From ebed48460be5abd86d9a24fa7c66378e58109f30 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli 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 Acked-by: Johannes Weiner Acked-by: Mel Gorman Acked-by: Rik van Riel Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mremap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index 506fa44403df..195e866568e0 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;