tests/dns_responder/dns_tls_frontend.cpp

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "dns_tls_frontend.h"

#include <arpa/inet.h>
#include <netdb.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/ssl.h>
#include <openssl/x509.h>
#include <sys/eventfd.h>
#include <sys/poll.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#define LOG_TAG "DnsTlsFrontend"
#include <android-base/logging.h>
#include <netdutils/InternetAddresses.h>
#include <netdutils/SocketOption.h>
#include "dns_responder.h"
#include "dns_tls_certificate.h"

using android::netdutils::enableSockopt;
using android::netdutils::ScopedAddrinfo;

namespace {
static bssl::UniquePtr<X509> stringToX509Certs(const char* certs) {
    bssl::UniquePtr<BIO> bio(BIO_new_mem_buf(certs, strlen(certs)));
    return bssl::UniquePtr<X509>(PEM_read_bio_X509(bio.get(), nullptr, nullptr, nullptr));
}

// Convert a string buffer containing an RSA Private Key into an OpenSSL RSA struct.
static bssl::UniquePtr<RSA> stringToRSAPrivateKey(const char* key) {
    bssl::UniquePtr<BIO> bio(BIO_new_mem_buf(key, strlen(key)));
    return bssl::UniquePtr<RSA>(PEM_read_bio_RSAPrivateKey(bio.get(), nullptr, nullptr, nullptr));
}

std::string addr2str(const sockaddr* sa, socklen_t sa_len) {
    char host_str[NI_MAXHOST] = {0};
    int rv = getnameinfo(sa, sa_len, host_str, sizeof(host_str), nullptr, 0, NI_NUMERICHOST);
    if (rv == 0) return std::string(host_str);
    return std::string();
}

}  // namespace

namespace test {

bool DnsTlsFrontend::startServer() {
    OpenSSL_add_ssl_algorithms();

    // reset queries_ to 0 every time startServer called
    // which would help us easy to check queries_ via calling waitForQueries
    queries_ = 0;

    ctx_.reset(SSL_CTX_new(TLS_server_method()));
    if (!ctx_) {
        LOG(ERROR) << "SSL context creation failed";
        return false;
    }

    SSL_CTX_set_ecdh_auto(ctx_.get(), 1);

    bssl::UniquePtr<X509> ca_certs(stringToX509Certs(kCertificate));
    if (!ca_certs) {
        LOG(ERROR) << "StringToX509Certs failed";
        return false;
    }

    if (SSL_CTX_use_certificate(ctx_.get(), ca_certs.get()) <= 0) {
        LOG(ERROR) << "SSL_CTX_use_certificate failed";
        return false;
    }

    bssl::UniquePtr<RSA> private_key(stringToRSAPrivateKey(kPrivatekey));
    if (SSL_CTX_use_RSAPrivateKey(ctx_.get(), private_key.get()) <= 0) {
        LOG(ERROR) << "Error loading client RSA Private Key data.";
        return false;
    }

    // Set up TCP server socket for clients.
    addrinfo frontend_ai_hints{
            .ai_flags = AI_PASSIVE,
            .ai_family = AF_UNSPEC,
            .ai_socktype = SOCK_STREAM,
    };
    addrinfo* frontend_ai_res = nullptr;
    int rv = getaddrinfo(listen_address_.c_str(), listen_service_.c_str(), &frontend_ai_hints,
                         &frontend_ai_res);
    ScopedAddrinfo frontend_ai_res_cleanup(frontend_ai_res);
    if (rv) {
        LOG(ERROR) << "frontend getaddrinfo(" << listen_address_.c_str() << ", "
                   << listen_service_.c_str() << ") failed: " << gai_strerror(rv);
        return false;
    }

    for (const addrinfo* ai = frontend_ai_res; ai; ai = ai->ai_next) {
        android::base::unique_fd s(socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol));
        if (s.get() < 0) {
            PLOG(INFO) << "ignore creating socket failed " << s.get();
            continue;
        }
        enableSockopt(s.get(), SOL_SOCKET, SO_REUSEADDR).ignoreError();
        std::string host_str = addr2str(ai->ai_addr, ai->ai_addrlen);
        if (bind(s.get(), ai->ai_addr, ai->ai_addrlen)) {
            PLOG(INFO) << "failed to bind TCP " << host_str.c_str() << ":"
                       << listen_service_.c_str();
            continue;
        }
        LOG(INFO) << "bound to TCP " << host_str.c_str() << ":" << listen_service_.c_str();
        socket_ = std::move(s);
        break;
    }

    if (listen(socket_.get(), 1) < 0) {
        PLOG(INFO) << "failed to listen socket " << socket_.get();
        return false;
    }

