[PATCH -next v5 0/6] md: fix uaf for sync_thread

[PATCH -next v5 0/6] md: fix uaf for sync_thread

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Changes in v5:
 - use rcu_dereference_protected() instead of rcu_access_pointer() where
 rcu_read_lock/unlock is not required.
 - add patch 4,5 to handle that bitmap timeout is set multiple times.

Changes in v4:
 - remove patch 2 from v3
 - fix sparse errors and warnings from v3, in order to do that, all access
 to md_thread need to be modified, patch 2-4 is splited to avoid a huge
 patch.

Changes in v3:
 - remove patch 3 from v2
 - use rcu instead of a new lock

Changes in v2:
 - fix a compile error for md-cluster in patch 2
 - replace spin_lock/unlock with spin_lock/unlock_irq in patch 5
 - don't wake up inside the new lock in md wakeup_thread in patch 5

Yu Kuai (6):
  md: pass a md_thread pointer to md_register_thread()
  md: factor out a helper to wake up md_thread directly
  dm-raid: remove useless checking in raid_message()
  md/bitmap: always wake up md_thread in timeout_store
  md/bitmap: factor out a helper to set timeout
  md: protect md_thread with rcu

 drivers/md/dm-raid.c      |   4 +-
 drivers/md/md-bitmap.c    |  50 +++++++++++------
 drivers/md/md-cluster.c   |  11 ++--
 drivers/md/md-multipath.c |   6 +--
 drivers/md/md.c           | 110 ++++++++++++++++++++------------------
 drivers/md/md.h           |  15 +++---
 drivers/md/raid1.c        |   9 ++--
 drivers/md/raid1.h        |   2 +-
 drivers/md/raid10.c       |  25 ++++-----
 drivers/md/raid10.h       |   2 +-
 drivers/md/raid5-cache.c  |  20 +++----
 drivers/md/raid5.c        |  19 +++----
 drivers/md/raid5.h        |   2 +-
 13 files changed, 148 insertions(+), 127 deletions(-)

-- 
2.39.2

[PATCH -next v5 1/6] md: pass a md_thread pointer to md_register_thread()

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Prepare to protect md_thread with rcu, there are no functional changes.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md-cluster.c   | 11 +++++------
 drivers/md/md-multipath.c |  6 +++---
 drivers/md/md.c           | 27 ++++++++++++++-------------
 drivers/md/md.h           |  7 +++----
 drivers/md/raid1.c        |  5 ++---
 drivers/md/raid10.c       | 15 ++++++---------
 drivers/md/raid5-cache.c  |  5 ++---
 drivers/md/raid5.c        | 15 ++++++---------
 8 files changed, 41 insertions(+), 50 deletions(-)

diff --git a/drivers/md/md-cluster.c b/drivers/md/md-cluster.c
index 10e0c5381d01..c19e29cb73bf 100644
--- a/drivers/md/md-cluster.c
+++ b/drivers/md/md-cluster.c
@@ -362,9 +362,8 @@ static void __recover_slot(struct mddev *mddev, int slot)
 
 	set_bit(slot, &cinfo->recovery_map);
 	if (!cinfo->recovery_thread) {
-		cinfo->recovery_thread = md_register_thread(recover_bitmaps,
-				mddev, "recover");
-		if (!cinfo->recovery_thread) {
+		if (md_register_thread(&cinfo->recovery_thread, recover_bitmaps,
+				       mddev, "recover")) {
 			pr_warn("md-cluster: Could not create recovery thread\n");
 			return;
 		}
@@ -888,9 +887,9 @@ static int join(struct mddev *mddev, int nodes)
 		goto err;
 	}
 	/* Initiate the communication resources */
-	ret = -ENOMEM;
-	cinfo->recv_thread = md_register_thread(recv_daemon, mddev, "cluster_recv");
-	if (!cinfo->recv_thread) {
+	ret = md_register_thread(&cinfo->recv_thread, recv_daemon, mddev,
+				 "cluster_recv");
+	if (ret) {
 		pr_err("md-cluster: cannot allocate memory for recv_thread!\n");
 		goto err;
 	}
diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
index 66edf5e72bd6..ceec9e4b2a60 100644
--- a/drivers/md/md-multipath.c
+++ b/drivers/md/md-multipath.c
@@ -400,9 +400,9 @@ static int multipath_run (struct mddev *mddev)
 	if (ret)
 		goto out_free_conf;
 
-	mddev->thread = md_register_thread(multipathd, mddev,
-					   "multipath");
-	if (!mddev->thread)
+	ret = md_register_thread(&mddev->thread, multipathd, mddev,
+				 "multipath");
+	if (ret)
 		goto out_free_conf;
 
 	pr_info("multipath: array %s active with %d out of %d IO paths\n",
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 9bc05f451d42..1459c2cfb0dd 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7896,29 +7896,32 @@ void md_wakeup_thread(struct md_thread *thread)
 }
 EXPORT_SYMBOL(md_wakeup_thread);
 
-struct md_thread *md_register_thread(void (*run) (struct md_thread *),
-		struct mddev *mddev, const char *name)
+int md_register_thread(struct md_thread **threadp,
+		       void (*run)(struct md_thread *),
+		       struct mddev *mddev, const char *name)
 {
 	struct md_thread *thread;
 
 	thread = kzalloc(sizeof(struct md_thread), GFP_KERNEL);
 	if (!thread)
-		return NULL;
+		return -ENOMEM;
 
 	init_waitqueue_head(&thread->wqueue);
 
 	thread->run = run;
 	thread->mddev = mddev;
 	thread->timeout = MAX_SCHEDULE_TIMEOUT;
-	thread->tsk = kthread_run(md_thread, thread,
-				  "%s_%s",
-				  mdname(thread->mddev),
-				  name);
+	thread->tsk = kthread_run(md_thread, thread, "%s_%s",
+				  mdname(thread->mddev), name);
 	if (IS_ERR(thread->tsk)) {
+		int err = PTR_ERR(thread->tsk);
+
 		kfree(thread);
-		return NULL;
+		return err;
 	}
-	return thread;
+
+	*threadp = thread;
+	return 0;
 }
 EXPORT_SYMBOL(md_register_thread);
 
