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

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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. In this case, null-pointer dereferences can occur when calling raid5_quiesce(): raid5_quiesce(mddev, true); raid5_quiesce(mddev, false); since mddev->private is assigned to conf again in raid5_quiesce(), and conf is dereferenced in several places, for example: conf->quiesce = 0; wake_up(&conf->wait_for_quiescent); To fix this issue, the function should unlock mddev and return before invoking raid5_quiesce() when conf is NULL, following the existing pattern in raid5_change_consistency_policy().

References

• https://git.kernel.org/stable/c/20597b7229aea8b5bc45cd92097640257c7fc33b
• https://git.kernel.org/stable/c/e5abb6af905de6b2fead8a0b3f32ab0b81468a01
• https://git.kernel.org/stable/c/7ad6ef91d8745d04aff9cce7bdbc6320d8e05fe9