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

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);

.