@@ -9199,10 +9202,8 @@ static void md_start_sync(struct work_struct *ws)
 {
 	struct mddev *mddev = container_of(ws, struct mddev, del_work);
 
-	mddev->sync_thread = md_register_thread(md_do_sync,
-						mddev,
-						"resync");
-	if (!mddev->sync_thread) {
+	if (md_register_thread(&mddev->sync_thread, md_do_sync, mddev,
+			       "resync")) {
 		pr_warn("%s: could not start resync thread...\n",
 			mdname(mddev));
 		/* leave the spares where they are, it shouldn't hurt */
diff --git a/drivers/md/md.h b/drivers/md/md.h
index e148e3c83b0d..7af45b8432e9 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -730,10 +730,9 @@ extern int register_md_cluster_operations(struct md_cluster_operations *ops,
 extern int unregister_md_cluster_operations(void);
 extern int md_setup_cluster(struct mddev *mddev, int nodes);
 extern void md_cluster_stop(struct mddev *mddev);
-extern struct md_thread *md_register_thread(
-	void (*run)(struct md_thread *thread),
-	struct mddev *mddev,
-	const char *name);
+extern int md_register_thread(struct md_thread **threadp,
+			      void (*run)(struct md_thread *thread),
+			      struct mddev *mddev, const char *name);
 extern void md_unregister_thread(struct md_thread **threadp);
 extern void md_wakeup_thread(struct md_thread *thread);
 extern void md_check_recovery(struct mddev *mddev);
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 68a9e2d9985b..1217c1db0a40 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -3083,9 +3083,8 @@ static struct r1conf *setup_conf(struct mddev *mddev)
 		}
 	}
 
-	err = -ENOMEM;
-	conf->thread = md_register_thread(raid1d, mddev, "raid1");
-	if (!conf->thread)
+	err = md_register_thread(&conf->thread, raid1d, mddev, "raid1");
+	if (err)
 		goto abort;
 
 	return conf;
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 6c66357f92f5..0171ba4f19b0 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -4077,9 +4077,8 @@ static struct r10conf *setup_conf(struct mddev *mddev)
 	init_waitqueue_head(&conf->wait_barrier);
 	atomic_set(&conf->nr_pending, 0);
 
-	err = -ENOMEM;
-	conf->thread = md_register_thread(raid10d, mddev, "raid10");
-	if (!conf->thread)
+	err = md_register_thread(&conf->thread, raid10d, mddev, "raid10");
+	if (err)
 		goto out;
 
 	conf->mddev = mddev;
@@ -4273,9 +4272,8 @@ static int raid10_run(struct mddev *mddev)
 		clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
 		set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
 		set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
-		mddev->sync_thread = md_register_thread(md_do_sync, mddev,
-							"reshape");
-		if (!mddev->sync_thread)
+		if (md_register_thread(&mddev->sync_thread, md_do_sync, mddev,
+				       "reshape"))
 			goto out_free_conf;
 	}
 
@@ -4686,9 +4684,8 @@ static int raid10_start_reshape(struct mddev *mddev)
 	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
 	set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
 
-	mddev->sync_thread = md_register_thread(md_do_sync, mddev,
-						"reshape");
-	if (!mddev->sync_thread) {
+	if (md_register_thread(&mddev->sync_thread, md_do_sync, mddev,
+			       "reshape")) {
 		ret = -EAGAIN;
 		goto abort;
 	}
diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 46182b955aef..0464d4d551fc 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -3121,9 +3121,8 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 	spin_lock_init(&log->tree_lock);
 	INIT_RADIX_TREE(&log->big_stripe_tree, GFP_NOWAIT | __GFP_NOWARN);
 
-	log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
-						 log->rdev->mddev, "reclaim");
-	if (!log->reclaim_thread)
+	if (md_register_thread(&log->reclaim_thread, r5l_reclaim_thread,
+			       log->rdev->mddev, "reclaim"))
 		goto reclaim_thread;
 	log->reclaim_thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 7b820b81d8c2..04b1093195d0 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7665,11 +7665,10 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	}
 
 	sprintf(pers_name, "raid%d", mddev->new_level);
-	conf->thread = md_register_thread(raid5d, mddev, pers_name);
-	if (!conf->thread) {
+	ret = md_register_thread(&conf->thread, raid5d, mddev, pers_name);
+	if (ret) {
 		pr_warn("md/raid:%s: couldn't allocate thread.\n",
 			mdname(mddev));
-		ret = -ENOMEM;
 		goto abort;
 	}
 
@@ -7989,9 +7988,8 @@ static int raid5_run(struct mddev *mddev)
 		clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
 		set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
 		set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
-		mddev->sync_thread = md_register_thread(md_do_sync, mddev,
-							"reshape");
-		if (!mddev->sync_thread)
+		if (md_register_thread(&mddev->sync_thread, md_do_sync, mddev,
+				       "reshape"))
 			goto abort;
 	}
 
@@ -8567,9 +8565,8 @@ static int raid5_start_reshape(struct mddev *mddev)
 	clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
 	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
 	set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
-	mddev->sync_thread = md_register_thread(md_do_sync, mddev,
-						"reshape");
-	if (!mddev->sync_thread) {
+	if (md_register_thread(&mddev->sync_thread, md_do_sync, mddev,
+			       "reshape")) {
 		mddev->recovery = 0;
 		spin_lock_irq(&conf->device_lock);
 		write_seqcount_begin(&conf->gen_lock);
-- 
2.39.2

Re: [PATCH -next v5 1/6] md: pass a md_thread pointer to md_register_thread()

[Song Liu]

On Mon, Apr 10, 2023 at 4:37 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> Prepare to protect md_thread with rcu, there are no functional changes.

Why do we need this change? To add __rcu later?

Can we do something like:

struct md_thread __rcu *md_register_thread(void (*run) (struct md_thread *),
               struct mddev *mddev, const char *name)

Thanks,
Song

Re: [PATCH -next v5 1/6] md: pass a md_thread pointer to md_register_thread()

[Yu Kuai]

Hi,

在 2023/04/11 9:15, Song Liu 写道:
> On Mon, Apr 10, 2023 at 4:37 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Prepare to protect md_thread with rcu, there are no functional changes.
> 
> Why do we need this change? To add __rcu later?

