Re: [PATCH v3 15/15] iommufd: Add a selftest

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Nov 01, 2022 at 01:32:23PM -0700, Nicolin Chen wrote:
> On Tue, Oct 25, 2022 at 03:12:24PM -0300, Jason Gunthorpe wrote:
>  
> > diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
> 
> > +static inline struct iommufd_hw_pagetable *
> > +get_md_pagetable(struct iommufd_ucmd *ucmd, u32 mockpt_id,
> > +		 struct mock_iommu_domain **mock)
> > +{
> > +	struct iommufd_hw_pagetable *hwpt;
> > +	struct iommufd_object *obj;
> > +
> > +	obj = iommufd_get_object(ucmd->ictx, mockpt_id,
> > +				 IOMMUFD_OBJ_HW_PAGETABLE);
> > +	if (IS_ERR(obj))
> > +		return ERR_CAST(obj);
> > +	hwpt = container_of(obj, struct iommufd_hw_pagetable, obj);
> > +	if (hwpt->domain->ops != mock_ops.default_domain_ops) {
> > +		return ERR_PTR(-EINVAL);
> > +		iommufd_put_object(&hwpt->obj);
> 
> Coverity reports that return is placed before iommufd_put_object.

I'm surprised no compiler warned about this!

> 
> > +static int iommufd_test_access_pages(struct iommufd_ucmd *ucmd,
> > +				     unsigned int access_id, unsigned long iova,
> > +				     size_t length, void __user *uptr,
> > +				     u32 flags)
> > +{
> > +	struct iommu_test_cmd *cmd = ucmd->cmd;
> > +	struct selftest_access_item *item;
> > +	struct selftest_access *staccess;
> > +	struct page **pages;
> > +	size_t npages;
> > +	int rc;
> > +
> > +	if (flags & ~MOCK_FLAGS_ACCESS_WRITE)
> > +		return -EOPNOTSUPP;
> > +
> > +	staccess = iommufd_access_get(access_id);
> > +	if (IS_ERR(staccess))
> > +		return PTR_ERR(staccess);
> > +
> > +	npages = (ALIGN(iova + length, PAGE_SIZE) -
> > +		  ALIGN_DOWN(iova, PAGE_SIZE)) /
> > +		 PAGE_SIZE;
> > +	pages = kvcalloc(npages, sizeof(*pages), GFP_KERNEL_ACCOUNT);
> > +	if (!pages) {
> > +		rc = -ENOMEM;
> > +		goto out_put;
> > +	}
> > +
> > +	rc = iommufd_access_pin_pages(staccess->access, iova, length, pages,
> > +				      flags & MOCK_FLAGS_ACCESS_WRITE);
> > +	if (rc)
> > +		goto out_free_pages;
> > +
> > +	rc = iommufd_test_check_pages(
> > +		uptr - (iova - ALIGN_DOWN(iova, PAGE_SIZE)), pages, npages);
> > +	if (rc)
> > +		goto out_unaccess;
> > +
> > +	item = kzalloc(sizeof(*item), GFP_KERNEL_ACCOUNT);
> > +	if (!item) {
> > +		rc = -ENOMEM;
> > +		goto out_unaccess;
> > +	}
> > +
> > +	item->iova = iova;
> > +	item->length = length;
> > +	spin_lock(&staccess->lock);
> > +	item->id = staccess->next_id++;
> > +	list_add_tail(&item->items_elm, &staccess->items);
> > +	spin_unlock(&staccess->lock);
> > +
> > +	cmd->access_pages.out_access_item_id = item->id;
> > +	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
> > +	if (rc)
> > +		goto out_free_item;
> > +	goto out_free_pages;
> > +
> > +out_free_item:
> > +	spin_lock(&staccess->lock);
> > +	list_del(&item->items_elm);
> > +	spin_unlock(&staccess->lock);
> > +	kfree(item);
> > +out_unaccess:
> > +	iommufd_access_unpin_pages(staccess->access, iova, length);
> > +out_free_pages:
> > +	kvfree(pages);
> 
> Coverity reports a double free here, call trace:
> 
> [jumped from] rc = iommufd_access_pin_pages(..., pages, ...);
> 	[in which] iopt_pages_add_access(..., out_pages, ...);
> 		[then] iopt_pages_fill_xarray(..., out_pages);
> 			[then] iopt_pages_fill_from_mm(..., out_pages);
> 				[then] user->upages = out_pages + ...;
> 				       pfn_reader_user_pin(user, ...);
> 					[then] kfree(user->upages);
> 					       return -EFAULT;
> 
> Should be the same potential issue in the other email.

Yes, looks like

Thanks,
Jason