[PATCH 6.1 0/2] md: fix mddev uaf while iterating all_mddevs list

[PATCH 6.1 0/2] md: fix mddev uaf while iterating all_mddevs list

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Hi, Greg

This is the manual adaptation version for 6.1, for 6.6/6.12 commit
8542870237c3 ("md: fix mddev uaf while iterating all_mddevs list") can
be applied cleanly, can you queue them as well?

Thanks!

Yu Kuai (2):
  md: factor out a helper from mddev_put()
  md: fix mddev uaf while iterating all_mddevs list

 drivers/md/md.c | 50 +++++++++++++++++++++++++++++--------------------
 1 file changed, 30 insertions(+), 20 deletions(-)

-- 
2.39.2

[PATCH 6.1 1/2] md: factor out a helper from mddev_put()

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

commit 3d8d32873c7b6d9cec5b40c2ddb8c7c55961694f upstream.

There are no functional changes, prepare to simplify md_seq_ops in next
patch.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230927061241.1552837-2-yukuai1@huaweicloud.com
[minor context conflict]
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 5e2751d42f64..639fe8ebaa68 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -667,24 +667,28 @@ static inline struct mddev *mddev_get(struct mddev *mddev)
 
 static void mddev_delayed_delete(struct work_struct *ws);
 
+static void __mddev_put(struct mddev *mddev)
+{
+	if (mddev->raid_disks || !list_empty(&mddev->disks) ||
+	    mddev->ctime || mddev->hold_active)
+		return;
+
+	/* Array is not configured at all, and not held active, so destroy it */
+	set_bit(MD_DELETED, &mddev->flags);
+
+	/*
+	 * Call queue_work inside the spinlock so that flush_workqueue() after
+	 * mddev_find will succeed in waiting for the work to be done.
+	 */
+	INIT_WORK(&mddev->del_work, mddev_delayed_delete);
+	queue_work(md_misc_wq, &mddev->del_work);
+}
+
 void mddev_put(struct mddev *mddev)
 {
 	if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
 		return;
-	if (!mddev->raid_disks && list_empty(&mddev->disks) &&
-	    mddev->ctime == 0 && !mddev->hold_active) {
-		/* Array is not configured at all, and not held active,
-		 * so destroy it */
-		set_bit(MD_DELETED, &mddev->flags);
-
-		/*
-		 * Call queue_work inside the spinlock so that
-		 * flush_workqueue() after mddev_find will succeed in waiting
-		 * for the work to be done.
-		 */
-		INIT_WORK(&mddev->del_work, mddev_delayed_delete);
-		queue_work(md_misc_wq, &mddev->del_work);
-	}
+	__mddev_put(mddev);
 	spin_unlock(&all_mddevs_lock);
 }
 
-- 
2.39.2

[PATCH 6.1 2/2] md: fix mddev uaf while iterating all_mddevs list

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

commit 8542870237c3a48ff049b6c5df5f50c8728284fa upstream.

While iterating all_mddevs list from md_notify_reboot() and md_exit(),
list_for_each_entry_safe is used, and this can race with deletint the
next mddev, causing UAF:

t1:
spin_lock
//list_for_each_entry_safe(mddev, n, ...)
 mddev_get(mddev1)
 // assume mddev2 is the next entry
 spin_unlock
            t2:
            //remove mddev2
            ...
            mddev_free
            spin_lock
            list_del
            spin_unlock
            kfree(mddev2)
 mddev_put(mddev1)
 spin_lock
 //continue dereference mddev2->all_mddevs

The old helper for_each_mddev() actually grab the reference of mddev2
while holding the lock, to prevent from being freed. This problem can be
fixed the same way, however, the code will be complex.

Hence switch to use list_for_each_entry, in this case mddev_put() can free
the mddev1 and it's not safe as well. Refer to md_seq_show(), also factor
out a helper mddev_put_locked() to fix this problem.

Cc: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/linux-raid/20250220124348.845222-1-yukuai1@huaweicloud.com
Fixes: f26514342255 ("md: stop using for_each_mddev in md_notify_reboot")
Fixes: 16648bac862f ("md: stop using for_each_mddev in md_exit")
Reported-and-tested-by: Guillaume Morin <guillaume@morinfr.org>
Closes: https://lore.kernel.org/all/Z7Y0SURoA8xwg7vn@bender.morinfr.org/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
[skip md_seq_show() that is not exist]
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 639fe8ebaa68..d5fbccc72810 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -684,6 +684,12 @@ static void __mddev_put(struct mddev *mddev)
 	queue_work(md_misc_wq, &mddev->del_work);
 }
 
