CVE-2025-37802 in Linux
Summary
by MITRE • 05/08/2025
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix WARNING "do not call blocking ops when !TASK_RUNNING"
wait_event_timeout() will set the state of the current task to TASK_UNINTERRUPTIBLE, before doing the condition check. This means that ksmbd_durable_scavenger_alive() will try to acquire the mutex while already in a sleeping state. The scheduler warns us by giving the following warning:
do not call blocking ops when !TASK_RUNNING; state=2 set at [] prepare_to_wait_event+0x9f/0x6c0
WARNING: CPU: 2 PID: 4147 at kernel/sched/core.c:10099 __might_sleep+0x12f/0x160
mutex lock is not needed in ksmbd_durable_scavenger_alive().
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Analysis
by VulDB Data Team • 03/14/2026
The vulnerability CVE-2025-37802 affects the Linux kernel's ksmbd subsystem, which provides SMB/CIFS file sharing capabilities for Linux systems. This issue manifests as a WARNING message indicating improper handling of kernel task states during synchronization operations. The problem occurs within the ksmbd_durable_scavenger_alive() function where the kernel scheduler detects an attempt to perform blocking operations while a task is in a non-running state, specifically when the task has been set to TASK_UNINTERRUPTIBLE by wait_event_timeout().
The technical flaw stems from the improper interaction between kernel scheduling primitives and mutex locking mechanisms. When wait_event_timeout() is invoked, it transitions the current task to TASK_UNINTERRUPTIBLE state before checking the wait condition, but the subsequent mutex acquisition attempt within ksmbd_durable_scavenger_alive() violates kernel scheduling constraints. This violates the fundamental principle that blocking operations should not be performed when a task is in a sleeping or non-running state, as documented in the Linux kernel's core scheduling mechanisms. The warning message specifically points to the prepare_to_wait_event function in kernel/sched/core.c at line 10099, which is part of the kernel's sleep preparation logic that enforces these constraints.
The operational impact of this vulnerability extends beyond simple warning messages to potentially destabilize the SMB/CIFS service provided by ksmbd. While the immediate effect appears to be a scheduler warning rather than a system crash, the improper synchronization can lead to resource contention, deadlocks, or inconsistent state management within the SMB server implementation. This could result in degraded service availability, connection timeouts, or potential denial of service conditions for clients accessing shared resources through the ksmbd service. The vulnerability particularly affects systems running Linux kernels with ksmbd support, making it relevant to enterprise file servers, NAS appliances, and any system providing SMB/CIFS services through the kernel's native implementation.
The fix for this vulnerability involves removing the unnecessary mutex lock operation from the ksmbd_durable_scavenger_alive() function, as the mutex acquisition is not required for the operations being performed. This aligns with the principle of minimal synchronization, ensuring that kernel code only acquires locks when absolutely necessary for protecting shared resources. The solution addresses the root cause by eliminating the conflict between the scheduling state management and the blocking operation, thereby preventing the scheduler warning from occurring. This fix adheres to the kernel's design principles and follows best practices for concurrent programming in kernel space as outlined in the Linux kernel documentation and security guidelines. The mitigation approach specifically targets the CWE-362 weakness category related to improper synchronization, ensuring that kernel subsystems properly manage task states and synchronization primitives without creating scenarios where blocking operations are attempted in inappropriate contexts.
This vulnerability demonstrates the importance of careful kernel development practices and adherence to established scheduling constraints. The issue highlights the need for thorough testing of kernel subsystems under various concurrent access scenarios, particularly those involving wait events and synchronization primitives. Security practitioners should monitor for this vulnerability in systems running affected Linux kernel versions, as improper handling of kernel task states can create potential attack vectors or service disruption scenarios. The fix represents a straightforward correction to the kernel's internal synchronization logic, emphasizing the critical nature of proper task state management in kernel space operations and the importance of following established kernel development patterns and security guidelines.