Add __rcu is one reason, more importantly is to assign md_thread inside
md_register_thread in patch 6:

rcu_assign_pointer(*threadp, thread);

> 
> Can we do something like:
> 
> struct md_thread __rcu *md_register_thread(void (*run) (struct md_thread *),
>                 struct mddev *mddev, const char *name)

I think this is not necessary, if we don't want to change api, we must
use rcu_assign_pointer for each caller to set md_thread.

Thanks,
Kuai
> 
> Thanks,
> Song
> .
> 

Re: [PATCH -next v5 1/6] md: pass a md_thread pointer to md_register_thread()

[Song Liu]

On Mon, Apr 10, 2023 at 6:34 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> Hi,
>
> 在 2023/04/11 9:15, Song Liu 写道:
> > On Mon, Apr 10, 2023 at 4:37 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
> >>
> >> From: Yu Kuai <yukuai3@huawei.com>
> >>
> >> Prepare to protect md_thread with rcu, there are no functional changes.
> >
> > Why do we need this change? To add __rcu later?
>
> Add __rcu is one reason, more importantly is to assign md_thread inside
> md_register_thread in patch 6:
>
> rcu_assign_pointer(*threadp, thread);

Got it.

> >
> > Can we do something like:
> >
> > struct md_thread __rcu *md_register_thread(void (*run) (struct md_thread *),
> >                 struct mddev *mddev, const char *name)
>
> I think this is not necessary, if we don't want to change api, we must
> use rcu_assign_pointer for each caller to set md_thread.

I think it is better to use rcu_assign_pointer at the caller side.

Thanks,
Song

Re: [PATCH -next v5 1/6] md: pass a md_thread pointer to md_register_thread()

[Logan Gunthorpe]

On 2023-04-10 23:26, Song Liu wrote:
> On Mon, Apr 10, 2023 at 6:34 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>
>> Hi,
>>
>> 在 2023/04/11 9:15, Song Liu 写道:
>>> On Mon, Apr 10, 2023 at 4:37 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>>>
>>>> From: Yu Kuai <yukuai3@huawei.com>
>>>>
>>>> Prepare to protect md_thread with rcu, there are no functional changes.
>>>
>>> Why do we need this change? To add __rcu later?
>>
>> Add __rcu is one reason, more importantly is to assign md_thread inside
>> md_register_thread in patch 6:
>>
>> rcu_assign_pointer(*threadp, thread);
> 
> Got it.
> 
>>>
>>> Can we do something like:
>>>
>>> struct md_thread __rcu *md_register_thread(void (*run) (struct md_thread *),
>>>                 struct mddev *mddev, const char *name)
>>
>> I think this is not necessary, if we don't want to change api, we must
>> use rcu_assign_pointer for each caller to set md_thread.
> 
> I think it is better to use rcu_assign_pointer at the caller side.

I agree.

Logan

Re: [PATCH -next v5 1/6] md: pass a md_thread pointer to md_register_thread()

[Yu Kuai]

Hi,

在 2023/04/11 23:46, Logan Gunthorpe 写道:

>>>> Can we do something like:
>>>>
>>>> struct md_thread __rcu *md_register_thread(void (*run) (struct md_thread *),
>>>>                  struct mddev *mddev, const char *name)
>>>
>>> I think this is not necessary, if we don't want to change api, we must
>>> use rcu_assign_pointer for each caller to set md_thread.
>>
>> I think it is better to use rcu_assign_pointer at the caller side.
> 
> I agree.
> 
> Logan
> .
> 
I'll remove this patch, and use rcu_assign_pointer() in the caller
directly in the next version.

Thanks,
Kuai

[PATCH -next v5 2/6] md: factor out a helper to wake up md_thread directly

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

md_wakeup_thread() can't wakeup md_thread->tsk if md_thread->run is
still in progress, and in some cases md_thread->tsk need to be woke up
directly, like md_set_readonly() and do_md_stop().

Commit 9dfbdafda3b3 ("md: unlock mddev before reap sync_thread in
action_store") introduce a new scenario where unregister sync_thread is
not protected by 'reconfig_mutex', this can cause null-ptr-deference in
theroy:

t1: md_set_readonly		t2: action_store
				md_unregister_thread
				// 'reconfig_mutex' is not held
// 'reconfig_mutex' is held by caller
if (mddev->sync_thread)
				 thread = *threadp
				 *threadp = NULL
 wake_up_process(mddev->sync_thread->tsk)
 // null-ptr-deference

This patch factor out a helper to wake up md_thread directly, so that
'sync_thread' won't be accessed multiple times from the reader side. And
perhaps this helper will be used later to fix action_store().

This patch also prepare to protect md_thread with rcu.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 1459c2cfb0dd..139c7b0202e3 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -92,6 +92,7 @@ static struct workqueue_struct *md_rdev_misc_wq;
 static int remove_and_add_spares(struct mddev *mddev,
 				 struct md_rdev *this);
 static void mddev_detach(struct mddev *mddev);
+static void md_wakeup_thread_directly(struct md_thread *thread);
 
 enum md_ro_state {
 	MD_RDWR,
@@ -6269,10 +6270,12 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev)
 	}
 	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-	if (mddev->sync_thread)
-		/* Thread might be blocked waiting for metadata update
-		 * which will now never happen */
-		wake_up_process(mddev->sync_thread->tsk);
+
+	/*
+	 * Thread might be blocked waiting for metadata update which will now
+	 * never happen
+	 */
+	md_wakeup_thread_directly(mddev->sync_thread);
 
 	if (mddev->external && test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags))
 		return -EBUSY;
@@ -6333,10 +6336,12 @@ static int do_md_stop(struct mddev *mddev, int mode,
 	}
 	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		set_bit(MD_RECOVERY_INTR, &mddev->recovery);
-	if (mddev->sync_thread)
-		/* Thread might be blocked waiting for metadata update
-		 * which will now never happen */
-		wake_up_process(mddev->sync_thread->tsk);
+
+	/*
+	 * Thread might be blocked waiting for metadata update which will now
+	 * never happen
+	 */
+	md_wakeup_thread_directly(mddev->sync_thread);
 
 	mddev_unlock(mddev);
 	wait_event(resync_wait, (mddev->sync_thread == NULL &&
@@ -7886,6 +7891,12 @@ static int md_thread(void *arg)
 	return 0;
 }
 
