[PATCH v2 0/4] md: Fix two raid5/raid10 bugs

Fix two raid5/raid10 bugs in error injection case.

v1->v2:
 Handle pers->run failure in level_store

Zhihao Cheng (4):
  md/raid5: Hide the origin mddev->thread before takeover
  md: Handle pers->run failure in level_store
  md/raid5: Don't free conf on raid5_run failure
  md/raid10: Don't free conf on raid10_run failure

 drivers/md/md.c     | 27 ++++++++++++++++++++++++++-
 drivers/md/raid10.c | 22 ++++++++++------------
 drivers/md/raid5.c  | 39 ++++++++++++++++++++++++++++-----------
 3 files changed, 64 insertions(+), 24 deletions(-)

-- 
2.52.0

Set 'raid_disks' after raid5_run() failure will trigger an
null-ptr-deref problem:
 BUG: kernel NULL pointer dereference, address: 0000000000000038
 RIP: 0010:raid5_check_reshape+0xad
 Call Trace:
  update_raid_disks+0x124
  raid_disks_store+0x145
  md_attr_store+0xd7
  sysfs_kf_write+0x7c

The trigger process is simple:
 mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda /dev/sdb
 --force --assume-clean # create raid1
 echo 5 > /sys/block/md0/md/level
  level_store
   mddev->pers = pers
   mddev->private = priv
   raid5_run
    fail to abort (eg. raid5_create_ctx_pool fails)
    mddev->private = NULL
 echo 10 > /sys/block/md0/md/raid_disks
  raid_disks_store
   if (mddev->pers) // true
    update_raid_disks
     raid5_check_reshape
      conf = mddev->private
       conf->algorithm = mddev->new_layout // null-ptr-deref !

Similar process exists in do_md_stop->__md_stop_writes->raid5_quiesce.
Similar process exists in raid10 too.

Fix it by handling the error from pers->run, next active-type order will
restart the mddev.

Fixes: 245f46c2c221e ("md: add ->takeover method to support changing the personality managing an array")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
---
 drivers/md/md.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 02798f2dbf0e..fdadd5ff338d 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -97,6 +97,7 @@ static struct workqueue_struct *md_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_stop(struct mddev *mddev);
 static void export_rdev(struct md_rdev *rdev);
 static void md_wakeup_thread_directly(struct md_thread __rcu **thread);
 

@@ -4243,7 +4244,31 @@ level_store(struct mddev *mddev, const char *buf, size_t len)
 		mddev->in_sync = 1;
 		timer_delete_sync(&mddev->safemode_timer);
 	}
-	pers->run(mddev);
+	rv = pers->run(mddev);
+	if (rv) {
+		/*
+		 * ->run() has released the private data of the new personality,
+		 * while the old one has already been released as well. There is
+		 * nothing to fall back to, so stop the array to avoid leaving
+		 * 'mddev->pers' pointing to a personality which has no private
+		 * data, and reminds user to try to active the mddev again.
+		 */
+		pr_warn("md: %s: failed to run %s after takeover, please try to active\n",
+			mdname(mddev), pers->head.name);
+		if (md_bitmap_enabled(mddev, true))
+			mddev->bitmap_ops->flush(mddev);
+		clear_bit(MD_SERIALIZE_POLICY, &mddev->flags);
+		mddev_destroy_serial_pool(mddev, NULL);
+		__md_stop(mddev);
+		rdev_for_each(rdev, mddev)
+			if (rdev->raid_disk >= 0)
+				sysfs_unlink_rdev(mddev, rdev);
+		set_capacity_and_notify(mddev->gendisk, 0);
+		mddev->changed = 1;
+		md_new_event();
+		sysfs_notify_dirent_safe(mddev->sysfs_state);
+		goto out_unlock;
+	}
 	set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
 	if (!mddev->thread)
 		md_update_sb(mddev, 1);

