[PATCH] md: fix null-ptr-deference in md_free_disk()

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

If md_run() failed after 'acitive_io' is initialized, then
percpu_ref_exit() is called in error path, however, later md_free_disk()
will call percpu_ref_exit() again, which lead to following
null-ptr-deference:

BUG: kernel NULL pointer dereference, address: 0000000000000038
Oops: 0000 [#1] PREEMPT SMP
CPU: 41 PID: 585 Comm: kworker/41:1 Not tainted 6.2.0-rc8-next-20230220 #1452
Workqueue: md_misc mddev_delayed_delete
RIP: 0010:free_percpu+0x110/0x630
Call Trace:
 <TASK>
 __percpu_ref_exit+0x44/0x70
 percpu_ref_exit+0x16/0x90
 md_free_disk+0x2f/0x80
 disk_release+0x101/0x180
 device_release+0x84/0x110
 kobject_put+0x12a/0x380
 kobject_put+0x160/0x380
 mddev_delayed_delete+0x19/0x30
 process_one_work+0x269/0x680
 worker_thread+0x266/0x640
 kthread+0x151/0x1b0
 ret_from_fork+0x1f/0x30

Since freeing mddev will exit 'active_io' unconditionally, fix the
problem by removing exiting 'active_io' from error path, this way
it will be delayed to free mddev.

Fixes: 72adae23a72c ("md: Change active_io to percpu")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 drivers/md/md.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 927a43db5dfb..77124679b3fd 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5851,7 +5851,7 @@ int md_run(struct mddev *mddev)
 	if (!bioset_initialized(&mddev->bio_set)) {
 		err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
 		if (err)
-			goto exit_active_io;
+			return err;
 	}
 	if (!bioset_initialized(&mddev->sync_set)) {
 		err = bioset_init(&mddev->sync_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
@@ -6039,8 +6039,6 @@ int md_run(struct mddev *mddev)
 	bioset_exit(&mddev->sync_set);
 exit_bio_set:
 	bioset_exit(&mddev->bio_set);
-exit_active_io:
-	percpu_ref_exit(&mddev->active_io);
 	return err;
 }
 EXPORT_SYMBOL_GPL(md_run);
-- 
2.31.1