/*
    microsoft-oms-auditd-plugin

    Copyright (c) Microsoft Corporation

    All rights reserved. 

    MIT License

    Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ""Software""), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED *AS IS*, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include "UserDB.h"

#include "Logger.h"
#include "Signals.h"

#include <cstring>
#include <fstream>

extern "C" {
#include <unistd.h>
#include <sys/inotify.h>
#include <poll.h>
}

std::string UserDB::GetUserName(int uid)
{
    std::lock_guard<std::mutex> lock(_lock);

    auto it = _users.find(uid);
    if (it != _users.end()) {
        return it->second;
    }

    return std::string();
}

std::string UserDB::GetGroupName(int gid)
{
    std::lock_guard<std::mutex> lock(_lock);

    auto it = _groups.find(gid);
    if (it != _groups.end()) {
        return it->second;
    }

    return std::string();
}

void UserDB::Start()
{
    std::unique_lock<std::mutex> lock(_lock);
    if (_stop) {
        _stop = false;
        lock.unlock();
        update();
        lock.lock();
        _last_update = std::chrono::steady_clock::now();
        _need_update = false;
        std::thread inotify_thread([this](){ this->inotify_task(); });
        std::thread update_thread([this](){ this->update_task(); });
        _inotify_thread = std::move(inotify_thread);
        _update_thread = std::move(update_thread);
    }
}

void UserDB::Stop()
{
    std::unique_lock<std::mutex> lock(_lock);
    if (!_stop) {
        _stop = true;
        _cond.notify_all();

        close(_inotify_fd);
        _inotify_fd = -1;
        lock.unlock();
        _inotify_thread.join();
        _update_thread.join();
    }
}


int _read(int fd, void *buf, size_t buf_size)
{
    struct pollfd fds;
    fds.fd = fd;
    fds.events = POLLIN;
    fds.revents = 0;

    for (;;) {
        auto ret = poll(&fds, 1, 250);
        if (ret < 0) {
            return ret;
        }

        if ((fds.revents & POLLIN) != 0) {
            return read(fd, buf, buf_size);
        }

        if (fds.revents & (POLLERR|POLLHUP|POLLNVAL)) {
            return 0;
        }
    }
}


void UserDB::inotify_task()
{
    Signals::InitThread();

    /* Create the file descriptor for accessing the inotify API */
    int fd = inotify_init();
    if (fd == -1) {
        Logger::Error("UserDB: Failed to init inotify socket: %s", std::strerror(errno));
        return;
    }

    int wd;
    wd = inotify_add_watch(fd, _dir.c_str(), IN_MODIFY|IN_MOVED_TO);
    if (wd == -1) {
        close(fd);
        Logger::Error("UserDB: Failed add watch for '%s': %s", _dir.c_str(), std::strerror(errno));
        return;
    }

    {
        std::lock_guard<std::mutex> lock(_lock);
        _inotify_fd = fd;
    }

    char buf[4096]
            __attribute__ ((aligned(__alignof__(struct inotify_event))));
    const struct inotify_event *event;
    ssize_t nr;
    char *ptr;

    for (;;) {
        nr = _read(fd, buf, sizeof buf);
        if (nr == -1) {
            close(fd);
            Logger::Warn("UserDB: failed to read from inotify socket: %s", std::strerror(errno));
            return;
        } else if (nr == 0) {
            return;
        }

        /* Loop over all events in the buffer */
        for (ptr = buf; ptr < buf + nr; ptr += sizeof(struct inotify_event) + event->len) {
            event = (const struct inotify_event *) ptr;

            if (event->mask & (IN_MODIFY|IN_MOVED_TO) && (strcmp(event->name, "passwd") == 0 || strcmp(event->name, "group") == 0)) {
                std::lock_guard<std::mutex> lock(_lock);
                _need_update = true;
                _need_update_ts = std::chrono::steady_clock::now();
                _cond.notify_all();
            }
        }
    }

}

constexpr int POST_MOD_DELAY = 100;
constexpr int REPEAT_UPDATE_DELAY = 500;

void UserDB::update_task()
{
    Signals::InitThread();

    std::unique_lock<std::mutex> lock(_lock);

    while (!_stop) {
        _cond.wait(lock, [this]() { return _stop || _need_update; });

        if (!_stop) {
            // Make sure it has been at lease 100 milliseconds since the last IN_MODIFY event
            // This will help avoid the race between the program making the modifications
            // and us reading the files.
            auto now = std::chrono::steady_clock::now();
            while ((now - _need_update_ts) < std::chrono::milliseconds(POST_MOD_DELAY)) {
                lock.unlock();
                std::this_thread::sleep_for(std::chrono::milliseconds(POST_MOD_DELAY)-(now - _need_update_ts));
                lock.lock();
                now = std::chrono::steady_clock::now();
            }

            // Limit how often we do updates
            auto delta = std::chrono::steady_clock::now() - _last_update;
            if (delta < std::chrono::milliseconds(REPEAT_UPDATE_DELAY)) {
                lock.unlock();
                std::this_thread::sleep_for(std::chrono::milliseconds(REPEAT_UPDATE_DELAY)-delta);
                lock.lock();
            }

            _last_update = std::chrono::steady_clock::now();
            _need_update = false;
            lock.unlock();
            update();
            lock.lock();
        }
    }
}

std::vector<std::pair<int, std::string>> parse_file(const std::string& path)
{
    std::vector<std::pair<int, std::string>> entries;
    std::ifstream fs(path);

    int line_num = 1;
    for (std::string line; std::getline(fs, line); line_num++) {
        size_t idx = line.find(':');
        if (idx == std::string::npos) {
            continue;
        }
        std::string name = line.substr(0, idx);
        line = line.substr(idx+1);
        idx = line.find(':');
        if (idx == std::string::npos) {
            continue;
        }
        line = line.substr(idx+1);
        idx = line.find(':');
        if (idx == std::string::npos) {
            continue;
        }
        std::string id_str = line.substr(0, idx);
        int id = 0;
        try {
            id = stoi(id_str);
        } catch (...) {
            continue;
        }
        entries.emplace_back(id, name);
    }
    return entries;
}

void UserDB::update()
{
    std::unordered_map<int, std::string> users;
    std::unordered_map<int, std::string> groups;

    try {
        for (auto& e : parse_file(_dir + "/passwd")) {
            // Just in case there are multiple entries, only the first id->name is used
            if (users.count(e.first) == 0) {
                users.emplace(e);
            }
        }
        for (auto& e : parse_file(_dir + "/group")) {
            // Just in case there are multiple entries, only the first id->name is used
            if (groups.count(e.first) == 0) {
                groups.emplace(e);
            }
        }
    } catch (const std::exception& ex) {
        Logger::Warn("UserDB: Update failed: %s", ex.what());
        return;
    }

    std::lock_guard<std::mutex> lock(_lock);
    _users = users;
    _groups = groups;
}

int UserDB::UserNameToUid(const std::string& name) {
    try {
        for (auto& e : parse_file("/etc/passwd")) {
            if (e.second == name) {
                return e.first;
            }
        }
    } catch (const std::exception& ex) {
        return -1;
    }
    return -1;
}

int UserDB::GroupNameToGid(const std::string& name) {
    try {
        for (auto& e : parse_file("/etc/group")) {
            if (e.second == name) {
                return e.first;
            }
        }
    } catch (const std::exception& ex) {
        return -1;
    }
    return -1;
}