dnsmasq_backend.cpp

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/*
 * BastionGuard™
 * Copyright (C) 2025–2026 Calogero Scarnà
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * BastionGuard™ is a trademark of Calogero Scarnà.
 * The BastionGuard™ name and branding are not licensed under the GPL.
 */
 
#include "../SafeProcess.hpp"
#include "dnsmasq_backend.hpp"
#include <fstream>
#include <filesystem>
#include <algorithm>
#include <thread>
#include <mutex>
#include <atomic>
#include <signal.h>
#include <sys/wait.h>
 
namespace fs = std::filesystem;
 
namespace BastionGuard {
 
static std::mutex g_mutex;
static std::atomic<bool> g_loaded{false};
static std::vector<std::string> g_blacklist;
static std::vector<std::string> g_whitelist;
 
DnsmasqBackend::DnsmasqBackend(const std::string& bl,
                               const std::string& wl,
                               const std::string& user)
    : blacklist_path_(bl),
      whitelist_path_(wl),
      dnsmasq_user_(user)
{
}
 
 
 
static void load_list_file(const std::string& path,
                           std::vector<std::string>& out,
                           bool is_blacklist)
{
    out.clear();
 
    if (!fs::exists(path)) return;
 
    std::ifstream ifs(path);
    std::string line;
 
    while (std::getline(ifs, line)) {
        if (line.empty()) continue;
 
        if (is_blacklist) {
            auto a = line.find("address=/");
            if (a != std::string::npos) {
                auto b = line.find('/', a + 9);
                if (b != std::string::npos)
                    out.push_back(line.substr(a + 9, b - (a + 9)));
            }
        } else {
            out.push_back(line);
        }
    }
}
 
static void ensure_loaded(const std::string& bl, const std::string& wl)
{
    if (g_loaded.load()) return;
 
    std::lock_guard<std::mutex> lock(g_mutex);
    if (g_loaded) return;
 
    load_list_file(bl, g_blacklist, true);
    load_list_file(wl, g_whitelist, false);
 
    g_loaded = true;
}
 
 
bool DnsmasqBackend::atomic_write(const std::string& path,
                                  const std::string& content)
{
    try {
        fs::path p(path);
        fs::path tmp = p.string() + ".tmp";
 
        {
            std::ofstream o(tmp);
            if (!o) return false;
            o << content;
        }
        fs::rename(tmp, p);
        return true;
    } catch (...) {
        return false;
    }
}
 
 
std::string DnsmasqBackend::make_dnsmasq_entries(
    const std::vector<std::string>& domains)
{
    std::ostringstream oss;
    for (auto& d : domains)
        oss << "address=/" << d << "/127.0.0.1\n";
    return oss.str();
}
 
 
bool DnsmasqBackend::add_to_blacklist(const std::string& domain)
{
    std::thread([this, domain] {
        ensure_loaded(blacklist_path_, whitelist_path_);
 
        std::lock_guard<std::mutex> lock(g_mutex);
        if (std::find(g_blacklist.begin(), g_blacklist.end(), domain)
            != g_blacklist.end())
            return;
 
        g_blacklist.push_back(domain);
 
        write_blacklist(g_blacklist);
        reload_dnsmasq();
    }).detach();
 
    return true;
}
 
bool DnsmasqBackend::remove_from_blacklist(const std::string& domain)
{
    std::thread([this, domain] {
        ensure_loaded(blacklist_path_, whitelist_path_);
 
        std::lock_guard<std::mutex> lock(g_mutex);
 
        g_blacklist.erase(
            std::remove(g_blacklist.begin(), g_blacklist.end(), domain),
            g_blacklist.end());
 
        write_blacklist(g_blacklist);
        reload_dnsmasq();
    }).detach();
 
    return true;
}
 
bool DnsmasqBackend::add_to_whitelist(const std::string& domain)
{
    std::thread([this, domain] {
        ensure_loaded(blacklist_path_, whitelist_path_);
 
        std::lock_guard<std::mutex> lock(g_mutex);
        if (std::find(g_whitelist.begin(), g_whitelist.end(), domain)
            != g_whitelist.end())
            return;
 
        g_whitelist.push_back(domain);
 
        write_whitelist(g_whitelist);
    }).detach();
 
    return true;
}
 
bool DnsmasqBackend::remove_from_whitelist(const std::string& domain)
{
    std::thread([this, domain] {
        ensure_loaded(blacklist_path_, whitelist_path_);
 
        std::lock_guard<std::mutex> lock(g_mutex);
 
        g_whitelist.erase(
            std::remove(g_whitelist.begin(), g_whitelist.end(), domain),
            g_whitelist.end());
 
        write_whitelist(g_whitelist);
    }).detach();
 
    return true;
}
 
 
bool DnsmasqBackend::write_blacklist(
    const std::vector<std::string>& domains)
{
    return atomic_write(blacklist_path_, make_dnsmasq_entries(domains));
}
 
bool DnsmasqBackend::write_whitelist(
    const std::vector<std::string>& domains)
{
    std::ostringstream oss;
    for (auto& d : domains)
        oss << d << "\n";
    return atomic_write(whitelist_path_, oss.str());
}
 
 
bool DnsmasqBackend::reload_dnsmasq()
{
    int st = (bg_process::run({"/usr/libexec/bastionguard/bastionguard-service", "--system", "try-reload-or-restart", "dnsmasq.service"}).exit_code);
    return WIFEXITED(st) && WEXITSTATUS(st) == 0;
}
 
} // namespace BastionGuard