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

Vulnerability Description

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. [akpm@linux-foundation.org: coding-style cleanups]

References

• https://git.kernel.org/stable/c/58f9e20e2a7602e1dd649a1ec4790077c251cb6c
• https://git.kernel.org/stable/c/8ff6f635a08c30559ded0c110c7ce03ba7747d11
• https://git.kernel.org/stable/c/f44e6d70c100614c211703f065cad448050e4a0e
• https://git.kernel.org/stable/c/2d431192486367eee03cc28d0b53b97dafcb8e63
• https://git.kernel.org/stable/c/2e3d203b1adede46bbba049e497765d67865be18
• https://git.kernel.org/stable/c/ba950a02d8d23811aa1120affd3adedcfac6153d
• https://git.kernel.org/stable/c/5f3fd772d152229d94602bca243fbb658068a597