CVE-2026-23463: Linux Kernel QBMAN Race Condition Flaw

CVE-2026-23463 Overview

A race condition vulnerability has been identified in the Linux kernel's QBMan (Queue Buffer Manager) subsystem, specifically in the qman_destroy_fq function within the Freescale/NXP System-on-Chip (SoC) driver. The vulnerability occurs when QMAN_FQ_FLAG_DYNAMIC_FQID is set, creating a timing window between the fq_table[fq->idx] state management and the freeing/allocating operations from the pool. This race condition triggers a WARN_ON(fq_table[fq->idx]) assertion in qman_create_fq(), potentially leading to system instability.

Critical Impact

This race condition can cause kernel warnings, system instability, and potential denial of service on systems utilizing Freescale/NXP QBMan hardware for high-performance packet processing.

Affected Products

• Linux Kernel (multiple stable versions)
• Freescale/NXP SoC platforms utilizing QBMan
• Systems with QMAN Frame Queue management enabled

Discovery Timeline

• 2026-04-03 - CVE CVE-2026-23463 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-23463

Vulnerability Analysis

The race condition exists in the QBMan driver's frame queue management system. When dynamically allocated frame queue IDs (FQIDs) are used, there is a window of opportunity between when a frame queue is destroyed and when its associated table entry is cleared. This timing issue allows another thread to allocate the same FQID before the original thread has completed cleanup, resulting in conflicting state in the fq_table data structure.

The vulnerability manifests when concurrent operations occur on frame queues: one thread executing qman_destroy_fq() to release a frame queue while another thread simultaneously calls qman_create_fq() to allocate a new one. The sequence of operations creates a problematic race:

1. Thread A calls qman_destroy_fq() and proceeds to qman_release_fqid()
2. Thread A calls qman_shutdown_fq() followed by gen_pool_free(), making the FQID available
3. Before Thread A sets fq_table[fq->idx] = NULL, Thread B acquires the same FQID
4. Thread B's WARN_ON(fq_table[fq->idx]) check triggers because the entry is still populated
5. Thread B overwrites the table entry, then Thread A clears it afterward, causing state corruption

Root Cause

The root cause is a missing memory barrier and incorrect ordering of operations in the qman_destroy_fq() function. The fq_table[fq->idx] entry is set to NULL after the FQID is returned to the pool via gen_pool_free(), when it should be cleared before the pool allocation becomes available. The fix requires ensuring proper ordering using smp_wmb() (write memory barrier) to guarantee that the table entry clearing is visible to other CPUs before the FQID is made available for reallocation.

Attack Vector

This is a local race condition vulnerability that requires the ability to trigger concurrent frame queue creation and destruction operations on the affected system. While primarily a reliability issue that causes kernel warnings and potential system instability, sustained exploitation could lead to denial of service conditions on systems relying on QBMan for packet processing, such as network appliances and embedded systems using Freescale/NXP SoCs.

The vulnerability is exploitable through:

• Concurrent kernel threads performing frame queue operations
• High-frequency allocation/deallocation of dynamic FQIDs
• Systems under heavy network or packet processing load

Detection Methods for CVE-2026-23463

Indicators of Compromise

• Kernel log messages containing WARN_ON(fq_table[fq->idx]) assertions
• Stack traces originating from qman_create_fq() function
• Unexpected system instability on Freescale/NXP SoC platforms
• QBMan-related kernel warnings in dmesg output

Detection Strategies

• Monitor kernel logs for QBMan-related WARN_ON messages using log aggregation tools
• Implement kernel crash dump analysis to identify race condition patterns
• Use kernel tracing tools (ftrace, perf) to monitor qman_create_fq and qman_destroy_fq function calls
• Deploy automated log parsing for soc: fsl: qbman subsystem warnings

Monitoring Recommendations

• Configure alerting on kernel warning messages from the QBMan driver subsystem
• Implement system stability monitoring on affected embedded platforms
• Monitor frame queue allocation/deallocation patterns for anomalies
• Track system uptime and unexpected reboots on Freescale/NXP SoC systems

How to Mitigate CVE-2026-23463

Immediate Actions Required

• Update the Linux kernel to a patched version containing the race condition fix
• Review systems using Freescale/NXP SoCs with QBMan functionality for exposure
• Monitor affected systems for kernel warnings while awaiting patch deployment
• Consider reducing concurrent frame queue operations as a temporary measure

Patch Information

Multiple kernel commits address this vulnerability by ensuring that fq_table[fq->idx] is set to NULL before gen_pool_free() is called, using smp_wmb() to enforce proper memory ordering. The fix is available in the following kernel commits:

• Kernel Commit 0140770
• Kernel Commit 265e567
• Kernel Commit 751f60b
• Kernel Commit 85dbbf7
• Kernel Commit 9e3d479
• Kernel Commit d21923a

Workarounds

• Reduce concurrent frame queue operations by serializing FQID allocation/deallocation where possible
• Implement application-level locking around QBMan frame queue management calls
• Monitor and restart affected services if kernel warnings are detected
• Consider disabling dynamic FQID allocation (QMAN_FQ_FLAG_DYNAMIC_FQID) if static allocation is feasible

# Check kernel version and QBMan driver status
uname -r
dmesg | grep -i qbman
# Monitor for race condition warnings
dmesg -w | grep -i "WARN_ON\|fq_table"