CVE-2022-49815 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
erofs: fix missing xas_retry() in fscache mode
The xarray iteration only holds the RCU read lock and thus may encounter XA_RETRY_ENTRY if there's process modifying the xarray concurrently. This will cause oops when referring to the invalid entry.
Fix this by adding the missing xas_retry(), which will make the iteration wind back to the root node if XA_RETRY_ENTRY is encountered.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 11/07/2025
The vulnerability identified as CVE-2022-49815 represents a critical flaw in the Linux kernel's implementation of the erofs filesystem, specifically within the fscache mode functionality. This issue stems from an inadequate handling of xarray iteration processes that occur during concurrent filesystem operations. The vulnerability manifests when the xarray iteration mechanism, which is designed to traverse data structures efficiently, fails to properly account for concurrent modifications that may occur during the iteration process.
The technical root cause of this vulnerability lies in the improper handling of XA_RETRY_ENTRY conditions within the xarray iteration framework. When processes concurrently modify the xarray data structure during iteration, the RCU read lock mechanism alone proves insufficient to prevent encountering invalid entries. This occurs because the RCU lock does not provide the necessary synchronization guarantees to prevent race conditions between iteration and modification operations. The absence of proper xas_retry() handling means that when XA_RETRY_ENTRY is encountered, the system cannot gracefully recover from the invalid state, leading to kernel oops conditions and potential system crashes.
This vulnerability directly impacts the stability and reliability of Linux systems utilizing the erofs filesystem with fscache mode enabled. The operational consequences are severe as the kernel panic resulting from this flaw can cause complete system instability, requiring manual intervention to recover from the crash state. The vulnerability affects systems where concurrent filesystem operations are common, particularly those employing caching mechanisms that rely on xarray data structures for efficient data management. The issue is particularly concerning in enterprise environments where filesystem stability is paramount for continuous operation.
The fix implemented addresses this vulnerability by incorporating the missing xas_retry() function call within the iteration logic. This modification ensures that when XA_RETRY_ENTRY conditions are encountered during xarray traversal, the iteration process properly rewinds back to the root node of the xarray structure, allowing for safe re-iteration after the concurrent modification has completed. This approach aligns with established best practices for concurrent data structure management and follows the principles outlined in CWE-362, which addresses concurrent execution timing issues that can lead to race conditions. The solution effectively implements the ATT&CK technique of privilege escalation through kernel exploitation by preventing the exploitation of improper synchronization mechanisms that could otherwise be leveraged for system compromise.
The mitigation strategy for this vulnerability requires immediate deployment of kernel updates that include the patched xarray iteration handling code. System administrators should prioritize patching affected systems, particularly those running erofs filesystems with fscache mode enabled. Organizations should also implement monitoring to detect potential kernel oops conditions that may indicate exploitation attempts. The fix demonstrates the importance of proper synchronization mechanisms in kernel code and highlights the critical nature of concurrent data structure management in operating system implementations. This vulnerability serves as a reminder of the complex challenges inherent in kernel-level programming where race conditions and concurrent access patterns must be carefully managed to prevent system instability and potential security implications.