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

Li Lingfeng
2025-10-22T08:21:44Z

Hi,

在 2025/10/22 16:10, Greg KH 写道:
> On Wed, Oct 22, 2025 at 04:01:04PM +0800, Li Lingfeng wrote:
>> 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?
> Those tags come directly from the original commit.
Thanks for the clarification. Since the patch has already been merged into
the mainline tree, we can't update the commit there. I was just wondering
if it would be acceptable to add an additional “Fixes” tag when applying
it to the stable branch, before merging.

Thanks,
Lingfeng.

>