Document Rbac module (#6107)

Introduces an interface file for the Rbac module within xapi in order to
document the intent of each of its functions.

---

Cherry picked from another branch concerning `server.ml` generation; I
want to reduce the surface area of these modules so we can be clear
about what they are doing.

ocaml/xapi/rbac.ml

@@ -243,11 +243,6 @@ let assert_permission_name ~__context ~permission =
 let assert_permission ~__context ~permission =
   assert_permission_name ~__context ~permission:permission.role_name_label
 
-(* this is necessary to break dependency cycle between rbac and taskhelper *)
-let init_task_helper_rbac_has_permission_fn =
-  if !TaskHelper.rbac_assert_permission_fn = None then
-    TaskHelper.rbac_assert_permission_fn := Some assert_permission
-
 let has_permission_name ~__context ~permission =
   let session_id = get_session_of_context ~__context ~permission in
   is_access_allowed ~__context ~session_id ~permission

ocaml/xapi/rbac.mli

@@ -0,0 +1,104 @@
+(*
+ * Copyright (c) Cloud Software Group, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *)
+
+val is_access_allowed :
+     __context:Context.t
+  -> session_id:[`session] Ref.t
+  -> permission:string
+  -> bool
+(** Determines whether the session associated with the provided
+    context has the specified permission. The permission set is cached
+    (on the coordinator only) to benefit successive queries for the
+    same session. *)
+
+val check :
+     ?extra_dmsg:string
+  -> ?extra_msg:string
+  -> ?args:(string * Rpc.t) list
+  -> ?keys:string list
+  -> __context:Context.t
+  -> fn:(unit -> 'a)
+  -> [`session] Ref.t
+  -> string
+  -> 'a
+(** [check] executes a function associated with an action if the
+    session associated with the provided context is authorised to
+    perform the action.
+
+    The [?extra_dmsg] and [?extra_msg] parameters allow for extra
+    information in debugging and error messages.
+
+    The [?keys] parameter specifies which fields of a (string -> _)
+    map are RBAC-protected. It is primarily associated with
+    auto-generated methods such as add_to_other_config. However, if
+    [?keys] is non-empty, then [?args] must also be consulted as the
+    related methods that require this protection specify their key
+    name as a parameter. Otherwise, [?args] is mostly used to log
+    calls within the RBAC audit log. *)
+
+val check_with_new_task :
+     ?extra_dmsg:string
+  -> ?extra_msg:string
+  -> ?task_desc:string
+  -> ?args:(string * Rpc.t) list
+  -> fn:(unit -> 'a)
+  -> [`session] Ref.t
+  -> string
+  -> 'a
+(** Defined in terms of [check] but using a context associated with a
+    freshly-created task. *)
+
+val assert_permission_name : __context:Context.t -> permission:string -> unit
+(** Performs a dry run of the [check] function with a no-op action
+    guarded by the provided permission (as a name). *)
+
+val assert_permission :
+  __context:Context.t -> permission:Db_actions.role_t -> unit
+(** Performs a dry run of the [check] function with a no-op action
+    guarded by the provided permission (as a database role). *)
+
+val has_permission : __context:Context.t -> permission:Db_actions.role_t -> bool
+(** [has_permission ctx p] determines if the session associated with
+    the context [ctx] is authorised to perform a specific action.
+
+    [p] is of the type defined by the generated [Db_actions] module,
+    as [Xapi_role] simulates a database for the checking of static
+    role sets (as emitted in [Rbac_static]) and only appeals to the
+    xapi DB for additional roles. *)
+
+val is_rbac_enabled_for_http_action : string -> bool
+(** [is_rbac_enabled_for_http_action route] determines whether RBAC
+    checks should be applied to the provided HTTP [route].
+
+    Some routes are precluded from RBAC checks because they are
+    assumed to only be used by code paths where RBAC has already been
+    checked or will be checked internally (e.g. /post_cli). *)
+
+val permission_of_action :
+  ?args:(string * Rpc.t) list -> keys:string list -> string -> string
+(** Constructs the name of a permission associated with using an
+    RBAC-protected key with a specified action.
+
+    For example, if [keys] specifies "folder" as a protected key name
+    for the action SR.remove_from_other_config, the permission name
+    associated with that is "SR.remove_from_other_config/key:folder"
+    - which is consistent with the format that [Rbac_static] contains. *)
+
+val nofn : unit -> unit
+(** Named function that does nothing, e.g. (fun _ -> ()).
+    Used as a dummy action for RBAC checking. *)
+
+val destroy_session_permissions_tbl : session_id:[`session] Ref.t -> unit
+(** Removes any cached permission set for the given session. This is
+    called when xapi destroys the DB entry for a session. *)

quality-gate.sh

@@ -25,7 +25,7 @@ verify-cert () {
 }
 
 mli-files () {
-  N=499
+  N=498
   # do not count ml files from the tests in ocaml/{tests/perftest/quicktest}
   MLIS=$(git ls-files -- '**/*.mli' | grep -vE "ocaml/tests|ocaml/perftest|ocaml/quicktest|ocaml/message-switch/core_test" | xargs -I {} sh -c "echo {} | cut -f 1 -d '.'" \;)
   MLS=$(git  ls-files -- '**/*.ml'  | grep -vE "ocaml/tests|ocaml/perftest|ocaml/quicktest|ocaml/message-switch/core_test" | xargs -I {} sh -c "echo {} | cut -f 1 -d '.'" \;)