+static void mddev_put_locked(struct mddev *mddev)
+{
+	if (atomic_dec_and_test(&mddev->active))
+		__mddev_put(mddev);
+}
+
 void mddev_put(struct mddev *mddev)
 {
 	if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
@@ -9704,11 +9710,11 @@ EXPORT_SYMBOL_GPL(rdev_clear_badblocks);
 static int md_notify_reboot(struct notifier_block *this,
 			    unsigned long code, void *x)
 {
-	struct mddev *mddev, *n;
+	struct mddev *mddev;
 	int need_delay = 0;
 
 	spin_lock(&all_mddevs_lock);
-	list_for_each_entry_safe(mddev, n, &all_mddevs, all_mddevs) {
+	list_for_each_entry(mddev, &all_mddevs, all_mddevs) {
 		if (!mddev_get(mddev))
 			continue;
 		spin_unlock(&all_mddevs_lock);
@@ -9720,8 +9726,8 @@ static int md_notify_reboot(struct notifier_block *this,
 			mddev_unlock(mddev);
 		}
 		need_delay = 1;
-		mddev_put(mddev);
 		spin_lock(&all_mddevs_lock);
+		mddev_put_locked(mddev);
 	}
 	spin_unlock(&all_mddevs_lock);
 
@@ -10043,7 +10049,7 @@ void md_autostart_arrays(int part)
 
 static __exit void md_exit(void)
 {
-	struct mddev *mddev, *n;
+	struct mddev *mddev;
 	int delay = 1;
 
 	unregister_blkdev(MD_MAJOR,"md");
@@ -10064,7 +10070,7 @@ static __exit void md_exit(void)
 	remove_proc_entry("mdstat", NULL);
 
 	spin_lock(&all_mddevs_lock);
-	list_for_each_entry_safe(mddev, n, &all_mddevs, all_mddevs) {
+	list_for_each_entry(mddev, &all_mddevs, all_mddevs) {
 		if (!mddev_get(mddev))
 			continue;
 		spin_unlock(&all_mddevs_lock);
@@ -10076,8 +10082,8 @@ static __exit void md_exit(void)
 		 * the mddev for destruction by a workqueue, and the
 		 * destroy_workqueue() below will wait for that to complete.
 		 */
-		mddev_put(mddev);
 		spin_lock(&all_mddevs_lock);
+		mddev_put_locked(mddev);
 	}
 	spin_unlock(&all_mddevs_lock);
 
-- 
2.39.2

Re: [PATCH 6.1 1/2] md: factor out a helper from mddev_put()

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 3d8d32873c7b6d9cec5b40c2ddb8c7c55961694f

WARNING: Author mismatch between patch and upstream commit:
Backport author: Yu Kuai<yukuai1@huaweicloud.com>
Commit author: Yu Kuai<yukuai3@huawei.com>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.13.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Present (different SHA1: 452f50807917)

Note: The patch differs from the upstream commit:
---
1:  3d8d32873c7b6 ! 1:  c3ea0d86c3059 md: factor out a helper from mddev_put()
    @@ Metadata
      ## Commit message ##
         md: factor out a helper from mddev_put()
     
    +    commit 3d8d32873c7b6d9cec5b40c2ddb8c7c55961694f upstream.
    +
         There are no functional changes, prepare to simplify md_seq_ops in next
         patch.
     
         Signed-off-by: Yu Kuai <yukuai3@huawei.com>
         Signed-off-by: Song Liu <song@kernel.org>
         Link: https://lore.kernel.org/r/20230927061241.1552837-2-yukuai1@huaweicloud.com
    +    [minor context conflict]
    +    Signed-off-by: Yu Kuai <yukuai3@huawei.com>
     
      ## drivers/md/md.c ##
     @@ drivers/md/md.c: static inline struct mddev *mddev_get(struct mddev *mddev)
    @@ drivers/md/md.c: static inline struct mddev *mddev_get(struct mddev *mddev)
     +	 * Call queue_work inside the spinlock so that flush_workqueue() after
     +	 * mddev_find will succeed in waiting for the work to be done.
     +	 */
    ++	INIT_WORK(&mddev->del_work, mddev_delayed_delete);
     +	queue_work(md_misc_wq, &mddev->del_work);
     +}
     +
    @@ drivers/md/md.c: static inline struct mddev *mddev_get(struct mddev *mddev)
     -		/* Array is not configured at all, and not held active,
     -		 * so destroy it */
     -		set_bit(MD_DELETED, &mddev->flags);
    - 
    +-
     -		/*
     -		 * Call queue_work inside the spinlock so that
     -		 * flush_workqueue() after mddev_find will succeed in waiting
     -		 * for the work to be done.
     -		 */
    +-		INIT_WORK(&mddev->del_work, mddev_delayed_delete);
     -		queue_work(md_misc_wq, &mddev->del_work);
     -	}
     +	__mddev_put(mddev);
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.1.y        |  Success    |  Success   |

