CVE-2026-68381: ksmbd: pin conn during async oplock break notification

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: pin conn during async oplock break notification

smb2oplockbreaknoti() and smb2leasebreaknoti() store a ksmbdconn pointer in an async ksmbdwork and then queue that work on ksmbd-io. The work only increments conn->rcount, which prevents teardown from passing the pending-request wait after the increment, but it does not pin the struct ksmbdconn object.

If connection teardown races with an oplock break notification, the last conn reference can be dropped before the queued worker finishes. The worker then uses the freed conn in ksmbdconnwrite() and ksmbdconnrcountdec().

Take a real conn reference when publishing the conn pointer to the async work item, and drop it after the notification work has decremented rcount. Apply the same lifetime rule to lease break notification, which uses the same work->conn pattern.