Date: June 2024
Author: Exclusive Linux Security Analysis

Overview

A recently fixed vulnerability, CVE-2025-21668, impacted the Linux kernel's handling of specific System on Chip (SoC) power domain drivers. The problem was discovered within the imx8mp-blk-ctrl driver, which is used primarily on NXP's i.MX8MP platforms. This bug, if left unresolved, could potentially crash your kernel or allow denial-of-service by causing the kernel to access memory out of bounds within its power management routines.

In this article, we’ll break down the vulnerability in simple terms, go through example code snippets, explain potential exploit scenarios, and back it up with original references.

The Problem

The vulnerability existed in the function imx8mp_blk_ctrl_remove(). This function is supposed to clean up resources, especially when the driver is removed or during a device shutdown or reboot. However, there was a missing break condition in a loop, which led to an out-of-bounds exception.

To put it plainly:
When the function ran, it would keep looping past the end of the array it was supposed to process, eventually accessing memory it wasn’t supposed to. This can crash the kernel—a classic *out-of-bounds* bug.

Here’s what the bug looked like in practice (from the kernel crash report)

pmdomain: imx8mp-blk-ctrl: add missing loop break condition

Currently imx8mp_blk_ctrl_remove() will continue the for loop
until an out-of-bounds exception occurs.

Call trace:
 dev_pm_domain_detach+x8/x48
 platform_shutdown+x2c/x48
 device_shutdown+x158/x268
 kernel_restart_prepare+x40/x58
 ...

Let’s understand the bug by reviewing a simplified version of the function before it was fixed

static int imx8mp_blk_ctrl_remove(struct platform_device *pdev) {
    struct imx8mp_blk_ctrl *bc = platform_get_drvdata(pdev);
    int i;
    for (i = ;; i++) {
        cleanup_resource(bc->resources[i]);
        // BUG: Missing break or end condition
    }
    return ;
}

In this buggy loop, there’s no check for how many resources actually exist. It just loops forever until the kernel attempts to access memory outside the array, causing an exception.

The Fix:

Developers added a proper break condition. Here’s a corrected sample

static int imx8mp_blk_ctrl_remove(struct platform_device *pdev) {
    struct imx8mp_blk_ctrl *bc = platform_get_drvdata(pdev);
    int i;
    for (i = ; i < bc->num_resources; i++) {
        cleanup_resource(bc->resources[i]);
    }
    return ;
}

Now, the loop only runs as many times as there are resources, preventing access outside the allocated array.

Trigger Device Removal

An attacker (with required privileges) could force the driver to unload, or schedule a shutdown/reboot event.

As the driver attempts to free resources, it steps outside memory bounds, crashing the kernel.

3. System Crash / Panic

The system can panic or stop responding, causing disruption.

Exploit Example:
A local attacker could write a script to repeatedly load and unload the affected driver (with root privileges), causing a kernel panic at will.

# WARNING: Do not run on production systems!
modprobe imx8mp-blk-ctrl
rmmod imx8mp-blk-ctrl  # Bug triggers here in the vulnerable version!

## How to Fix / Mitigations

Upgrade your Kernel:

Make sure you’re running a Linux kernel version with the fix for CVE-2025-21668. Most recent kernels (June 2024+) are patched.

If You Can’t Patch:

Limit driver removal actions to trusted administrators. Prevent untrusted code from interacting with device management APIs.

References & Sources

- Patch: "imx8mp-blk-ctrl: add missing loop break condition"
- CVE Details for CVE-2025-21668
- NXP i.MX8MP Reference Manual
- Linux Kernel Power Management Domains

Upgrade your kernel and watch for crashes if you’re on affected SoCs

*Stay secure, and always keep your systems patched!*

Timeline

Published on: 01/31/2025 12:15:27 UTC
Last modified on: 05/04/2025 07:18:40 UTC