CVE-2021-47074 in Linux
Summary
by MITRE • 03/02/2024
In the Linux kernel, the following vulnerability has been resolved:
nvme-loop: fix memory leak in nvme_loop_create_ctrl()
When creating loop ctrl in nvme_loop_create_ctrl(), if nvme_init_ctrl() fails, the loop ctrl should be freed before jumping to the "out" label.
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Analysis
by VulDB Data Team • 11/23/2025
The vulnerability identified as CVE-2021-47074 represents a memory leak condition within the Linux kernel's NVMe over Fabrics loopback implementation. This flaw exists in the nvme-loop subsystem which provides loopback functionality for NVMe (Non-Volatile Memory Express) storage devices, allowing userspace applications to communicate with NVMe controllers through a virtual loopback interface. The vulnerability specifically affects the nvme_loop_create_ctrl() function where proper resource cleanup is not performed when certain initialization failures occur, creating a persistent memory allocation that cannot be reclaimed by the system.
The technical root cause of this memory leak stems from improper error handling within the kernel's NVMe loopback driver implementation. When nvme_init_ctrl() function fails during the controller creation process, the code path does not properly release the previously allocated loop controller structure before jumping to the error handling label. This failure to clean up allocated memory resources results in a memory leak that accumulates over time, potentially leading to system performance degradation and eventual memory exhaustion. The flaw demonstrates a classic improper resource management issue that violates fundamental kernel programming practices and security principles.
From an operational perspective, this vulnerability poses significant risks to systems relying on NVMe loopback functionality for storage virtualization or testing environments. The memory leak can gradually consume available system memory, leading to degraded performance, application crashes, or system instability. Attackers could potentially exploit this vulnerability by repeatedly creating and failing to destroy NVMe loop controllers, amplifying the memory consumption impact. The vulnerability affects systems running Linux kernel versions where the nvme-loop subsystem is active and is particularly concerning in high-availability environments where memory resources are critical. This type of resource leak vulnerability can be leveraged in denial-of-service scenarios and aligns with attack patterns documented in the MITRE ATT&CK framework under resource exhaustion techniques.
The fix for CVE-2021-47074 involves implementing proper error handling in the nvme_loop_create_ctrl() function to ensure that the loop controller structure is freed when nvme_init_ctrl() fails, before proceeding to the error handling path. This remediation follows established kernel development practices and security guidelines for resource management. The fix aligns with CWE-404, which catalogs improper resource management issues in software systems, and addresses the fundamental requirement that all allocated resources must be properly released upon error conditions. Organizations should prioritize applying the kernel updates containing this fix, particularly in production environments where NVMe loopback functionality is utilized. System administrators should monitor memory usage patterns after applying the patch to confirm that the memory leak has been resolved and that system stability has been restored. The vulnerability underscores the importance of rigorous error handling in kernel space code and demonstrates how seemingly minor resource management oversights can create significant security and stability implications in operating system components.