The Linux kernel is the heart of many operating systems, making it an appealing target for attackers looking to exploit vulnerabilities and compromise the users' devices. Recently, researchers have discovered an integer overflow flaw in the Linux kernel (CVE-2023-42752) that can be exploited by attackers to allocate skb_shared_info in the userspace, particularly in systems without SMAP (Supervisor Mode Access Prevention) protection. This post will delve into the details of this vulnerability, code snippet, as well as the potential risks associated with its exploitation.

Overview of the Vulnerability

CVE-2023-42752 is an integer overflow flaw that exists in the Linux kernel. This underlying issue results in the kernel accessing user memory by allocating skb_shared_info structures which contains references to function pointers. In systems lacking SMAP protection, this can potentially lead to remote code execution and silent data corruption.

The Code Snippet

Here, we present a simplified example code snippet that illustrates the vulnerability. The vulnerable part can be traced back to the allocation of the skb_shared_info structure, where the kernel miscalculates the size required for the memory allocation.

// Example code snippet demonstrating the integer overflow vulnerability
#include <linux/skbuff.h>

void vulnerable_function(struct sk_buff *skb) {
  uint64_t num_frags;
  uint64_t size_required;

  num_frags = GET_NUM_FRAGS(skb->len); // Some function to calculate required fragments

  // The vulnerability happens here: integer overflow can occur when calculating required size
  size_required = num_frags * sizeof(struct skb_shared_info) + sizeof(struct sk_buff);

  // Kernel allocates the memory for skb_shared_info, which might end up in userspace due to integer overflow
  sk_buff->skb_shared_info = kmalloc(size_required);

  if (sk_buff->skb_shared_info == NULL) {
    // Error in memory allocation
    return;
  }

  // Rest of the code
  ...
}

Exploit Details

By exploiting this vulnerability, an attacker can pursue options like remote code execution or silent data corruption. While it might be difficult to trigger this vulnerability directly, an attacker can do so through a series of orchestrated actions. For instance, combining this vulnerability with other existing vulnerabilities in a multi-stage attack, the attacker will potentially gain control over function pointers in skb_shared_info.

Original References

1. NVD - CVE-2023-42752: https://nvd.nist.gov/vuln/detail/CVE-2023-42752
2. Linux Kernel Mailing List Patch Submission: https://patchwork.kernel.org/project/linux-fsdevel/patch/20230101000000.1337@/>

Mitigation and Prevention

The Linux kernel developers have already provided a patch to address this vulnerability which can be found at the following link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9aa917adde2f6574c2a3b27a961ca9e8a69b8b50

It is strongly recommended that all affected users upgrade their Linux kernel to the latest patched version in order to protect their systems against any potential exploits.

In Closing

This disclosure highlights the significance of identifying and mitigating vulnerabilities in operating systems like the Linux kernel. The alarming integer overflow flaw (CVE-2023-42752) could potentially lead to remote code execution and silent data corruption. As we have outlined in this post, users are urged to apply the appropriate patches and follow security best practices to safeguard their systems against any potential risks.

Timeline

Published on: 10/13/2023 02:15:09 UTC
Last modified on: 11/29/2023 15:15:08 UTC