In the world of Linux kernel security, every vulnerability needs urgent attention, and a fix should be implemented as soon as possible. One such vulnerability that has plagued the Linux kernel is the null-ptr-deref (null pointer dereference) issue in qt2_process_read_urb(). But fear not, fellow Linux enthusiasts, the problem has been resolved, and we're about to show you the details.

First, let's understand the original issue. The null-ptr-deref vulnerability was caused by an incorrect bounds check in this piece of code:

if (newport > serial->num_ports) {
        dev_err(&port->dev,
                "%s - port change to invalid port: %i\n",
                __func__, newport);
        break;
}

The condition in the code snippet above was not accounting for the valid range of the serial->port buffer, which should be from to serial->num_ports - 1. When newport was equal to serial->num_ports, the next piece of code assigning the value to "port" was going out-of-bounds and returning NULL. This caused the null-ptr-deref issue later in the code execution.

serial_priv->current_port = newport;
port = serial->port[serial_priv->current_port];

To fix the error, the condition needs to check whether newport is greater than or equal to serial->num_ports, thereby indicating that it is out-of-bounds. This change in the code snippet helps avoid the null-ptr-deref issue.

Now that we know the background, let's dive into the details of the exploit and how it's patched.

Technical Details

The Linux kernel had a bug in the qt2_process_read_urb() function under the USB: serial: quatech2 section. The root of the vulnerability was the incorrect boundary check, which led to a null-ptr-deref issue. The bug was patched, and the fixed code snippet is provided below:

if (newport >= serial->num_ports) {
        dev_err(&port->dev,
                "%s - port change to invalid port: %i\n",
                __func__, newport);
        break;
}

As you can see, the only change required was to modify the condition to newport >= serial->num_ports. By performing this minor modification, the vulnerability was patched, and the null-ptr-deref issue has been resolved.

Original References

For more detailed information on this specific vulnerability, you can refer to these original sources:

1. Linux Kernel Vulnerabilities - Overview
2. Linux Kernel Mailing List (LKML) - Discussion Thread

Conclusion

It is essential to stay up-to-date with exploitable vulnerabilities and their patches in the Linux kernel, as these issues can cause severe security problems in Linux-based systems. The null-ptr-deref issue in qt2_process_read_urb() was an exploitable vulnerability but was quickly fixed by adjusting the conditional check. It's crucial to keep an eye on updated patches and apply them to your Linux systems, ensuring stability and security.

Timeline

Published on: 02/10/2025 16:15:38 UTC
Last modified on: 03/24/2025 15:38:56 UTC