[22/24] mm/page_alloc: do bulk array bounds check after checking populated elements

Commit Message

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

From: Mel Gorman <[e-mail]>
Subject: mm/page_alloc: do bulk array bounds check after checking populated elements

Dan Carpenter reported the following

  The patch 0f87d9d30f21: "mm/page_alloc: add an array-based interface
  to the bulk page allocator" from Apr 29, 2021, leads to the following
  static checker warning:

        mm/page_alloc.c:5338 __alloc_pages_bulk()
        warn: potentially one past the end of array 'page_array[nr_populated]'

The problem can occur if an array is passed in that is fully populated. 
That potentially ends up allocating a single page and storing it past the
end of the array.  This patch returns 0 if the array is fully populated.

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: Mel Gorman <[e-mail]>
Reported-by: Dan Carpenter <[e-mail]>
Cc: Jesper Dangaard Brouer <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_alloc.c |    4 ++++
 1 file changed, 4 insertions(+)

Patch

--- a/mm/page_alloc.c~mm-page_alloc-do-bulk-array-bounds-check-after-checking-populated-elements
+++ a/mm/page_alloc.c
@@ -5056,6 +5056,10 @@  unsigned long __alloc_pages_bulk(gfp_t g
 	while (page_array && nr_populated < nr_pages && page_array[nr_populated])
 		nr_populated++;
 
+	/* Already populated array? */
+	if (unlikely(page_array && nr_pages - nr_populated == 0))
+		return 0;
+
 	/* Use the single page allocator for one page. */
 	if (nr_pages - nr_populated == 1)
 		goto failed;