loop: loop_set_status_from_info() check before assignment

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>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20230221095027.3656193-1-zhongjinghua@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 5f04235e4ff75f7cfe977827589a7029420d72a1..839373451c2b7dc8d2db845decfeca198fce0452 100644 (file)
--- 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;