+static void md_wakeup_thread_directly(struct md_thread *thread)
+{
+	if (thread)
+		wake_up_process(thread->tsk);
+}
+
 void md_wakeup_thread(struct md_thread *thread)
 {
 	if (thread) {
-- 
2.39.2

[PATCH -next v5 3/6] dm-raid: remove useless checking in raid_message()

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

md_wakeup_thread() handle the case that pass in md_thread is NULL, there
is no need to check this. Prepare to protect md_thread with rcu.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/dm-raid.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 2dfd51509647..9db45f3508e3 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3750,11 +3750,11 @@ static int raid_message(struct dm_target *ti, unsigned int argc, char **argv,
 		 * canceling read-auto mode
 		 */
 		mddev->ro = 0;
-		if (!mddev->suspended && mddev->sync_thread)
+		if (!mddev->suspended)
 			md_wakeup_thread(mddev->sync_thread);
 	}
 	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
-	if (!mddev->suspended && mddev->thread)
+	if (!mddev->suspended)
 		md_wakeup_thread(mddev->thread);
 
 	return 0;
-- 
2.39.2

[PATCH -next v5 4/6] md/bitmap: always wake up md_thread in timeout_store

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

md_wakeup_thread() can handle the case that pass in md_thread is NULL,
the only difference is that md_wakeup_thread() will be called when
current timeout is 'MAX_SCHEDULE_TIMEOUT', this should not matter
because timeout_store() is not hot path, and the daemon process is
woke up more than demand from other context already.

This patch prepare to factor out a helper to set timeout.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md-bitmap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index e7cc6ba1b657..014e5c8a4fe0 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -2452,11 +2452,11 @@ timeout_store(struct mddev *mddev, const char *buf, size_t len)
 		 * the bitmap is all clean and we don't need to
 		 * adjust the timeout right now
 		 */
-		if (mddev->thread->timeout < MAX_SCHEDULE_TIMEOUT) {
+		if (mddev->thread->timeout < MAX_SCHEDULE_TIMEOUT)
 			mddev->thread->timeout = timeout;
-			md_wakeup_thread(mddev->thread);
-		}
 	}
+
+	md_wakeup_thread(mddev->thread);
 	return len;
 }
 
-- 
2.39.2

[PATCH -next v5 5/6] md/bitmap: factor out a helper to set timeout

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Register/unregister 'mddev->thread' are both under 'reconfig_mutex',
however, some context didn't hold the mutex to access mddev->thread,
which can cause null-ptr-deference:

1) md_bitmap_daemon_work() can be called from md_check_recovery() where
'reconfig_mutex' is not held, deference 'mddev->thread' might cause
null-ptr-deference, because md_unregister_thread() reset the pointer
before stopping the thread.

2) timeout_store() access 'mddev->thread' multiple times,
null-ptr-deference can be triggered if 'mddev->thread' is reset in the
middle.

This patch factor out a helper to set timeout, the new helper always
check if 'mddev->thread' is null first, so that problem 1 can be fixed.

Now that this helper only access 'mddev->thread' once, but it's possible
that 'mddev->thread' is freed while this helper is still in progress,
hence the problem is not fixed yet. Follow up patches will fix this by
protecting md_thread with rcu.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md-bitmap.c | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 014e5c8a4fe0..29fd41ef55a6 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1218,11 +1218,22 @@ static bitmap_counter_t *md_bitmap_get_counter(struct bitmap_counts *bitmap,
 					       sector_t offset, sector_t *blocks,
 					       int create);
 
+static void mddev_set_timeout(struct mddev *mddev, unsigned long timeout,
+			      bool force)
+{
+	struct md_thread *thread = mddev->thread;
+
+	if (!thread)
+		return;
+
+	if (force || thread->timeout < MAX_SCHEDULE_TIMEOUT)
+		thread->timeout = timeout;
+}
+
 /*
  * bitmap daemon -- periodically wakes up to clean bits and flush pages
  *			out to disk
  */
-
 void md_bitmap_daemon_work(struct mddev *mddev)
 {
 	struct bitmap *bitmap;
@@ -1246,7 +1257,7 @@ void md_bitmap_daemon_work(struct mddev *mddev)
 
 	bitmap->daemon_lastrun = jiffies;
 	if (bitmap->allclean) {
-		mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
+		mddev_set_timeout(mddev, MAX_SCHEDULE_TIMEOUT, true);
 		goto done;
 	}
 	bitmap->allclean = 1;
@@ -1343,8 +1354,7 @@ void md_bitmap_daemon_work(struct mddev *mddev)
 
  done:
 	if (bitmap->allclean == 0)
-		mddev->thread->timeout =
-			mddev->bitmap_info.daemon_sleep;
+		mddev_set_timeout(mddev, mddev->bitmap_info.daemon_sleep, true);
 	mutex_unlock(&mddev->bitmap_info.mutex);
 }
 
@@ -1797,8 +1807,7 @@ void md_bitmap_destroy(struct mddev *mddev)
 	mddev->bitmap = NULL; /* disconnect from the md device */
 	spin_unlock(&mddev->lock);
 	mutex_unlock(&mddev->bitmap_info.mutex);
-	if (mddev->thread)
-		mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
+	mddev_set_timeout(mddev, MAX_SCHEDULE_TIMEOUT, true);
 
 	md_bitmap_free(bitmap);
 }
@@ -1941,7 +1950,7 @@ int md_bitmap_load(struct mddev *mddev)
 	/* Kick recovery in case any bits were set */
 	set_bit(MD_RECOVERY_NEEDED, &bitmap->mddev->recovery);
 
