CVE-2022-49914 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix inode list leak during backref walking at resolve_indirect_refs()
During backref walking, at resolve_indirect_refs(), if we get an error we jump to the 'out' label and call ulist_free() on the 'parents' ulist, which frees all the elements in the ulist - however that does not free any inode lists that may be attached to elements, through the 'aux' field of a ulist node, so we end up leaking lists if we have any attached to the unodes.
Fix this by calling free_leaf_list() instead of ulist_free() when we exit from resolve_indirect_refs(). The static function free_leaf_list() is moved up for this to be possible and it's slightly simplified by removing unnecessary code.
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Analysis
by VulDB Data Team • 11/12/2025
The vulnerability identified as CVE-2022-49914 represents a memory management flaw within the Linux kernel's btrfs file system implementation that specifically affects the indirect reference resolution process. This issue occurs during backref walking operations when the kernel attempts to resolve indirect references within the btrfs file system structure. The flaw manifests in the resolve_indirect_refs() function where error handling paths fail to properly clean up all allocated memory resources, leading to memory leaks that can accumulate over time and potentially impact system stability and performance.
The technical root cause of this vulnerability lies in improper memory cleanup during error conditions within the btrfs kernel module. When the resolve_indirect_refs() function encounters an error condition, it executes a jump to the 'out' label and calls ulist_free() on the 'parents' ulist structure. However, this cleanup function only frees the basic ulist nodes themselves without addressing the auxiliary data structures that may be attached through the 'aux' field of each ulist node. These auxiliary inode lists contain critical metadata and reference information that, when not properly freed, result in memory leaks that persist until the kernel module is unloaded or the system reboots.
This memory leak vulnerability specifically impacts the btrfs file system's ability to efficiently manage memory resources during complex reference resolution operations. The flaw creates a persistent memory consumption issue that can lead to gradual system performance degradation, particularly on systems with heavy btrfs usage or those performing frequent file system operations. The vulnerability affects systems running Linux kernels with btrfs file system support and represents a classic example of improper resource management that can be exploited to cause denial of service conditions through memory exhaustion.
The fix implemented for CVE-2022-49914 addresses the memory leak by modifying the error handling path in resolve_indirect_refs() to use free_leaf_list() instead of ulist_free() when exiting from the function. This change ensures that all auxiliary data structures attached through the 'aux' field of ulist nodes are properly freed, eliminating the memory leak that occurred during error conditions. The solution involves moving the static free_leaf_list() function to make it accessible from the error handling path and simplifying its implementation by removing unnecessary code. This approach aligns with security best practices for memory management and follows the principle of proper resource cleanup in kernel space operations.
From a cybersecurity perspective, this vulnerability demonstrates the importance of proper error handling and resource management in kernel modules, particularly in file system implementations where memory leaks can have significant operational impacts. The flaw could potentially be exploited by malicious actors to cause system instability or denial of service conditions through memory exhaustion attacks. This vulnerability is categorized under CWE-404, which deals with improper resource management, and aligns with ATT&CK technique T1490 for resource hijacking through memory exhaustion. The fix represents a defensive programming approach that emphasizes complete resource cleanup during error conditions, which is critical for maintaining system integrity and preventing potential exploitation scenarios that could lead to privilege escalation or system compromise.