src/connection.c

   1 /*
   2  * Handle connections.
   3  *
   4  * Copyright (C) 2011-2013  Simon Ruderich
   5  *
   6  * This program is free software: you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation, either version 3 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include "tlsproxy.h"
  21 #include "connection.h"
  22 #include "verify.h"
  23
  24 #include <assert.h>
  25 #include <errno.h>
  26 #include <limits.h>
  27 #include <netdb.h>
  28 #include <poll.h>
  29 #include <unistd.h>
  30
  31
  32 /* Maximum length of a HTTP request line. Longer request lines are aborted
  33  * with an error. The standard doesn't specify a maximum line length but this
  34  * should be a good limit to make processing simpler. As HTTPS is used this
  35  * doesn't limit long GET requests. */
  36 #define MAX_REQUEST_LINE 4096
  37
  38 /* Format string used to send HTTP/1.0 error responses to the client.
  39  *
  40  * %s is used 5 times, first is the error code, then additional headers, next
  41  * two are the error code (no %n$s!), the last is the message. */
  42 #define HTTP_RESPONSE_FORMAT "HTTP/1.0 %s\r\n\
  43 Content-Type: text/html; charset=US-ASCII\r\n\
  44 %s\r\n\
  45 <!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML 2.0//EN\">\n\
  46 <html>\n\
  47 <head><title>%s</title></head>\n\
  48 <body>\n\
  49 <h1>%s</h1>\n\
  50 <p>%s</p>\n\
  51 </body>\n\
  52 </html>\n"
  53
  54
  55 static int initialize_tls_session_client(int peer_socket,
  56         const char *hostname,
  57         gnutls_session_t *session,
  58         gnutls_certificate_credentials_t *x509_cred);
  59 static int initialize_tls_session_server(int peer_socket,
  60         gnutls_session_t *session,
  61         gnutls_certificate_credentials_t *x509_cred);
  62 static int initialize_tls_session_both(int flags,
  63         int peer_socket,
  64         gnutls_session_t *session,
  65         gnutls_certificate_credentials_t *x509_cred);
  66
  67 static int fdopen_read_write(int socket, FILE **read_fd, FILE **write_fd);
  68 static int read_http_request(FILE *client_fd, char *request, size_t length);
  69 static void send_bad_request(FILE *client_fd);
  70 static void send_authentication_required(FILE *client_fd);
  71 static void send_forwarding_failure(FILE *client_fd);
  72 static void tls_send_invalid_cert_message(gnutls_session_t session);
  73
  74 static void transfer_data(int client, int server);
  75 static int read_from_write_to(int from, int to);
  76 static void transfer_data_tls(int client, int server,
  77                               gnutls_session_t client_session,
  78                               gnutls_session_t server_session);
  79 static int read_from_write_to_tls(gnutls_session_t from, gnutls_session_t to,
  80                                   size_t buffer_size);
  81
  82 static int connect_to_host(const char *hostname, const char *port);
  83
  84 static int parse_request(const char *buffer, char *host, char *port,
  85                                              int *version_minor);
  86
  87
  88 void handle_connection(int client_socket) {
  89     int server_socket;
  90     FILE *client_fd_read, *client_fd_write, *server_fd_read, *server_fd_write;
  91
  92     char buffer[MAX_REQUEST_LINE];
  93     char host[MAX_REQUEST_LINE];
  94     char port[5 + 1];
  95
  96     int version_minor; /* x in HTTP/1.x */
  97     int result;
  98
  99     /* client_x509_cred is used when talking to the client (acting as a TSL
 100      * server), server_x509_cred is used when talking to the server (acting as
 101      * a TSL client). */
 102     gnutls_certificate_credentials_t client_x509_cred, server_x509_cred;
 103
 104     gnutls_session_t client_session, server_session;
 105     /* initialize_tls_session_*() called? - used for goto out */
 106     int client_session_init, server_session_init;
 107     /* gnutls_handshake() called? - used for goto out */
 108     int client_session_started, server_session_started;
 109     /* Validation failed? If yes we need to send the special "invalid"
 110      * certificate. */
 111     int validation_failed;
 112
 113     LOG(DEBUG1, "new connection");
 114
 115     server_socket = -1;
 116     client_fd_read = NULL;
 117     client_fd_write = NULL;
 118     server_fd_read = NULL;
 119     server_fd_write = NULL;
 120     client_session_init = 0;
 121     server_session_init = 0;
 122     client_session_started = 0;
 123     server_session_started = 0;
 124     validation_failed = 0;
 125
 126     if (fdopen_read_write(client_socket, &client_fd_read,
 127                                          &client_fd_write) != 0) {
 128         goto out;
 129     }
 130
 131     /* Read request line (CONNECT ..) and headers (they are discarded). */
 132     result = read_http_request(client_fd_read, buffer, sizeof(buffer));
 133     if (result == -1) {
 134         LOG(WARNING, "read_http_request(): client read error");
 135         goto out;
 136     } else if (result == -2) {
 137         LOG(WARNING, "read_http_request(): client EOF");
 138         send_bad_request(client_fd_write);
 139         goto out;
 140     } else if (result == -3) {
