CVE-2026-31492: Linux Kernel Use-After-Free Vulnerability

CVE-2026-31492 Overview

A vulnerability has been resolved in the Linux kernel's RDMA/irdma driver related to the improper initialization of a completion object. In the irdma_create_qp function, if ib_copy_to_udata fails, it calls irdma_destroy_qp to clean up resources. However, this cleanup routine attempts to wait on the free_qp completion structure which has not yet been initialized, leading to undefined behavior and potential system instability.

Critical Impact

Uninitialized completion use in the kernel RDMA subsystem can cause kernel panics, system hangs, or denial of service conditions when RDMA queue pair creation fails during error handling paths.

Affected Products

• Linux kernel with RDMA/irdma driver enabled
• Systems utilizing Intel RDMA Ethernet adapters
• Kernel configurations with CONFIG_INFINIBAND_IRDMA enabled

Discovery Timeline

• 2026-04-22 - CVE CVE-2026-31492 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-31492

Vulnerability Analysis

This vulnerability exists in the error handling path of the irdma_create_qp function within the Linux kernel's RDMA/irdma driver. The RDMA (Remote Direct Memory Access) subsystem allows for high-performance, low-latency networking by enabling direct memory access between systems without involving the CPU.

When creating a Queue Pair (QP) in the irdma driver, the irdma_create_qp function performs several initialization steps. One critical step involves copying data to userspace via ib_copy_to_udata. If this operation fails, the function enters an error handling path that calls irdma_destroy_qp to clean up any partially initialized resources.

The problem arises because the free_qp completion structure is not initialized before the ib_copy_to_udata call. When irdma_destroy_qp is invoked during error cleanup, it attempts to wait on this uninitialized completion object using a call such as wait_for_completion. Operating on an uninitialized completion structure results in undefined behavior, which can manifest as kernel panics, system hangs, or other stability issues.

Root Cause

The root cause is a missing initialization of the free_qp completion structure in the irdma_create_qp function. The completion object must be initialized using init_completion() before any potential code path could attempt to wait on it. The original code positioned the initialization after the ib_copy_to_udata call, leaving a window where failure of that function would trigger cleanup code that references the uninitialized completion.

Attack Vector

This vulnerability is triggered through the error handling path when RDMA queue pair creation fails. While the attack vector is not fully characterized, it could potentially be exploited by:

1. A local user with permissions to create RDMA resources causing the ib_copy_to_udata function to fail
2. Crafting userspace RDMA operations that trigger the specific error condition
3. Memory exhaustion or other system stress conditions that could cause the copy-to-userspace operation to fail

The fix involves moving the init_completion(&iwqp->free_qp) call to occur before the ib_copy_to_udata invocation, ensuring the completion structure is always properly initialized before any error path could attempt to use it. See the kernel commit 11a95521 for the complete fix implementation.

Detection Methods for CVE-2026-31492

Indicators of Compromise

• Kernel panic logs referencing irdma_destroy_qp or wait_for_completion functions
• System hangs during RDMA queue pair creation or destruction operations
• Kernel oops or BUG messages in system logs related to the irdma driver
• Unexpected RDMA connection failures accompanied by system instability

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for irdma driver errors or completion-related panics
• Implement kernel tracing on RDMA subsystem functions to identify abnormal error paths
• Deploy SentinelOne Singularity platform for real-time kernel-level monitoring and anomaly detection
• Review audit logs for unusual RDMA resource creation patterns from non-privileged processes

Monitoring Recommendations

• Configure kernel panic logging to persistent storage to capture crash dumps for analysis
• Enable RDMA subsystem debugging with echo 1 > /sys/kernel/debug/dynamic_debug/control for irdma module
• Set up alerting on repeated RDMA queue pair creation failures from the same process
• Use SentinelOne's kernel visibility features to monitor driver behavior patterns

How to Mitigate CVE-2026-31492

Immediate Actions Required

• Update the Linux kernel to a version containing the fix (check kernel changelogs for commits 11a95521, 3cb88c12, ac1da7bd, af310407, cd1534c8, or f7299683)
• If kernel updates cannot be immediately applied, consider temporarily unloading the irdma module if RDMA functionality is not critical
• Review systems using Intel RDMA adapters and prioritize patching based on exposure
• Monitor affected systems for signs of instability or kernel panics related to RDMA operations

Patch Information

The vulnerability has been fixed across multiple kernel stable branches. The fix involves initializing the free_qp completion before the ib_copy_to_udata call to ensure proper cleanup can occur on error. Patches are available in the following commits:

• Linux Kernel Commit 11a95521
• Linux Kernel Commit 3cb88c12
• Linux Kernel Commit ac1da7bd
• Linux Kernel Commit af310407
• Linux Kernel Commit cd1534c8
• Linux Kernel Commit f7299683

Workarounds

• Temporarily disable the irdma kernel module using modprobe -r irdma if RDMA functionality is not required
• Blacklist the irdma module in /etc/modprobe.d/blacklist.conf to prevent automatic loading
• Restrict access to RDMA device files to limit exposure to trusted users only
• Consider using alternative RDMA drivers if available for your hardware

# Disable irdma module temporarily
sudo modprobe -r irdma

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

# Update initramfs after blacklisting
sudo update-initramfs -u