From: =?UTF-8?q?Edwin=20T=C3=B6r=C3=B6k?= <edvin.torok@citrix.com>
Subject: tools/ocaml/xenstored: introduce permissions for special watches
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The special watches "@introduceDomain" and "@releaseDomain" should be
allowed for privileged callers only, as they allow to gain information
about presence of other guests on the host. So send watch events for
those watches via privileged connections only.

Start to address this by treating the special watches as regular nodes
in the tree, which gives them normal semantics for permissions.  A later
change will restrict the handling, so that they can't be listed, etc.

This is part of XSA-115.

Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/tools/ocaml/xenstored/process.ml b/tools/ocaml/xenstored/process.ml
index fd79ef564f..e528d1ecb2 100644
--- a/tools/ocaml/xenstored/process.ml
+++ b/tools/ocaml/xenstored/process.ml
@@ -420,7 +420,7 @@ let do_introduce con _t domains cons data =
 		else try
 			let ndom = Domains.create domains domid mfn port in
 			Connections.add_domain cons ndom;
-			Connections.fire_spec_watches cons "@introduceDomain";
+			Connections.fire_spec_watches cons Store.Path.introduce_domain;
 			ndom
 		with _ -> raise Invalid_Cmd_Args
 	in
@@ -439,7 +439,7 @@ let do_release con _t domains cons data =
 	Domains.del domains domid;
 	Connections.del_domain cons domid;
 	if fire_spec_watches
-	then Connections.fire_spec_watches cons "@releaseDomain"
+	then Connections.fire_spec_watches cons Store.Path.release_domain
 	else raise Invalid_Cmd_Args
 
 let do_resume con _t domains _cons data =
diff --git a/tools/ocaml/xenstored/store.ml b/tools/ocaml/xenstored/store.ml
index 92b6289b5e..52b88b3ee1 100644
--- a/tools/ocaml/xenstored/store.ml
+++ b/tools/ocaml/xenstored/store.ml
@@ -214,6 +214,11 @@ let rec lookup node path fct =
 
 let apply rnode path fct =
 	lookup rnode path fct
+
+let introduce_domain = "@introduceDomain"
+let release_domain = "@releaseDomain"
+let specials = List.map of_string [ introduce_domain; release_domain ]
+
 end
 
 (* The Store.t type *)
diff --git a/tools/ocaml/xenstored/utils.ml b/tools/ocaml/xenstored/utils.ml
index b252db799b..e8c9fe4e94 100644
--- a/tools/ocaml/xenstored/utils.ml
+++ b/tools/ocaml/xenstored/utils.ml
@@ -88,19 +88,17 @@ let read_file_single_integer filename =
 	Unix.close fd;
 	int_of_string (Bytes.sub_string buf 0 sz)
 
-let path_complete path connection_path =
-	if String.get path 0 <> '/' then
-		connection_path ^ path
-	else
-		path
-
+(* @path may be guest data and needs its length validating.  @connection_path
+ * is generated locally in xenstored and always of the form "/local/domain/$N/" *)
 let path_validate path connection_path =
-	if String.length path = 0 || String.length path > 1024 then
-		raise Define.Invalid_path
-	else
-		let cpath = path_complete path connection_path in
-		if String.get cpath 0 <> '/' then
-			raise Define.Invalid_path
-		else
-			cpath
+	let len = String.length path in
+
+	if len = 0 || len > 1024 then raise Define.Invalid_path;
+
+	let abs_path =
+		match String.get path 0 with
+		| '/' | '@' -> path
+		| _   -> connection_path ^ path
+	in
 
+	abs_path
diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml
index 7e7824761b..8d0c50bfa4 100644
--- a/tools/ocaml/xenstored/xenstored.ml
+++ b/tools/ocaml/xenstored/xenstored.ml
@@ -286,6 +286,8 @@ let _ =
 	let quit = ref false in
 
 	Logging.init_xenstored_log();
+	List.iter (fun path ->
+		Store.write store Perms.Connection.full_rights path "") Store.Path.specials;
 
 	let filename = Paths.xen_run_stored ^ "/db" in
 	if cf.restart && Sys.file_exists filename then (
@@ -335,7 +337,7 @@ let _ =
 					let (notify, deaddom) = Domains.cleanup domains in
 					List.iter (Connections.del_domain cons) deaddom;
 					if deaddom <> [] || notify then
-						Connections.fire_spec_watches cons "@releaseDomain"
+						Connections.fire_spec_watches cons Store.Path.release_domain
 				)
 				else
 					let c = Connections.find_domain_by_port cons port in