-- 
2.52.0

The raid5 takeover invokes setup_conf and allocates strip heads, but
it wakes up the wrong thread, which lefts strip heads in the list
'conf->released_stripes' and not being processed. If raid5_run fails,
the strip heads won't be released, which triggers the following slab
warnings (CONFIG_SLUB_DEBUG):
 BUG raid5-md0 (Not tainted): Objects remaining on __kmem_cache_shutdown()
 Object 0x0000000062fad548 @offset=3968
 Object 0x000000007f74683c @offset=4960
 WARNING: mm/slub.c:1268 at __slab_err+0x31/0x40, CPU#0: bash/865
 RIP: 0010:__slab_err+0x31
 Call Trace:
  __kmem_cache_shutdown.cold+0x15b
  kmem_cache_destroy+0x71
  free_conf+0xf8
  raid5_run.cold+0x463
  level_store+0x64e
  md_attr_store+0xd7

The detailed triggering process is as follows:
 mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda /dev/sdb
 --force --assume-clean # create raid1, mddev->thread is raid1d
 echo 5 > /sys/block/md0/md/level
  level_store
   raid5_takeover_raid1
     setup_conf
      grow_stripes
       grow_one_stripe
        sh = alloc_stripe
        raid5_release_stripe
          md_wakeup_thread(conf->mddev->thread) // wakeup raid1d
     raid5_run
      ENOMEM = raid5_create_ctx_pool
      free_conf
       shrink_stripes
        drop_one_stripe // no strips found from the conf->inactive_list
        kmem_cache_destroy(conf->slab_cache)
	 __kmem_cache_shutdown
	  free_partial
	   list_slab_objects // some entries are not released !

Fix it by hiding the origin mddev->thread before takeover, so that
new allocating strip heads can be put into 'conf->inactive_list',
which can be found by drop_one_stripe().

Fixes: 773ca82fa1ee ("raid5: make release_stripe lockless")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
---
 drivers/md/raid5.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c091bba95c31..7e87e8a60f5f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c

@@ -9039,19 +9039,38 @@ static void *raid5_takeover(struct mddev *mddev)
 	 *  raid4 - trivial - just use a raid4 layout.
 	 *  raid6 - Providing it is a *_6 layout
 	 */
-	if (mddev->level == 0)
-		return raid45_takeover_raid0(mddev, 5);
-	if (mddev->level == 1)
-		return raid5_takeover_raid1(mddev);
-	if (mddev->level == 4) {
+	void *ret = ERR_PTR(-EINVAL);
+	struct md_thread *thread;
+
+	thread = rcu_dereference_protected(mddev->thread,
+				lockdep_is_held(&mddev->reconfig_mutex));
+	/*
+	 * Set mddev->thread to NULL before setup_conf() to avoid waking up
+	 * wrong thread(eg. raid1), which can prevent the strips from being
+	 * left unreleased in the error handling path(free_conf) of raid5_run.
+	 */
+	rcu_assign_pointer(mddev->thread, NULL);
+
+	switch (mddev->level) {
+	case 0:
+		ret = raid45_takeover_raid0(mddev, 5);
+		break;
+	case 1:
+		ret = raid5_takeover_raid1(mddev);
+		break;
+	case 4:
 		mddev->new_layout = ALGORITHM_PARITY_N;
 		mddev->new_level = 5;
-		return setup_conf(mddev);
+		ret = setup_conf(mddev);
+		break;
+	case 6:
+		ret = raid5_takeover_raid6(mddev);
+		break;
 	}
-	if (mddev->level == 6)
-		return raid5_takeover_raid6(mddev);
 
-	return ERR_PTR(-EINVAL);
+	rcu_assign_pointer(mddev->thread, thread);
+
+	return ret;
 }
 
 static void *raid4_takeover(struct mddev *mddev)

-- 
2.52.0

Since all pers->run() callers handle the error case, no need to free
conf when raid5_run() fails.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
---
 drivers/md/raid5.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 7e87e8a60f5f..913e5a709e35 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c

@@ -8263,8 +8263,6 @@ static int raid5_run(struct mddev *mddev)
 abort:
 	md_unregister_thread(mddev, &mddev->thread);
 	print_raid5_conf(conf);
-	free_conf(conf);
-	mddev->private = NULL;
 	pr_warn("md/raid:%s: failed to run raid set.\n", mdname(mddev));
 	return ret;
 }

-- 
2.52.0

Since all pers->run() callers handle the error case, no need to free
conf when raid10_run() fails.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
---
 drivers/md/raid10.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 1093c798d9dd..9e4d4202f35c 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c

