md: don't write more than is required of the last page of a bitmap

It is possible that real data or metadata follows the bitmap without full page
alignment.

So limit the last write to be only the required number of bytes, rounded up to
the hard sector size of the device.

Signed-off-by: Neil Brown <neilb@suse.de>
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, 12 insertions, 5 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 5a4a74c1097c..9620d452d030 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -255,19 +255,25 @@ static struct page *read_sb_page(mddev_t *mddev, long offset, unsigned long inde
 
 }
 
-static int write_sb_page(mddev_t *mddev, long offset, struct page *page, int wait)
+static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 {
         mdk_rdev_t *rdev;
         struct list_head *tmp;
+        mddev_t *mddev = bitmap->mddev;
 
         ITERATE_RDEV(mddev, rdev, tmp)
                 if (test_bit(In_sync, &rdev->flags)
-                    && !test_bit(Faulty, &rdev->flags))
+                    && !test_bit(Faulty, &rdev->flags)) {
+                        int size = PAGE_SIZE;
+                        if (page->index == bitmap->file_pages-1)
+                                size = roundup(bitmap->last_page_size,
+                                               bdev_hardsect_size(rdev->bdev));
                         md_super_write(mddev, rdev,
-                                       (rdev->sb_offset<<1) + offset
+                                       (rdev->sb_offset<<1) + bitmap->offset
                                        + page->index * (PAGE_SIZE/512),
-                                       PAGE_SIZE,
+                                       size,
                                        page);
+                }
 
         if (wait)
                 md_super_wait(mddev);
@@ -282,7 +288,7 @@ static int write_page(struct bitmap *bitmap, struct page *page, int wait)
         struct buffer_head *bh;
 
         if (bitmap->file == NULL)
-                return write_sb_page(bitmap->mddev, bitmap->offset, page, wait);
+                return write_sb_page(bitmap, page, wait);
 
         bh = page_buffers(page);
 
@@ -923,6 +929,7 @@ static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
                         }
 
                         bitmap->filemap[bitmap->file_pages++] = page;
+                        bitmap->last_page_size = count;
                 }
                 paddr = kmap_atomic(page, KM_USER0);
                 if (bitmap->flags & BITMAP_HOSTENDIAN)