SurrealDB: USE NS/DB implicit creation bypasses DEFINE authorization

Summary

An anonymous caller could create new namespaces and databases on a running SurrealDB instance without holding `DEFINE NAMESPACE` or `DEFINE DATABASE` permission. `USE NS <name>` and `USE DB <name>` automatically create the target when it does not exist. The three places `USE` is handled — the RPC `use` method, `Datastore::process_use`, and the SurrealQL executor — did not check whether the caller was allowed to create the resource. Under default capabilities any session reached this path, including an unauthenticated guest. ### Impact What an attacker **can** do: - Create new namespaces and databases without `DEFINE NAMESPACE` / `DEFINE DATABASE` permission. An unauthenticated guest is enough under default capabilities. - Recreate a parent namespace that an operator deliberately dropped, using a stale namespace-Editor token, by running `USE NS <dropped> DB anything`. - Exhaust catalog storage by repeatedly creating new resources. What it **can't** do: - Read or modify data inside any pre-existing namespace or database. - Escalate to root or namespace-owner privileges on existing resources. - Affect deployments running with `auth_enabled=false`. ### Patches All three `USE` entry points now check whether the caller has `DEFINE NAMESPACE` / `DEFINE DATABASE` authority before creating a missing target. Sessions still update their context regardless of authorization, so SDKs that send `use` before `signin` continue to work — only the catalog creation step is gated. The parent-namespace side-effect path is closed by the same check. Versions 3.1.0 and later are not affected. ### Workarounds - Set `--deny-arbitrary-query *` for guest principals to remove the entry point. - Run with `--auth` and require all callers to `signin` before issuing `use`. - Revoke namespace-level tokens promptly when a namespace is dropped.