linux-kernel - [PATCH] block: loop: fix filesystem corruption in case of aio/dio

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Message-Id: <1460717488-19796-1-git-send-email-ming.lei@canonical.com>
Date:	Fri, 15 Apr 2016 18:51:28 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org
Cc:	linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
	Ming Lei <ming.lei@...onical.com>,
	Keith Busch <keith.busch@...el.com>,
	Al Viro <viro@...iv.linux.org.uk>, stable@...r.kernel.org (4.5)
Subject: [PATCH] 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@...el.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: stable@...r.kernel.org (4.5)
Signed-off-by: Ming Lei <ming.lei@...onical.com>
---
 drivers/block/loop.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 7e5e27a..1fa8cc2 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;
-- 
1.9.1