-	mddev->thread->timeout = mddev->bitmap_info.daemon_sleep;
+	mddev_set_timeout(mddev, mddev->bitmap_info.daemon_sleep, true);
 	md_wakeup_thread(mddev->thread);
 
 	md_bitmap_update_sb(bitmap);
@@ -2446,17 +2455,11 @@ timeout_store(struct mddev *mddev, const char *buf, size_t len)
 		timeout = MAX_SCHEDULE_TIMEOUT-1;
 	if (timeout < 1)
 		timeout = 1;
-	mddev->bitmap_info.daemon_sleep = timeout;
-	if (mddev->thread) {
-		/* if thread->timeout is MAX_SCHEDULE_TIMEOUT, then
-		 * the bitmap is all clean and we don't need to
-		 * adjust the timeout right now
-		 */
-		if (mddev->thread->timeout < MAX_SCHEDULE_TIMEOUT)
-			mddev->thread->timeout = timeout;
-	}
 
+	mddev->bitmap_info.daemon_sleep = timeout;
+	mddev_set_timeout(mddev, timeout, false);
 	md_wakeup_thread(mddev->thread);
+
 	return len;
 }
 
-- 
2.39.2

[PATCH -next v5 6/6] md: protect md_thread with rcu

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Our test reports a uaf for 'mddev->sync_thread':

T1                      T2
md_start_sync
 md_register_thread
 // mddev->sync_thread is set
			raid1d
			 md_check_recovery
			  md_reap_sync_thread
			   md_unregister_thread
			    kfree

 md_wakeup_thread
  wake_up
  ->sync_thread was freed

Root cause is that there is a small windown between register thread and
wake up thread, where the thread can be freed concurrently.

Currently, a global spinlock 'pers_lock' is borrowed to protect
'mddev->thread', this problem can be fixed likewise, however, there might
be similar problem elsewhere, and use a global lock for all the cases is
not good.

This patch protect md_thread with rcu.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md-bitmap.c   | 29 ++++++++++++-----
 drivers/md/md.c          | 68 +++++++++++++++++++---------------------
 drivers/md/md.h          | 10 +++---
 drivers/md/raid1.c       |  4 +--
 drivers/md/raid1.h       |  2 +-
 drivers/md/raid10.c      | 10 ++++--
 drivers/md/raid10.h      |  2 +-
 drivers/md/raid5-cache.c | 15 +++++----
 drivers/md/raid5.c       |  4 +--
 drivers/md/raid5.h       |  2 +-
 10 files changed, 81 insertions(+), 65 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 29fd41ef55a6..b9baeea5605e 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1219,15 +1219,27 @@ static bitmap_counter_t *md_bitmap_get_counter(struct bitmap_counts *bitmap,
 					       int create);
 
 static void mddev_set_timeout(struct mddev *mddev, unsigned long timeout,
-			      bool force)
+			      bool force, bool protected)
 {
-	struct md_thread *thread = mddev->thread;
+	struct md_thread *thread;
+
+	if (!protected) {
+		rcu_read_lock();
+		thread = rcu_dereference(mddev->thread);
+	} else {
+		thread = rcu_dereference_protected(mddev->thread,
+				lockdep_is_held(&mddev->reconfig_mutex));
+	}
 
 	if (!thread)
-		return;
+		goto out;
 
 	if (force || thread->timeout < MAX_SCHEDULE_TIMEOUT)
 		thread->timeout = timeout;
+
+out:
+	if (!protected)
+		rcu_read_unlock();
 }
 
 /*
@@ -1257,7 +1269,7 @@ void md_bitmap_daemon_work(struct mddev *mddev)
 
 	bitmap->daemon_lastrun = jiffies;
 	if (bitmap->allclean) {
-		mddev_set_timeout(mddev, MAX_SCHEDULE_TIMEOUT, true);
+		mddev_set_timeout(mddev, MAX_SCHEDULE_TIMEOUT, true, false);
 		goto done;
 	}
 	bitmap->allclean = 1;
@@ -1354,7 +1366,8 @@ void md_bitmap_daemon_work(struct mddev *mddev)
 
  done:
 	if (bitmap->allclean == 0)
-		mddev_set_timeout(mddev, mddev->bitmap_info.daemon_sleep, true);
+		mddev_set_timeout(mddev, mddev->bitmap_info.daemon_sleep, true,
+				  false);
 	mutex_unlock(&mddev->bitmap_info.mutex);
 }
 
@@ -1807,7 +1820,7 @@ void md_bitmap_destroy(struct mddev *mddev)
 	mddev->bitmap = NULL; /* disconnect from the md device */
 	spin_unlock(&mddev->lock);
 	mutex_unlock(&mddev->bitmap_info.mutex);
-	mddev_set_timeout(mddev, MAX_SCHEDULE_TIMEOUT, true);
+	mddev_set_timeout(mddev, MAX_SCHEDULE_TIMEOUT, true, true);
 
 	md_bitmap_free(bitmap);
 }
@@ -1950,7 +1963,7 @@ int md_bitmap_load(struct mddev *mddev)
 	/* Kick recovery in case any bits were set */
 	set_bit(MD_RECOVERY_NEEDED, &bitmap->mddev->recovery);
 
-	mddev_set_timeout(mddev, mddev->bitmap_info.daemon_sleep, true);
+	mddev_set_timeout(mddev, mddev->bitmap_info.daemon_sleep, true, true);
 	md_wakeup_thread(mddev->thread);
 
 	md_bitmap_update_sb(bitmap);
@@ -2457,7 +2470,7 @@ timeout_store(struct mddev *mddev, const char *buf, size_t len)
 		timeout = 1;
 
 	mddev->bitmap_info.daemon_sleep = timeout;
-	mddev_set_timeout(mddev, timeout, false);
+	mddev_set_timeout(mddev, timeout, false, false);
 	md_wakeup_thread(mddev->thread);
 
 	return len;
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 139c7b0202e3..3afece35f0ee 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -70,11 +70,7 @@
 #include "md-bitmap.h"
 #include "md-cluster.h"
 
-/* pers_list is a list of registered personalities protected
- * by pers_lock.
- * pers_lock does extra service to protect accesses to
- * mddev->thread when the mutex cannot be held.
- */
+/* pers_list is a list of registered personalities protected by pers_lock. */
 static LIST_HEAD(pers_list);
 static DEFINE_SPINLOCK(pers_lock);
 
