From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
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
readibility.
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
diff --git a/mm/mremap.c b/mm/mremap.c
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -141,9 +141,10 @@ unsigned long move_page_tables(struct vm
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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