CVE-2024-26946: Linux Kernel Vulnerability in Kprobes/x86 Resolved - Preventing Kernel Panic, and Ensuring System Stability

The Linux kernel is one of the most critical components of any Linux-based operating system, providing an interface between the computer's hardware and its software. As such, it is crucial that any vulnerability within the kernel be addressed and resolved as soon as possible. In this post, we will discuss the recent resolution of a Linux kernel vulnerability, identified as CVE-2024-26946. This vulnerability pertained to the "kprobes/x86" module, and specifically, the use of the copy_from_kernel_nofault() function to read from an unsafe address. Additionally, we will provide details regarding the exploit, its impact, and the steps taken to resolve the issue.

The Linux kernel vulnerability was initially reported by the Syzcaller bot, which is an automated program that tests different kernel builds for potential bugs. In this case, the bot identified a bug within the arch_adjust_kprobe_addr() function, which is responsible for adjusting the address of a Kprobe, given its current code address. The specifics of the bug were that if a user were to specify an inaccessible or unsafe data area as the address, the arch_adjust_kprobe_addr() function would cause a kernel panic—an unexpected and unrecoverable crash of the kernel.

To better understand the issue at hand, let's take a look at the problematic code snippet in question:

int arch_adjust_kprobe_addr(struct kprobe *p)
{
    /* Code before the fix */
    unsigned long *insn;

    /* Read one instruction */
    memcpy(insn, (void *)p->addr, MAX_INSN_SIZE * sizeof(*insn));

    /* ... rest of the function ... */
}

As seen above, the function utilizes the memcpy() function to read the contents of an address specified by the user. However, the function does not verify beforehand whether the address is safe to read, thus leading to the potential kernel panic.

To address this issue, the developers opted to replace the use of memcpy() with copy_from_kernel_nofault(), which is a built-in Linux kernel function that attempts to read from an address without causing the system to crash or enter an unrecoverable state. The updated code snippet can be found below:

int arch_adjust_kprobe_addr(struct kprobe *p)
{
    /* Code after the fix */
    unsigned long *insn;
    int ret;

    /* Read one instruction */
    ret = copy_from_kernel_nofault(insn, (void *)p->addr, MAX_INSN_SIZE * sizeof(*insn));

    /* ... rest of the function ... */
}

With this change, the function now uses copy_from_kernel_nofault() to read the contents of the specified address, effectively mitigating the risk of a kernel panic.

For further information and original references, please refer to the following resources

- Linux kernel Git repository containing the commit that resolves this vulnerability
- Linux kernel mailing list archive discussing the discovery and resolution of the bug

In summary, the CVE-2024-26946 Linux kernel vulnerability highlights the importance of constantly assessing and improving the kernel's safety and stability. Through the diligent efforts of kernel developers and automated tools such as the Syzcaller bot, this particular vulnerability has been resolved, ensuring that the potential for kernel panics and subsequent system instability is minimized for Linux-based systems around the world.

Timeline

Published on: 05/01/2024 06:15:10 UTC
Last modified on: 12/19/2024 08:50:52 UTC