From: Alex Williamson alex.williamson@redhat.com
commit 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4 upstream.
There's currently a reference count leak on the zero page. We increment the reference via pin_user_pages_remote(), but the page is later handled as an invalid/reserved page, therefore it's not accounted against the user and not unpinned by our put_pfn().
Introducing special zero page handling in put_pfn() would resolve the leak, but without accounting of the zero page, a single user could still create enough mappings to generate a reference count overflow.
The zero page is always resident, so for our purposes there's no reason to keep it pinned. Therefore, add a loop to walk pages returned from pin_user_pages_remote() and unpin any zero pages.
Cc: stable@vger.kernel.org Reported-by: Luboslav Pivarc lpivarc@redhat.com Reviewed-by: David Hildenbrand david@redhat.com Link: https://lore.kernel.org/r/166182871735.3518559.8884121293045337358.stgit@ome... Signed-off-by: Alex Williamson alex.williamson@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/vfio/vfio_iommu_type1.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
--- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -561,6 +561,18 @@ static int vaddr_get_pfns(struct mm_stru ret = pin_user_pages_remote(mm, vaddr, npages, flags | FOLL_LONGTERM, pages, NULL, NULL); if (ret > 0) { + int i; + + /* + * The zero page is always resident, we don't need to pin it + * and it falls into our invalid/reserved test so we don't + * unpin in put_pfn(). Unpin all zero pages in the batch here. + */ + for (i = 0 ; i < ret; i++) { + if (unlikely(is_zero_pfn(page_to_pfn(pages[i])))) + unpin_user_page(pages[i]); + } + *pfn = page_to_pfn(pages[0]); goto done; }