Utilities+Base: Add unveil utility

This utility essentially creates a filesystem sandbox for a specified
command, so it can be tested with only the unveiled paths the user
specifies beforehand.

Base/usr/share/man/man1/unveil.md

@@ -0,0 +1,29 @@
+## Name
+
+unveil - unveil certain paths when running a command
+
+## Synopsis
+
+```**sh
+$ unveil [--path] [command...]
+```
+
+## Description
+
+Run a command under certain path restrictions by using [`unveil`(2)](help://man/2/unveil).
+
+## Options
+
+* `-u`, `--path`: Unveil a path, with the format of `permissions,path`
+
+## Examples
+
+Run `ls -la /sys/kernel` with restricted access to certain paths:
+```sh
+$ unveil --path=r,/etc/timezone --path=r,/usr/lib --path=r,/sys/ --path=r,/etc/passwd --path=r,/etc/group ls -la /sys/kernel
+```
+
+Run `ps -ef` with restricted access to certain paths:
+```sh
+$ unveil --path=r,/etc/timezone --path=r,/usr/lib --path=r,/sys/ --path=r,/etc/passwd --path=r,/etc/group ps -ef
+```

Userland/Utilities/CMakeLists.txt

@@ -120,6 +120,7 @@ target_link_libraries(telws PRIVATE LibProtocol LibLine)
 target_link_libraries(test-fuzz PRIVATE LibGemini LibGfx LibHTTP LibIPC LibJS LibMarkdown LibRegex LibShell)
 target_link_libraries(test-imap PRIVATE LibIMAP)
 target_link_libraries(test-pthread PRIVATE LibThreading)
+target_link_libraries(unveil PRIVATE LibMain)
 target_link_libraries(unzip PRIVATE LibArchive LibCompress)
 target_link_libraries(update-cpp-test-results PRIVATE LibCpp)
 target_link_libraries(useradd PRIVATE LibCrypt)

Userland/Utilities/unveil.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <LibCore/MappedFile.h>
+#include <LibCore/System.h>
+#include <LibELF/Image.h>
+#include <LibMain/Main.h>
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    Vector<String> unveil_paths;
+    Vector<StringView> command;
+
+    Core::ArgsParser args_parser;
+    args_parser.set_stop_on_first_non_option(true);
+    args_parser.add_option(unveil_paths, "Path to unveil [permissions,path]", "path", 'u', "");
+    args_parser.add_positional_argument(command, "Command to execute", "command");
+    args_parser.parse(arguments);
+
+    if (unveil_paths.is_empty()) {
+        return Error::from_string_view("No unveil paths were specified."sv);
+    }
+
+    for (auto& path : unveil_paths) {
+        auto parts = path.split_view(',');
+        if (parts.size() != 2)
+            return Error::from_string_literal("Unveil path being specified is invalid.");
+        TRY(Core::System::unveil_after_exec(parts[1], parts[0]));
+    }
+
+    TRY(Core::System::exec(command[0], command, Core::System::SearchInPath::Yes));
+    return 0;
+}