CVE-2024-46677: Resolving Linux Kernel Vulnerability in GTP Encapsulation - Fixing a Potential NULL Pointer Dereference

A recent vulnerability discovered in the Linux kernel involves an issue with GTP (GPRS Tunneling Protocol) Encapsulation. This vulnerability, assigned the CVE identifier CVE-2024-46677, can potentially cause a NULL pointer dereference, leading to application crashes and other undesired behaviors. This post aims to provide an overview of the vulnerability, the associated code snippet, and links to relevant resources. We will also delve into the details of the exploit and the solution proposed to fix it.

Vulnerability Overview

In the Linux kernel, during the GTP encapsulation process, an issue arises when the sockfd_lookup() function fails. If this occurs, the gtp_encap_enable_socket() function returns a NULL pointer. However, the callers of this function only check for error pointers and miss this NULL pointer case. This can potentially lead to a NULL pointer dereference, which can cause applications to crash or exhibit other undesired behaviors.

To fix this vulnerability, the proposed solution is to have the gtp_encap_enable_socket() function return an error pointer with the error code carried from sockfd_lookup().

Below is an excerpt showcasing the affected code in the Linux kernel

static struct sock *gtp_encap_enable_socket(int fd, int type)
{
    struct sock *sk;
    int err;

    sk = sockfd_lookup(fd, &err);
    if (!sk)
        return ERR_PTR(-err);

    // Additional code
}

// Callers of gtp_encap_enable_socket()
struct gtp_dev *gtp_create(struct net_device *dev)
{
    // Code omitted for brevity

    gtp->sk = gtp_encap_enable_socket(cfg->fd, GTP_V);
    if (IS_ERR(gtp->sk)) {
        ret = PTR_ERR(gtp->sk);
        goto err;
}

As seen above, the gtp_create() function calls the gtp_encap_enable_socket() function and only checks for error pointers using the IS_ERR() macro. Thus, when sockfd_lookup() fails and returns NULL, this goes unchecked and can lead to a NULL pointer dereference later on.

Solution

To fix this issue, the gtp_encap_enable_socket() function should return an error pointer with the error code provided from sockfd_lookup(). This can be done by modifying the relevant code segment as shown below:

// Proposed solution
static struct sock *gtp_encap_enable_socket(int fd, int type)
{
    struct sock *sk;
    int err;

    sk = sockfd_lookup(fd, &err);
    if (!sk)
        return ERR_PTR(err); // Change made here to include error code

    // Additional code
}

With this change, when sockfd_lookup() fails and returns NULL, the gtp_encap_enable_socket() function will now return an error pointer with the error code. This will then properly address the potential for NULL pointer dereference issues.

Original References and Exploit Details

For further information regarding this vulnerability and its associated exploit, you can refer to the following links:

1. Official Linux kernel commit - Fixing GTP encapsulation NULL pointer dereference
2. CVE Details - CVE-2024-46677
3. NVD - National Vulnerability Database - CVE-2024-46677

By understanding the importance of proper error handling and NULL pointer checks, developers can mitigate and fix such Linux kernel vulnerabilities. Keep an eye on this space for more updates and discussions on emerging CVEs and their potential implications.

Timeline

Published on: 09/13/2024 06:15:12 UTC
Last modified on: 09/15/2024 17:57:26 UTC