[PATCH 4.4 002/163] block: loop: fix filesystem corruption in case of aio/dio

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ming Lei <ming.lei@xxxxxxxxxxxxx>

commit a7297a6a3a3322b054592e8e988981d2f5f29cc4 upstream.

Starting from commit e36f620428(block: split bios to max possible length),
block core starts to split bio in the middle of bvec.

Unfortunately loop dio/aio doesn't consider this situation, and
always treat 'iter.iov_offset' as zero. Then filesystem corruption
is observed.

This patch figures out the offset of the base bvevc via
'bio->bi_iter.bi_bvec_done' and fixes the issue by passing the offset
to iov iterator.

Fixes: e36f6204288088f (block: split bios to max possible length)
Cc: Keith Busch <keith.busch@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 423f4ca7d712..80cf8add46ff 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -488,6 +488,12 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 	bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
 	iov_iter_bvec(&iter, ITER_BVEC | rw, bvec,
 		      bio_segments(bio), blk_rq_bytes(cmd->rq));
+	/*
+	 * This bio may be started from the middle of the 'bvec'
+	 * because of bio splitting, so offset from the bvec must
+	 * be passed to iov iterator
+	 */
+	iter.iov_offset = bio->bi_iter.bi_bvec_done;
 
 	cmd->iocb.ki_pos = pos;
 	cmd->iocb.ki_filp = file;