Re: [PATCH 5.10.y] dm: fix NULL pointer dereference in __dm_suspend()

Li Lingfeng
2025-10-22T08:01:07Z

Hi,

在 2025/10/14 11:03, Sasha Levin 写道:
> From: Zheng Qixing <zhengqixing@huawei.com>
>
> [ Upstream commit 8d33a030c566e1f105cd5bf27f37940b6367f3be ]
>
> There is a race condition between dm device suspend and table load that
> can lead to null pointer dereference. The issue occurs when suspend is
> invoked before table load completes:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000054
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 6 PID: 6798 Comm: dmsetup Not tainted 6.6.0-g7e52f5f0ca9b #62
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
> RIP: 0010:blk_mq_wait_quiesce_done+0x0/0x50
> Call Trace:
> <TASK>
> blk_mq_quiesce_queue+0x2c/0x50
> dm_stop_queue+0xd/0x20
> __dm_suspend+0x130/0x330
> dm_suspend+0x11a/0x180
> dev_suspend+0x27e/0x560
> ctl_ioctl+0x4cf/0x850
> dm_ctl_ioctl+0xd/0x20
> vfs_ioctl+0x1d/0x50
> __se_sys_ioctl+0x9b/0xc0
> __x64_sys_ioctl+0x19/0x30
> x64_sys_call+0x2c4a/0x4620
> do_syscall_64+0x9e/0x1b0
>
> The issue can be triggered as below:
>
> T1 T2
> dm_suspend table_load
> __dm_suspend dm_setup_md_queue
> dm_mq_init_request_queue
> blk_mq_init_allocated_queue
> => q->mq_ops = set->ops; (1)
> dm_stop_queue / dm_wait_for_completion
> => q->tag_set NULL pointer! (2)
> => q->tag_set = set; (3)
>
> Fix this by checking if a valid table (map) exists before performing
> request-based suspend and waiting for target I/O. When map is NULL,
> skip these table-dependent suspend steps.
>
> Even when map is NULL, no I/O can reach any target because there is
> no table loaded; I/O submitted in this state will fail early in the
> DM layer. Skipping the table-dependent suspend logic in this case
> is safe and avoids NULL pointer dereferences.
>
> Fixes: c4576aed8d85 ("dm: fix request-based dm's use of dm_wait_for_completion")
> Cc: stable@vger.kernel.org
> Signed-off-by: Zheng Qixing <zhengqixing@huawei.com>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> [ omitted DMF_QUEUE_STOPPED flag setting and braces absent in 5.15 ]
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> drivers/md/dm.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 0868358a7a8d2..b51281ce15d4c 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -2457,7 +2457,7 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
> {
> bool do_lockfs = suspend_flags & DM_SUSPEND_LOCKFS_FLAG;
> bool noflush = suspend_flags & DM_SUSPEND_NOFLUSH_FLAG;
> - int r;
> + int r = 0;
>
> lockdep_assert_held(&md->suspend_lock);
>
> @@ -2509,7 +2509,7 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
> * Stop md->queue before flushing md->wq in case request-based
> * dm defers requests to md->wq from md->queue.
> */
> - if (dm_request_based(md))
> + if (map && dm_request_based(md))
> dm_stop_queue(md->queue);
>
It seems that before commit 80bd4a7aab4c ("blk-mq: move the srcu_struct
used for quiescing to the tagset") was merged, blk_mq_wait_quiesce_done()
would not attempt to access q->tag_set, so in dm_stop_queue() this kind
of race condition would not cause a null pointer dereference. The change
may not be necessary for 5.10, but adding it doesn’t appear to cause any
issues either.
> flush_workqueue(md->wq);
> @@ -2519,7 +2519,8 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
> * We call dm_wait_for_completion to wait for all existing requests
> * to finish.
> */
> - r = dm_wait_for_completion(md, task_state);
> + if (map)
> + r = dm_wait_for_completion(md, task_state);
The fix tag c4576aed8d85 ("dm: fix request-based dm's use of
dm_wait_for_completion") seems to correspond to the modification of
dm_wait_for_completion().
> if (!r)
> set_bit(dmf_suspended_flag, &md->flags);
>

Perhaps adding another fix tag would be more appropriate?

Thanks,
Lingfeng