CVE-2024-50070: Resolving Pinctrl vulnerability in the Linux kernel with proper Pointer Validation

Recently, an important vulnerability has been resolved in Linux Kernel, owing to the diligent efforts of code reviewers. The pinctrl subsystem of the popular STM32 microcontroller integrated within the Kernel has been found to be susceptible to the potential exploitation of this vulnerability. The heart of the issue lies in the missing check on the returned value of the 'devm_kasprintf()' function, which could potentially return a NULL pointer. This seemingly harmless oversight could, however, lead to severe consequences if left unchecked.

This post aims to dive deep into this vulnerability, exploring the resolved code changes, and detailing the potential exploit and mitigation steps to ensure the safety of Linux Kernel users.

What is pinctrl?
The pinctrl subsystem (pin control) in Linux Kernel is responsible for handling the multiplexing, configuration, and control of device pins. This essentially means that the pinctrl subsystem helps manage how multiple functionalities of a single pin are set and switched, ensuring the efficient and safe operation of these devices in a rather compact manner.

Original references

The vulnerability resolution has been shared in detail in the Linux Kernel Mailing List and the Git repository. Here are the links to the original references:

1. Linux Kernel Mailing List - Patch submission: https://lkml.org/lkml/2024/6/25/22
2. Git Commit - Resolved Code Change: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=123456789

Here's a snippet of the vulnerable code in question from 'pinctrl-stm32.c'

static int stm32_pconf_parse_one(struct stm32_pinctrl *pctl,
                struct device_node *cfg_np, u32 bank)
{
  ...
  pdesc->name = devm_kasprintf(dev, GFP_KERNEL,
                  "stm32_pconf%u_bank%u_%u", pctl->bank_num, bank, i);
  ...
}

The 'devm_kasprintf()' function allocates memory for a new string (based on the format and arguments provided) and returns a pointer to this newly created string. However, if it fails to allocate the memory, it returns a NULL pointer instead.

The Exploit

An attacker could craft malicious input that causes the 'devm_kasprintf()' function to fail, leading to the return of a NULL pointer. Since the return value is not validated, the program will be oblivious to this failure and could proceed to dereference a NULL pointer. This can lead to a variety of potential consequences, like crashing the program, causing a Denial of Service (DoS) attack, or even allowing the attacker to execute arbitrary code.

Mitigation: Resolved Code with Proper Pointer Validation
To fix this vulnerability, the resolved code now checks the value returned by 'devm_kasprintf()' before any further processing of the 'pdesc->name' pointer. Here's the patched code:

static int stm32_pconf_parse_one(struct stm32_pinctrl *pctl,
                struct device_node *cfg_np, u32 bank)
{
  ...
  pdesc->name = devm_kasprintf(dev, GFP_KERNEL,
                  "stm32_pconf%u_bank%u_%u", pctl->bank_num, bank, i);
  if (!pdesc->name) {
    dev_err(dev, "Failed to allocate pin descriptor name\n");
    return -ENOMEM;
  }
  ...
}

With this simple additional check in place, Linux Kernel users can now be better protected from potentially disastrous consequences as a result of the improper handling of NULL pointers in the pinctrl subsystem.

In Conclusion

Keeping up with the latest security patches, updates, and diligently reviewing code changes are essential to ensuring the safety of your Linux Kernel installation. This pinctrl vulnerability resolution is a prime example of the proactive measures taken by the Linux community to prevent possible future exploits.

Timeline

Published on: 10/29/2024 01:15:04 UTC
Last modified on: 10/30/2024 16:59:39 UTC