Overview
CVE-2025-40231 describes a resolved lock inversion vulnerability in the Linux kernel’s Virtual Socket (vsock) implementation. This flaw could lead to a deadlock, potentially causing a denial-of-service condition. The vulnerability was discovered by Syzbot and addressed in recent kernel updates.
Technical Details
The vulnerability stems from a potential lock inversion deadlock between vsock_register_mutex and sk_lock-AF_VSOCK when vsock_linger() is called. Specifically, the issue arises in the vsock_assign_transport() function.
The vulnerability was introduced by commit 687aa0c5581b (“vsock: Fix transport_* TOCTOU”). This commit added vsock_register_mutex locking in vsock_assign_transport() around the transport->release() call, which can trigger vsock_linger(). vsock_assign_transport() can be invoked while holding sk_lock.
vsock_linger() then calls sk_wait_event(), which temporarily releases and re-acquires sk_lock. During this brief window, if another thread is holding vsock_register_mutex and attempts to acquire sk_lock, a circular dependency is created, leading to the deadlock.
The fix involves releasing vsock_register_mutex before calling transport->release() and vsock_deassign_transport(). To ensure the new transport doesn’t disappear prematurely, a module reference is obtained first using try_module_get(). This ensures the module remains loaded during the operation.
CVSS Analysis
Currently, a CVSS score is not available (N/A) for CVE-2025-40231. While the vulnerability can lead to a deadlock, assessing the exploitability and impact requires further analysis. Factors to consider include the likelihood of the race condition occurring and the specific system context.
Possible Impact
The primary impact of CVE-2025-40231 is a potential denial-of-service (DoS). A successful exploitation of this lock inversion vulnerability could lead to a system deadlock, rendering the affected system unresponsive. This is a high-severity outcome for systems relying on vsock for inter-VM communication or other critical functions.
Mitigation or Patch Steps
The recommended mitigation is to update to a Linux kernel version that includes the fix for CVE-2025-40231. The fix has been backported to several stable kernel branches. Check your distribution’s security advisories for specific instructions on how to update your kernel.
Alternatively, if updating the kernel is not immediately feasible, monitor system logs for signs of deadlocks related to vsock. However, this is a reactive measure and does not prevent the vulnerability from being exploited.
References
- Kernel Commit: 09bba278ccde25a14b6e5088a9e65a8717d0cccf
- Kernel Commit: 251caee792a21eb0b781aab91362b422c945e162
- Kernel Commit: 42ed0784d11adebf748711e503af0eb9f1e6d81d
- Kernel Commit: a2a4346eea8b4cb75037dbcb20b98cb454324f80
- Kernel Commit: b44182c116778feaa05da52a426aeb9da1878dcf
- Kernel Commit: ce4f856c64f0bc30e29302a0ce41f4295ca391c5
- Kernel Commit: f7c877e7535260cc7a21484c994e8ce7e8cb6780