@@ -92,7 +88,7 @@ static struct workqueue_struct *md_rdev_misc_wq;
 static int remove_and_add_spares(struct mddev *mddev,
 				 struct md_rdev *this);
 static void mddev_detach(struct mddev *mddev);
-static void md_wakeup_thread_directly(struct md_thread *thread);
+static void md_wakeup_thread_directly(struct md_thread __rcu *thread);
 
 enum md_ro_state {
 	MD_RDWR,
@@ -458,8 +454,10 @@ static void md_submit_bio(struct bio *bio)
  */
 void mddev_suspend(struct mddev *mddev)
 {
-	WARN_ON_ONCE(mddev->thread && current == mddev->thread->tsk);
-	lockdep_assert_held(&mddev->reconfig_mutex);
+	struct md_thread *thread = rcu_dereference_protected(mddev->thread,
+			lockdep_is_held(&mddev->reconfig_mutex));
+
+	WARN_ON_ONCE(thread && current == thread->tsk);
 	if (mddev->suspended++)
 		return;
 	wake_up(&mddev->sb_wait);
@@ -801,13 +799,8 @@ void mddev_unlock(struct mddev *mddev)
 	} else
 		mutex_unlock(&mddev->reconfig_mutex);
 
-	/* As we've dropped the mutex we need a spinlock to
-	 * make sure the thread doesn't disappear
-	 */
-	spin_lock(&pers_lock);
 	md_wakeup_thread(mddev->thread);
 	wake_up(&mddev->sb_wait);
-	spin_unlock(&pers_lock);
 }
 EXPORT_SYMBOL_GPL(mddev_unlock);
 
@@ -7891,23 +7884,33 @@ static int md_thread(void *arg)
 	return 0;
 }
 
-static void md_wakeup_thread_directly(struct md_thread *thread)
+static void md_wakeup_thread_directly(struct md_thread __rcu *thread)
 {
-	if (thread)
-		wake_up_process(thread->tsk);
+	struct md_thread *t;
+
+	rcu_read_lock();
+	t = rcu_dereference(thread);
+	if (t)
+		wake_up_process(t->tsk);
+	rcu_read_unlock();
 }
 
-void md_wakeup_thread(struct md_thread *thread)
+void md_wakeup_thread(struct md_thread __rcu *thread)
 {
-	if (thread) {
-		pr_debug("md: waking up MD thread %s.\n", thread->tsk->comm);
-		set_bit(THREAD_WAKEUP, &thread->flags);
-		wake_up(&thread->wqueue);
+	struct md_thread *t;
+
+	rcu_read_lock();
+	t = rcu_dereference(thread);
+	if (t) {
+		pr_debug("md: waking up MD thread %s.\n", t->tsk->comm);
+		set_bit(THREAD_WAKEUP, &t->flags);
+		wake_up(&t->wqueue);
 	}
+	rcu_read_unlock();
 }
 EXPORT_SYMBOL(md_wakeup_thread);
 
-int md_register_thread(struct md_thread **threadp,
+int md_register_thread(struct md_thread __rcu **threadp,
 		       void (*run)(struct md_thread *),
 		       struct mddev *mddev, const char *name)
 {
@@ -7931,27 +7934,20 @@ int md_register_thread(struct md_thread **threadp,
 		return err;
 	}
 
-	*threadp = thread;
+	rcu_assign_pointer(*threadp, thread);
 	return 0;
 }
 EXPORT_SYMBOL(md_register_thread);
 
-void md_unregister_thread(struct md_thread **threadp)
+void md_unregister_thread(struct md_thread __rcu **threadp)
 {
-	struct md_thread *thread;
+	struct md_thread *thread = rcu_dereference_protected(*threadp, true);
 
-	/*
-	 * Locking ensures that mddev_unlock does not wake_up a
-	 * non-existent thread
-	 */
-	spin_lock(&pers_lock);
-	thread = *threadp;
-	if (!thread) {
-		spin_unlock(&pers_lock);
+	if (!thread)
 		return;
-	}
-	*threadp = NULL;
-	spin_unlock(&pers_lock);
+
+	rcu_assign_pointer(*threadp, NULL);
+	synchronize_rcu();
 
 	pr_debug("interrupting MD-thread pid %d\n", task_pid_nr(thread->tsk));
 	kthread_stop(thread->tsk);
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 7af45b8432e9..621a3f183afd 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -367,8 +367,8 @@ struct mddev {
 	int				new_chunk_sectors;
 	int				reshape_backwards;
 
-	struct md_thread		*thread;	/* management thread */
-	struct md_thread		*sync_thread;	/* doing resync or reconstruct */
+	struct md_thread __rcu		*thread;	/* management thread */
+	struct md_thread __rcu		*sync_thread;	/* doing resync or reconstruct */
 
 	/* 'last_sync_action' is initialized to "none".  It is set when a
 	 * sync operation (i.e "data-check", "requested-resync", "resync",
@@ -730,11 +730,11 @@ extern int register_md_cluster_operations(struct md_cluster_operations *ops,
 extern int unregister_md_cluster_operations(void);
 extern int md_setup_cluster(struct mddev *mddev, int nodes);
 extern void md_cluster_stop(struct mddev *mddev);
-extern int md_register_thread(struct md_thread **threadp,
+extern int md_register_thread(struct md_thread __rcu **threadp,
 			      void (*run)(struct md_thread *thread),
 			      struct mddev *mddev, const char *name);
-extern void md_unregister_thread(struct md_thread **threadp);
-extern void md_wakeup_thread(struct md_thread *thread);
+extern void md_unregister_thread(struct md_thread __rcu **threadp);
+extern void md_wakeup_thread(struct md_thread __rcu *thread);
 extern void md_check_recovery(struct mddev *mddev);
 extern void md_reap_sync_thread(struct mddev *mddev);
 extern int mddev_init_writes_pending(struct mddev *mddev);
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 1217c1db0a40..64f019e3615f 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -3176,8 +3176,8 @@ static int raid1_run(struct mddev *mddev)
 	/*
 	 * Ok, everything is just fine now
 	 */
-	mddev->thread = conf->thread;
-	conf->thread = NULL;
+	rcu_assign_pointer(mddev->thread, conf->thread);
+	rcu_assign_pointer(conf->thread, NULL);
 	mddev->private = conf;
 	set_bit(MD_FAILFAST_SUPPORTED, &mddev->flags);
 
