[PATCH] md/raid5: fix possible null-pointer dereferences in raid5_store_group_thread_cnt()

The variable mddev->private is first assigned to conf and then checked:

  conf = mddev->private;
  if (!conf) ...

If conf is NULL, then mddev->private is also NULL. However, the function
does not return at this point, and raid5_quiesce() is later called with
mddev as the argument. Inside raid5_quiesce(), mddev->private is again
assigned to conf, which is then dereferenced in multiple places, for
example:

  conf->quiesce = 0;
  wake_up(&conf->wait_for_quiescent);
  ...

This can lead to several null-pointer dereferences.

To fix these issues, the function should unlock mddev and return early when
conf is NULL, following the pattern in raid5_change_consistency_policy().

Signed-off-by: Tuo Li <[email protected]>
---
 drivers/md/raid5.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e57ce3295292..be3f9a127212 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7190,9 +7190,10 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
 	raid5_quiesce(mddev, true);
 
 	conf = mddev->private;
-	if (!conf)
-		err = -ENODEV;
-	else if (new != conf->worker_cnt_per_group) {
+	if (!conf) {
+		mddev_unlock_and_resume(mddev);
+		return -ENODEV;
+	} else if (new != conf->worker_cnt_per_group) {
 		old_groups = conf->worker_groups;
 		if (old_groups)
 			flush_workqueue(raid5_wq);
-- 
2.43.0