 141         LOG(DEBUG1, "read_http_request(): proxy authentication failed");
 142         send_authentication_required(client_fd_write);
 143         goto out;
 144     }
 145
 146     if (parse_request(buffer, host, port, &version_minor) != 0) {
 147         LOG(WARNING, "bad request: %s", buffer);
 148         send_bad_request(client_fd_write);
 149         goto out;
 150     }
 151
 152     LOG(DEBUG1, "target: %s:%s (HTTP 1.%d)", host, port, version_minor);
 153
 154     /* Connect to proxy server or directly to server. */
 155     if (global_proxy_host != NULL && global_proxy_port != NULL) {
 156         LOG(DEBUG1, "connecting to %s:%s", global_proxy_host,
 157                                            global_proxy_port);
 158         server_socket = connect_to_host(global_proxy_host, global_proxy_port);
 159     } else {
 160         LOG(DEBUG1, "connecting to %s:%s", host, port);
 161         server_socket = connect_to_host(host, port);
 162     }
 163
 164     if (server_socket < 0) {
 165         LOG(WARNING, "failed to connect to server");
 166         send_forwarding_failure(client_fd_write);
 167         goto out;
 168     }
 169     if (fdopen_read_write(server_socket, &server_fd_read,
 170                                          &server_fd_write) != 0) {
 171         send_forwarding_failure(client_fd_write);
 172         goto out;
 173     }
 174
 175     /* Connect to proxy if requested (command line option). */
 176     if (global_proxy_host != NULL && global_proxy_port != NULL) {
 177         fprintf(server_fd_write, "CONNECT %s:%s HTTP/1.0\r\n", host, port);
 178         fprintf(server_fd_write, "\r\n");
 179         fflush(server_fd_write);
 180
 181         /* Read response line from proxy server. */
 182         result = read_http_request(server_fd_read, buffer, sizeof(buffer));
 183         if (result == -1) {
 184             LOG(WARNING, "read_http_request(): proxy read error");
 185             send_forwarding_failure(client_fd_write);
 186             goto out;
 187         } else if (result == -2) {
 188             LOG(WARNING, "read_http_request(): proxy EOF");
 189             send_forwarding_failure(client_fd_write);
 190             goto out;
 191         }
 192
 193         /* Check response of proxy server. */
 194         if (strncmp(buffer, "HTTP/1.0 200", 12)) {
 195             LOG(WARNING, "bad proxy response: %s", buffer);
 196             send_forwarding_failure(client_fd_write);
 197             goto out;
 198         }
 199     }
 200
 201     LOG(DEBUG1, "connection to server established");
 202
 203     /* If the -u option is used and we don't know this hostname's server
 204      * certificate then just pass through the connection and let the client
 205      * verify the server certificate. */
 206     if (global_passthrough_unknown) {
 207         char path[TLSPROXY_MAX_PATH_LENGTH];
 208         FILE *file = NULL;
 209
 210         if (server_certificate_file(&file, host, path, sizeof(path)) == -2) {
 211             /* We've established a connection, tell the client. */
 212             fprintf(client_fd_write, "HTTP/1.0 200 Connection established\r\n");
 213             fprintf(client_fd_write, "\r\n");
 214             fflush(client_fd_write);
 215
 216             LOG(DEBUG1, "transferring data");
 217
 218             /* Proxy data between client and server until one side is done
 219              * (EOF or error). */
 220             transfer_data(client_socket, server_socket);
 221
 222             LOG(DEBUG1, "finished transferring data");
 223
 224             goto out;
 225         }
 226         /* server_certificate_file() may have opened the file, close it. */
 227         if (file != NULL) {
 228             fclose(file);
 229         }
 230     }
 231
 232     /* Initialize TLS client credentials to talk to the server. */
 233     result = initialize_tls_session_server(server_socket, &server_session,
 234                                                           &server_x509_cred);
 235     if (result != 0) {
 236         LOG(WARNING, "initialize_tls_session_server() failed");
 237         send_forwarding_failure(client_fd_write);
 238         goto out;
 239     }
 240     server_session_init = 1;
 241
 242     LOG(DEBUG1, "starting server TLS handshake");
 243
 244     /* Try to establish TLS handshake between us and server. */
 245     result = gnutls_handshake(server_session);
 246     if (result != GNUTLS_E_SUCCESS) {
 247         LOG(WARNING, "server TLS handshake failed: %s",
 248                      gnutls_strerror(result));
 249         send_forwarding_failure(client_fd_write);
 250         goto out;
 251     }
 252     server_session_started = 1;
 253
 254     LOG(DEBUG1, "server TLS handshake finished");
 255
 256     /* Make sure the server certificate is valid and known. */
 257     if (verify_tls_connection(server_session, host) != 0) {
 258         LOG(ERROR, "server certificate validation failed!");
 259         /* We'll send the error message over our TLS connection to the client,
 260          * but with an invalid certificate. No data is transfered from/to the
 261          * target server. */
