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

From: Mel Gorman <redacted>
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/20210618125102.GU30378@techsingularity.net
Fixes: 0f87d9d30f21 ("mm/page_alloc: add an array-based interface to the bulk page allocator")
Signed-off-by: Mel Gorman <redacted>
Reported-by: Dan Carpenter <redacted>
Cc: Jesper Dangaard Brouer <redacted>
Cc: Vlastimil Babka <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- 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;

_