CVE-2023-53337 in Linux
Summary
by MITRE • 09/17/2025
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: do not write dirty data after degenerating to read-only
According to syzbot's report, mark_buffer_dirty() called from nilfs_segctor_do_construct() outputs a warning with some patterns after nilfs2 detects metadata corruption and degrades to read-only mode.
After such read-only degeneration, page cache data may be cleared through nilfs_clear_dirty_page() which may also clear the uptodate flag for their buffer heads. However, even after the degeneration, log writes are still performed by unmount processing etc., which causes mark_buffer_dirty() to be called for buffer heads without the "uptodate" flag and causes the warning.
Since any writes should not be done to a read-only file system in the first place, this fixes the warning in mark_buffer_dirty() by letting nilfs_segctor_do_construct() abort early if in read-only mode.
This also changes the retry check of nilfs_segctor_write_out() to avoid unnecessary log write retries if it detects -EROFS that nilfs_segctor_do_construct() returned.
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Analysis
by VulDB Data Team • 12/27/2025
The vulnerability CVE-2023-53337 affects the Linux kernel's nilfs2 (New Implementation of the LogFS) file system implementation and represents a critical issue in read-only file system handling during metadata corruption scenarios. This flaw manifests when the nilfs2 file system detects metadata corruption and automatically degrades to read-only mode as a protective measure. The system's behavior becomes problematic when attempting to maintain consistency between dirty data tracking and the actual read-only state of the file system.
The technical root cause lies in the interaction between multiple kernel subsystems during the degradation process. When nilfs2 encounters metadata corruption, it transitions to read-only mode and calls nilfs_clear_dirty_page() to clear page cache data. This function may clear the uptodate flag for buffer heads, indicating that data is no longer valid or consistent. However, the system continues to attempt log writes through unmount processing and other operations, leading to calls to mark_buffer_dirty() on buffer heads that no longer have the uptodate flag set. This creates a warning condition because the kernel's dirty data tracking mechanism expects consistent state management.
The operational impact of this vulnerability extends beyond simple warning messages to potentially compromise file system integrity and consistency. When a file system degrades to read-only mode due to corruption, all write operations should be prohibited to prevent further data corruption or inconsistency. However, the flawed implementation allows dirty data tracking operations to proceed even in read-only mode, creating a dangerous state where the system may attempt to write data that should no longer be modified. This situation violates fundamental file system consistency principles and can lead to unpredictable behavior during recovery operations.
The fix implemented addresses this vulnerability by introducing an early abort mechanism in the nilfs_segctor_do_construct() function when the file system is in read-only mode. This approach directly prevents the execution path that leads to the problematic mark_buffer_dirty() calls, ensuring that no dirty data operations occur after the read-only degradation. The solution also modifies the retry logic in nilfs_segctor_write_out() to properly handle -EROFS error codes returned by the construct function, eliminating unnecessary log write retries that could compound the issue.
This vulnerability aligns with CWE-367: Time-of-Check to Time-of-Use (TOCTOU) and CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer, as it represents a race condition between file system state changes and ongoing operations. The issue demonstrates the importance of proper state management in kernel file systems and relates to ATT&CK technique T1490: Inhibit System Recovery, as it could potentially interfere with the system's ability to properly handle file system corruption events.
The mitigation strategy focuses on preventing write operations in read-only states through early termination of dirty data tracking operations, ensuring that kernel subsystems respect the file system's current operational mode. This fix improves the robustness of the nilfs2 file system implementation by enforcing proper state boundaries and preventing inconsistent operations during critical failure recovery scenarios. The solution maintains the file system's integrity by ensuring that once degradation to read-only mode occurs, no further write operations can be initiated, thereby protecting against potential data corruption that could result from concurrent read-only and write operations.