CVE-2026-31440: Linux Kernel Memory Leak Vulnerability

CVE-2026-31440 Overview

A memory leak vulnerability has been identified in the Linux kernel's dmaengine/idxd driver. During the device removal process, the driver fails to properly deallocate event log memory due to an incorrect condition check. When the device is reset, configuration registers return to their default state (zero), which causes the driver's deallocation logic to incorrectly skip freeing the event log memory because it checks whether event log support was enabled rather than simply checking if the memory was allocated.

Critical Impact

This vulnerability can lead to memory leaks in the Linux kernel, potentially causing resource exhaustion and system instability over time as memory is not properly freed during device removal operations.

Affected Products

• Linux kernel (dmaengine/idxd driver)
• Systems utilizing Intel Data Accelerators with IDXD driver support

Discovery Timeline

• 2026-04-22 - CVE-2026-31440 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-31440

Vulnerability Analysis

The vulnerability resides in the Intel Data Accelerator (IDXD) driver within the Linux kernel's DMA engine subsystem. The IDXD driver manages event logs for hardware accelerator devices, allocating memory for these logs when the device is initialized and the hardware capability is available.

The flaw occurs during the device removal lifecycle. When a device is removed, the kernel resets the device, which causes all configuration registers to return to their default values (zero). The driver's cleanup code incorrectly uses a conditional check to determine whether event log support was enabled before attempting to deallocate the memory. Since the reset clears this configuration state, the check fails, and the allocated event log memory is never freed.

The correct approach, implemented in the fix, is to simply check whether the idxd->evl pointer is valid (non-NULL), as this pointer is only allocated when the hardware capability is present. This eliminates the dependency on the configuration register state that gets cleared during reset.

Root Cause

The root cause is an improper conditional check in the IDXD driver's device removal path. The driver checks whether event log support was enabled via configuration registers before deallocating memory. However, these registers are reset to zero during device removal, causing the condition to evaluate as false even when event log memory was previously allocated. The fix removes this unnecessary check and relies solely on validating that the idxd->evl pointer is non-NULL.

Attack Vector

This is a local kernel vulnerability that requires the ability to trigger device removal operations. While the attack vector is not fully characterized, potential exploitation scenarios include:

• Repeated device hotplug operations to trigger the memory leak
• Privileged access to trigger device unbind/bind cycles
• Automated systems that frequently manage IDXD devices

The vulnerability manifests in the event log memory deallocation logic within the IDXD driver. When a device reset occurs before the cleanup routine runs, the configuration registers are cleared, causing the deallocation check to fail. The fix modifies the conditional logic to check only whether the idxd->evl pointer is valid rather than relying on the configuration register state. See the kernel commit for technical implementation details.

Detection Methods for CVE-2026-31440

Indicators of Compromise

• Gradual increase in kernel memory usage over time, particularly in systems with frequent IDXD device operations
• Memory pressure warnings in kernel logs related to SLAB or SLUB allocators
• Unexplained memory exhaustion on systems utilizing Intel Data Accelerators
• Kernel messages indicating IDXD device removal or reset operations

Detection Strategies

• Monitor kernel memory allocation statistics using /proc/meminfo and /proc/slabinfo
• Track IDXD driver operations via kernel tracing (ftrace) for device removal events
• Implement memory leak detection tools such as kmemleak on affected systems
• Review system logs for IDXD driver messages indicating device reset or removal

Monitoring Recommendations

• Enable kernel memory debugging options (CONFIG_DEBUG_KMEMLEAK) in development environments
• Set up alerting for unusual memory growth patterns on systems with IDXD hardware
• Monitor dmesg output for IDXD-related warnings or errors
• Use SentinelOne Singularity platform for real-time kernel behavior monitoring

How to Mitigate CVE-2026-31440

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the IDXD memory leak fix
• Minimize unnecessary device removal operations until patches are applied
• Monitor memory usage on affected systems for signs of memory exhaustion
• Review and apply kernel updates from your distribution vendor

Patch Information

Patches have been released through the Linux kernel stable tree. The fix modifies the event log deallocation logic to check only the validity of the idxd->evl pointer rather than the configuration register state. Multiple commit patches are available:

• Kernel commit 9dfa00967e6e
• Kernel commit d94f9b0ba28a
• Kernel commit ee66bc295783
• Kernel commit facd0012708e

Workarounds

• Avoid frequent IDXD device removal/hotplug operations until the kernel is patched
• Schedule system reboots periodically to reclaim leaked memory on unpatched systems
• Consider disabling IDXD driver if not actively required for workloads
• Implement memory monitoring and alerting to detect memory exhaustion before system impact

# Check current kernel version
uname -r

# Check if IDXD driver is loaded
lsmod | grep idxd

# Monitor kernel memory usage
watch -n 5 'cat /proc/meminfo | grep -E "MemFree|MemAvailable|Slab"'

# Temporarily unload IDXD driver if not required (requires root)
# modprobe -r idxd