Re: [PATCH 6.1 2/2] md: fix mddev uaf while iterating all_mddevs list

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 8542870237c3a48ff049b6c5df5f50c8728284fa

WARNING: Author mismatch between patch and upstream commit:
Backport author: Yu Kuai<yukuai1@huaweicloud.com>
Commit author: Yu Kuai<yukuai3@huawei.com>

Status in newer kernel trees:
6.14.y | Present (different SHA1: 5462544ccbad)
6.13.y | Not found
6.12.y | Not found
6.6.y | Not found

Note: The patch differs from the upstream commit:
---
1:  8542870237c3a ! 1:  dd49667d64662 md: fix mddev uaf while iterating all_mddevs list
    @@ Metadata
      ## Commit message ##
         md: fix mddev uaf while iterating all_mddevs list
     
    +    commit 8542870237c3a48ff049b6c5df5f50c8728284fa upstream.
    +
         While iterating all_mddevs list from md_notify_reboot() and md_exit(),
         list_for_each_entry_safe is used, and this can race with deletint the
         next mddev, causing UAF:
    @@ Commit message
         Closes: https://lore.kernel.org/all/Z7Y0SURoA8xwg7vn@bender.morinfr.org/
         Signed-off-by: Yu Kuai <yukuai3@huawei.com>
         Reviewed-by: Christoph Hellwig <hch@lst.de>
    +    [skip md_seq_show() that is not exist]
    +    Signed-off-by: Yu Kuai <yukuai3@huawei.com>
     
      ## drivers/md/md.c ##
     @@ drivers/md/md.c: static void __mddev_put(struct mddev *mddev)
    @@ drivers/md/md.c: static void __mddev_put(struct mddev *mddev)
      void mddev_put(struct mddev *mddev)
      {
      	if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
    -@@ drivers/md/md.c: static int md_seq_show(struct seq_file *seq, void *v)
    - 	if (mddev == list_last_entry(&all_mddevs, struct mddev, all_mddevs))
    - 		status_unused(seq);
    - 
    --	if (atomic_dec_and_test(&mddev->active))
    --		__mddev_put(mddev);
    --
    -+	mddev_put_locked(mddev);
    - 	return 0;
    - }
    - 
     @@ drivers/md/md.c: EXPORT_SYMBOL_GPL(rdev_clear_badblocks);
      static int md_notify_reboot(struct notifier_block *this,
      			    unsigned long code, void *x)
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.6.y        |  Success    |  Success   |

Re: [PATCH 6.1 0/2] md: fix mddev uaf while iterating all_mddevs list

[Salvatore Bonaccorso]

Hi Greg, Sasha, Yu,

On Sat, Apr 19, 2025 at 09:23:01AM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Hi, Greg
> 
> This is the manual adaptation version for 6.1, for 6.6/6.12 commit
> 8542870237c3 ("md: fix mddev uaf while iterating all_mddevs list") can
> be applied cleanly, can you queue them as well?
> 
> Thanks!
> 
> Yu Kuai (2):
>   md: factor out a helper from mddev_put()
>   md: fix mddev uaf while iterating all_mddevs list
> 
>  drivers/md/md.c | 50 +++++++++++++++++++++++++++++--------------------
>  1 file changed, 30 insertions(+), 20 deletions(-)

I noticed that the change 8542870237c3 was queued for 6.6.y and 6.12.y
and is in the review now, but wonder should we do something more with
6.1.y as this requires this series/manual adaption?

Or will it make for the next round of stable updates in 6.1.y? 

(or did it just felt through the cracks and it is actually fine that I
ping the thread on this question).

Regards,
Salvatore

Re: [PATCH 6.1 0/2] md: fix mddev uaf while iterating all_mddevs list

[Greg KH]

On Wed, Apr 23, 2025 at 08:14:09PM +0200, Salvatore Bonaccorso wrote:
> Hi Greg, Sasha, Yu,
> 
> On Sat, Apr 19, 2025 at 09:23:01AM +0800, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@huawei.com>
> > 
> > Hi, Greg
> > 
> > This is the manual adaptation version for 6.1, for 6.6/6.12 commit
> > 8542870237c3 ("md: fix mddev uaf while iterating all_mddevs list") can
> > be applied cleanly, can you queue them as well?
> > 
> > Thanks!
> > 
> > Yu Kuai (2):
> >   md: factor out a helper from mddev_put()
> >   md: fix mddev uaf while iterating all_mddevs list
> > 
> >  drivers/md/md.c | 50 +++++++++++++++++++++++++++++--------------------
> >  1 file changed, 30 insertions(+), 20 deletions(-)
> 
> I noticed that the change 8542870237c3 was queued for 6.6.y and 6.12.y
> and is in the review now, but wonder should we do something more with
> 6.1.y as this requires this series/manual adaption?
> 
> Or will it make for the next round of stable updates in 6.1.y? 
> 
> (or did it just felt through the cracks and it is actually fine that I
> ping the thread on this question).

