CVE-2024-26981 in Linux
Summary
by MITRE • 05/01/2024
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: fix OOB in nilfs_set_de_type
The size of the nilfs_type_by_mode array in the fs/nilfs2/dir.c file is defined as "S_IFMT >> S_SHIFT", but the nilfs_set_de_type() function, which uses this array, specifies the index to read from the array in the same way as "(mode & S_IFMT) >> S_SHIFT".
static void nilfs_set_de_type(struct nilfs_dir_entry *de, struct inode *inode) {
umode_t mode = inode->i_mode;
de->file_type = nilfs_type_by_mode[(mode & S_IFMT)>>S_SHIFT]; // oob
}
However, when the index is determined this way, an out-of-bounds (OOB) error occurs by referring to an index that is 1 larger than the array size when the condition "mode & S_IFMT == S_IFMT" is satisfied. Therefore, a patch to resize the nilfs_type_by_mode array should be applied to prevent OOB errors.
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Analysis
by VulDB Data Team • 02/06/2026
The vulnerability identified as CVE-2024-26981 affects the Linux kernel's nilfs2 file system implementation and represents a classic out-of-bounds memory access flaw that could potentially lead to system instability or privilege escalation. This issue resides within the fs/nilfs2/dir.c source file where the nilfs_set_de_type function performs operations on directory entries. The flaw stems from a mismatch between the array size definition and the indexing mechanism used to access elements within the nilfs_type_by_mode array, creating a scenario where memory access occurs beyond the allocated bounds of the array structure.
The technical root cause of this vulnerability can be traced to the improper calculation of array indices when determining file type information for directory entries in the nilfs2 file system. The array nilfs_type_by_mode is defined with a size of "S_IFMT >> S_SHIFT" which calculates to 8 elements, corresponding to the standard file type constants such as S_IFREG, S_IFDIR, S_IFLNK, etc. However, the nilfs_set_de_type function computes the array index using the expression "(mode & S_IFMT) >> S_SHIFT" which can produce an index value of 8 when the mode value equals S_IFMT, thereby exceeding the array bounds. This occurs because the bitwise AND operation with S_IFMT can return the maximum value that S_IFMT represents, and when shifted by S_SHIFT, it results in an index that is exactly one position beyond the array's valid range.
From an operational security perspective, this out-of-bounds access vulnerability presents significant risks to system integrity and availability. When exploited, the vulnerability could allow a malicious actor to trigger memory corruption within kernel space, potentially leading to system crashes, data corruption, or in more severe scenarios, privilege escalation to kernel-level execution. The vulnerability affects systems running Linux kernels with the nilfs2 file system enabled, making it particularly concerning for embedded systems, storage servers, and any environment where this specific file system implementation is utilized. The flaw demonstrates a common pattern of integer overflow or underflow issues that frequently appear in kernel space code where bit manipulation operations are performed without proper bounds checking.
The vulnerability aligns with CWE-129, which specifically addresses "Improper Validation of Array Index" in software security contexts, and represents a clear example of how insufficient input validation can lead to memory safety issues. From an attacker's perspective, this vulnerability could be leveraged as part of a broader exploitation chain within the MITRE ATT&CK framework, particularly under the techniques related to privilege escalation and execution of malicious code in kernel space. The patch implementation should involve resizing the nilfs_type_by_mode array to accommodate the maximum possible index value that could be generated by the indexing calculation, ensuring that the array bounds properly encompass all valid file type combinations that can be represented in the file system.
Mitigation strategies for this vulnerability should include immediate application of the kernel patch that addresses the array sizing issue and proper kernel version updates. System administrators should prioritize deployment of patched kernel versions across all affected systems, particularly those running nilfs2 file systems in production environments. Additional defensive measures could include monitoring for unusual system behavior or kernel memory access patterns that might indicate exploitation attempts. The vulnerability also underscores the importance of thorough code review processes for kernel space operations, particularly those involving bit manipulation and array indexing where the potential for integer overflow or underflow exists. Organizations should implement comprehensive testing procedures for file system operations and memory access patterns to prevent similar issues from arising in other kernel components.