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index ebb6788820e7..468f189da7a0 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -130,7 +130,7 @@ struct r1conf {
 	/* When taking over an array from a different personality, we store
 	 * the new thread here until we fully activate the array.
 	 */
-	struct md_thread	*thread;
+	struct md_thread __rcu	*thread;
 
 	/* Keep track of cluster resync window to send to other
 	 * nodes.
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 0171ba4f19b0..8fa4e61c3f79 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -980,6 +980,7 @@ static void lower_barrier(struct r10conf *conf)
 static bool stop_waiting_barrier(struct r10conf *conf)
 {
 	struct bio_list *bio_list = current->bio_list;
+	struct md_thread *thread;
 
 	/* barrier is dropped */
 	if (!conf->barrier)
@@ -995,8 +996,11 @@ static bool stop_waiting_barrier(struct r10conf *conf)
 	    (!bio_list_empty(&bio_list[0]) || !bio_list_empty(&bio_list[1])))
 		return true;
 
+	/* daemon thread must exist while handling io */
+	thread = rcu_dereference_protected(conf->mddev->thread, true);
+
 	/* move on if recovery thread is blocked by us */
-	if (conf->mddev->thread->tsk == current &&
+	if (thread->tsk == current &&
 	    test_bit(MD_RECOVERY_RUNNING, &conf->mddev->recovery) &&
 	    conf->nr_queued > 0)
 		return true;
@@ -4140,8 +4144,8 @@ static int raid10_run(struct mddev *mddev)
 		}
 	}
 
-	mddev->thread = conf->thread;
-	conf->thread = NULL;
+	rcu_assign_pointer(mddev->thread, conf->thread);
+	rcu_assign_pointer(conf->thread, NULL);
 
 	if (mddev->queue) {
 		blk_queue_max_write_zeroes_sectors(mddev->queue, 0);
diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index 8c072ce0bc54..63e48b11b552 100644
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -100,7 +100,7 @@ struct r10conf {
 	/* When taking over an array from a different personality, we store
 	 * the new thread here until we fully activate the array.
 	 */
-	struct md_thread	*thread;
+	struct md_thread __rcu	*thread;
 
 	/*
 	 * Keep track of cluster resync window to send to other nodes.
diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 0464d4d551fc..68c4d3a1fd25 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -120,7 +120,7 @@ struct r5l_log {
 	struct bio_set bs;
 	mempool_t meta_pool;
 
-	struct md_thread *reclaim_thread;
+	struct md_thread __rcu *reclaim_thread;
 	unsigned long reclaim_target;	/* number of space that need to be
 					 * reclaimed.  if it's 0, reclaim spaces
 					 * used by io_units which are in
@@ -1576,17 +1576,18 @@ void r5l_wake_reclaim(struct r5l_log *log, sector_t space)
 
 void r5l_quiesce(struct r5l_log *log, int quiesce)
 {
-	struct mddev *mddev;
+	struct mddev *mddev = log->rdev->mddev;
+	struct md_thread *thread = rcu_dereference_protected(
+		log->reclaim_thread, lockdep_is_held(&mddev->reconfig_mutex));
 
 	if (quiesce) {
 		/* make sure r5l_write_super_and_discard_space exits */
-		mddev = log->rdev->mddev;
 		wake_up(&mddev->sb_wait);
-		kthread_park(log->reclaim_thread->tsk);
+		kthread_park(thread->tsk);
 		r5l_wake_reclaim(log, MaxSector);
 		r5l_do_reclaim(log);
 	} else
-		kthread_unpark(log->reclaim_thread->tsk);
+		kthread_unpark(thread->tsk);
 }
 
 bool r5l_log_disk_error(struct r5conf *conf)
@@ -3124,7 +3125,9 @@ int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
 	if (md_register_thread(&log->reclaim_thread, r5l_reclaim_thread,
 			       log->rdev->mddev, "reclaim"))
 		goto reclaim_thread;
-	log->reclaim_thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;
+
+	rcu_dereference_protected(log->reclaim_thread, true)->timeout =
+						R5C_RECLAIM_WAKEUP_INTERVAL;
 
 	init_waitqueue_head(&log->iounit_wait);
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 04b1093195d0..a7e47c37daf3 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7888,8 +7888,8 @@ static int raid5_run(struct mddev *mddev)
 	}
 
 	conf->min_offset_diff = min_offset_diff;
-	mddev->thread = conf->thread;
-	conf->thread = NULL;
+	rcu_assign_pointer(mddev->thread, conf->thread);
+	rcu_assign_pointer(conf->thread, NULL);
 	mddev->private = conf;
 
 	for (i = 0; i < conf->raid_disks && conf->previous_raid_disks;
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index e873938a6125..f19707189a7b 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -679,7 +679,7 @@ struct r5conf {
 	/* When taking over an array from a different personality, we store
 	 * the new thread here until we fully activate the array.
 	 */
-	struct md_thread	*thread;
+	struct md_thread __rcu	*thread;
 	struct list_head	temp_inactive_list[NR_STRIPE_HASH_LOCKS];
 	struct r5worker_group	*worker_groups;
 	int			group_cnt;
-- 
2.39.2

Re: [PATCH -next v5 6/6] md: protect md_thread with rcu

[Logan Gunthorpe]

