[PATCH 4.5 003/200] block: loop: fix filesystem corruption in case of aio/dio

From: Greg Kroah-Hartman
Date: Mon May 02 2016 - 20:34:25 EST

4.5-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>

drivers/block/loop.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -488,6 +488,12 @@ static int lo_rw_aio(struct loop_device
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;