Author: Hugh Dickins <hughd@google.com>
Date: Mon, 19 Jun 2017 21:40:56 -0700
Description: mm: Guard against under-sized gap in unmapped_area{,_topdown}()
Origin: https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1426125.html

--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1817,7 +1817,8 @@ unsigned long unmapped_area(struct vm_un
 		/* Check if current node has a suitable gap */
 		if (gap_start > high_limit)
 			return -ENOMEM;
-		if (gap_end >= low_limit && gap_end - gap_start >= length)
+		if (gap_end >= low_limit &&
+		    gap_end > gap_start && gap_end - gap_start >= length)
 			goto found;
 
 		/* Visit right subtree if it looks promising */
@@ -1920,7 +1921,8 @@ unsigned long unmapped_area_topdown(stru
 		gap_end = vm_start_gap(vma);
 		if (gap_end < low_limit)
 			return -ENOMEM;
-		if (gap_start <= high_limit && gap_end - gap_start >= length)
+		if (gap_start <= high_limit &&
+		    gap_end > gap_start && gap_end - gap_start >= length)
 			goto found;
 
 		/* Visit left subtree if it looks promising */