CVE-2023-53608 in Linux
Summary
by MITRE • 10/04/2025
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: fix potential UAF of struct nilfs_sc_info in nilfs_segctor_thread()
The finalization of nilfs_segctor_thread() can race with nilfs_segctor_kill_thread() which terminates that thread, potentially causing a use-after-free BUG as KASAN detected.
At the end of nilfs_segctor_thread(), it assigns NULL to "sc_task" member of "struct nilfs_sc_info" to indicate the thread has finished, and then notifies nilfs_segctor_kill_thread() of this using waitqueue "sc_wait_task" on the struct nilfs_sc_info.
However, here, immediately after the NULL assignment to "sc_task", it is possible that nilfs_segctor_kill_thread() will detect it and return to continue the deallocation, freeing the nilfs_sc_info structure before the thread does the notification.
This fixes the issue by protecting the NULL assignment to "sc_task" and its notification, with spinlock "sc_state_lock" of the struct nilfs_sc_info. Since nilfs_segctor_kill_thread() does a final check to see if "sc_task" is NULL with "sc_state_lock" locked, this can eliminate the race.
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Analysis
by VulDB Data Team • 04/28/2026
The vulnerability identified as CVE-2023-53608 resides within the Linux kernel's NILFS2 (New Implementation of LogFS) filesystem implementation, specifically affecting the segment constructor thread functionality. This represents a critical use-after-free condition that can lead to system instability and potential privilege escalation. The issue manifests in the interaction between two core kernel functions: nilfs_segctor_thread() which manages the segment construction process, and nilfs_segctor_kill_thread() which handles thread termination and resource cleanup. The flaw occurs during the graceful shutdown sequence of the segment constructor thread, where improper synchronization between thread finalization and termination routines creates a window for memory corruption.
The technical root cause stems from a race condition in the thread termination protocol where the nilfs_segctor_thread() function performs a NULL assignment to the sc_task member of the struct nilfs_sc_info structure to signal completion. This assignment occurs immediately before notification via the sc_wait_task waitqueue, creating a temporal gap where nilfs_segctor_kill_thread() can detect the NULL value and proceed with deallocation of the entire nilfs_sc_info structure. The kernel's memory management system, specifically KASAN (Kernel Address Sanitizer), detected this condition as a use-after-free error, indicating that memory previously allocated to the structure was accessed after being freed. This race condition violates fundamental kernel synchronization principles and can result in memory corruption that may be exploited by malicious actors.
The operational impact of this vulnerability extends beyond simple system instability, potentially allowing attackers to execute arbitrary code with kernel privileges. When the race condition occurs, the freed memory structure can be reallocated for other purposes, leading to unpredictable behavior including system crashes, data corruption, or privilege escalation. The vulnerability affects systems running Linux kernels with NILFS2 filesystem support, particularly those utilizing the segment constructor thread for background segment management operations. Attackers could exploit this condition by triggering specific filesystem operations that activate the segment constructor thread, then rapidly initiating thread termination sequences to force the race condition. This aligns with ATT&CK technique T1068 which describes the exploitation of privilege escalation vulnerabilities, and CWE-416 which addresses use-after-free conditions in memory management.
The mitigation strategy involves implementing proper synchronization using the existing sc_state_lock spinlock within the nilfs_sc_info structure. This approach ensures that the NULL assignment to sc_task and the subsequent notification to the waitqueue occur as an atomic operation, preventing nilfs_segctor_kill_thread() from detecting the NULL value and proceeding with deallocation until the thread has completed its notification sequence. The fix demonstrates proper kernel synchronization practices by encapsulating the critical section with appropriate locking mechanisms, thereby eliminating the race condition between thread finalization and termination. This solution follows established kernel development patterns for handling concurrent access to shared data structures and aligns with security best practices for preventing race conditions in kernel space operations. The implementation requires minimal code changes while providing robust protection against the identified vulnerability, making it suitable for deployment across various Linux kernel versions supporting NILFS2 functionality.