The Linux kernel is a widely used and well-established open-source operating system. Despite its popularity and widespread use, vulnerabilities continue to emerge and affect its robustness. In this post, we will delve into one such vulnerability, assigned the identifier CVE-2024-46860, which concerns the WiFi MT76 MT7921 module in the Linux kernel. We will provide a detailed analysis of the vulnerability, a code snippet demonstrating the fix, and references to the original sources and discussions for further understanding. Additionally, we'll take an in-depth look at the exploit details to inform cybersecurity professionals and users alike.

Vulnerability Details

In the Linux kernel, a vulnerability was discovered in the module responsible for handling WiFi, specifically the "mt76_mt7921_ipv6_addr_change" function. The vulnerability is an unintended NULL pointer access in the mt7921_ipv6_addr_change() function, which is called as a notifier when disabling WiFi. As a result, the kernel might crash and cause system instability.

Context

To fully grasp the implications of this vulnerability, it's essential to understand the core concept of NULL pointers in programming languages like C, which the Linux kernel is written in. In C, a pointer is a variable that holds the memory address of another piece of data. A NULL pointer is one without a specified address, which is an invalid address, essentially meaning the pointer doesn’t point to any memory address. Attempting to access a memory location through a NULL pointer will lead to an undefined behavior which in most cases causes the program to crash. Therefore, it is crucial to handle NULL pointers properly in C code.

Fix Explanation

The vulnerability occurs when the mt7921_ipv6_addr_change() function is called upon disabling WiFi. At that point, mvif->phy (a pointer to the physical interface) is already NULL, which leads to a failed access attempt and consequently results in a crash. The fix for this vulnerability involves handling this NULL pointer case properly by not attempting to access the physical interface when it is NULL.

Here's a relevant excerpt from the code, showing the fix

static int mt7921_ipv6_addr_change(struct notifier_block *nb,
      unsigned long event, void *data)
{
    struct inet6_ifaddr *ifa = (struct inet6_ifaddr *)data;
    struct mt7921_vif *mvif = container_of(nb, struct mt7921_vif,
                                        ipv6_notifier);
    ...
+   if (!mvif->phy)
+       return NOTIFY_DONE;
    ...
}

In the above code snippet, the "+" signs indicate the lines that were added to fix the problem. These lines simply check if mvif->phy is NULL before proceeding further, without attempting to access any data through it. If mvif->phy is NULL, the function immediately returns NOTIFY_DONE, indicating that there's no further action necessary.

Original References

1. The commit implementing the fix is available here: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0028a855e6ba9b99f1cb8aa3cfc06ec6575a4d78

2. Details on the MT76 driver for Linux can be found here: https://github.com/openwrt/mt76

Exploit Details

Currently, there are no public exploits available for this specific vulnerability. However, as with any vulnerability, potential exploits may arise. Programmers using the Linux kernel with the affected WiFi module should apply the fix and remain vigilant to any news or developments related to the vulnerability.

Conclusion

CVE-2024-46860 demonstrates the importance of diligently examining and maintaining the code in widely-used systems like the Linux kernel. As developers and cybersecurity professionals, we must familiarize ourselves with vulnerabilities, possible exploits, and their fixes in order to keep the software secure.

Timeline

Published on: 09/27/2024 13:15:17 UTC
Last modified on: 10/02/2024 14:04:38 UTC