In the world of cybersecurity, one of the critical tasks is to keep up with the latest vulnerabilities and exploits. The recently resolved vulnerability CVE-2024-56606 addresses a use-after-free bug in the Linux kernel. This post will cover the details of this vulnerability, how it can be exploited, and the steps taken to resolve it. We will also present a code snippet that demonstrates the issue and provide links to the original references.

Vulnerability Details

The vulnerability lies within the Linux kernel, specifically in the "af_packet" implementation. The af_packet is a low-level interface to capture and inject raw packets directly into the kernel. The issue arises in the "packet_create()" function when calling the "sock_init_data()" function.

The problem occurs when the "sock_init_data()" function is called, and if there is an error, the "packet_create()" function frees the "sk" object. However, this leaves a dangling pointer in the "sock" object on return. The unintended consequence is that other code may try to use this freed pointer, leading to a use-after-free bug.

Here is a snippet of the problematic code

static int packet_create(struct net *net, struct socket *sock, int protocol,
			 int kern)
{
	struct sock *sk;
	...
	sock_init_data(sock, sk);
	...
error_proto:
	sock_put(sk); // sk object is freed here
	return ret;
}

Exploit Details

A use-after-free bug can have severe consequences when exploited, including unauthorized access to system resources, crashes, or even arbitrary code execution. Although this particular vulnerability has limited impact due to its position within the kernel and the lack of direct access from userspace, it highlights the need for vigilance in keeping systems secure.

1. CVE Details - CVE-2024-56606
2. Kernel Git Repository - Linux af_packet fix

Resolution

To fix this vulnerability, the key is to avoid freeing the "sk" object after calling the "sock_init_data()" function. Instead, the code must ensure proper error handling and clean up without leaving dangling pointers. Below is the corrected code snippet provided by the Linux kernel maintainers:

static int packet_create(struct net *net, struct socket *sock, int protocol,
			 int kern)
{
	struct sock *sk;
	...
	sock_init_data(sock, sk);
	...
error_proto:
	if (ret)
		sock_reset_flag(sk, SOCK_EXTERNALLY_ALLOCATED);
	else
		sock_put(sk);
	return ret;
}

Conclusion

Keeping your systems updated and patched is essential to maintain security. While the impact of CVE-2024-56606 may be limited, it serves as a reminder for developers and system administrators alike to remain vigilant and stay informed about potential vulnerabilities within the software they use.

Stay tuned for more updates on the latest vulnerabilities and exploits, and ensure you follow best practices in maintaining a secure system.

Timeline

Published on: 12/27/2024 15:15:20 UTC
Last modified on: 02/11/2025 16:15:45 UTC