[21/24] mm/page_alloc: __alloc_pages_bulk(): do bounds check before accessing array

Commit Message

Andrew Morton June 25, 2021, 1:40 a.m. UTC

From: Rasmus Villemoes <[e-mail]>
Subject: mm/page_alloc: __alloc_pages_bulk(): do bounds check before accessing array

In the event that somebody would call this with an already fully populated
page_array, the last loop iteration would do an access beyond the end of
page_array.

It's of course extremely unlikely that would ever be done, but this
triggers my internal static analyzer.  Also, if it really is not supposed
to be invoked this way (i.e., with no NULL entries in page_array), the
nr_populated<nr_pages check could simply be removed instead.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 0f87d9d30f21 ("mm/page_alloc: add an array-based interface to the bulk page allocator")
Signed-off-by: Rasmus Villemoes <[e-mail]>
Acked-by: Mel Gorman <[e-mail]>
Reviewed-by: Andrew Morton <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_alloc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

--- a/mm/page_alloc.c~mm-page_alloc-__alloc_pages_bulk-do-bounds-check-before-accessing-array
+++ a/mm/page_alloc.c
@@ -5053,7 +5053,7 @@  unsigned long __alloc_pages_bulk(gfp_t g
 	 * Skip populated array elements to determine if any pages need
 	 * to be allocated before disabling IRQs.
 	 */
-	while (page_array && page_array[nr_populated] && nr_populated < nr_pages)
+	while (page_array && nr_populated < nr_pages && page_array[nr_populated])
 		nr_populated++;
 
 	/* Use the single page allocator for one page. */