CVE-2022-3061: Linux Kernel i740 Driver DoS Vulnerability

CVE-2022-3061 Overview

CVE-2022-3061 is a divide by zero vulnerability found in the Linux Kernel's i740 graphics driver. The flaw exists because userspace programs can pass arbitrary values to the driver through the ioctl() interface without proper validation. Specifically, the driver fails to validate the pixclock parameter, allowing a malicious local user to trigger a divide by zero error, resulting in a denial of service condition.

Critical Impact

Local attackers with low privileges can cause a system crash or denial of service by passing a zero value to the pixclock parameter in the i740 driver, triggering a kernel panic.

Affected Products

• Linux Kernel 5.18-rc5
• Debian Linux 10.0
• Debian Linux 11.0

Discovery Timeline

• 2022-09-01 - CVE-2022-3061 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-3061

Vulnerability Analysis

This vulnerability represents a classic input validation failure in the Linux kernel's framebuffer device (fbdev) subsystem, specifically within the Intel i740 graphics driver. The i740 driver exposes an ioctl() interface that allows userspace applications to configure display parameters such as screen resolution and pixel clock frequencies.

When a userspace program invokes the ioctl() system call to set display parameters, the driver accepts the pixclock value directly without performing boundary validation. If a zero value is passed for pixclock, subsequent calculations within the driver that use this value as a divisor will trigger a divide by zero exception. In kernel context, this type of arithmetic exception typically results in a kernel panic or system crash.

The attack requires local access and low privileges, as the attacker must be able to open the framebuffer device and issue ioctl commands. While the impact is limited to availability (denial of service), the ability for a low-privileged user to crash the entire system represents a significant security concern in multi-user or shared hosting environments.

Root Cause

The root cause is improper input validation (CWE-369: Divide By Zero) in the i740 driver code. The driver accepts the pixclock parameter from userspace without validating that it is non-zero before using it in division operations. This missing boundary check allows attackers to intentionally trigger arithmetic exceptions in kernel space.

Attack Vector

The attack requires local access to the system with at least low-level user privileges. An attacker can exploit this vulnerability by:

1. Opening the i740 framebuffer device (/dev/fb*)
2. Crafting an ioctl() call with the pixclock parameter set to zero
3. Sending this malicious request to the driver

When the driver processes this request, it attempts to perform a calculation using pixclock as a divisor. With a zero value, this triggers a divide by zero exception in kernel space, causing a kernel panic and system crash. The attack does not require any user interaction and can be executed programmatically.

Detection Methods for CVE-2022-3061

Indicators of Compromise

• Unexpected system crashes or kernel panics with divide by zero errors in kernel logs
• Repeated attempts to access framebuffer devices (/dev/fb*) by unauthorized or suspicious processes
• System log entries showing ioctl calls to i740 driver with unusual parameter values
• Kernel oops messages referencing the i740fb driver module

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for divide by zero exceptions originating from the i740 driver
• Implement auditd rules to track ioctl system calls on framebuffer devices
• Deploy host-based intrusion detection to alert on abnormal framebuffer device access patterns
• Use kernel tracing tools (ftrace, eBPF) to monitor i740 driver function calls

Monitoring Recommendations

• Enable kernel crash dump collection to analyze the root cause of unexpected system crashes
• Configure centralized logging to capture kernel panic events across all affected systems
• Set up alerting for systems running vulnerable kernel versions that experience unexpected reboots
• Monitor for processes attempting to open multiple framebuffer devices in rapid succession

How to Mitigate CVE-2022-3061

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the fix (commit 15cf0b82271b1823fb02ab8c377badba614d95d5)
• For Debian 10.0 and 11.0 systems, apply the patches from DSA-5257 and Debian LTS announcement
• If immediate patching is not possible, consider blacklisting the i740fb kernel module if not required
• Review and restrict access to framebuffer devices using appropriate file permissions

Patch Information

The vulnerability has been addressed in the Linux kernel framebuffer subsystem. The official fix is available in the kernel git repository. The patch adds proper validation of the pixclock parameter to ensure non-zero values before performing division operations. Debian has released security updates addressing this vulnerability in DSA-5257 for stable releases and through Debian LTS for long-term support versions.

Workarounds

• Blacklist the i740fb kernel module if the Intel i740 graphics hardware is not in use: add blacklist i740fb to /etc/modprobe.d/blacklist.conf
• Restrict access to framebuffer devices by modifying device permissions in udev rules
• Limit local user access to systems running vulnerable kernel versions until patching is complete
• Consider running critical workloads in containers or VMs to isolate them from potential kernel-level crashes

# Blacklist i740fb module to prevent loading
echo "blacklist i740fb" | sudo tee /etc/modprobe.d/blacklist-i740fb.conf

# Remove module if currently loaded
sudo modprobe -r i740fb

# Verify module is not loaded
lsmod | grep i740

# Update initramfs to persist changes across reboots
sudo update-initramfs -u