On Mon, Jun 03, 2019 at 02:34:12PM +0800, Pingfan Liu wrote:
> As for FOLL_LONGTERM, it is checked in the slow path
> __gup_longterm_unlocked(). But it is not checked in the fast path, which
> means a possible leak of CMA page to longterm pinned requirement through
> this crack.
>
> Place a check in the fast path.
>
> Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> mm/gup.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index f173fcb..6fe2feb 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2196,6 +2196,29 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
> return ret;
> }
>
> +#if defined(CONFIG_CMA)
> +static inline int reject_cma_pages(int nr_pinned, unsigned int gup_flags,
> + struct page **pages)
> +{
> + if (unlikely(gup_flags & FOLL_LONGTERM)) {
> + int i = 0;
> +
> + for (i = 0; i < nr_pinned; i++)
> + if (is_migrate_cma_page(pages[i])) {
> + put_user_pages(pages + i, nr_pinned - i);
> + return i;
> + }
> + }
> + return nr_pinned;
> +}
> +#else
> +static inline int reject_cma_pages(int nr_pinned, unsigned int gup_flags,
> + struct page **pages)
> +{
> + return nr_pinned;
> +}
> +#endif
> +
> /**
> * get_user_pages_fast() - pin user pages in memory
> * @start: starting user address
> @@ -2236,6 +2259,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
> ret = nr;
> }
>
> + nr = reject_cma_pages(nr, gup_flags, pages);
> if (nr < nr_pages) {
> /* Try to get the remaining pages with get_user_pages */
> start += nr << PAGE_SHIFT;
> --
> 2.7.5
>
