CVE-2023-53016 in Linux
Summary
by MITRE • 03/27/2025
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: Fix possible deadlock in rfcomm_sk_state_change
syzbot reports a possible deadlock in rfcomm_sk_state_change [1].
While rfcomm_sock_connect acquires the sk lock and waits for the rfcomm lock, rfcomm_sock_release could have the rfcomm lock and hit a deadlock for acquiring the sk lock. Here's a simplified flow:
rfcomm_sock_connect: lock_sock(sk) rfcomm_dlc_open: rfcomm_lock()
rfcomm_sock_release: rfcomm_sock_shutdown: rfcomm_lock() __rfcomm_dlc_close: rfcomm_k_state_change: lock_sock(sk)
This patch drops the sk lock before calling rfcomm_dlc_open to avoid the possible deadlock and holds sk's reference count to prevent use-after-free after rfcomm_dlc_open completes.
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Analysis
by VulDB Data Team • 12/07/2025
The vulnerability identified as CVE-2023-53016 represents a critical deadlock condition within the Linux kernel's Bluetooth subsystem, specifically affecting the RFCOMM protocol implementation. This issue manifests in the rfcomm_sk_state_change function where competing lock acquisition patterns create a circular dependency that can halt system operations. The vulnerability was discovered through automated fuzzing by syzbot, which identified a race condition in the Bluetooth socket management code that could lead to complete system unresponsiveness. The flaw occurs when multiple threads attempt to manipulate Bluetooth socket states simultaneously, creating a scenario where one thread holds a socket lock while waiting for a RFCOMM lock, and another thread holds the RFCOMM lock while waiting for the socket lock.
The technical root cause of this vulnerability stems from improper lock ordering in the Bluetooth RFCOMM socket implementation. When rfcomm_sock_connect attempts to establish a connection, it first acquires the socket lock using lock_sock(sk) and then proceeds to call rfcomm_dlc_open which requires acquiring the rfcomm_lock. However, during the rfcomm_sock_release process, the system may already hold the rfcomm_lock while attempting to call rfcomm_k_state_change, which subsequently tries to acquire the socket lock through lock_sock(sk). This creates a classic deadlock scenario where each thread waits indefinitely for the lock held by the other. This pattern directly corresponds to CWE-362, which describes concurrent execution using a lock that is not properly ordered, and aligns with ATT&CK technique T1499.004 for resource exhaustion through system instability.
The operational impact of this vulnerability extends beyond simple system hangs, potentially affecting any system running Linux kernel versions with Bluetooth support and active RFCOMM connections. The deadlock condition can occur during normal Bluetooth socket operations including connection establishment, disconnection, and state transitions, making it particularly dangerous in embedded systems, IoT devices, or any environment where Bluetooth connectivity is essential. Attackers could potentially exploit this vulnerability to cause denial of service conditions, particularly in systems where Bluetooth services are critical for operation such as automotive systems, industrial control equipment, or network infrastructure devices. The vulnerability affects systems where multiple Bluetooth threads operate concurrently, with the risk increasing in environments with high Bluetooth traffic or frequent connection cycling.
The mitigation strategy implemented in the patch addresses the core issue by modifying the lock acquisition sequence in the rfcomm_sock_connect function. The solution involves releasing the socket lock before calling rfcomm_dlc_open, thereby breaking the circular dependency that leads to the deadlock. Additionally, the patch ensures proper reference counting of the socket to prevent use-after-free conditions that could occur after rfcomm_dlc_open completes. This approach follows established best practices for avoiding lock ordering issues and aligns with the principle of minimizing lock hold times. The fix also incorporates proper reference counting mechanisms to ensure that socket resources remain valid throughout the operation, addressing potential memory safety concerns that could arise from the modified execution flow. System administrators should apply the kernel patches immediately to all affected systems, particularly those running embedded Linux distributions or IoT platforms where Bluetooth connectivity is prevalent. The vulnerability demonstrates the complexity of lock management in kernel space and highlights the importance of thorough testing of concurrent operations in operating system components.