On Tue, Jun 22, 2021 at 10:03:00PM +0300, Dan Carpenter wrote:
> The get_user_pages_remote() function returns a long type, but we are
> using "unsigned long i;" as the list iterator. If "npages" is -ENOMEM,
> the comparison "i < npages" is type promoted and "npages" becomes a very
> high positive value. The loop will then iterate until the kernel
> crashes.
>
> There are two ways to fix this. Declare "i" as a long type or add an
> explicit check for get_user_pages_remote() error returns. Either
> approach will work so let's do both.
>
> Fixes: fa1e686e5f53 ("mm: device exclusive memory access")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
> mm/rmap.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index e5210dde0c4d..fb5c59b95826 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -2187,11 +2187,14 @@ int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
> void *owner)
> {
> long npages = (end - start) >> PAGE_SHIFT;
> - unsigned long i;
> + long i;
>
> npages = get_user_pages_remote(mm, start, npages,
> FOLL_GET | FOLL_WRITE | FOLL_SPLIT_PMD,
> pages, NULL, NULL);
> + if (npages < 0)
> + return npages;
> +
> for (i = 0; i < npages; i++, start += PAGE_SIZE) {
> if (!trylock_page(pages[i])) {
> put_page(pages[i]);
> --
> 2.30.2
Ouch.. The check should be enough, imho; looping over an long seems a tiny
little bit odd, but still looks okay.
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Thanks,
--
Peter Xu
