu: Store device instead of group in arm_smmu_s2cr
Hi Robin,

thanks for looking into this.

On Wed, Apr 08, 2020 at 01:09:40PM +0100, Robin Murphy wrote:
> For a hot-pluggable bus where logical devices may share Stream IDs (like
> fsl-mc), this could happen:
>
> create device A
> iommu_probe_device(A)
> iommu_device_group(A) -> alloc group X
> create device B
> iommu_probe_device(B)
> iommu_device_group(A) -> lookup returns group X
> ...
> iommu_remove_device(A)
> delete device A
> create device C
> iommu_probe_device(C)
> iommu_device_group(C) -> use-after-free of A
>
> Preserving the logical behaviour here would probably look *something* like
> the mangled diff below, but I haven't thought it through 100%.

Yeah, I think you are right. How about just moving the loop which sets
s2crs[idx].group to arm_smmu_device_group()? In that case I can drop
this patch and leave the group pointer in place.

Regards,

Joerg

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