This fell through the cracks and yes, it is great that you pinged it.
I'll queue it up for the next release, thanks!

greg k-h

Re: [PATCH 6.1 0/2] md: fix mddev uaf while iterating all_mddevs list

[Salvatore Bonaccorso]

Hi Greg,

On Thu, Apr 24, 2025 at 08:40:41AM +0200, Greg KH wrote:
> On Wed, Apr 23, 2025 at 08:14:09PM +0200, Salvatore Bonaccorso wrote:
> > Hi Greg, Sasha, Yu,
> > 
> > On Sat, Apr 19, 2025 at 09:23:01AM +0800, Yu Kuai wrote:
> > > From: Yu Kuai <yukuai3@huawei.com>
> > > 
> > > Hi, Greg
> > > 
> > > This is the manual adaptation version for 6.1, for 6.6/6.12 commit
> > > 8542870237c3 ("md: fix mddev uaf while iterating all_mddevs list") can
> > > be applied cleanly, can you queue them as well?
> > > 
> > > Thanks!
> > > 
> > > Yu Kuai (2):
> > >   md: factor out a helper from mddev_put()
> > >   md: fix mddev uaf while iterating all_mddevs list
> > > 
> > >  drivers/md/md.c | 50 +++++++++++++++++++++++++++++--------------------
> > >  1 file changed, 30 insertions(+), 20 deletions(-)
> > 
> > I noticed that the change 8542870237c3 was queued for 6.6.y and 6.12.y
> > and is in the review now, but wonder should we do something more with
> > 6.1.y as this requires this series/manual adaption?
> > 
> > Or will it make for the next round of stable updates in 6.1.y? 
> > 
> > (or did it just felt through the cracks and it is actually fine that I
> > ping the thread on this question).
> 
> This fell through the cracks and yes, it is great that you pinged it.
> I'll queue it up for the next release, thanks!

Thank you! Very much appreciated! (People installing Debian will be
happy as it affects kernel under certiain circumstances, cf.
https://bugs.debian.org/1086175, https://bugs.debian.org/1089158, but
was longstanding already).

Thank you,
Regards,
Salvatore

Re: [PATCH 6.1 0/2] md: fix mddev uaf while iterating all_mddevs list

[Greg KH]

On Thu, Apr 24, 2025 at 11:32:52AM +0200, Salvatore Bonaccorso wrote:
> Hi Greg,
> 
> On Thu, Apr 24, 2025 at 08:40:41AM +0200, Greg KH wrote:
> > On Wed, Apr 23, 2025 at 08:14:09PM +0200, Salvatore Bonaccorso wrote:
> > > Hi Greg, Sasha, Yu,
> > > 
> > > On Sat, Apr 19, 2025 at 09:23:01AM +0800, Yu Kuai wrote:
> > > > From: Yu Kuai <yukuai3@huawei.com>
> > > > 
> > > > Hi, Greg
> > > > 
> > > > This is the manual adaptation version for 6.1, for 6.6/6.12 commit
> > > > 8542870237c3 ("md: fix mddev uaf while iterating all_mddevs list") can
> > > > be applied cleanly, can you queue them as well?
> > > > 
> > > > Thanks!
> > > > 
> > > > Yu Kuai (2):
> > > >   md: factor out a helper from mddev_put()
> > > >   md: fix mddev uaf while iterating all_mddevs list
> > > > 
> > > >  drivers/md/md.c | 50 +++++++++++++++++++++++++++++--------------------
> > > >  1 file changed, 30 insertions(+), 20 deletions(-)
> > > 
> > > I noticed that the change 8542870237c3 was queued for 6.6.y and 6.12.y
> > > and is in the review now, but wonder should we do something more with
> > > 6.1.y as this requires this series/manual adaption?
> > > 
> > > Or will it make for the next round of stable updates in 6.1.y? 
> > > 
> > > (or did it just felt through the cracks and it is actually fine that I
> > > ping the thread on this question).
> > 
> > This fell through the cracks and yes, it is great that you pinged it.
> > I'll queue it up for the next release, thanks!
> 
> Thank you! Very much appreciated! (People installing Debian will be
> happy as it affects kernel under certiain circumstances, cf.
> https://bugs.debian.org/1086175, https://bugs.debian.org/1089158, but
> was longstanding already).

Now queued up, thanks.

greg k-h