Re: [PATCH] iommu: Avoid NULL group dereference

Joerg Roedel
2017-08-17T15:41:01Z

On Thu, Aug 17, 2017 at 11:40:08AM +0100, Robin Murphy wrote:
> The recently-removed FIXME in iommu_get_domain_for_dev() turns out to
> have been a little misleading, since that check is still worthwhile even
> when groups *are* universal. We have a few IOMMU-aware drivers which
> only care whether their device is already attached to an existing domain
> or not, for which the previous behaviour of iommu_get_domain_for_dev()
> was ideal, and who now crash if their device does not have an IOMMU.
>
> With IOMMU groups now serving as a reliable indicator of whether a
> device has an IOMMU or not (barring false-positives from VFIO no-IOMMU
> mode), drivers could arguably do this:
>
> group = iommu_group_get(dev);
> if (group) {
> domain = iommu_get_domain_for_dev(dev);
> iommu_group_put(group);
> }

Okay, so just to check I got it right: Drivers do the above to check
whether a device is managed by an IOMMU, and that crashes now because
the 'group == NULL' check was removed?

Regards,

Joerg