mm: fix possible off-by-one in walk_pte_range()

After the loop in walk_pte_range() pte might point to the first address after
the pmd it walks.  The pte_unmap() is then applied to something bad.

Spotted by Roel Kluin and Andreas Schwab.

Signed-off-by: Johannes Weiner <hannes@saeurebad.de>
Cc: Roel Kluin <12o3l@tiscali.nl>
Cc: Andreas Schwab <schwab@suse.de>
Acked-by: Matt Mackall <mpm@selenic.com>
Acked-by: Mikael Pettersson <mikpe@it.uu.se>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 1cf1417ef8b7..0afd2387e507 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -9,11 +9,15 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
         int err = 0;
 
         pte = pte_offset_map(pmd, addr);
-        do {
+        for (;;) {
                 err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, private);
                 if (err)
                        break;
-        } while (pte++, addr += PAGE_SIZE, addr != end);
+                addr += PAGE_SIZE;
+                if (addr == end)
+                        break;
+                pte++;
+        }
 
         pte_unmap(pte);
         return err;