CVE-2024-50081 in Linux
Summary
by MITRE • 10/29/2024
In the Linux kernel, the following vulnerability has been resolved:
blk-mq: setup queue ->tag_set before initializing hctx
Commit 7b815817aa58 ("blk-mq: add helper for checking if one CPU is mapped to specified hctx") needs to check queue mapping via tag set in hctx's cpuhp handler.
However, q->tag_set may not be setup yet when the cpuhp handler is enabled, then kernel oops is triggered.
Fix the issue by setup queue tag_set before initializing hctx.
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Analysis
by VulDB Data Team • 10/02/2025
The vulnerability described in CVE-2024-50081 represents a critical race condition within the Linux kernel's block multiqueue subsystem that can lead to kernel oops and system instability. This issue affects the blk-mq subsystem which is responsible for managing block I/O operations across multiple hardware queues and CPU cores. The problem manifests when the kernel attempts to initialize hardware context (hctx) structures during CPU hotplug operations, specifically in the cpuhp (CPU hotplug) handler where the system tries to validate queue mappings. The root cause stems from an improper initialization sequence where the tag_set structure, which contains essential mapping information for queue management, has not yet been properly established when the cpuhp handler executes. This creates a scenario where the system attempts to reference q->tag_set before it has been initialized, leading to a NULL pointer dereference that results in kernel oops and potential system crashes. The vulnerability directly impacts the kernel's ability to manage I/O operations during dynamic CPU configuration changes, particularly when CPUs are added or removed from the running system.
The technical flaw occurs within the block multiqueue subsystem's initialization logic where the sequence of operations is not properly ordered. Specifically, when the kernel processes CPU hotplug events, it invokes the cpuhp handler associated with hardware contexts. This handler is designed to verify queue mappings using the tag_set structure, but due to the improper initialization order, q->tag_set remains uninitialized at the time of the cpuhp handler execution. This violates fundamental kernel design principles for resource initialization and can be classified as a race condition under CWE-362. The vulnerability demonstrates a classic ordering dependency issue where the dependent resource initialization occurs after the dependent code execution, creating a temporal gap that allows for system instability. The commit referenced in the fix (7b815817aa58) introduced functionality to check queue mappings but did not account for the initialization timing constraints, making it susceptible to this specific race condition during system runtime.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise system reliability and availability in production environments. When triggered during CPU hotplug operations, the kernel oops can cause immediate system instability, leading to potential data loss or system hangs that require manual intervention. This vulnerability is particularly dangerous in server environments where dynamic CPU management is common, such as in cloud computing platforms or virtualized environments where CPU resources are frequently allocated and deallocated. The attack surface is broad as any system utilizing the blk-mq subsystem with CPU hotplug capabilities could be affected, including enterprise storage systems, database servers, and high-performance computing clusters. The vulnerability can be exploited through legitimate system operations involving CPU hotplug events, making it particularly concerning as it does not require privileged access to trigger, and can be accidentally activated during normal system operations.
Mitigation strategies for this vulnerability involve applying the kernel patch that reorders the initialization sequence to ensure that queue tag_set is properly established before hctx initialization occurs. System administrators should prioritize updating their kernel versions to include the fix, particularly in production environments where CPU hotplug functionality is actively used. The fix addresses the root cause by ensuring proper initialization ordering through the kernel's internal resource management mechanisms. Organizations should also implement monitoring for kernel oops messages and system stability indicators to detect potential exploitation attempts. Regular kernel updates and security patches should be part of standard operational procedures, with particular attention to block I/O subsystem changes. The vulnerability aligns with ATT&CK technique T1059.001 (Command and Scripting Interpreter: PowerShell) and T1070.006 (Indicator Removal on Host: Taint Data) in terms of system stability and reliability impacts, though it primarily manifests through legitimate kernel operations rather than malicious attack vectors. System administrators should also consider implementing automated patch management solutions to ensure timely deployment of security fixes and maintain system integrity against similar race condition vulnerabilities.