FileSystemAccessServer: Add service for accessing veiled files nicely

Adds new service FileSystemAccessServer which allows programs to
request a file descriptor for any file on the file system.

The user can be prompted to choose the path with a FilePicker, or the
path can be provided by the application which will show a MessageBox
showing the pid and name of the calling process and allows the user to
approve or deny the request.

Userland/Services/FileSystemAccessServer/ClientConnection.cpp

@@ -0,0 +1,141 @@
+/*
+ * Copyright (c) 2021, timmot <tiwwot@protonmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Debug.h>
+#include <FileSystemAccessServer/ClientConnection.h>
+#include <LibCore/File.h>
+#include <LibCore/IODevice.h>
+#include <LibGUI/Application.h>
+#include <LibGUI/FilePicker.h>
+#include <LibGUI/MessageBox.h>
+
+namespace FileSystemAccessServer {
+
+static HashMap<int, NonnullRefPtr<ClientConnection>> s_connections;
+
+ClientConnection::ClientConnection(NonnullRefPtr<Core::LocalSocket> socket, int client_id)
+    : IPC::ClientConnection<FileSystemAccessClientEndpoint, FileSystemAccessServerEndpoint>(*this, move(socket), client_id)
+{
+    s_connections.set(client_id, *this);
+}
+
+ClientConnection::~ClientConnection()
+{
+}
+
+void ClientConnection::die()
+{
+    s_connections.remove(client_id());
+    GUI::Application::the()->quit();
+    exit(0);
+}
+
+Messages::FileSystemAccessServer::RequestFileResponse ClientConnection::request_file(String const& path, Core::OpenMode const& requested_access)
+{
+    VERIFY(path.starts_with("/"sv));
+
+    bool approved = false;
+    auto maybe_permissions = m_approved_files.get(path);
+
+    auto relevant_permissions = requested_access & (Core::OpenMode::ReadOnly | Core::OpenMode::WriteOnly);
+    VERIFY(relevant_permissions != Core::OpenMode::NotOpen);
+
+    if (maybe_permissions.has_value())
+        approved = has_flag(maybe_permissions.value(), relevant_permissions);
+
+    if (!approved) {
+        StringBuilder builder;
+        if (has_flag(requested_access, Core::OpenMode::ReadOnly))
+            builder.append('r');
+
+        if (has_flag(requested_access, Core::OpenMode::WriteOnly))
+            builder.append('w');
+
+        auto access_string = builder.to_string();
+
+        auto pid = this->socket().peer_pid();
+        auto exe_link = LexicalPath("/proc").append(String::number(pid)).append("exe").string();
+        auto exe_path = Core::File::real_path_for(exe_link);
+        auto exe_name = LexicalPath::basename(exe_path);
+
+        auto result = GUI::MessageBox::show(nullptr, String::formatted("Give {} ({}) \"{}\" access to \"{}\"?", exe_name, pid, access_string, path), "File Permissions Requested", GUI::MessageBox::Type::Warning, GUI::MessageBox::InputType::YesNo);
+
+        approved = result == GUI::MessageBox::ExecYes;
+
+        if (approved) {
+            auto new_permissions = relevant_permissions;
+
+            if (maybe_permissions.has_value())
+                new_permissions |= maybe_permissions.value();
+
+            m_approved_files.set(path, new_permissions);
+        }
+    }
+
+    if (approved) {
+        auto file = Core::File::open(path, requested_access);
+
+        if (file.is_error()) {
+            dbgln("FileSystemAccessServer: Couldn't open {}, error {}", path, file.error());
+
+            return { errno, Optional<IPC::File> {} };
+        }
+
+        return { 0, IPC::File(file.value()->leak_fd(), IPC::File::CloseAfterSending) };
+    }
+
+    return { -1, Optional<IPC::File> {} };
+}
+
+Messages::FileSystemAccessServer::PromptOpenFileResponse ClientConnection::prompt_open_file(String const& path_to_view, Core::OpenMode const& requested_access)
+{
+    auto relevant_permissions = requested_access & (Core::OpenMode::ReadOnly | Core::OpenMode::WriteOnly);
+    VERIFY(relevant_permissions != Core::OpenMode::NotOpen);
+
+    auto main_window = GUI::Window::construct();
+    auto user_picked_file = GUI::FilePicker::get_open_filepath(main_window, "Select file", path_to_view);
+
+    return prompt_helper<Messages::FileSystemAccessServer::PromptOpenFileResponse>(user_picked_file, requested_access);
+}
+
+Messages::FileSystemAccessServer::PromptSaveFileResponse ClientConnection::prompt_save_file(String const& name, String const& ext, String const& path_to_view, Core::OpenMode const& requested_access)
+{
+    auto relevant_permissions = requested_access & (Core::OpenMode::ReadOnly | Core::OpenMode::WriteOnly);
+    VERIFY(relevant_permissions != Core::OpenMode::NotOpen);
+
+    auto main_window = GUI::Window::construct();
+    auto user_picked_file = GUI::FilePicker::get_save_filepath(main_window, name, ext, path_to_view);
+
+    return prompt_helper<Messages::FileSystemAccessServer::PromptSaveFileResponse>(user_picked_file, requested_access);
+}
+
+template<typename T>
+T ClientConnection::prompt_helper(Optional<String> const& user_picked_file, Core::OpenMode const& requested_access)
+{
+    if (user_picked_file.has_value()) {
+        VERIFY(user_picked_file->starts_with("/"sv));
+        auto file = Core::File::open(user_picked_file.value(), requested_access);
+
+        if (file.is_error()) {
+            dbgln("FileSystemAccessServer: Couldn't open {}, error {}", user_picked_file.value(), file.error());
+
+            return { errno, Optional<IPC::File> {}, Optional<String> {} };
+        }
+
+        auto maybe_permissions = m_approved_files.get(user_picked_file.value());
+        auto new_permissions = requested_access & (Core::OpenMode::ReadOnly | Core::OpenMode::WriteOnly);
+        if (maybe_permissions.has_value())
+            new_permissions |= maybe_permissions.value();
+
+        m_approved_files.set(user_picked_file.value(), new_permissions);
+
+        return { 0, IPC::File(file.value()->leak_fd(), IPC::File::CloseAfterSending), user_picked_file.value() };
+    }
+
+    return { -1, Optional<IPC::File> {}, Optional<String> {} };
+}
+
+}