CVE-2026-64390 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: track the connection owning a byte-range lock
SMB2_LOCK adds each granted byte-range lock to both the file lock list and the lock list of the connection which handled the request. The final close and durable handle paths, however, remove the connection list entry while holding fp->conn->llist_lock.
With SMB3 multichannel, the connection handling the LOCK request can be different from the connection which opened the file. The entry can therefore be removed under a different spinlock from the one protecting the list it belongs to. A concurrent traversal can then access freed struct ksmbd_lock and struct file_lock objects.
Record the connection owning each lock's clist entry and hold a reference to it while the entry is linked. Use that connection and its llist_lock for unlock, rollback, close, and durable preserve. Durable reconnect assigns the new connection as the owner when publishing the locks again.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability in question affects the ksmbd kernel module which implements smb2/smb3 server functionality in linux systems. This issue specifically targets the handling of byte-range locks within the SMB2_LOCK operation mechanism. The flaw stems from improper tracking of connection ownership for file locks, creating a race condition scenario that can lead to use-after-free vulnerabilities and potential privilege escalation opportunities. The vulnerability is particularly concerning as it affects the core locking mechanisms that ensure data consistency in shared file environments.
The technical root cause involves the inconsistent management of lock list entries across different connection contexts. When an SMB2_LOCK request is processed, the system correctly adds the granted byte-range lock to both the file lock list and the connection's lock list. However, during final close or durable handle operations, the cleanup process removes entries from the connection list while holding locks from a different connection context. This occurs because SMB3 multichannel allows different connections to handle LOCK requests versus file opening operations, creating a scenario where the spinlock protecting one list may differ from the one protecting another.
The operational impact of this vulnerability extends beyond simple memory corruption. Attackers could exploit this race condition to manipulate lock structures and potentially gain unauthorized access to shared resources or escalate privileges within the system. The freed struct ksmbd_lock and struct file_lock objects create opportunities for memory corruption that could be leveraged for arbitrary code execution. This represents a critical security gap in enterprise file sharing environments where multiple connections might interact with the same files simultaneously.
The mitigation strategy implemented addresses this by recording the connection owning each lock's clist entry and maintaining proper reference counting during the lock lifecycle. The solution ensures that when performing unlock, rollback, close, or durable preserve operations, the system uses the correct connection and its associated llist_lock for synchronization. During durable reconnect scenarios, the new connection properly assumes ownership of previously published locks, maintaining consistency across connection transitions. This approach aligns with established security principles for concurrent access control and memory management in kernel space operations.
The vulnerability demonstrates characteristics consistent with CWE-119 (Improper Access Control) and CWE-415 (Double Free) while potentially enabling techniques aligned with ATT&CK tactics such as privilege escalation through kernel exploitation. The fix ensures proper lock ownership tracking and maintains data integrity across multichannel SMB3 connections, preventing potential attackers from exploiting the race condition to manipulate file locking mechanisms. This represents a fundamental improvement in kernel memory safety for shared file systems and aligns with industry standards for secure concurrent programming practices in operating system kernels.