[PATCH] MTD: fix slab-use-after-free due to dangling pointer in notifier chain

[Dennis Lam]

When attaching MTDs, a reboot notifier is added to the blocking
notification chain. However, when detaching a MTD and freeing its
related objects, the notifier is never unregistered from the
notification chain and is freed during the detaching process. This
results in the slab-use-after-free.

To fix this, I added an unregister notifier function in the ubi_wl_close
function to ensure that the notifier is removed from the chain after the
device has been detached.

Signed-off-by: Dennis Lam <dennis.lamerice at gmail.com>
Reported-by: syzbot+0988a383ae7c57b99dd9 at syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67409091.050a0220.363a1b.013d.GAE@google.com/T/
---
 drivers/mtd/ubi/wl.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 4f6f339d8fb8..31a1e5515d98 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -1995,6 +1995,7 @@ static void protection_queue_destroy(struct ubi_device *ubi)
 void ubi_wl_close(struct ubi_device *ubi)
 {
 	dbg_wl("close the WL sub-system");
+	unregister_reboot_notifier(&ubi->wl_reboot_notifier);
 	ubi_fastmap_close(ubi);
 	shutdown_work(ubi);
 	protection_queue_destroy(ubi);
-- 
2.47.0