Advisory [CVE-2026-64390] track the connection owning a byte-range lock

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. A flaw was found in the Linux kernel's ksmbd component, which provides Server Message Block (SMB) protocol support.

This vulnerability involves incorrect management of byte-range locks when multiple connections are used with SMB3 multichannel. An attacker could exploit this by sending specially crafted SMB requests, potentially causing memory corruption.