Utilities: Implement usermod command

Previously there was no way to modify existing user accounts.

Userland/Utilities/usermod.cpp

@@ -0,0 +1,163 @@
+/*
+ * Copyright (c) 2021, Brandon Pruitt <brapru@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Types.h>
+#include <LibCore/Account.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    if (geteuid() != 0) {
+        warnln("Not running as root :^(");
+        return 1;
+    }
+
+    if (setegid(0) < 0) {
+        perror("setegid");
+        return 1;
+    }
+
+    if (pledge("stdio wpath rpath cpath fattr tty", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    if (unveil("/etc", "rwc") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    int uid = 0;
+    int gid = 0;
+    bool lock = false;
+    bool unlock = false;
+    const char* new_home_directory = nullptr;
+    bool move_home = false;
+    const char* shell = nullptr;
+    const char* gecos = nullptr;
+    const char* username = nullptr;
+
+    auto args_parser = Core::ArgsParser();
+    args_parser.set_general_help("Modify a user account");
+    args_parser.add_option(uid, "The new numerical value of the user's ID", "uid", 'u', "uid");
+    args_parser.add_option(gid, "The group number of the user's new initial login group", "gid", 'g', "gid");
+    args_parser.add_option(lock, "Lock password", "lock", 'L');
+    args_parser.add_option(unlock, "Unlock password", "unlock", 'U');
+    args_parser.add_option(new_home_directory, "The user's new login directory", "home", 'd', "new-home");
+    args_parser.add_option(move_home, "Move the content of the user's home directory to the new location", "move", 'm');
+    args_parser.add_option(shell, "The name of the user's new login shell", "shell", 's', "path-to-shell");
+    args_parser.add_option(gecos, "Change the GECOS field of the user", "gecos", 'n', "general-info");
+    args_parser.add_positional_argument(username, "Username of the account to modify", "username");
+
+    args_parser.parse(argc, argv);
+
+    auto account_or_error = Core::Account::from_name(username);
+
+    if (account_or_error.is_error()) {
+        warnln("Core::Account::from_name: {}", account_or_error.error());
+        return 1;
+    }
+
+    // target_account is the account we are modifying.
+    auto& target_account = account_or_error.value();
+
+    if (move_home) {
+        if (unveil(target_account.home_directory().characters(), "c") < 0) {
+            perror("unveil");
+            return 1;
+        }
+
+        if (unveil(new_home_directory, "wc") < 0) {
+            perror("unveil");
+            return 1;
+        }
+    }
+
+    unveil(nullptr, nullptr);
+
+    if (uid) {
+        if (uid < 0) {
+            warnln("invalid uid {}", uid);
+            return 1;
+        }
+
+        if (getpwuid(static_cast<uid_t>(uid))) {
+            warnln("uid {} already exists", uid);
+            return 1;
+        }
+
+        target_account.set_uid(uid);
+    }
+
+    if (gid) {
+        if (gid < 0) {
+            warnln("invalid gid {}", gid);
+            return 1;
+        }
+
+        target_account.set_gid(gid);
+    }
+
+    if (lock) {
+        target_account.set_password_enabled(false);
+    }
+
+    if (unlock) {
+        target_account.set_password_enabled(true);
+    }
+
+    if (new_home_directory) {
+        if (move_home) {
+            int rc = rename(target_account.home_directory().characters(), new_home_directory);
+            if (rc < 0) {
+                if (errno == EXDEV) {
+                    auto result = Core::File::copy_file_or_directory(
+                        new_home_directory, target_account.home_directory().characters(),
+                        Core::File::RecursionMode::Allowed,
+                        Core::File::LinkMode::Disallowed,
+                        Core::File::AddDuplicateFileMarker::No);
+
+                    if (result.is_error()) {
+                        warnln("usermod: could not move directory {} : {}", target_account.home_directory().characters(), result.error().error_code);
+                        return 1;
+                    }
+                    rc = unlink(target_account.home_directory().characters());
+                    if (rc < 0)
+                        warnln("usermod: unlink {} : {}", target_account.home_directory().characters(), strerror(errno));
+                } else {
+                    warnln("usermod: could not move directory {} : {}", target_account.home_directory().characters(), strerror(errno));
+                }
+            }
+        }
+
+        target_account.set_home_directory(new_home_directory);
+    }
+
+    if (shell) {
+        target_account.set_shell(shell);
+    }
+
+    if (gecos) {
+        target_account.set_gecos(gecos);
+    }
+
+    if (pledge("stdio wpath rpath cpath fattr", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    if (!target_account.sync()) {
+        perror("Core::Account::Sync");
+        return 1;
+    }
+
+    return 0;
+}