From:   Zhong Jinghua <zhongjinghua@huaweicloud.com>
To:     axboe@kernel.dk, code@siddh.me, willy@infradead.org
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        zhongjinghua@huawei.com, yi.zhang@huawei.com, yukuai3@huawei.com,
        houtao1@huawei.com
Subject: [PATCH-next v4] loop: loop_set_status_from_info() check before assignment
Date:   Tue, 21 Feb 2023 17:50:27 +0800
Message-Id: <20230221095027.3656193-1-zhongjinghua@huaweicloud.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Zhong Jinghua <zhongjinghua@huawei.com>

In loop_set_status_from_info(), lo->lo_offset and lo->lo_sizelimit should
be checked before reassignment, because if an overflow error occurs, the
original correct value will be changed to the wrong value, and it will not
be changed back.

More, the original patch did not solve the problem, the value was set and
ioctl returned an error, but the subsequent io used the value in the loop
driver, which still caused an alarm:

loop_handle_cmd
 do_req_filebacked
  loff_t pos = ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset;
  lo_rw_aio
   cmd->iocb.ki_pos = pos

Fixes: c490a0b5a4f3 ("loop: Check for overflow while configuring loop")
Signed-off-by: Zhong Jinghua <zhongjinghua@huawei.com>
---
 v2: Modify note: overflowing -> overflow
 v3: Modify commit message
 v4: Modify commit message
 drivers/block/loop.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1518a6423279..1b35cbd029c7 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -977,13 +977,13 @@ loop_set_status_from_info(struct loop_device *lo,
 		return -EINVAL;
 	}
 
+	/* Avoid assigning overflow values */
+	if (info->lo_offset > LLONG_MAX || info->lo_sizelimit > LLONG_MAX)
+		return -EOVERFLOW;
+
 	lo->lo_offset = info->lo_offset;
 	lo->lo_sizelimit = info->lo_sizelimit;
 
-	/* loff_t vars have been assigned __u64 */
-	if (lo->lo_offset < 0 || lo->lo_sizelimit < 0)
-		return -EOVERFLOW;
-
 	memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE);
 	lo->lo_file_name[LO_NAME_SIZE-1] = 0;
 	lo->lo_flags = info->lo_flags;
-- 
2.31.1