CVE-2026-31436: Linux Kernel Race Condition Vulnerability

CVE-2026-31436 Overview

A vulnerability has been discovered in the Linux kernel's DMA engine IDXD (Intel Data Accelerator) subsystem. The flaw exists in the llist_abort_desc() function where incorrect descriptor completion logic can lead to NULL pointer dereferences, double completion, or descriptor leaks. This issue stems from a programming error where the traversal cursor variable is misused during the final processing loop.

Critical Impact

Systems utilizing Intel Data Accelerator hardware with affected Linux kernel versions may experience kernel crashes, memory corruption, or resource leaks due to improper DMA descriptor handling.

Affected Products

• Linux kernel versions with vulnerable IDXD DMA engine driver
• Systems with Intel Data Accelerator (IDXD) hardware

Discovery Timeline

• 2026-04-22 - CVE-2026-31436 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-31436

Vulnerability Analysis

The vulnerability resides in the llist_abort_desc() function within the Linux kernel's IDXD DMA engine driver. The function is responsible for aborting and cleaning up DMA descriptors in a linked list structure. During the traversal of the flist linked list, the variable d serves as the cursor to iterate through descriptor entries. However, at the conclusion of the function, the code erroneously completes the found variable instead of the current cursor d.

This logic error creates several potential failure scenarios: if found is NULL, a NULL pointer dereference will occur; if found points to an already-completed descriptor, double completion can corrupt kernel memory management structures; and if valid descriptors are left incomplete, memory leaks and resource exhaustion may result over time.

Root Cause

The root cause is a variable reference error in the list_for_each_entry_safe() loop at the end of llist_abort_desc(). The code incorrectly references the found variable for completion operations instead of the loop cursor d. This represents a classic programming error where the wrong variable is used after list traversal, a pattern that can be subtle to detect during code review.

Attack Vector

The vulnerability is triggered during DMA descriptor abort operations in the IDXD subsystem. While exploitation requires local access to a system with Intel IDXD hardware and the ability to trigger DMA operations, the impact includes kernel crashes via NULL pointer dereference, potential memory corruption through double-free scenarios, and denial of service through resource exhaustion.

The attack vector is local, as it requires the ability to interact with the DMA engine through legitimate kernel interfaces or driver operations that invoke the llist_abort_desc() function.

Detection Methods for CVE-2026-31436

Indicators of Compromise

• Kernel panic or oops messages referencing llist_abort_desc or IDXD subsystem functions
• Unexpected system crashes on servers utilizing Intel Data Accelerator hardware
• Memory leak warnings or resource exhaustion events in DMA subsystems
• Double-free or use-after-free kernel warnings in system logs

Detection Strategies

• Monitor kernel logs for panics or oops referencing drivers/dma/idxd/ or related IDXD functions
• Implement kernel memory debugging tools like KASAN to detect memory corruption patterns
• Deploy system stability monitoring to identify unexpected reboots on IDXD-enabled systems
• Review dmesg output for DMA engine error messages or descriptor handling anomalies

Monitoring Recommendations

• Enable kernel crash dump collection (kdump) to capture diagnostic information during crashes
• Configure alerting on kernel oops events in centralized logging systems
• Monitor system uptime metrics for unexpected restarts on affected hardware platforms
• Track memory allocation patterns for DMA descriptors to identify leak conditions

How to Mitigate CVE-2026-31436

Immediate Actions Required

• Apply available kernel patches from your Linux distribution's security repository
• Consider disabling IDXD functionality if not required, pending patch deployment
• Schedule maintenance windows to apply kernel updates on affected systems
• Prioritize patching on systems with Intel Data Accelerator hardware in production environments

Patch Information

The Linux kernel development team has released patches addressing this vulnerability. The fix modifies the llist_abort_desc() function to correctly complete the descriptor referenced by cursor variable d instead of the found variable in the final list_for_each_entry_safe() loop.

Patches are available through the following kernel git commits:

• Kernel Git Commit 0e4f437
• Kernel Git Commit 82656e8
• Kernel Git Commit e1c9866
• Kernel Git Commit e21da2a

Workarounds

• Disable the IDXD driver module if Intel Data Accelerator functionality is not required: modprobe -r idxd
• Blacklist the IDXD module to prevent automatic loading by adding blacklist idxd to /etc/modprobe.d/blacklist.conf
• Implement workload isolation to limit exposure of systems with IDXD hardware pending patch deployment
• Deploy kernel live patching solutions if available for your distribution to minimize downtime

# Disable IDXD module temporarily
modprobe -r idxd

# Blacklist IDXD module to prevent loading at boot
echo "blacklist idxd" >> /etc/modprobe.d/blacklist.conf