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

[Greg KH <gregkh@linuxfoundation.org>]

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?

thanks,

greg k-h