apps+initrd: Add a login utility and make it run at startup

apps/CMakeLists.txt

@@ -22,3 +22,4 @@ luna_app(rm.cpp rm)
 luna_app(stat.cpp stat)
 luna_app(uname.cpp uname)
 luna_app(base64.cpp base64)
+luna_app(login.cpp login)

apps/login.cpp

@@ -0,0 +1,45 @@
+#include <luna/String.h>
+#include <os/ArgumentParser.h>
+#include <os/File.h>
+#include <stdio.h>
+#include <unistd.h>
+
+Result<int> luna_main(int argc, char** argv)
+{
+    StringView username;
+
+    os::ArgumentParser parser;
+    parser.add_description("Begin a new session on the system.");
+    parser.add_system_program_info("login"_sv);
+    parser.add_positional_argument(username, "user", false);
+    parser.parse(argc, argv);
+
+    if (geteuid() != 0)
+    {
+        os::eprintln("error: login must be run as root.");
+        return 1;
+    }
+
+    putchar('\n');
+
+    String name;
+
+    if (username.is_empty())
+    {
+        auto input = os::File::standard_input();
+
+        os::print("Username: ");
+
+        name = TRY(input->read_line());
+        name.trim("\n");
+
+        if (name.is_empty()) return 0;
+
+        username = name.view();
+    }
+
+    execl("/bin/su", "login", "-p", "--", username.chars(), nullptr);
+
+    perror("su");
+    return 1;
+}

apps/su.cpp

@@ -54,10 +54,11 @@ char* getpass()
 Result<int> luna_main(int argc, char** argv)
 {
     StringView name;
+    bool prompt_password;
 
     if (geteuid() != 0)
     {
-        fprintf(stderr, "su must be setuid root!\n");
+        fprintf(stderr, "%s must be setuid root!\n", argv[0]);
         return 1;
     }
 
@@ -65,23 +66,24 @@ Result<int> luna_main(int argc, char** argv)
     parser.add_description("Switch to a different user (by default, root)."_sv);
     parser.add_system_program_info("su"_sv);
     parser.add_positional_argument(name, "name"_sv, "root"_sv);
+    parser.add_switch_argument(prompt_password, 'p', "prompt", "prompt for a password even if running as root");
     parser.parse(argc, argv);
 
     struct passwd* entry = getpwnam(name.chars());
     if (!entry)
     {
-        fprintf(stderr, "su: user %s not found!\n", name.chars());
+        fprintf(stderr, "%s: user %s not found!\n", argv[0], name.chars());
         return 1;
     }
 
-    if (getuid() != geteuid() && *entry->pw_passwd)
+    if ((prompt_password || getuid() != geteuid()) && *entry->pw_passwd)
     {
         char* pass = getpass();
         if (!pass) return 1;
 
         if (strcmp(pass, entry->pw_passwd))
         {
-            fprintf(stderr, "Wrong password!\n");
+            fprintf(stderr, "%s: wrong password!\n", argv[0]);
             return 1;
         }
 

initrd/etc/init/99-login

@@ -1,4 +1,4 @@
-Name=shell
-Command=/bin/sh
+Name=login
+Command=/bin/login
 Restart=true
 Environment=PATH=/bin:/sbin