Re: [PATCHv2 1/2] mm/gup: fix omission of check on FOLL_LONGTERM in get_user_pages_fast()

[Ira Weiny]

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
>