CVE-2024-36947 in Linux
Summary
by MITRE • 05/30/2024
In the Linux kernel, the following vulnerability has been resolved:
qibfs: fix dentry leak
simple_recursive_removal() drops the pinning references to all positives in subtree. For the cases when its argument has been kept alive by the pinning alone that's exactly the right thing to do, but here the argument comes from dcache lookup, that needs to be balanced by explicit dput().
Fucked-up-by: Al Viro
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Analysis
by VulDB Data Team • 09/18/2025
The vulnerability identified as CVE-2024-36947 represents a memory management flaw within the Linux kernel's qibfs filesystem implementation that manifests as a directory entry (dentry) leak. This issue specifically affects the simple_recursive_removal() function which handles the removal of directory subtrees. The flaw occurs when the function processes directory entries that have been retrieved through dcache lookup operations, creating an imbalance in reference counting that leads to memory leaks. The vulnerability was introduced by changes made in the Al Viro commit that modified how dentry pinning operates within the filesystem subsystem. When the function drops pinning references to all positive entries in a subtree, it properly handles cases where entries are kept alive by pinning alone, but fails to account for the fact that some entries come from dcache lookup operations that require explicit dput() calls to maintain proper reference counting balance.
This memory leak vulnerability stems from improper handling of dentry reference counting mechanisms within the kernel's filesystem layer. The qibfs filesystem, which is part of the InfiniBand subsystem, uses a recursive removal function to clean up directory structures when files are deleted. When this function processes directory entries that were obtained through dcache lookups, it fails to properly release these entries, causing them to remain in memory indefinitely. The flaw demonstrates a classic case of resource management error where the kernel's reference counting logic is not properly balanced. According to CWE-404, this represents an improper resource management issue where the system fails to properly release resources, leading to resource exhaustion over time. The vulnerability impacts the kernel's ability to efficiently manage memory resources and can potentially lead to system performance degradation or memory exhaustion under sustained load conditions.
The operational impact of CVE-2024-36947 extends beyond simple memory consumption issues as it represents a fundamental flaw in the kernel's filesystem management capabilities. When multiple qibfs directory operations occur repeatedly, the accumulation of leaked dentries can cause progressive memory bloat that affects overall system performance. This type of vulnerability is particularly concerning in high-performance computing environments where InfiniBand networks are extensively used, as these systems often perform intensive filesystem operations. The leak can compound over time, especially in systems with heavy I/O workloads, potentially leading to memory pressure that affects other kernel subsystems. From an ATT&CK perspective, this vulnerability could be leveraged by adversaries to perform resource exhaustion attacks against systems running affected kernel versions, potentially leading to denial of service conditions. The vulnerability also highlights the complexity of kernel-level reference counting in filesystem implementations where multiple subsystems interact with the same data structures.
Mitigation strategies for CVE-2024-36947 require immediate kernel updates to the patched versions that address the improper dentry reference handling in the qibfs subsystem. System administrators should prioritize updating their kernel versions to those containing the fix, which typically involves applying patches that ensure proper dput() calls are made for entries retrieved through dcache lookups. The fix specifically addresses the imbalance in reference counting by ensuring that all directory entries obtained through dcache operations receive appropriate cleanup calls. Organizations should also implement monitoring systems to track memory usage patterns and identify potential resource exhaustion scenarios that might indicate the presence of this vulnerability. Additionally, security teams should consider implementing kernel hardening measures such as disabling unnecessary filesystem modules when not required, which can reduce the attack surface. The vulnerability demonstrates the importance of thorough testing of filesystem operations and proper reference counting mechanisms, particularly in kernel subsystems that handle high-frequency I/O operations. Regular kernel security audits and vulnerability assessments should be conducted to identify similar issues in other filesystem implementations and kernel subsystems.