From ebed48460be5abd86d9a24fa7c66378e58109f30 Mon Sep 17 00:00:00 2001
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Mon, 31 Oct 2011 17:08:22 -0700
Subject: [PATCH] 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>
---
mm/mremap.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/mm/mremap.c b/mm/mremap.c
index 506fa44403df5..195e866568e04 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;
--
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