CVE-2021-47000 in Linux
Summary
by MITRE • 02/28/2024
In the Linux kernel, the following vulnerability has been resolved:
ceph: fix inode leak on getattr error in __fh_to_dentry
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Analysis
by VulDB Data Team • 11/23/2025
The vulnerability identified as CVE-2021-47000 represents a critical resource management flaw within the Linux kernel's Ceph file system implementation. This issue specifically affects the ceph file system's handling of file handle conversions and directory entry operations, where improper error handling leads to persistent resource leaks. The vulnerability occurs during the execution of the __fh_to_dentry function, which serves as a crucial bridge between file system handles and directory entry structures in the Ceph distributed storage system. When an error condition arises during the getattr operation within this function, the system fails to properly release allocated inode resources, resulting in a memory leak that can progressively degrade system performance and stability.
The technical root cause of this vulnerability lies in the insufficient cleanup mechanism within the Ceph file system driver's error handling path. During normal operation, the __fh_to_dentry function processes file handles to convert them into directory entry structures, which requires retrieving metadata through getattr calls. When these getattr operations encounter errors such as network timeouts, permission denials, or corrupted metadata, the function should gracefully release all allocated resources including inodes. However, the current implementation fails to execute proper cleanup routines in error scenarios, leaving inode structures in memory indefinitely. This represents a classic case of resource leak vulnerability where allocated system resources are not properly deallocated, creating a persistent memory consumption issue that can accumulate over time.
The operational impact of CVE-2021-47000 extends beyond simple memory consumption, potentially leading to system instability and performance degradation in environments heavily utilizing Ceph file systems. Attackers or system administrators may exploit this vulnerability by repeatedly triggering error conditions during file handle operations, causing progressive memory exhaustion and eventually leading to system crashes or denial of service conditions. The vulnerability is particularly concerning in enterprise environments where Ceph is used as a primary storage solution, as it can silently consume system resources without immediate detection. The leak affects inode structures which are fundamental to file system operations, meaning that over time the system may experience reduced file system performance, increased latency in file operations, and potential failure to allocate new inodes for legitimate file system operations. This type of vulnerability aligns with CWE-404, which describes improper resource cleanup, and falls under the ATT&CK technique T1490 for resource exhaustion attacks.
Mitigation strategies for CVE-2021-47000 primarily focus on applying the official kernel patches released by the Linux kernel development team. System administrators should immediately update their kernel versions to include the fix that properly implements error handling and resource cleanup in the __fh_to_dentry function. The patch ensures that when getattr operations fail, all allocated inode resources are properly released through appropriate cleanup routines. Additionally, monitoring systems should be implemented to track memory usage patterns and inode consumption in Ceph environments, as early detection of resource leaks can help identify potential exploitation attempts. Organizations should also consider implementing rate limiting and circuit breaker patterns in applications that interact with Ceph file systems to prevent excessive error conditions that could trigger the vulnerability. Regular system audits and memory profiling should be conducted to identify any residual memory leaks that might persist after patch application, ensuring complete remediation of the vulnerability. The fix addresses the underlying issue by ensuring proper error propagation and resource management, aligning with best practices for secure kernel development and system reliability.