block: loop: fix filesystem corruption in case of aio/dio

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@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org (4.5)
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 423f4ca7d712dda6f012c32954f19c9ce3af9d9c..80cf8add46ff3667d896fca88aaea3fbf338ad27 100644 (file)
--- 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;