@@ -3972,7 +3972,7 @@ static int raid10_run(struct mddev *mddev)
 		if (fc > 1 || fo > 0) {
 			pr_err("only near layout is supported by clustered"
 				" raid10\n");
-			goto out_free_conf;
+			goto out_unregister_thread;
 		}
 	}
 

@@ -3989,11 +3989,11 @@ static int raid10_run(struct mddev *mddev)
 
 		if (test_bit(Replacement, &rdev->flags)) {
 			if (disk->replacement)
-				goto out_free_conf;
+				goto out_unregister_thread;
 			disk->replacement = rdev;
 		} else {
 			if (disk->rdev)
-				goto out_free_conf;
+				goto out_unregister_thread;
 			disk->rdev = rdev;
 		}
 		diff = (rdev->new_data_offset - rdev->data_offset);

@@ -4013,7 +4013,7 @@ static int raid10_run(struct mddev *mddev)
 
 		if (err) {
 			ret = err;
-			goto out_free_conf;
+			goto out_unregister_thread;
 		}
 	}
 

@@ -4021,17 +4021,17 @@ static int raid10_run(struct mddev *mddev)
 	if (!enough(conf, -1)) {
 		pr_err("md/raid10:%s: not enough operational mirrors.\n",
 		       mdname(mddev));
-		goto out_free_conf;
+		goto out_unregister_thread;
 	}
 
 	if (conf->reshape_progress != MaxSector) {
 		/* must ensure that shape change is supported */
 		if (conf->geo.far_copies != 1 &&
 		    conf->geo.far_offset == 0)
-			goto out_free_conf;
+			goto out_unregister_thread;
 		if (conf->prev.far_copies != 1 &&
 		    conf->prev.far_offset == 0)
-			goto out_free_conf;
+			goto out_unregister_thread;
 	}
 
 	mddev->degraded = 0;

@@ -4081,7 +4081,7 @@ static int raid10_run(struct mddev *mddev)
 	set_bit(MD_FAILFAST_SUPPORTED, &mddev->flags);
 
 	if (md_integrity_register(mddev))
-		goto out_free_conf;
+		goto out_unregister_thread;
 
 	if (conf->reshape_progress != MaxSector) {
 		unsigned long before_length, after_length;

@@ -4094,7 +4094,7 @@ static int raid10_run(struct mddev *mddev)
 		if (max(before_length, after_length) > min_offset_diff) {
 			/* This cannot work */
 			pr_warn("md/raid10: offset difference not enough to continue reshape\n");
-			goto out_free_conf;
+			goto out_unregister_thread;
 		}
 		conf->offset_diff = min_offset_diff;
 

@@ -4106,10 +4106,8 @@ static int raid10_run(struct mddev *mddev)
 
 	return 0;
 
-out_free_conf:
+out_unregister_thread:
 	md_unregister_thread(mddev, &mddev->thread);
-	raid10_free_conf(conf);
-	mddev->private = NULL;
 out:
 	return ret;
 }

-- 
2.52.0

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] md: NULL pointer dereference in md_handle_request() when resuming array after pers->run() failure
- [Medium] md: sysfs group md_redundancy_group leaked on pers->run() failure
--

commit 4ab3c278fcfe04083eb0fb2b801da26eb96c6cec
Author: Zhihao Cheng [off-list ref]

md: Handle pers->run failure in level_store

This commit fixes a NULL pointer dereference that occurs when raid_disks
is set after raid5_run() fails during array conversion. It handles the
error by stopping the array if the new personality fails to run, allowing
a subsequent active order to restart it.

[ ... ]

[Severity: High]
Does calling __md_stop() here introduce a NULL pointer dereference for in-flight IOs?

If level_store() is called while IOs are active, mddev_suspend_and_lock() will
force them to wait in md_handle_request(). __md_stop() sets mddev->pers = NULL.

When the error path later reaches out_unlock and calls mddev_unlock_and_resume(),
will the trapped IOs wake up and unconditionally call mddev->pers->make_request()
while mddev->pers is NULL, panicking the kernel?

[Severity: Medium]
When converting from a non-redundancy array to a redundancy array,
sysfs_create_group() is called earlier in level_store() to add md_redundancy_group.

Does this error path leak the sysfs group and its kernfs_node references, since
mddev->to_remove is not set to &md_redundancy_group to trigger cleanup in
mddev_unlock()?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260922141456.738937-1-chengzhihao1@huawei.com?part=2