SystemServer+LibCore: Move /tmp/rpc/ directory creation to SystemServer

This doesn't solve half of the problems with /tmp/rpc, but this way we
can at least make it sticky instead of having it fully world-writable
and owned by whoever was the first to bind an RPC socket.

Libraries/LibCore/EventLoop.cpp

@@ -314,22 +314,8 @@ EventLoop::~EventLoop()
 
 bool EventLoop::start_rpc_server()
 {
-    // Create /tmp/rpc if it doesn't exist.
+    auto rpc_path = String::formatted("/tmp/rpc/{}", getpid());
-    int rc = mkdir("/tmp/rpc", 0777);
+    auto rc = unlink(rpc_path.characters());
-    if (rc == 0) {
-        // Ensure it gets created as 0777 despite our umask.
-        rc = chmod("/tmp/rpc", 0777);
-        if (rc < 0) {
-            perror("chmod /tmp/rpc");
-            // Continue further.
-        }
-    } else if (errno != EEXIST) {
-        perror("mkdir /tmp/rpc");
-        return false;
-    }
-
-    auto rpc_path = String::format("/tmp/rpc/%d", getpid());
-    rc = unlink(rpc_path.characters());
     if (rc < 0 && errno != ENOENT) {
         perror("unlink");
         return false;

Services/SystemServer/main.cpp

@@ -180,6 +180,18 @@ static void mount_all_filesystems()
     }
 }
 
+static void create_tmp_rpc_directory()
+{
+    dbgln("Creating /tmp/rpc directory");
+    auto old_umask = umask(0);
+    auto rc = mkdir("/tmp/rpc", 01777);
+    if (rc < 0) {
+        perror("mkdir(/tmp/rpc)");
+        ASSERT_NOT_REACHED();
+    }
+    umask(old_umask);
+}
+
 int main(int, char**)
 {
     prepare_devfs();
@@ -190,6 +202,7 @@ int main(int, char**)
     }
 
     mount_all_filesystems();
+    create_tmp_rpc_directory();
     parse_boot_mode();
 
     Core::EventLoop event_loop;