CVE-2022-50864 in Linux
Summary
by MITRE • 12/30/2025
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: fix shift-out-of-bounds due to too large exponent of block size
If field s_log_block_size of superblock data is corrupted and too large, init_nilfs() and load_nilfs() still can trigger a shift-out-of-bounds warning followed by a kernel panic (if panic_on_warn is set):
shift exponent 38973 is too large for 32-bit type 'int' Call Trace: <TASK> dump_stack_lvl+0xcd/0x134 ubsan_epilogue+0xb/0x50 __ubsan_handle_shift_out_of_bounds.cold.12+0x17b/0x1f5 init_nilfs.cold.11+0x18/0x1d [nilfs2]
nilfs_mount+0x9b5/0x12b0 [nilfs2]
...
This fixes the issue by adding and using a new helper function for getting block size with sanity check.
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Analysis
by VulDB Data Team • 04/26/2026
The vulnerability CVE-2022-50864 represents a critical integer overflow condition within the Linux kernel's nilfs2 file system implementation that can lead to kernel panic and system instability. This flaw exists in the nilfs2 (New Implementation of LogFS) file system driver which is designed for log-structured file systems. The issue manifests when the superblock's s_log_block_size field becomes corrupted with an excessively large value, creating a scenario where arithmetic operations exceed the bounds of 32-bit integer types. The vulnerability specifically affects the init_nilfs() and load_nilfs() functions that process file system superblock data during mount operations, making it particularly dangerous as it can compromise system stability at boot time or during file system access.
The technical root cause of this vulnerability stems from improper input validation and lack of bounds checking when processing the s_log_block_size field in the nilfs2 superblock structure. When this field contains a value that, when used as an exponent in bit shift operations, exceeds the maximum representable value for a 32-bit signed integer, the kernel's undefined behavior sanitizer (UBSan) detects the violation and triggers a shift-out-of-bounds warning. This condition occurs because the code performs bit shift operations without validating whether the shift exponent falls within acceptable ranges, directly violating the principles of secure coding practices outlined in CWE-190, which addresses integer overflow and underflow conditions. The vulnerability specifically targets the arithmetic operation where a large value is used as a shift exponent, causing the kernel to panic when panic_on_warn is enabled, effectively creating a denial-of-service condition.
The operational impact of CVE-2022-50864 extends beyond simple system instability to potentially compromise the entire system's availability and integrity. When a system attempts to mount a corrupted nilfs2 file system, the kernel will immediately trigger a panic condition, rendering the system unusable until reboot. This vulnerability affects systems that utilize nilfs2 file systems, which are commonly found in embedded systems, storage appliances, and specialized computing environments where log-structured file systems are employed. The attack vector is particularly concerning as it can be triggered by simply mounting a corrupted or maliciously crafted file system image, making it exploitable in scenarios involving untrusted file system media or network storage. The vulnerability aligns with ATT&CK technique T1499.001 which covers File System Wipe, as it can effectively render file systems inaccessible through kernel panic conditions.
The fix for this vulnerability involves implementing a new helper function that performs proper sanity checks on the block size values before they are used in arithmetic operations. This approach follows the defensive programming principle of validating all inputs and implementing proper bounds checking to prevent integer overflow conditions. The solution addresses the underlying issue by ensuring that any value extracted from the s_log_block_size field is validated against reasonable limits before being used in shift operations. This mitigation strategy aligns with security best practices for preventing integer overflows and follows the guidance provided in the Linux kernel security documentation for handling file system superblock validation. The patch ensures that the kernel can gracefully handle corrupted superblock data rather than crashing, thereby providing better error handling and preventing the escalation of minor data corruption into system-wide failures. This fix demonstrates the importance of input validation and proper error handling in kernel space code, as specified in security frameworks that emphasize robustness against malformed data inputs.
This vulnerability highlights the critical importance of proper input validation in kernel-level code, particularly in file system drivers where corrupted data can originate from various sources including user-generated content, network storage, or compromised media. The flaw demonstrates how seemingly minor validation gaps in kernel code can lead to catastrophic system failures, emphasizing the need for comprehensive testing and security reviews of kernel subsystems. The implementation of proper bounds checking and sanity validation functions serves as a model for other kernel subsystems to follow when dealing with user-provided or potentially corrupted data, as recommended by security standards that prioritize robustness and fault tolerance in operating system components. Organizations should ensure their systems are updated with the patched kernel versions to prevent exploitation of this vulnerability, particularly in environments where nilfs2 file systems are actively used or where systems might be exposed to untrusted file system content.