Re: [PATCH v2] md: Fix the null-ptr-deref of 'mddev->private' while submitting IO
From: yu kuai
Date: Fri Sep 18 2026 - 02:30:57 EST
Hi,
在 2026/9/18 14:19, Zhihao Cheng 写道:
> 在 2026/9/18 14:06, yu kuai 写道:
>> Hi,
>>
>> 在 2026/9/17 10:42, Zhihao Cheng 写道:
>>> Concurrent processes md_stop and IO submitting could trigger a
>>> null-ptr-deref of 'mddev->private':
>>>
>>> BUG: kernel NULL pointer dereference, address: 0000000000000070
>>> RIP: 0010:_wait_barrier+0x2f/0x250
>>> Call Trace:
>>> raid1_make_request+0x150/0xf50
>>> md_handle_request+0x104/0x530
>>> md_submit_bio+0x76/0x130
>>> submit_bio+0xdd/0x250
>>> submit_bio_wait+0x1f/0x40
>>> __blkdev_direct_IO_simple+0x1f6/0x370
>>> blkdev_write_iter+0x3b2/0x520
>>> ksys_write+0x7d/0x190
>>>
>>> P1
>>> fd = open(/dev/md0, O_RDWR)
>>> P2 (forked from P1, fd' <= fd)
>>> write(fd)
>>> submit_bio
>>> md_handle_request
>>> raid1_make_request
>>> raid1_write_request
>>> ioctl(fd, STOP_ARRAY)
>>> mddev_set_closing_and_sync_blockdev
>>> // check passed, mddev->openers = 1,
>>> // because md_open() is only called
>>> // once in P1->open
>>> do_md_stop
>>> __md_stop
>>> mddev->private = NULL
>>>
>>> conf = mddev->private // NULL
>>> wait_barrier(conf, sector) // null-ptr-deref !
>>>
>>> It is a common problem for raid0/1/10/5, and __md_stop could be
>>> triggered by several paths(eg. ioctl, sysfs, ->dtr). Fix it by
>>> replacing mddev_lock() with mddev_suspend_and_lock() for all
>>> __md_stop() callers. The caller dm_table_destroy() is guaranteed
>>> being invoked with device suspended, so raid_dtr() could keep
>>> using mddev_lock_nointr(). Besides, fail the submitting IO in
>>> md_handle_request() if the 'mddev->pers' becomes NULL.
>>>
>>> Fetch a reproducer in
>>> https://bugzilla.kernel.org/show_bug.cgi?id=222020
>>>
>>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>>> Reported-by: syzbot+3fe892ea5fc292e1353f@xxxxxxxxxxxxxxxxxxxxxxxxx
>>> Closes: https://syzkaller.appspot.com/bug?extid=3fe892ea5fc292e1353f
>>> Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
>>> ---
>>> v1->v2:
>>> 1. Add 'mddev->pers != NULL' check before make_request
>>> 2. Delete dm-raid caller(->dtr) modifications
>>> 3. Move memalloc_noio_restore after mddev_unlock_and_resume
>>> drivers/md/md.c | 32 +++++++++++++++++++++++++++++---
>>> 1 file changed, 29 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>>> index 680b34a63cb3..3dfc34caa2dc 100644
>>> --- a/drivers/md/md.c
>>> +++ b/drivers/md/md.c
>>> @@ -414,6 +414,20 @@ bool md_handle_request(struct mddev *mddev,
>>> struct bio *bio)
>>> if (!percpu_ref_tryget_live(&mddev->active_io))
>>> goto check_suspended;
>>> }
>>> + if (!mddev->pers) {
>>> + /*
>>> + * The __md_stop() sets 'mddev->private' to NULL during
>>> + * the IO submitting, check 'mddev->pers' before the IO
>>> + * being processed by specific driver to avoid the
>>> + * null-ptr-deref of 'mddev-><member>'. The check is
>>> + * safe because the IO has got the 'mddev->active_io'
>>> + * reference, and all __md_stop() callers will wait for
>>> + * the reference to be zero.
>>> + */
>>> + bio_io_error(bio);
>>> + percpu_ref_put(&mddev->active_io);
>>> + return true;
>>> + }
>>> if (!mddev->pers->make_request(mddev, bio)) {
>>> percpu_ref_put(&mddev->active_io);
>>> if (mddev_is_dm(mddev) && mddev->pers->prepare_suspend)
>>> @@ -4657,6 +4671,8 @@ array_state_store(struct mddev *mddev, const
>>> char *buf, size_t len)
>>> {
>>> int err = 0;
>>> enum array_state st = match_word(buf, array_states);
>>> + unsigned int noio_flags = 0;
>>> + bool suspend = false;
>>> /* No lock dependent actions */
>>> switch (st) {
>>> @@ -4666,9 +4682,11 @@ array_state_store(struct mddev *mddev, const
>>> char *buf, size_t len)
>>> case broken: /* cannot be set */
>>> case bad_word:
>>> return -EINVAL;
>>> + case inactive:
>>> case clear:
>>> + suspend = true;
>>> + fallthrough;
>>> case readonly:
>>> - case inactive:
>>> case read_auto:
>>> if (!mddev->pers || !md_is_rdwr(mddev))
>>> break;
>>> @@ -4702,9 +4720,11 @@ array_state_store(struct mddev *mddev, const
>>> char *buf, size_t len)
>>> spin_unlock(&mddev->lock);
>>> return err ?: len;
>>> }
>>> - err = mddev_lock(mddev);
>>> + err = suspend ? mddev_suspend_and_lock(mddev) : mddev_lock(mddev);
>>
>> Unlike ioctl path, where the checking of opener is just 1,
>> mddev_set_closing_and_sync_blockdev() here
>> already check there is no opener, so there can't be any IO inflight.
>
> Hi, yukuai
> I thought of a scene. If someone open '/dev/md0, write(buffer) 4K, and
> close the corresponding fd. Then writeback kworker submit IO,
> array_state_store will pass the mddev_set_closing_and_sync_blockdev()
> check, which could lead to the similar problem.
This should not happen, that last one to close /dev/md0 will wait for
full disk flush to be done.
>>
>>> if (err)
>>> return err;
>>> + if (suspend)
>>> + noio_flags = memalloc_noio_save();
>>> switch (st) {
>>> case inactive:
>>> @@ -4775,7 +4795,12 @@ array_state_store(struct mddev *mddev, const
>>> char *buf, size_t len)
>>> mddev->hold_active = 0;
>>> sysfs_notify_dirent_safe(mddev->sysfs_state);
>>> }
>>> - mddev_unlock(mddev);
>>> + if (suspend) {
>>> + mddev_unlock_and_resume(mddev);
>>> + memalloc_noio_restore(noio_flags);
>>> + } else {
>>> + mddev_unlock(mddev);
>>> + }
>>> if (st == readonly || st == read_auto || st == inactive ||
>>> (err && st == clear))
>>> @@ -8299,6 +8324,7 @@ static bool md_ioctl_need_suspend(unsigned int
>>> cmd)
>>> case HOT_REMOVE_DISK:
>>> case SET_BITMAP_FILE:
>>> case SET_ARRAY_INFO:
>>> + case STOP_ARRAY:
>>> return true;
>>> default:
>>> return false;
>>
>
--
Thanks,
Kuai