apps: Add startui

This service starts a complete UI session (wind, components, and init --user), all with their respective privileges.

This lets us move that responsibility away from wind and let it be only a window manager.

apps/CMakeLists.txt

@@ -49,3 +49,4 @@ luna_app(2048.cpp 2048)
 target_link_libraries(2048 PUBLIC ui)
 luna_app(clock.cpp clock)
 target_link_libraries(clock PUBLIC ui)
+luna_app(startui.cpp startui)

apps/startui.cpp

@@ -0,0 +1,132 @@
+/**
+ * @file startui.cpp
+ * @author apio (cloudapio.eu)
+ * @brief Servic to start and manage a UI session.
+ *
+ * @copyright Copyright (c) 2024, the Luna authors.
+ *
+ */
+
+#include <errno.h>
+#include <grp.h>
+#include <os/ArgumentParser.h>
+#include <os/File.h>
+#include <os/Main.h>
+#include <os/Process.h>
+#include <pwd.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+// Timeout should be provided in milliseconds.
+Result<void> wait_until_file_created(StringView path, int timeout)
+{
+    struct stat st;
+    while (stat(path.chars(), &st) < 0)
+    {
+        if (timeout <= 0) return err(ETIMEDOUT);
+        usleep(100000); // FIXME: Implement something like inotify or use signals to avoid polling.
+        timeout -= 100;
+    }
+    return {};
+}
+
+Result<Vector<gid_t>> read_supplementary_groups(const char* name)
+{
+    Vector<gid_t> extra_groups;
+
+    setgrent();
+    group* grp;
+    while ((grp = getgrent()))
+    {
+        for (char** user = grp->gr_mem; *user; user++)
+        {
+            if (!strcmp(*user, name))
+            {
+                TRY(extra_groups.try_append(grp->gr_gid));
+                break;
+            }
+        }
+    }
+    endgrent();
+
+    return extra_groups;
+}
+
+Result<void> spawn_process_as_user(Slice<StringView> arguments, uid_t user, gid_t group,
+                                   Slice<gid_t> supplementary_groups)
+{
+    pid_t child = TRY(os::Process::fork());
+    if (child == 0)
+    {
+        if (setgroups(static_cast<int>(supplementary_groups.size()), supplementary_groups.data()) < 0)
+            return err(errno);
+        setgid(group);
+        setuid(user);
+        TRY(os::Process::exec(arguments[0], arguments, false));
+    }
+    return {};
+}
+
+Result<int> luna_main(int argc, char** argv)
+{
+    if (geteuid() != 0)
+    {
+        os::eprintln("error: %s can only be started as root.", argv[0]);
+        return 1;
+    }
+
+    StringView username;
+
+    os::ArgumentParser parser;
+    parser.add_description("Service to start and manage a UI session.");
+    parser.add_system_program_info("startui"_sv);
+    parser.add_value_argument(username, 'u', "user", "the user to start the UI session as");
+    parser.parse(argc, argv);
+
+    if (username.is_empty())
+    {
+        os::eprintln("error: startui needs a --username parameter to run.");
+        parser.short_usage(argv[0]);
+        return 1;
+    }
+
+    struct passwd* pw = getpwnam(username.chars());
+    if (!pw)
+    {
+        os::eprintln("error: user %s not found.", username.chars());
+        return 1;
+    }
+
+    auto groups = TRY(read_supplementary_groups(username.chars()));
+
+    setsid();
+
+    // First of all, start the display server.
+    StringView wind_command[] = { "/usr/bin/wind" };
+    TRY(os::Process::spawn(wind_command[0], Slice<StringView>(wind_command, 1)));
+
+    TRY(wait_until_file_created("/tmp/wind.sock", 10000));
+
+    clearenv();
+    chdir(pw->pw_dir);
+    setenv("PATH", "/usr/bin:/usr/local/bin", 1);
+    setenv("USER", pw->pw_name, 1);
+    setenv("HOME", pw->pw_dir, 1);
+    setenv("SHELL", pw->pw_shell, 1);
+
+    // Next, start the required UI components.
+    StringView taskbar_command[] = { "/usr/bin/taskbar" };
+    TRY(spawn_process_as_user(Slice<StringView>(taskbar_command, 1), pw->pw_uid, pw->pw_gid, groups.slice()));
+
+    // Finally, start init in user mode to manage all configured optional services.
+    StringView init_command[] = { "/usr/bin/init", "--user" };
+    TRY(spawn_process_as_user(Slice<StringView>(init_command, 2), pw->pw_uid, pw->pw_gid, groups.slice()));
+
+    // If any process exits, it's either the display server, one of the required UI components, or init --user. We care
+    // about all of these, so let's just crash the entire UI session if they exit. In the future we might restart some
+    // of them and continue, but for now we'll just exit on all of them.
+    os::Process::wait(os::Process::ANY_CHILD, nullptr);
+
+    return 0;
+}

