CVE-2023-52638 in Linux
Summary
by MITRE • 04/03/2024
In the Linux kernel, the following vulnerability has been resolved:
can: j1939: prevent deadlock by changing j1939_socks_lock to rwlock
The following 3 locks would race against each other, causing the deadlock situation in the Syzbot bug report:
- j1939_socks_lock - active_session_list_lock - sk_session_queue_lock
A reasonable fix is to change j1939_socks_lock to an rwlock, since in the rare situations where a write lock is required for the linked list that j1939_socks_lock is protecting, the code does not attempt to acquire any more locks. This would break the circular lock dependency, where, for example, the current thread already locks j1939_socks_lock and attempts to acquire sk_session_queue_lock, and at the same time, another thread attempts to acquire j1939_socks_lock while holding sk_session_queue_lock.
NOTE: This patch along does not fix the unregister_netdevice bug reported by Syzbot; instead, it solves a deadlock situation to prepare for one or more further patches to actually fix the Syzbot bug, which appears to be a reference counting problem within the j1939 codebase.
[mkl: remove unrelated newline change]
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Analysis
by VulDB Data Team • 01/14/2026
The vulnerability identified as CVE-2023-52638 affects the Linux kernel's J1939 protocol implementation within the CAN (Controller Area Network) subsystem. This issue represents a critical deadlock condition that can occur during concurrent operations involving network device management and socket operations. The J1939 protocol is used for communication in automotive and industrial environments, making this vulnerability particularly concerning for systems where real-time communication and reliability are paramount. The vulnerability was discovered through automated testing by Syzbot, highlighting the complexity of modern kernel locking mechanisms and their potential for circular dependency issues.
The technical flaw stems from a three-way race condition involving three distinct locks within the J1939 subsystem: j1939_socks_lock, active_session_list_lock, and sk_session_queue_lock. This circular dependency creates a scenario where threads become deadlocked when attempting to acquire multiple locks in different orders. When one thread holds j1939_socks_lock while attempting to acquire sk_session_queue_lock, and simultaneously another thread holds sk_session_queue_lock while attempting to acquire j1939_socks_lock, the system enters a deadlock state. This type of race condition falls under the CWE-367 category of Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities, specifically manifesting as a deadlock condition in concurrent programming. The issue is classified as a lock ordering problem that violates the principle of consistent lock acquisition ordering.
The operational impact of this vulnerability extends beyond simple system unresponsiveness to potentially compromising the reliability of automotive and industrial systems that depend on J1939 communication. When a deadlock occurs in the kernel, it can lead to complete system hangs or crashes, particularly during network device registration and unregistration operations. The vulnerability affects systems using CAN bus communication, which are prevalent in modern vehicles, agricultural machinery, construction equipment, and industrial control systems. From an ATT&CK framework perspective, this vulnerability could be leveraged in a denial of service attack against automotive or industrial systems, potentially leading to safety-critical failures in environments where communication reliability is essential.
The proposed solution involves transforming j1939_socks_lock from a simple mutex to a read-write lock (rwlock) structure. This change is strategically designed to break the circular dependency by allowing multiple readers to access the protected linked list simultaneously while ensuring exclusive access only when necessary for write operations. The fix addresses the root cause by eliminating the scenario where write lock acquisition would conflict with other lock acquisitions, thereby preventing the deadlock condition. This approach aligns with kernel development best practices for managing concurrent access to shared resources and follows the principle of minimizing lock hold times. The solution specifically targets the locking hierarchy without addressing the underlying reference counting issue identified by Syzbot, indicating this is a preparatory fix that enables subsequent patches to resolve the complete bug. This remediation strategy demonstrates the complexity of kernel-level concurrency control and the importance of careful lock design in preventing subtle but critical race conditions.