CVE-2024-38582 in Linux
Summary
by MITRE • 06/19/2024
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: fix potential hang in nilfs_detach_log_writer()
Syzbot has reported a potential hang in nilfs_detach_log_writer() called during nilfs2 unmount.
Analysis revealed that this is because nilfs_segctor_sync(), which synchronizes with the log writer thread, can be called after nilfs_segctor_destroy() terminates that thread, as shown in the call trace below:
nilfs_detach_log_writer nilfs_segctor_destroy nilfs_segctor_kill_thread --> Shut down log writer thread flush_work nilfs_iput_work_func nilfs_dispose_list iput nilfs_evict_inode nilfs_transaction_commit nilfs_construct_segment (if inode needs sync) nilfs_segctor_sync --> Attempt to synchronize with log writer thread *** DEADLOCK ***
Fix this issue by changing nilfs_segctor_sync() so that the log writer thread returns normally without synchronizing after it terminates, and by forcing tasks that are already waiting to complete once after the thread terminates.
The skipped inode metadata flushout will then be processed together in the subsequent cleanup work in nilfs_segctor_destroy().
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/04/2025
The vulnerability CVE-2024-38582 affects the Linux kernel's nilfs2 file system implementation and represents a critical deadlock condition that can cause system hangs during unmount operations. This issue manifests when the nilfs_detach_log_writer() function attempts to synchronize with a log writer thread that has already been terminated, creating a circular dependency that prevents proper system shutdown. The problem was identified through syzbot automated testing, which revealed a systematic hang pattern during nilfs2 unmount procedures, indicating a fundamental race condition in the file system's cleanup mechanism.
The technical flaw stems from improper thread lifecycle management within the nilfs2 subsystem where nilfs_segctor_sync() function is invoked after nilfs_segctor_destroy() has already terminated the log writer thread. This creates a deadlock scenario as demonstrated in the call trace showing the sequence: nilfs_detach_log_writer() calls nilfs_segctor_destroy(), which terminates the log writer thread through nilfs_segctor_kill_thread(), followed by flush_work() that triggers nilfs_iput_work_func(), leading to nilfs_evict_inode(), nilfs_transaction_commit(), and eventually nilfs_construct_segment(), which attempts to call nilfs_segctor_sync() on a dead thread. This violates standard thread management protocols and creates a classic deadlock condition where a thread waits for itself to complete.
The operational impact of this vulnerability extends beyond simple system hangs to potentially affect system stability and availability in production environments where nilfs2 file systems are in use. When triggered, the deadlock prevents proper unmount operations and can cause the system to become unresponsive, requiring manual intervention or system reboot to recover. The vulnerability affects systems running Linux kernels with nilfs2 support, particularly those utilizing this file system for logging or journaling operations, making it a significant concern for embedded systems and servers that rely on nilfs2's specific features for data integrity and recovery mechanisms.
The fix implemented addresses the root cause by modifying nilfs_segctor_sync() to handle the case where the log writer thread has already terminated, allowing the thread to return normally without attempting synchronization. Additionally, the solution forces completion of any tasks that were already waiting to finish once the thread terminates, ensuring proper cleanup without creating deadlock conditions. This approach follows established patterns for handling thread lifecycle management and prevents the race condition that led to the original vulnerability. The solution aligns with CWE-362 (Concurrent Execution using Shared Resource with Unprotected Synchronization) and addresses the deadlock scenario through proper synchronization mechanisms. The fix also incorporates elements of ATT&CK technique T1489 (Service Stop) by ensuring proper cleanup of system resources during file system unmount operations. The implementation ensures that skipped inode metadata flush operations are processed in subsequent cleanup work within nilfs_segctor_destroy(), maintaining data integrity while preventing system hangs. This remediation approach demonstrates proper kernel programming practices for managing shared resources and thread synchronization in file system drivers, aligning with Linux kernel development standards and security best practices for preventing deadlock conditions in concurrent systems.