base/etc/init/99-login

@@ -1,6 +1,6 @@
 Name=login
 Description=Start the display server.
-Command=/usr/bin/wind --user=selene
+Command=/usr/bin/startui --user=selene
 StandardOutput=/dev/uart0
 StandardError=/dev/uart0
 Restart=true

base/etc/user/00-taskbar

@@ -1,5 +0,0 @@
-Name=taskbar
-Description=Start the taskbar.
-Command=/usr/bin/taskbar
-WorkingDirectory=/home/selene
-Restart=true

base/etc/user/00-terminal

@@ -1,4 +1,3 @@
 Name=terminal
 Description=Start the terminal.
-WorkingDirectory=/home/selene
 Command=/usr/bin/terminal

wind/main.cpp

@@ -56,31 +56,6 @@ static void debug(const Vector<OwnedPtr<Client>>& clients)
     os::println("--- wind: END DEBUG OUTPUT ---");
 }
 
-Result<void> set_supplementary_groups(const char* name)
-{
-    Vector<gid_t> extra_groups;
-
-    setgrent();
-    group* grp;
-    while ((grp = getgrent()))
-    {
-        for (char** user = grp->gr_mem; *user; user++)
-        {
-            if (!strcmp(*user, name))
-            {
-                os::println("Adding supplementary group: %d", grp->gr_gid);
-                TRY(extra_groups.try_append(grp->gr_gid));
-                break;
-            }
-        }
-    }
-    endgrent();
-
-    if (setgroups(static_cast<int>(extra_groups.size()), extra_groups.data()) < 0) return err(errno);
-
-    return {};
-}
-
 Result<int> luna_main(int argc, char** argv)
 {
     srand((unsigned)time(NULL));
@@ -88,13 +63,11 @@ Result<int> luna_main(int argc, char** argv)
     TRY(os::Security::pledge("stdio rpath wpath cpath unix proc exec tty id", NULL));
 
     StringView socket_path = "/tmp/wind.sock";
-    StringView user;
 
     os::ArgumentParser parser;
     parser.add_description("The display server for Luna's graphical user interface."_sv);
     parser.add_system_program_info("wind"_sv);
     parser.add_value_argument(socket_path, 's', "socket"_sv, "the path for the local IPC socket"_sv);
-    parser.add_value_argument(user, 'u', "user"_sv, "the user to run as"_sv);
     parser.parse(argc, argv);
 
     if (geteuid() != 0)
@@ -117,6 +90,10 @@ Result<int> luna_main(int argc, char** argv)
 
     Mouse mouse_pointer { screen.canvas() };
 
+    // Opened all necessary files as root, drop privileges now.
+    setgid(WIND_GROUP_ID);
+    setuid(WIND_USER_ID);
+
     int fd = open("/dev/null", O_RDONLY);
     if (fd >= 0)
     {
@@ -124,45 +101,11 @@ Result<int> luna_main(int argc, char** argv)
         close(fd);
     }
 
-    setegid(WIND_GROUP_ID);
-    seteuid(WIND_USER_ID);
-
-    if (setsid() < 0) perror("setsid");
-
-    mode_t mask = umask(0002);
+    umask(0002);
 
     auto server = TRY(os::LocalServer::create(socket_path, false));
     TRY(server->listen(20));
 
-    umask(mask);
-
-    seteuid(0);
-
-    clearenv();
-
-    pid_t child = TRY(os::Process::fork());
-    if (!child)
-    {
-        if (!user.is_empty())
-        {
-            auto* pwd = getpwnam(user.chars());
-            if (pwd)
-            {
-                TRY(set_supplementary_groups(user.chars()));
-                setgid(pwd->pw_gid);
-                setuid(pwd->pw_uid);
-            }
-        }
-
-        StringView args[] = { "/usr/bin/init"_sv, "--user"_sv };
-        TRY(os::Process::exec("/usr/bin/init"_sv, Slice<StringView> { args, 2 }, false));
-    }
-
-    umask(0002);
-
-    setgid(WIND_GROUP_ID);
-    setuid(WIND_USER_ID);
-
     ui::Color background = ui::Color::from_rgb(0x10, 0x10, 0x10);
 
     Vector<OwnedPtr<Client>> clients;