From: Andrea Arcangeli <aarcange@redhat.com>
Date: Tue, 1 Nov 2011 00:08:22 +0000 (-0700)
Subject: mremap: check for overflow using deltas
X-Git-Tag: upstream/snapshot3+hdmi~8868^2~90
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=ebed48460be5abd86d9a24fa7c66378e58109f30;p=platform%2Fadaptation%2Frenesas_rcar%2Frenesas_kernel.git

mremap: check for overflow using deltas

Using "- 1" relies on the old_end to be page aligned and PAGE_SIZE > 1,
those are reasonable requirements but the check remains obscure and it
looks more like an off by one error than an overflow check.  This I feel
will improve readability.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/mremap.c b/mm/mremap.c
index 506fa44..195e866 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -141,9 +141,10 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 		cond_resched();
 		next = (old_addr + PMD_SIZE) & PMD_MASK;
-		if (next - 1 > old_end)
-			next = old_end;
+		/* even if next overflowed, extent below will be ok */
 		extent = next - old_addr;
+		if (extent > old_end - old_addr)
+			extent = old_end - old_addr;
 		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 		if (!old_pmd)
 			continue;