CVE-2021-47466 in Linux
Summary
by MITRE • 05/22/2024
In the Linux kernel, the following vulnerability has been resolved:
mm, slub: fix potential memoryleak in kmem_cache_open()
In error path, the random_seq of slub cache might be leaked. Fix this by using __kmem_cache_release() to release all the relevant resources.
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Analysis
by VulDB Data Team • 01/08/2025
The vulnerability identified as CVE-2021-47466 represents a memory leak issue within the Linux kernel's memory management subsystem, specifically affecting the SLUB (Simple Low Usage Buffer) allocator. This flaw exists in the kmem_cache_open() function which is responsible for initializing kernel memory caches. The SLUB allocator is a core component of the kernel's slab memory management system that handles dynamic memory allocation for kernel objects. When an error occurs during the cache initialization process, the random_seq field associated with the SLUB cache is not properly released, leading to a memory leak that persists until the system reboots or the cache is explicitly destroyed.
The technical root cause of this vulnerability lies in improper resource management during error handling paths within the SLUB implementation. The random_seq field serves as a cryptographic randomization mechanism used to enhance security by randomizing cache layouts and prevent certain types of attacks. When kmem_cache_open() encounters an error condition, it should ensure all allocated resources are properly cleaned up before returning to the caller. However, the original implementation failed to invoke the appropriate cleanup function __kmem_cache_release() which would have properly deallocated all resources including the random_seq field. This oversight results in a memory leak where the random_seq data remains allocated in kernel memory, consuming valuable resources that could otherwise be reused by the system.
The operational impact of this vulnerability extends beyond simple resource wastage, as it represents a potential vector for resource exhaustion attacks. While the individual memory leak may appear minor, in systems under heavy memory pressure or those subjected to repeated cache creation and destruction operations, these accumulated leaks could contribute to system instability or performance degradation. The vulnerability is particularly concerning in environments where kernel memory allocation is frequently performed, such as in high-throughput servers, containers, or systems handling numerous concurrent operations. Attackers could potentially exploit this weakness to gradually consume available kernel memory, leading to denial of service conditions where the system becomes unresponsive due to memory exhaustion.
The fix implemented for CVE-2021-47466 addresses this issue by ensuring proper resource cleanup through the use of __kmem_cache_release() function during error paths. This approach aligns with established security practices for resource management and follows the principle of least privilege by ensuring that all allocated resources are properly accounted for and released. The solution demonstrates proper error handling methodology that prevents resource leaks while maintaining the integrity of the kernel's memory management system. From a cybersecurity perspective, this fix helps maintain the overall security posture of Linux systems by preventing potential attackers from exploiting resource exhaustion vulnerabilities. The vulnerability maps to CWE-404, which describes improper resource release or unbalanced resource management, and aligns with ATT&CK technique T1499.001 for resource exhaustion attacks. The resolution ensures that all kernel memory allocated during cache initialization is properly managed regardless of whether the operation succeeds or fails, thereby maintaining system stability and preventing potential exploitation scenarios that could lead to persistent resource consumption issues.