md: check that internal bitmap does not overlap other data

We current completely trust user-space to set up metadata describing an
consistant array. In particlar, that the metadata, data, and bitmap do not
overlap.

But userspace can be buggy, and it is better to report an error than corrupt
data. So put in some appropriate checks.

Signed-off-by: Neil Brown <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/md/bitmap.c

···
 			if (page->index == bitmap->file_pages-1)
 				size = roundup(bitmap->last_page_size,
 					       bdev_hardsect_size(rdev->bdev));
+			/* Just make sure we aren't corrupting data or
+			 * metadata
+			 */
+			if (bitmap->offset < 0) {
+				/* DATA  BITMAP METADATA  */
+				if (bitmap->offset
+				    + page->index * (PAGE_SIZE/512)
+				    + size/512 > 0)
+					/* bitmap runs in to metadata */
+					return -EINVAL;
+				if (rdev->data_offset + mddev->size*2
+				    > rdev->sb_offset*2 + bitmap->offset)
+					/* data runs in to bitmap */
+					return -EINVAL;
+			} else if (rdev->sb_offset*2 < rdev->data_offset) {
+				/* METADATA BITMAP DATA */
+				if (rdev->sb_offset*2
+				    + bitmap->offset
+				    + page->index*(PAGE_SIZE/512) + size/512
+				    > rdev->data_offset)
+					/* bitmap runs in to data */
+					return -EINVAL;
+			} else {
+				/* DATA METADATA BITMAP - no problems */
+			}
 			md_super_write(mddev, rdev,
 				       (rdev->sb_offset<<1) + bitmap->offset
 				       + page->index * (PAGE_SIZE/512),
···
 {
 	struct buffer_head *bh;
 
-	if (bitmap->file == NULL)
-		return write_sb_page(bitmap, page, wait);
+	if (bitmap->file == NULL) {
+		switch (write_sb_page(bitmap, page, wait)) {
+		case -EINVAL:
+			bitmap->flags |= BITMAP_WRITE_ERROR;
+			return -EIO;
+		}
+		return 0;
+	}
 
 	bh = page_buffers(page);
 

drivers/md/md.c

···
 	 * Drop all container device buffers, from now on
 	 * the only valid external interface is through the md
 	 * device.
-	 * Also find largest hardsector size
 	 */
 	ITERATE_RDEV(mddev,rdev,tmp) {
 		if (test_bit(Faulty, &rdev->flags))
 			continue;
 		sync_blockdev(rdev->bdev);
 		invalidate_bdev(rdev->bdev);
+
+		/* perform some consistency tests on the device.
+		 * We don't want the data to overlap the metadata,
+		 * Internal Bitmap issues has handled elsewhere.
+		 */
+		if (rdev->data_offset < rdev->sb_offset) {
+			if (mddev->size &&
+			    rdev->data_offset + mddev->size*2
+			    > rdev->sb_offset*2) {
+				printk("md: %s: data overlaps metadata\n",
+				       mdname(mddev));
+				return -EINVAL;
+			}
+		} else {
+			if (rdev->sb_offset*2 + rdev->sb_size/512
+			    > rdev->data_offset) {
+				printk("md: %s: metadata overlaps data\n",
+				       mdname(mddev));
+				return -EINVAL;
+			}
+		}
 	}
 
 	md_probe(mddev->unit, NULL, NULL);