[PATCH] fix loop driver for large BIOs

Fix the loop driver for loop-on-blockdev setups.

When presented with a multipage BIO, loop_make_request overindexes the
first page and corrupts kernel memory.  Fix it to walk the individual
pages.

BTW, I suspect the IV handling in loop may be incorrect for multipage
BIOs.  Should we not be recalculating the IV for each page in the BIOs,
or incrementing the offset by the size of the preceding pages, or such?

drivers/block/loop.c

@@ -168,6 +168,15 @@ static void figure_loop_size(struct loop_device *lo)
 					
 }
 
+static inline int lo_do_transfer(struct loop_device *lo, int cmd, char *rbuf,
+				 char *lbuf, int size, int rblock)
+{
+	if (!lo->transfer)
+		return 0;
+
+	return lo->transfer(lo, cmd, rbuf, lbuf, size, rblock);
+}
+
 static int
 do_lo_send(struct loop_device *lo, struct bio_vec *bvec, int bsize, loff_t pos)
 {
@@ -454,20 +463,43 @@ static struct bio *loop_get_buffer(struct loop_device *lo, struct bio *rbh)
 out_bh:
 	bio->bi_sector = rbh->bi_sector + (lo->lo_offset >> 9);
 	bio->bi_rw = rbh->bi_rw;
-	spin_lock_irq(&lo->lo_lock);
 	bio->bi_bdev = lo->lo_device;
-	spin_unlock_irq(&lo->lo_lock);
 
 	return bio;
 }
 
-static int loop_make_request(request_queue_t *q, struct bio *rbh)
+static int
+bio_transfer(struct loop_device *lo, struct bio *to_bio,
+			      struct bio *from_bio)
 {
-	struct bio *bh = NULL;
+	unsigned long IV = loop_get_iv(lo, from_bio->bi_sector);
+	struct bio_vec *from_bvec, *to_bvec;
+	char *vto, *vfrom;
+	int ret = 0, i;
+
+	__bio_for_each_segment(from_bvec, from_bio, i, 0) {
+		to_bvec = &to_bio->bi_io_vec[i];
+
+		kmap(from_bvec->bv_page);
+		kmap(to_bvec->bv_page);
+		vfrom = page_address(from_bvec->bv_page) + from_bvec->bv_offset;
+		vto = page_address(to_bvec->bv_page) + to_bvec->bv_offset;
+		ret |= lo_do_transfer(lo, bio_data_dir(to_bio), vto, vfrom,
+					from_bvec->bv_len, IV);
+		kunmap(from_bvec->bv_page);
+		kunmap(to_bvec->bv_page);
+	}
+
+	return ret;
+}
+		
+static int loop_make_request(request_queue_t *q, struct bio *old_bio)
+{
+	struct bio *new_bio = NULL;
 	struct loop_device *lo;
 	unsigned long IV;
-	int rw = bio_rw(rbh);
-	int unit = minor(to_kdev_t(rbh->bi_bdev->bd_dev));
+	int rw = bio_rw(old_bio);
+	int unit = minor(to_kdev_t(old_bio->bi_bdev->bd_dev));
 
 	if (unit >= max_loop)
 		goto out;
@@ -489,60 +521,41 @@ static int loop_make_request(request_queue_t *q, struct bio *rbh)
 		goto err;
 	}
 
-	blk_queue_bounce(q, &rbh);
+	blk_queue_bounce(q, &old_bio);
 
 	/*
 	 * file backed, queue for loop_thread to handle
 	 */
 	if (lo->lo_flags & LO_FLAGS_DO_BMAP) {
-		loop_add_bio(lo, rbh);
+		loop_add_bio(lo, old_bio);
 		return 0;
 	}
 
 	/*
 	 * piggy old buffer on original, and submit for I/O
 	 */
-	bh = loop_get_buffer(lo, rbh);
-	IV = loop_get_iv(lo, rbh->bi_sector);
+	new_bio = loop_get_buffer(lo, old_bio);
+	IV = loop_get_iv(lo, old_bio->bi_sector);
 	if (rw == WRITE) {
-		if (lo_do_transfer(lo, WRITE, bio_data(bh), bio_data(rbh),
-				   bh->bi_size, IV))
+		if (bio_transfer(lo, new_bio, old_bio))
 			goto err;
 	}
 
-	generic_make_request(bh);
+	generic_make_request(new_bio);
 	return 0;
 
 err:
 	if (atomic_dec_and_test(&lo->lo_pending))
 		up(&lo->lo_bh_mutex);
-	loop_put_buffer(bh);
+	loop_put_buffer(new_bio);
 out:
-	bio_io_error(rbh);
+	bio_io_error(old_bio);
 	return 0;
 inactive:
 	spin_unlock_irq(&lo->lo_lock);
 	goto out;
 }
 
-static int do_bio_blockbacked(struct loop_device *lo, struct bio *bio,
-			      struct bio *rbh)
-{
-	unsigned long IV = loop_get_iv(lo, rbh->bi_sector);
-	struct bio_vec *from;
-	char *vto, *vfrom;
-	int ret = 0, i;
-
-	bio_for_each_segment(from, rbh, i) {
-		vfrom = page_address(from->bv_page) + from->bv_offset;
-		vto = page_address(bio->bi_io_vec[i].bv_page) + bio->bi_io_vec[i].bv_offset;
-		ret |= lo_do_transfer(lo, bio_data_dir(bio), vto, vfrom,
-					from->bv_len, IV);
-	}
-
-	return ret;
-}
-
 static inline void loop_handle_bio(struct loop_device *lo, struct bio *bio)
 {
 	int ret;
@@ -556,7 +569,7 @@ static inline void loop_handle_bio(struct loop_device *lo, struct bio *bio)
 	} else {
 		struct bio *rbh = bio->bi_private;
 
-		ret = do_bio_blockbacked(lo, bio, rbh);
+		ret = bio_transfer(lo, bio, rbh);
 
 		bio_endio(rbh, !ret);
 		loop_put_buffer(bio);
@@ -588,10 +601,8 @@ static int loop_thread(void *data)
 
 	set_user_nice(current, -20);
 
-	spin_lock_irq(&lo->lo_lock);
 	lo->lo_state = Lo_bound;
 	atomic_inc(&lo->lo_pending);
-	spin_unlock_irq(&lo->lo_lock);
 
 	/*
 	 * up sem, we are running

include/linux/loop.h

@@ -62,14 +62,6 @@ typedef	int (* transfer_proc_t)(struct loop_device *, int cmd,
 				char *raw_buf, char *loop_buf, int size,
 				int real_block);
 
-static inline int lo_do_transfer(struct loop_device *lo, int cmd, char *rbuf,
-				 char *lbuf, int size, int rblock)
-{
-	if (!lo->transfer)
-		return 0;
-
-	return lo->transfer(lo, cmd, rbuf, lbuf, size, rblock);
-}
 #endif /* __KERNEL__ */
 
 /*