NOMMU: Fix __get_user_pages() to pin last page on offset buffers

Fix __get_user_pages() to make it pin the last page on a buffer that doesn't
begin at the start of a page, but is a multiple of PAGE_SIZE in size.

The problem is that __get_user_pages() advances the pointer too much when it
iterates to the next page if the page it's currently looking at isn't used from
the first byte.  This can cause the end of a short VMA to be reached
prematurely, resulting in the last page being lost.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/nommu.c b/mm/nommu.c
index 089982f5a4cfb02b68dbdb4c7c5a6975252b16ef..63fa17d121f027ca5c75f09eab994db346316d2b 100644 (file)
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -162,7 +162,7 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                }
                if (vmas)
                        vmas[i] = vma;
-               start += PAGE_SIZE;
+               start = (start + PAGE_SIZE) & PAGE_MASK;
        }
 
        return i;