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

Li Lingfeng
2025-10-22T09:10:39Z

在 2025/10/22 16:45, Greg KH 写道:
> On Wed, Oct 22, 2025 at 04:21:33PM +0800, Li Lingfeng wrote:
>> 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.
> I can, if needed, can you please provide that line?

Fixes: 80bd4a7aab4c ("blk-mq: move the srcu_struct used for quiescing to
the tagset")

Thanks,
Lingfeng

>
> thanks,
>
> greg k-h
>