Re: [PATCH v1 01/16] iommufd/viommu: Add IOMMUFD_OBJ_VIOMMU and IOMMU_VIOMMU_ALLOC ioctl

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Aug 15, 2024 at 03:11:17PM -0300, Jason Gunthorpe wrote:
> On Wed, Aug 07, 2024 at 01:10:42PM -0700, Nicolin Chen wrote:
> 
> > +int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd)
> > +{
> > +	struct iommu_viommu_alloc *cmd = ucmd->cmd;
> > +	struct iommufd_hwpt_paging *hwpt_paging;
> > +	struct iommufd_viommu *viommu;
> > +	struct iommufd_device *idev;
> > +	int rc;
> > +
> > +	if (cmd->flags)
> > +		return -EOPNOTSUPP;
> > +
> > +	idev = iommufd_get_device(ucmd, cmd->dev_id);
> > +	if (IS_ERR(idev))
> > +		return PTR_ERR(idev);
> > +
> > +	hwpt_paging = iommufd_get_hwpt_paging(ucmd, cmd->hwpt_id);
> > +	if (IS_ERR(hwpt_paging)) {
> > +		rc = PTR_ERR(hwpt_paging);
> > +		goto out_put_idev;
> > +	}
> > +
> > +	if (!hwpt_paging->nest_parent) {
> > +		rc = -EINVAL;
> > +		goto out_put_hwpt;
> > +	}
> > +
> > +	if (cmd->type != IOMMU_VIOMMU_TYPE_DEFAULT) {
> > +		rc = -EOPNOTSUPP;
> > +		goto out_put_hwpt;
> > +	}
> > +
> > +	viommu = iommufd_object_alloc(ucmd->ictx, viommu, IOMMUFD_OBJ_VIOMMU);
> > +	if (IS_ERR(viommu)) {
> > +		rc = PTR_ERR(viommu);
> > +		goto out_put_hwpt;
> > +	}
> > +
> > +	viommu->type = cmd->type;
> > +	viommu->ictx = ucmd->ictx;
> > +	viommu->hwpt = hwpt_paging;
> > +	viommu->iommu_dev = idev->dev->iommu->iommu_dev;
> 
> Pedantically this is troublesome because we don't have any lifetime
> control on this pointer. 
> 
> iommu unplug is fairly troubled on real HW, but the selftest does do
> it.
> 
> At least for this series the value isn't used so lets remove it.

I recall one of my local versions had a validation using that, but
not that crucial either. Will drop it.

> I don't have an easy solution in mind though later as surely we will
> need this when we start to create more iommu bound objects. I'm pretty
> sure syzkaller would eventually find such a UAF using the iommufd
> selftest framework.

Would adding a user count in struct iommu_device help?

Thanks
Nicolin