    // Set up UDP client socket to backend.
    addrinfo backend_ai_hints{.ai_family = AF_UNSPEC, .ai_socktype = SOCK_DGRAM};
    addrinfo* backend_ai_res = nullptr;
    rv = getaddrinfo(backend_address_.c_str(), backend_service_.c_str(), &backend_ai_hints,
                     &backend_ai_res);
    ScopedAddrinfo backend_ai_res_cleanup(backend_ai_res);
    if (rv) {
        LOG(ERROR) << "backend getaddrinfo(" << listen_address_.c_str() << ", "
                   << listen_service_.c_str() << ") failed: " << gai_strerror(rv);
        return false;
    }
    backend_socket_.reset(socket(backend_ai_res->ai_family, backend_ai_res->ai_socktype,
                                 backend_ai_res->ai_protocol));
    if (backend_socket_.get() < 0) {
        PLOG(INFO) << "backend socket " << backend_socket_.get() << " creation failed";
        return false;
    }

    // connect() always fails in the test DnsTlsSocketTest.SlowDestructor because of
    // no backend server. Don't check it.
    static_cast<void>(
            connect(backend_socket_.get(), backend_ai_res->ai_addr, backend_ai_res->ai_addrlen));

    // Set up eventfd socket.
    event_fd_.reset(eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC));
    if (event_fd_.get() == -1) {
        PLOG(INFO) << "failed to create eventfd " << event_fd_.get();
        return false;
    }

    {
        std::lock_guard lock(update_mutex_);
        handler_thread_ = std::thread(&DnsTlsFrontend::requestHandler, this);
    }
    LOG(INFO) << "server started successfully";
    return true;
}

void DnsTlsFrontend::requestHandler() {
    LOG(DEBUG) << "Request handler started";
    enum { EVENT_FD = 0, LISTEN_FD = 1 };
    pollfd fds[2] = {{.fd = event_fd_.get(), .events = POLLIN},
                     {.fd = socket_.get(), .events = POLLIN}};
    android::base::unique_fd clientFd;

    while (true) {
        int poll_code = poll(fds, std::size(fds), -1);
        if (poll_code <= 0) {
            PLOG(WARNING) << "Poll failed with error " << poll_code;
            break;
        }

        if (fds[EVENT_FD].revents & (POLLIN | POLLERR)) {
            handleEventFd();
            break;
        }
        if (fds[LISTEN_FD].revents & (POLLIN | POLLERR)) {
            sockaddr_storage addr;
            socklen_t len = sizeof(addr);

            LOG(DEBUG) << "Trying to accept a client";
            android::base::unique_fd client(
                    accept4(socket_.get(), reinterpret_cast<sockaddr*>(&addr), &len, SOCK_CLOEXEC));
            if (client.get() < 0) {
                // Stop
                PLOG(INFO) << "failed to accept client socket " << client.get();
                break;
            }

            accept_connection_count_++;
            if (hangOnHandshake_) {
                LOG(DEBUG) << "TEST ONLY: unresponsive to SSL handshake";

                // The previous fd already stored in clientFd will be closed automatically.
                clientFd = std::move(client);
                continue;
            }

            bssl::UniquePtr<SSL> ssl(SSL_new(ctx_.get()));
            SSL_set_fd(ssl.get(), client.get());

            LOG(DEBUG) << "Doing SSL handshake";
            if (SSL_accept(ssl.get()) <= 0) {
                LOG(INFO) << "SSL negotiation failure";
            } else {
                LOG(DEBUG) << "SSL handshake complete";
                // Increment queries_ as late as possible, because it represents
                // a query that is fully processed, and the response returned to the
                // client, including cleanup actions.
                queries_ += handleRequests(ssl.get(), client.get());
            }

            if (passiveClose_) {
                LOG(DEBUG) << "hold the current connection until next connection request";
                clientFd = std::move(client);
            }
        }
    }
    LOG(DEBUG) << "Ending loop";
}

