bunpen: finish wiring the xdg-dbus-proxy instance

this isn't tested, except to see that it doesn't interfere with the *existing* bunpen use

pkgs/by-name/bunpen/restrict/dbus_proxy.ha

@@ -61,24 +61,33 @@
 use config;
 use errors;
 use errors::ext;
-use strings;
+use io;
 use os;
 use os::exec;
 use path;
 use ps;
 use resources;
+use rt;
 use rt::ext;
+use strings;
 
 // given an existing, unfiltered bus at the fs path `upstream`,
 // proxy the bus into the fs path indicated by `downstream`.
 // clients attaching to the `downstream` path are provided access only to the
 // resources indicated by `dbus`.
-fn dbus_restrict(dbus: resources::dbus_subset, upstream: str, downstream: str) void = {
+fn dbus_restrict(dbus: resources::dbus_subset, upstream_fd: io::file, downstream_path: path::buffer) void = {
+  // TODO: restrict resources to the xdg-dbus-proxy instance
   match (ps::fork_and_die_with_parent()) {
     case let child_pid: os::exec::process =>
+      // dup the upstream to give it a predictable fd
+      rt::dup2(upstream_fd, 0)!;
+      io::close(upstream_fd)!;
+      os::setenv("DBUS_SESSION_BUS_ADDRES", "path:unix=/proc/self/fd/0")!;  // TODO: pass this to execvpe's env instead of setenv'ing it here
+
       let proxy_args: []str = [
         "xdg-dbus-proxy",
         "--filter",
+        path::string(&downstream_path),
       ];
       for (let spec .. dbus.talk) {
         append(proxy_args, "--talk");

pkgs/by-name/bunpen/restrict/restrict.ha

@@ -1,9 +1,12 @@
 // vim: set shiftwidth=2 :
 use errors;
+use errors::ext;
+use io;
 use log;
 use path;
 use resources;
 use restrict::ns;
+use rt;
 
 export fn restrict(what: *resources::resources) void = {
   // map the user-requested networking into internal mechanisms:
@@ -18,14 +21,26 @@ export fn restrict(what: *resources::resources) void = {
       yield (true, void);
   };
 
-  let (any_dbus, dbus_session_path, dbus_resources): (bool, path::buffer, resources::dbus_subset) = match (what.dbus) {
-    case let d: resources::dbus_subset => yield match (get_dbus_session_path()) {
-      case let s: path::buffer => yield (true, s, d);
+  // map the user-requested dbus settings into internal mechanisms:
+  // also, obtain a handle to the bus *before* entering the outer sandbox,
+  // so that we can proxy it into the main sandbox.
+  let dbus_proxy: (void | dbus_details) = match (what.dbus) {
+    case let res: resources::dbus_subset => yield match (get_dbus_session_path()) {
+      case let session: path::buffer =>
+        yield match (rt::open(path::string(&session), rt::O_RDONLY, 0o400)) { //< TODO: correct mode?
+          case let outer_fd: int => yield dbus_details {
+            outer_fd = outer_fd,
+            session_path = session,
+            resources = res,
+          };
+          case let err: rt::errno =>
+            errors::ext::swallow("restrict: open(DBUS_SESSION_BUS_ADDRESS)", err);
+        };
       case =>
         log::println("restrict: dbus requested, but failed to parse dbus session path");
-        yield (false, path::init("")!, resources::dbus_subset { ... });
+        yield void;
     };
-    case void => yield (false, path::init("")!, resources::dbus_subset { ... });
+    case void => yield void;
   };
 
   // sandbox the entire process early, now, before any forking/exec'ing.
@@ -40,8 +55,6 @@ export fn restrict(what: *resources::resources) void = {
     append(outer_paths, p);
   if (outer_pid)
     append(outer_paths, path::init("/proc")!);
-  if (any_dbus)
-    append(outer_paths, dbus_session_path);
   let outer_ns_resources = ns::ns_resources {
     paths = outer_paths,
     ipc = what.ipc,
@@ -58,6 +71,13 @@ export fn restrict(what: *resources::resources) void = {
   };
 
   // sandbox the user process
+  match (dbus_proxy) {
+    case void => void;
+    case let details: dbus_details =>
+      dbus_restrict(details.resources, details.outer_fd, details.session_path);
+      // the bus at this path is now proxied, so grant access to the user
+      append(what.paths, details.session_path);
+  };
   let user_ns_resources = ns::ns_resources {
     paths = what.paths,
     ipc = what.ipc,
@@ -68,3 +88,9 @@ export fn restrict(what: *resources::resources) void = {
   ns::namespace_restrict(&user_ns_resources);
   capability_restrict(what.caps);
 };
+
+type dbus_details = struct {
+  outer_fd: io::file,
+  session_path: path::buffer,
+  resources: resources::dbus_subset,
+};