New subject: Patch "md: call del_gendisk in control path" has been added to the 6.6-stable tree

18 Aug 2025

Hi,
在 2025/08/17 22:18, Sasha Levin 写道:
...
This is a note to let you know that I've just added the patch titled
 md: call del_gendisk in control path


to the 6.6-stable tree which can be found at:
     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is:
      md-call-del_gendisk-in-control-path.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let stable@vger.kernel.org know about it.
This patch should be be backported to any stable kernel, this change
will break user tools mdadm:
https://lore.kernel.org/all/f654db67-a5a5-114b-09b8-00db303daab7@redhat.com/
Thanks,
Kuai
...
commit fa738623105e2dd4865274dc8525856feaec3ae9
Author: Xiao Ni xni@redhat.com
Date:   Wed Jun 11 15:31:06 2025 +0800
 md: call del_gendisk in control path
 
 [ Upstream commit 9e59d609763f70a992a8f3808dabcce60f14eb5c ]
 
 Now del_gendisk and put_disk are called asynchronously in workqueue work.
 The asynchronous way has a problem that the device node can still exist
 after mdadm --stop command returns in a short window. So udev rule can
 open this device node and create the struct mddev in kernel again. So put
 del_gendisk in control path and still leave put_disk in md_kobj_release
 to avoid uaf of gendisk.
 
 Function del_gendisk can't be called with reconfig_mutex. If it's called
 with reconfig mutex, a deadlock can happen. del_gendisk waits all sysfs
 files access to finish and sysfs file access waits reconfig mutex. So
 put del_gendisk after releasing reconfig mutex.
 
 But there is still a window that sysfs can be accessed between mddev_unlock
 and del_gendisk. So some actions (add disk, change level, .e.g) can happen
 which lead unexpected results. MD_DELETED is used to resolve this problem.
 MD_DELETED is set before releasing reconfig mutex and it should be checked
 for these sysfs access which need reconfig mutex. For sysfs access which
 don't need reconfig mutex, del_gendisk will wait them to finish.
 
 But it doesn't need to do this in function mddev_lock_nointr. There are
 ten places that call it.
 * Five of them are in dm raid which we don't need to care. MD_DELETED is
 only used for md raid.
 * stop_sync_thread, md_do_sync and md_start_sync are related sync request,
 and it needs to wait sync thread to finish before stopping an array.
 * md_ioctl: md_open is called before md_ioctl, so ->openers is added. It
 will fail to stop the array. So it doesn't need to check MD_DELETED here
 * md_set_readonly:
 It needs to call mddev_set_closing_and_sync_blockdev when setting readonly
 or read_auto. So it will fail to stop the array too because MD_CLOSING is
 already set.
 
 Reviewed-by: Yu Kuai <yukuai3@huawei.com>
 Signed-off-by: Xiao Ni <xni@redhat.com>
 Link: https://lore.kernel.org/linux-raid/20250611073108.25463-2-xni@redhat.com
 Signed-off-by: Yu Kuai <yukuai3@huawei.com>
 Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index b086cbf24086..8e3939c0d2ed 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -639,9 +639,6 @@ static void __mddev_put(struct mddev *mddev)
       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.



@@ -837,6 +834,16 @@ void mddev_unlock(struct mddev *mddev)
   	kobject_del(&rdev->kobj);
   	export_rdev(rdev, mddev);
   }


/* Call del_gendisk after release reconfig_mutex to avoid
* deadlock (e.g. call del_gendisk under the lock and an


* access to sysfs files waits the lock)


* And MD_DELETED is only used for md raid which is set in


* do_md_stop. dm raid only uses md_stop to stop. So dm raid


* doesn't need to check MD_DELETED when getting reconfig lock


*/


if (test_bit(MD_DELETED, &mddev->flags))
del_gendisk(mddev->gendisk);

}
EXPORT_SYMBOL_GPL(mddev_unlock);

@@ -5616,19 +5623,30 @@ md_attr_store(struct kobject *kobj, struct attribute *attr,
   struct md_sysfs_entry *entry = container_of(attr, struct md_sysfs_entry, attr);
   struct mddev *mddev = container_of(kobj, struct mddev, kobj);
   ssize_t rv;

struct kernfs_node *kn = NULL;

if (!entry->store)
   	return -EIO;
   if (!capable(CAP_SYS_ADMIN))
   	return -EACCES;


if (entry->store == array_state_store && cmd_match(page, "clear"))
kn = sysfs_break_active_protection(kobj, attr);


spin_lock(&all_mddevs_lock);
 if (!mddev_get(mddev)) {
  spin_unlock(&all_mddevs_lock);
if (kn)


	sysfs_unbreak_active_protection(kn);

return -EBUSY;
}
spin_unlock(&all_mddevs_lock);
rv = entry->store(mddev, page, length);
mddev_put(mddev);

if (kn)
sysfs_unbreak_active_protection(kn);


return rv;
}

@@ -5636,12 +5654,6 @@ static void md_kobj_release(struct kobject *ko)
  {
   struct mddev *mddev = container_of(ko, struct mddev, kobj);

if (mddev->sysfs_state)
sysfs_put(mddev->sysfs_state);


if (mddev->sysfs_level)
sysfs_put(mddev->sysfs_level);



del_gendisk(mddev->gendisk);
put_disk(mddev->gendisk);
}

@@ -6531,8 +6543,9 @@ static int do_md_stop(struct mddev *mddev, int mode,
   	mddev->bitmap_info.offset = 0;
  
   	export_array(mddev);

md_clean(mddev);


set_bit(MD_DELETED, &mddev->flags);


if (mddev->hold_active == UNTIL_STOP)
  	mddev->hold_active = 0;
 }

diff --git a/drivers/md/md.h b/drivers/md/md.h
index 46995558d3bd..0a7c9122db50 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -589,11 +589,26 @@ static inline bool is_md_suspended(struct mddev *mddev)
  
  static inline int __must_check mddev_lock(struct mddev *mddev)
  {

return mutex_lock_interruptible(&mddev->reconfig_mutex);


int ret;

ret = mutex_lock_interruptible(&mddev->reconfig_mutex);

/* MD_DELETED is set in do_md_stop with reconfig_mutex.
* So check it here.


*/


if (!ret && test_bit(MD_DELETED, &mddev->flags)) {
ret = -ENODEV;


mutex_unlock(&mddev->reconfig_mutex);


}

return ret;
}

/* Sometimes we need to take the lock in a situation where

failure due to interrupts is not acceptable.



It doesn't need to check MD_DELETED here, the owner which



holds the lock here can't be stopped. And all paths can't



call this function after do_md_stop.

*/
static inline void mddev_lock_nointr(struct mddev *mddev)
{

@@ -602,7 +617,14 @@ static inline void mddev_lock_nointr(struct mddev *mddev)
  
  static inline int mddev_trylock(struct mddev *mddev)
  {

return mutex_trylock(&mddev->reconfig_mutex);


int ret;

ret = mutex_trylock(&mddev->reconfig_mutex);
if (!ret && test_bit(MD_DELETED, &mddev->flags)) {
ret = -ENODEV;


mutex_unlock(&mddev->reconfig_mutex);


}
return ret;
}
extern void mddev_unlock(struct mddev *mddev);

.

    

Re: Patch "md: call del_gendisk in control path" has been added to the 6.6-stable tree