ocfs2: fix slab-use-after-free due to dangling pointer dqi_priv

In the Linux kernel, the following vulnerability has been resolved: ocfs2: fix slab-use-after-free due to dangling pointer dqi_priv When mounting ocfs2 and then remounting it as read-only, a slab-use-after-free occurs after the user uses a syscall to quota_getnextquota. Specifically, sb_dqinfo(sb, type)->dqi_priv is the dangling pointer. During the remounting process, the pointer dqi_priv is freed but is never set as null leaving it to be accessed. Additionally, the read-only option for remounting sets the DQUOT_SUSPENDED flag instead of setting the DQUOT_USAGE_ENABLED flags. Moreover, later in the process of getting the next quota, the function ocfs2_get_next_id is called and only checks the quota usage flags and not the quota suspended flags. To fix this, I set dqi_priv to null when it is freed after remounting with read-only and put a check for DQUOT_SUSPENDED in ocfs2_get_next_id. [[email protected]: coding-style cleanups]