Userland: Add support for jails

This happens in two ways:
1. LibCore now has two new methods for creating Jails and attaching
   processes to a Jail.
2. We introduce 3 new utilities - lsjails, jail-create and jails-attach,
   which list jails, create jails and attach processes to a Jail,
   respectively.

Userland/Utilities/CMakeLists.txt

@@ -90,6 +90,8 @@ target_link_libraries(grep PRIVATE LibRegex)
 target_link_libraries(gunzip PRIVATE LibCompress)
 target_link_libraries(gzip PRIVATE LibCompress)
 target_link_libraries(headless-browser PRIVATE LibCrypto LibGemini LibGfx LibHTTP LibTLS LibWeb LibWebSocket)
+target_link_libraries(jail-attach PRIVATE LibCore LibMain)
+target_link_libraries(jail-create PRIVATE LibCore LibMain)
 target_link_libraries(js PRIVATE LibCrypto LibJS LibLine LibLocale LibTextCodec)
 link_with_locale_data(js)
 target_link_libraries(keymap PRIVATE LibKeyboard)

Userland/Utilities/jail-attach.cpp

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ArgsParser.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+#include <unistd.h>
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    unsigned jail_index = 0;
+    Vector<StringView> command;
+    Core::ArgsParser args_parser;
+    bool preserve_env = false;
+    args_parser.set_stop_on_first_non_option(true);
+    args_parser.add_option(preserve_env, "Preserve user environment when running command", "preserve-env", 'E');
+    args_parser.add_positional_argument(jail_index, "Jail Index", "jail index");
+    args_parser.add_positional_argument(command, "Command to execute", "command");
+    args_parser.parse(arguments);
+
+    TRY(Core::System::pledge("stdio rpath exec id jail tty"));
+    TRY(Core::System::join_jail(jail_index));
+    TRY(Core::System::exec_command(command, preserve_env));
+    return 0;
+}

Userland/Utilities/jail-create.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ArgsParser.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+#include <unistd.h>
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    StringView new_jail_name;
+    Core::ArgsParser args_parser;
+    args_parser.add_positional_argument(new_jail_name, "New jail name", "jail name");
+    args_parser.parse(arguments);
+
+    TRY(Core::System::pledge("stdio jail"));
+
+    if (!new_jail_name.is_null() && !new_jail_name.is_empty()) {
+        TRY(Core::System::create_jail(new_jail_name));
+        return 0;
+    }
+
+    return Error::from_string_view("Can't create a jail with empty name."sv);
+}

Userland/Utilities/lsjails.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <LibCore/Stream.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+
+ErrorOr<int> serenity_main(Main::Arguments)
+{
+    TRY(Core::System::pledge("stdio rpath"));
+    TRY(Core::System::unveil("/sys/kernel/jails", "r"));
+    TRY(Core::System::unveil(nullptr, nullptr));
+
+    auto jails_data = TRY(Core::Stream::File::open("/sys/kernel/jails"sv, Core::Stream::OpenMode::Read));
+
+    TRY(Core::System::pledge("stdio"));
+
+    outln("Index    Name");
+    auto file_contents = TRY(jails_data->read_all());
+    auto json = TRY(JsonValue::from_string(file_contents));
+    json.as_array().for_each([](auto& value) {
+        auto& jail = value.as_object();
+        auto index = jail.get("index"sv).to_string();
+        auto name = jail.get("name"sv).to_string();
+
+        outln("{:4}     {:10}", index, name);
+    });
+
+    return 0;
+}