[ Upstream commit 72ce11ddfa4e9e1879103581a60b7e34547eaa0a ]

In null_init, null_add_dev(dev) is called.
In null_add_dev, it calls null_free_zoned_dev(dev) to free dev->zones
via kvfree(dev->zones) in out_cleanup_zone branch and returns err.
Then null_init accept the err code and then calls null_free_dev(dev).

But in null_free_dev(dev), dev->zones is freed again by
null_free_zoned_dev().

My patch set dev->zones to NULL in null_free_zoned_dev() after
kvfree(dev->zones) is called, to avoid the double free.

Fixes: 2984c8684f962 ("nullb: factor disk parameters")
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Link: https://lore.kernel.org/r/20210426143229.7374-1-lyl2019@mail.ustc.edu.cn
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

[ Upstream commit de3510e52b0a398261271455562458003b8eea62 ]

Memory backed or zoned null block devices may generate actual request
timeout errors due to the submission path being blocked on memory
allocation or zone locking. Unlike fake timeouts or injected timeouts,
the request submission path will call blk_mq_complete_request() or
blk_mq_end_request() for these real timeout errors, causing a double
completion and use after free situation as the block layer timeout
handler executes blk_mq_rq_timed_out() and __blk_mq_free_request() in
blk_mq_check_expired(). This problem often triggers a NULL pointer
dereference such as:

BUG: kernel NULL pointer dereference, address: 0000000000000050
RIP: 0010:blk_mq_sched_mark_restart_hctx+0x5/0x20
...
Call Trace:
  dd_finish_request+0x56/0x80
  blk_mq_free_request+0x37/0x130
  null_handle_cmd+0xbf/0x250 [null_blk]
  ? null_queue_rq+0x67/0xd0 [null_blk]
  blk_mq_dispatch_rq_list+0x122/0x850
  __blk_mq_do_dispatch_sched+0xbb/0x2c0
  __blk_mq_sched_dispatch_requests+0x13d/0x190
  blk_mq_sched_dispatch_requests+0x30/0x60
  __blk_mq_run_hw_queue+0x49/0x90
  process_one_work+0x26c/0x580
  worker_thread+0x55/0x3c0
  ? process_one_work+0x580/0x580
  kthread+0x134/0x150
  ? kthread_create_worker_on_cpu+0x70/0x70
  ret_from_fork+0x1f/0x30

This problem very often triggers when running the full btrfs xfstests
on a memory-backed zoned null block device in a VM with limited amount
of memory.

Avoid this by executing blk_mq_complete_request() in null_timeout_rq()
only for commands that are marked for a fake timeout completion using
the fake_timeout boolean in struct null_cmd. For timeout errors injected
through debugfs, the timeout handler will execute
blk_mq_complete_request()i as before. This is safe as the submission
path does not execute complete requests in this case.

In null_timeout_rq(), also make sure to set the command error field to
BLK_STS_TIMEOUT and to propagate this error through to the request
completion.

Reported-by: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Tested-by: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Reviewed-by: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210331225244.126426-1-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

To avoid potential compilation problems, replaced the badly written
MB_TO_SECTS() macro (missing parenthesis around the argument use) with
the inline function mb_to_sects(). And while at it, simplify the
calculation of the total number of zones of the device using the
round_up() macro.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Move null_blk driver code into the new sub-directory
drivers/block/null_blk.

Suggested-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>