int DnsTlsFrontend::handleRequests(SSL* ssl, int clientFd) {
    int queryCounts = 0;
    std::vector<uint8_t> reply;
    bool isDotProbe = false;
    pollfd fds = {.fd = clientFd, .events = POLLIN};
again:
    do {
        uint8_t queryHeader[2];
        if (SSL_read(ssl, &queryHeader, 2) != 2) {
            LOG(INFO) << "Not enough header bytes";
            return queryCounts;
        }
        const uint16_t qlen = (queryHeader[0] << 8) | queryHeader[1];
        uint8_t query[qlen];
        size_t qbytes = 0;
        while (qbytes < qlen) {
            int ret = SSL_read(ssl, query + qbytes, qlen - qbytes);
            if (ret <= 0) {
                LOG(INFO) << "Error while reading query";
                return queryCounts;
            }
            qbytes += ret;
        }
        int sent = send(backend_socket_.get(), query, qlen, 0);
        if (sent != qlen) {
            LOG(INFO) << "Failed to send query";
            return queryCounts;
        }

        if (!isDotProbe) {
            DNSHeader dnsHdr;
            dnsHdr.read((char*)query, (char*)query + qlen);
            for (const auto& question : dnsHdr.questions) {
                if (question.qname.name.find("dnsotls-ds.metric.gstatic.com") !=
                    std::string::npos) {
                    isDotProbe = true;
                    break;
                }
            }
        }

        const int max_size = 4096;
        uint8_t recv_buffer[max_size];
        int rlen = recv(backend_socket_.get(), recv_buffer, max_size, 0);
        if (rlen <= 0) {
            LOG(INFO) << "Failed to receive response";
            return queryCounts;
        }
        uint8_t responseHeader[2];
        responseHeader[0] = rlen >> 8;
        responseHeader[1] = rlen;
        reply.insert(reply.end(), responseHeader, responseHeader + 2);
        reply.insert(reply.end(), recv_buffer, recv_buffer + rlen);

        ++queryCounts;
        if (queryCounts >= delayQueries_) {
            break;
        }
    } while (poll(&fds, 1, delayQueriesTimeout_) > 0);

    if (queryCounts < delayQueries_) {
        LOG(WARNING) << "Expect " << delayQueries_ << " queries, but actually received "
                     << queryCounts << " queries";
    }

    const int replyLen = reply.size();
    LOG(DEBUG) << "Sending " << queryCounts << "queries at once, byte = " << replyLen;
    if (SSL_write(ssl, reply.data(), replyLen) != replyLen) {
        LOG(WARNING) << "Failed to write response body";
    }

    // Poll again because the same DoT probe might be sent again.
    if (isDotProbe && queryCounts == 1) {
        int n = poll(&fds, 1, 50);
        if (n > 0 && fds.revents & POLLIN) {
            goto again;
        }
    }

    LOG(DEBUG) << __func__ << " return: " << queryCounts;
    return queryCounts;
}

bool DnsTlsFrontend::stopServer() {
    std::lock_guard lock(update_mutex_);
    if (!running()) {
        LOG(INFO) << "server not running";
        return false;
    }

    LOG(INFO) << "stopping frontend";
    if (!sendToEventFd()) {
        return false;
    }
    handler_thread_.join();
    socket_.reset();
    backend_socket_.reset();
    event_fd_.reset();
    ctx_.reset();
    LOG(INFO) << "frontend stopped successfully";
    return true;
}

// TODO: use a condition variable instead of polling
// TODO: also clear queries_ to eliminate potential race conditions
bool DnsTlsFrontend::waitForQueries(int expected_count) const {
    constexpr int intervalMs = 20;
    constexpr int timeoutMs = 5000;
    int limit = timeoutMs / intervalMs;
    for (int count = 0; count <= limit; ++count) {
        bool done = queries_ >= expected_count;
        // Always sleep at least one more interval after we are done, to wait for
        // any immediate post-query actions that the client may take (such as
        // marking this server as reachable during validation).
        usleep(intervalMs * 1000);
        if (done) {
            // For ensuring that calls have sufficient headroom for slow machines
            LOG(DEBUG) << "Query arrived in " << count << "/" << limit << " of allotted time";
            return true;
        }
    }
    return false;
}

bool DnsTlsFrontend::sendToEventFd() {
    const uint64_t data = 1;
    if (const ssize_t rt = write(event_fd_.get(), &data, sizeof(data)); rt != sizeof(data)) {
        PLOG(INFO) << "failed to write eventfd, rt=" << rt;
        return false;
    }
    return true;
}

void DnsTlsFrontend::handleEventFd() {
    int64_t data;
    if (const ssize_t rt = read(event_fd_.get(), &data, sizeof(data)); rt != sizeof(data)) {
        PLOG(INFO) << "ignore reading eventfd failed, rt=" << rt;
    }
}

}  // namespace test