On Thu, Oct 28, 2021 at 8:06 AM Ding, Xuan <xuan.d...@intel.com> wrote:
> >> Partial unmap support was introduced in commit c13ca4e81cac, and with it
> >> was added a check that dereferenced the IOMMU type to determine
> >whether
> >> partial ummapping is supported for currently configured IOMMU type. In
> >> certain circumstances (such as when VFIO is supported, but no devices
> >> were bound to the VFIO driver), the IOMMU type pointer can be NULL.
> >>
> >> However, dereferencing of IOMMU type was guarded by access to the user
> >> maps list - that is, we were always checking the user map list first,
> >> and then, if we found a memory region that encloses the one we're trying
> >> to unmap, we would have performed the IOMMU type check.
> >>
> >> This ensured that the IOMMU type check will not cause any NULL pointer
> >> dereferences, because in order for an IOMMU type check to have been
> >> performed, there necessarily must have been at least one memory region
> >> that was previously mapped successfully, and that implies having a
> >> defined IOMMU type.
> >>
> >> When 56259f7fc010 was introduced, the IOMMU type check was moved to
> >> before we were traversing the user mem maps list, thereby introducing a
> >> potential NULL dereference, because the IOMMU type access was no longer
> >> guarded by the user mem maps list traversal.
> >>
> >> Fix the issue by moving the IOMMU type check to after the user mem maps
> >> traversal, thereby ensuring that by the time the check happens, the
> >> IOMMU type is always valid.
> >>
> >> Fixes: 56259f7fc010 ("vfio: allow partially unmapping adjacent memory")
> >> Cc: xuan.d...@intel.com
> >>
> >> Signed-off-by: Anatoly Burakov <anatoly.bura...@intel.com>
> >Reviewed-by: David Marchand <david.march...@redhat.com>
> Tested-by: Xuan Ding <xuan.d...@intel.com>Applied, thanks. -- David Marchand
