CVE-2024-26955 in Linux
Summary
by MITRE • 05/01/2024
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: prevent kernel bug at submit_bh_wbc()
Fix a bug where nilfs_get_block() returns a successful status when searching and inserting the specified block both fail inconsistently. If this inconsistent behavior is not due to a previously fixed bug, then an unexpected race is occurring, so return a temporary error -EAGAIN instead.
This prevents callers such as __block_write_begin_int() from requesting a read into a buffer that is not mapped, which would cause the BUG_ON check for the BH_Mapped flag in submit_bh_wbc() to fail.
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Analysis
by VulDB Data Team • 01/26/2026
The vulnerability identified as CVE-2024-26955 resides within the Linux kernel's nilfs2 file system implementation, specifically addressing a critical inconsistency in block handling operations that could lead to kernel panics and system instability. This flaw manifests in the nilfs_get_block() function which is responsible for managing block allocation and retrieval within the Next-Generation Log-Structured File System version 2. The issue occurs when the function attempts to both search for and insert a specified block, but fails to handle the case where both operations return failures in an inconsistent manner. This inconsistency creates a scenario where the function returns a successful status code despite the actual block operation failing, leading to unpredictable behavior in the file system's block management subsystem.
The technical core of this vulnerability stems from an improper error handling mechanism within the nilfs2 subsystem where the nilfs_get_block() function does not correctly account for race conditions that can occur during concurrent block operations. When both search and insert operations fail simultaneously, the function should return an appropriate error code indicating the failure state. However, due to the flawed implementation, it returns a success status code instead, which creates a dangerous inconsistency in the file system's internal state management. This particular race condition scenario is particularly concerning because it can occur under normal file system operations, making it difficult to predict or prevent. The vulnerability directly impacts the kernel's buffer management system, as the inconsistent return status causes downstream functions like __block_write_begin_int() to proceed with operations that expect mapped buffers, ultimately leading to kernel BUG_ON assertions in the submit_bh_wbc() function.
The operational impact of CVE-2024-26955 extends beyond simple file system corruption, as it represents a potential denial-of-service vector that could cause complete system crashes. When the kernel attempts to submit a block write operation with unmapped buffers due to the inconsistent block handling, the submit_bh_wbc() function's BUG_ON check for the BH_Mapped flag fails catastrophically, resulting in kernel oops or system panics. This vulnerability affects systems running Linux kernels with nilfs2 file system support, particularly those handling concurrent file I/O operations or systems that rely heavily on log-structured file system operations. The issue is especially problematic in environments where multiple processes simultaneously access the same file system, as the race conditions that trigger this bug are more likely to occur under concurrent load. From a cybersecurity perspective, this vulnerability represents a potential attack surface that could be exploited by malicious actors to cause system instability or perform denial-of-service attacks against vulnerable systems.
The fix implemented for CVE-2024-26955 addresses the root cause by modifying the nilfs_get_block() function to properly handle the inconsistent failure scenario by returning a temporary error code -EAGAIN instead of a success status. This change ensures that when both search and insert operations fail in an inconsistent manner, the calling functions receive appropriate error signals that prevent them from proceeding with invalid buffer operations. The solution aligns with established kernel development practices for handling race conditions and error propagation in concurrent systems. From a security standards perspective, this vulnerability maps to CWE-362, which describes Race Conditions, and could potentially be leveraged in attacks targeting the ATT&CK technique T1499.004 for network denial-of-service. The mitigation strategy involves updating to kernel versions that contain the patched implementation, which ensures proper error handling and prevents the kernel BUG_ON assertion from triggering. System administrators should prioritize applying this patch to systems running nilfs2 file systems, particularly those in production environments where system stability and availability are critical requirements. The fix demonstrates the importance of proper error handling in kernel space code and highlights the necessity of thorough testing for concurrent operations in file system implementations to prevent similar race condition vulnerabilities from manifesting in production systems.