Re: [PATCH 3/6] VT-d: don't leak domid mapping on error path

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Nov 12, 2021 at 02:45:14PM +0100, Jan Beulich wrote:
> On 12.11.2021 14:42, Roger Pau Monné wrote:
> > On Fri, Nov 12, 2021 at 10:48:43AM +0100, Jan Beulich wrote:
> >> While domain_context_mapping() invokes domain_context_unmap() in a sub-
> >> case of handling DEV_TYPE_PCI when encountering an error, thus avoiding
> >> a leak, individual calls to domain_context_mapping_one() aren't
> >> similarly covered. Such a leak might persist until domain destruction.
> >> Leverage that these cases can be recognized by pdev being non-NULL.
> > 
> > Would it help to place the domid cleanup in domain_context_unmap_one,
> > as that would then cover calls from domain_context_unmap and the
> > failure path in domain_context_mapping_one.
> 
> I don't think that would work (without further convolution), because of
> the up to 3 successive calls in DEV_TYPE_PCI handling. Cleanup may happen
> only on the first map's error path or after the last unmap.

Hm, I see. And AFAICT that's because some devices that get assigned to
a guest iommu context are not actually assigned to the guest (ie:
pdev->domain doesn't get set, neither the device is added to the
per-domain list), which makes them invisible to
any_pdev_behind_iommu.

I dislike that the domid is added in domain_context_mapping_one, while
the cleanup is not done in domain_context_unmap_one, and that some
devices context could be using the domain id without being assigned to
the domain.

Thanks, Roger.