CVE-2024-57892

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]

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

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