On 2023-04-10 05:35, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Our test reports a uaf for 'mddev->sync_thread':
> 
> T1                      T2
> md_start_sync
>  md_register_thread
>  // mddev->sync_thread is set
> 			raid1d
> 			 md_check_recovery
> 			  md_reap_sync_thread
> 			   md_unregister_thread
> 			    kfree
> 
>  md_wakeup_thread
>   wake_up
>   ->sync_thread was freed
> 
> Root cause is that there is a small windown between register thread and
> wake up thread, where the thread can be freed concurrently.
> 
> Currently, a global spinlock 'pers_lock' is borrowed to protect
> 'mddev->thread', this problem can be fixed likewise, however, there might
> be similar problem elsewhere, and use a global lock for all the cases is
> not good.
> 
> This patch protect md_thread with rcu.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  drivers/md/md-bitmap.c   | 29 ++++++++++++-----
>  drivers/md/md.c          | 68 +++++++++++++++++++---------------------
>  drivers/md/md.h          | 10 +++---
>  drivers/md/raid1.c       |  4 +--
>  drivers/md/raid1.h       |  2 +-
>  drivers/md/raid10.c      | 10 ++++--
>  drivers/md/raid10.h      |  2 +-
>  drivers/md/raid5-cache.c | 15 +++++----
>  drivers/md/raid5.c       |  4 +--
>  drivers/md/raid5.h       |  2 +-
>  10 files changed, 81 insertions(+), 65 deletions(-)
> 
> diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
> index 29fd41ef55a6..b9baeea5605e 100644
> --- a/drivers/md/md-bitmap.c
> +++ b/drivers/md/md-bitmap.c
> @@ -1219,15 +1219,27 @@ static bitmap_counter_t *md_bitmap_get_counter(struct bitmap_counts *bitmap,
>  					       int create);
>  
>  static void mddev_set_timeout(struct mddev *mddev, unsigned long timeout,
> -			      bool force)
> +			      bool force, bool protected)
>  {
> -	struct md_thread *thread = mddev->thread;
> +	struct md_thread *thread;
> +
> +	if (!protected) {
> +		rcu_read_lock();
> +		thread = rcu_dereference(mddev->thread);
> +	} else {
> +		thread = rcu_dereference_protected(mddev->thread,
> +				lockdep_is_held(&mddev->reconfig_mutex));
> +	}

Why not just always use rcu_read_lock()? Even if it's safe with
reconfig_mutex, it wouldn't harm much and would make the code a bit less
ugly.


> @@ -458,8 +454,10 @@ static void md_submit_bio(struct bio *bio)
>   */
>  void mddev_suspend(struct mddev *mddev)
>  {
> -	WARN_ON_ONCE(mddev->thread && current == mddev->thread->tsk);
> -	lockdep_assert_held(&mddev->reconfig_mutex);
> +	struct md_thread *thread = rcu_dereference_protected(mddev->thread,
> +			lockdep_is_held(&mddev->reconfig_mutex));

Do we know that reconfig_mutex is always held when we call
md_unregister_thread()? Seems plausible, but maybe it's worth adding a
lockdep_assert_held() to md_unregsiter_thread().

Thanks,

Logan

Re: [PATCH -next v5 6/6] md: protect md_thread with rcu

[Yu Kuai]

Hi,

在 2023/04/10 23:42, Logan Gunthorpe 写道:
> 
> 
> On 2023-04-10 05:35, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Our test reports a uaf for 'mddev->sync_thread':
>>
>> T1                      T2
>> md_start_sync
>>   md_register_thread
>>   // mddev->sync_thread is set
>> 			raid1d
>> 			 md_check_recovery
>> 			  md_reap_sync_thread
>> 			   md_unregister_thread
>> 			    kfree
>>
>>   md_wakeup_thread
>>    wake_up
>>    ->sync_thread was freed
>>
>> Root cause is that there is a small windown between register thread and
>> wake up thread, where the thread can be freed concurrently.
>>
>> Currently, a global spinlock 'pers_lock' is borrowed to protect
>> 'mddev->thread', this problem can be fixed likewise, however, there might
>> be similar problem elsewhere, and use a global lock for all the cases is
>> not good.
>>
>> This patch protect md_thread with rcu.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   drivers/md/md-bitmap.c   | 29 ++++++++++++-----
>>   drivers/md/md.c          | 68 +++++++++++++++++++---------------------
>>   drivers/md/md.h          | 10 +++---
>>   drivers/md/raid1.c       |  4 +--
>>   drivers/md/raid1.h       |  2 +-
>>   drivers/md/raid10.c      | 10 ++++--
>>   drivers/md/raid10.h      |  2 +-
>>   drivers/md/raid5-cache.c | 15 +++++----
>>   drivers/md/raid5.c       |  4 +--
>>   drivers/md/raid5.h       |  2 +-
>>   10 files changed, 81 insertions(+), 65 deletions(-)
>>
>> diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
>> index 29fd41ef55a6..b9baeea5605e 100644
>> --- a/drivers/md/md-bitmap.c
>> +++ b/drivers/md/md-bitmap.c
>> @@ -1219,15 +1219,27 @@ static bitmap_counter_t *md_bitmap_get_counter(struct bitmap_counts *bitmap,
>>   					       int create);
>>   
>>   static void mddev_set_timeout(struct mddev *mddev, unsigned long timeout,
>> -			      bool force)
>> +			      bool force, bool protected)
>>   {
>> -	struct md_thread *thread = mddev->thread;
>> +	struct md_thread *thread;
>> +
>> +	if (!protected) {
>> +		rcu_read_lock();
>> +		thread = rcu_dereference(mddev->thread);
>> +	} else {
>> +		thread = rcu_dereference_protected(mddev->thread,
>> +				lockdep_is_held(&mddev->reconfig_mutex));
>> +	}
> 
> Why not just always use rcu_read_lock()? Even if it's safe with
> reconfig_mutex, it wouldn't harm much and would make the code a bit less
> ugly.
> 
Of course, I'll do that in next version.

> 
>> @@ -458,8 +454,10 @@ static void md_submit_bio(struct bio *bio)
>>    */
>>   void mddev_suspend(struct mddev *mddev)
>>   {
>> -	WARN_ON_ONCE(mddev->thread && current == mddev->thread->tsk);
>> -	lockdep_assert_held(&mddev->reconfig_mutex);
>> +	struct md_thread *thread = rcu_dereference_protected(mddev->thread,
>> +			lockdep_is_held(&mddev->reconfig_mutex));
> 
> Do we know that reconfig_mutex is always held when we call
> md_unregister_thread()? Seems plausible, but maybe it's worth adding a
> lockdep_assert_held() to md_unregsiter_thread().

Unfortunally this is not true for now, md_unregister_thread() can be
called without this mutex from action_store(), and this is problematic,
I'm tring to revert this change in the other thread:

md: fix that MD_RECOVERY_RUNNING can be cleared while sync_thread is
still running.

I think it's not good to add lockdep_assert_held() for now...

Thanks,
Kuai
> 
> Thanks,
> 
> Logan
> .
>