CVE-2026-90167 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: serialize oplock close with pending break ownership
close may abort an in-flight oplock break while another breaker already holds an opinfo reference. Releasing pending_break wakes that waiter, but without serializing the close transition with bit acquisition it can become a new break owner through the test_and_set_bit() fast path. It can then overwrite OPLOCK_CLOSING with OPLOCK_ACK_WAIT and continue a break for a dying opinfo.
Make OPLOCK_CLOSING terminal once the opinfo is removed from the inode list. Serialize that transition, pending_break acquisition, and OPLOCK_ACK_WAIT setup with an opinfo state lock. A breaker which loses the race releases its ownership and returns -ENOENT. Explicitly wake pending_break waiters during close so they can observe the terminal state.
Also prevent ACK and timeout paths from replacing OPLOCK_CLOSING with OPLOCK_STATE_NONE.
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Analysis
by VulDB Data Team • 09/17/2026
The ksmbd subsystem within the Linux kernel contains a concurrency vulnerability related to the handling of oplock breaks, specifically involving race conditions during file close operations. Oplocks, or opportunistic locks, are mechanisms used by SMB servers to optimize file access performance by allowing clients to cache data locally under certain locking assumptions. When an application closes a file that holds an active oplock, the server must terminate that lock and potentially notify other interested parties through break notifications. The identified flaw arises from improper synchronization between the close operation and ongoing or pending oplock breaks. Specifically, when a close request is processed, it may attempt to abort an in-flight oplock break while another breaker already holds a reference to the opinfo structure representing the open file handle. This scenario creates a window where state transitions are not atomic with respect to ownership acquisition, leading to inconsistent internal states that compromise data integrity and system stability.
The core technical flaw lies in how the kernel manages the transition of an oplock into a closing state versus its acknowledgment by waiting breakers. In the vulnerable implementation, releasing a pending_break signal wakes up waiters who might then acquire the opinfo reference through a fast path involving test_and_set_bit operations. Without proper serialization between the close transition and this bit acquisition, a breaker can incorrectly become the new owner of an oplock that is already marked for closure. Consequently, this erroneous ownership allows the process to overwrite the OPLOCK_CLOSING state with OPLOCK_ACK_WAIT, effectively continuing a break notification sequence for an opinfo structure that has been logically removed from the inode list and should no longer be active. This race condition means that operations intended to finalize resource cleanup are instead kept alive or restarted incorrectly, violating the expected lifecycle of kernel objects associated with file handles.
The operational impact of this vulnerability includes potential denial of service conditions due to resource leaks or infinite loops within the locking logic, as well as data corruption risks if clients proceed under false assumptions about lock validity. If a breaker continues processing an oplock that is supposed to be closed, it may write cached data back to storage based on stale metadata, leading to inconsistencies between client caches and server-side files. Furthermore, because the kernel object remains in an ambiguous state rather than being properly released or finalized, memory management issues such as use-after-free scenarios could theoretically arise if other parts of the subsystem attempt to access freed structures expecting them to be valid but finding corrupted pointers due to the race condition. This affects the reliability and security posture of systems running ksmbd services exposed to network traffic.
To mitigate this vulnerability, the fix implements strict serialization using an opinfo state lock that governs the transition into OPLOCK_CLOSING, the acquisition of pending_break ownership, and the setup of OPLOCK_ACK_WAIT states. By making OPLOCK_CLOSING a terminal state once the opinfo is removed from the inode list, the kernel ensures that no new breakers can claim ownership after closure has been initiated. The solution also explicitly wakes up pending_break waiters during close operations so they can observe this terminal state and abort their processing accordingly. Additionally, race conditions in acknowledgment and timeout paths are addressed by preventing these mechanisms from replacing OPLOCK_CLOSING with OPLOCK_STATE_NONE prematurely. This ensures that the closing process completes fully before any other state changes occur. From a classification perspective, this issue aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition), as it involves multiple execution paths accessing shared kernel structures without adequate locking mechanisms to prevent inconsistent states.