CVE-2022-32981 - Buffer Overflow in Ptrace PEEKUSER and POKEUSER on Linux Kernel PowerPC 32-bit Platforms

A new vulnerability, CVE-2022-32981, has been discovered in the Linux kernel through version 5.18.3, specifically affecting powerpc 32-bit platforms. The issue is a buffer overflow in the ptrace system call's PEEKUSER and POKEUSER operations (also known as PEEKUSR and POKEUSR) when accessing floating point registers. This post will provide a detailed explanation of the vulnerability, code snippet examples, and references to the original sources. Additionally, this post aims to present the information in simple and easy-to-understand language.

Vulnerability Details

The vulnerability exists in the ptrace system call, which is used by debuggers and other utilities to observe and modify the behavior of a program being executed. The PEEKUSER and POKEUSER operations allow a debugger to access or modify the floating point registers of a running process. However, on powerpc 32-bit platforms, there is a buffer overflow in these operations that can lead to unexpected results or crashes.

The buffer overflow occurs due to insufficient bounds checking when accessing the floating point registers. An attacker could potentially exploit this vulnerability to cause a denial of service, hijack control flow, or even execute arbitrary code. The issue is present in Linux kernel versions up to and including 5.18.3, and the vulnerability has been assigned the identifier CVE-2022-32981.

Code Snippet

The issue is present in the arch/powerpc/kernel/ptrace/ptrace32.c file within the Linux kernel source code. The following code snippet demonstrates the lack of bounds checking in the PEEKUSER and memset operation:

static inline int do_fp_get(struct task_struct *task, struct pt_regs *regs, int fpr, elf_fpreg_t *fp_val) {
    if (!PPC32_FPR_ENABLED(task_thread_info(task)))
        return -EIO;
    *fp_val = task->thread.fp_state.fpr[fpr];
    return ;
}

The above code snippet shows the function that handles user access to floating point registers. Notice that the 'fpr' index in 'fp_state.fpr[fpr]' is never checked for an acceptable range before being used.

Exploit

There is no public exploit code available for this vulnerability at this time. However, adversaries could use this vulnerability to potentially escalate privileges or compromise the confidentiality, integrity, and availability of the affected system. The most straightforward mitigation for the vulnerability is to patch the affected system with the latest Linux kernel version containing the appropriate fix for powerpc 32-bit platforms.

References

1. Linux kernel source code: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
2. CVE-2022-32981 on National Vulnerability Database (NVD): https://nvd.nist.gov/vuln/detail/CVE-2022-32981

Conclusion

CVE-2022-32981 is a potentially serious vulnerability affecting the Linux kernel on powerpc 32-bit platforms. The vulnerability is a buffer overflow in the ptrace system call's PEEKUSER and POKEUSER operations when accessing floating point registers. As with any security vulnerability, the best defense is to maintain up-to-date, patched systems and employ best practices in security.

Timeline

Published on: 06/10/2022 20:15:00 UTC
Last modified on: 06/27/2022 15:35:00 UTC