 262         validation_failed = 1;
 263     }
 264
 265     /* Initialize TLS server credentials to talk to the client. */
 266     result = initialize_tls_session_client(client_socket,
 267                                            /* use a special host if the server
 268                                             * certificate was invalid */
 269                                            (validation_failed) ? "invalid"
 270                                                                : host,
 271                                            &client_session,
 272                                            &client_x509_cred);
 273     if (result != 0) {
 274         LOG(WARNING, "initialize_tls_session_client() failed");
 275         send_forwarding_failure(client_fd_write);
 276         goto out;
 277     }
 278     client_session_init = 1;
 279
 280     /* We've established a connection, tell the client. */
 281     fprintf(client_fd_write, "HTTP/1.0 200 Connection established\r\n");
 282     fprintf(client_fd_write, "\r\n");
 283     fflush(client_fd_write);
 284
 285     LOG(DEBUG1, "starting client TLS handshake");
 286
 287     /* Try to establish TLS handshake between client and us. */
 288     result = gnutls_handshake(client_session);
 289     if (result != GNUTLS_E_SUCCESS) {
 290         LOG(WARNING, "client TLS handshake failed: %s",
 291                      gnutls_strerror(result));
 292         send_forwarding_failure(client_fd_write);
 293         goto out;
 294     }
 295     client_session_started = 1;
 296
 297     LOG(DEBUG1, "client TLS handshake finished");
 298
 299     /* Tell the client that the verification failed. Shouldn't be necessary as
 300      * the client should terminate the connection because he received the
 301      * invalid certificate but better be sure. */
 302     if (validation_failed) {
 303         tls_send_invalid_cert_message(client_session);
 304         goto out;
 305     }
 306
 307     LOG(DEBUG1, "transferring TLS data");
 308
 309     /* Proxy data between client and server until one side is done (EOF or
 310      * error). */
 311     transfer_data_tls(client_socket, server_socket,
 312                       client_session, server_session);
 313
 314     LOG(DEBUG1, "finished transferring TLS data");
 315
 316 out:
 317     /* Close TLS sessions if necessary. Use GNUTLS_SHUT_RDWR so the data is
 318      * reliable transmitted. */
 319     if (server_session_started) {
 320         /* Recent gnutls-serv (used in the test-suite) won't terminate the
 321          * connection when gnutls_bye(session, GNUTLS_SHUT_RDWR) is used
 322          * before any other data was received. If the validation failed just
 323          * close the connection without waiting for data, we won't read it
 324          * anyway.
 325          *
 326          * For verified connections GNUTLS_SHUT_RDWR is important or we might
 327          * lose data. */
 328         gnutls_bye(server_session, validation_failed ? GNUTLS_SHUT_WR
 329                                                      : GNUTLS_SHUT_RDWR);
 330     }
 331     if (client_session_started) {
 332         gnutls_bye(client_session, GNUTLS_SHUT_RDWR);
 333     }
 334     if (server_session_init) {
 335         gnutls_deinit(server_session);
 336         gnutls_certificate_free_credentials(server_x509_cred);
 337     }
 338     if (client_session_init) {
 339         gnutls_deinit(client_session);
 340         gnutls_certificate_free_cas(client_x509_cred);
 341         gnutls_certificate_free_keys(client_x509_cred);
 342         gnutls_certificate_free_credentials(client_x509_cred);
 343     }
 344
 345     /* Close connection to server/proxy. */
 346     if (server_fd_read != NULL) {
 347         if (server_fd_write != NULL) {
 348             fclose(server_fd_write);
 349         }
 350         fclose(server_fd_read);
 351     } else if (server_socket != -1) {
 352         close(server_socket);
 353     }
 354     LOG(DEBUG1, "connection to server closed");
 355     /* Close connection to client. */
 356     if (client_fd_read != NULL) {
 357         if (client_fd_write != NULL) {
 358             fclose(client_fd_write);
 359         }
 360         fclose(client_fd_read);
 361     } else {
 362         close(client_socket);
 363     }
 364     LOG(DEBUG1, "connection to client closed");
 365
 366     LOG(DEBUG1, "connection finished");
 367 }
 368
 369
 370 static int initialize_tls_session_client(int peer_socket,
 371         const char *hostname,
 372         gnutls_session_t *session,
 373         gnutls_certificate_credentials_t *x509_cred) {
 374     int result;
 375     int use_invalid_cert;
 376     char path[TLSPROXY_MAX_PATH_LENGTH];
 377
 378     /* The "invalid" hostname is special. If it's used we send an invalid
 379      * certificate to let the client know something is wrong. */
 380     use_invalid_cert = (!strcmp(hostname, "invalid"));
 381
 382     if (proxy_certificate_path(hostname, path, sizeof(path)) != 0) {
 383         LOG(ERROR,
 384             "initialize_tls_session_client(): "
 385             "failed to get proxy certificate path");
 386         return -1;
 387     }
 388
 389     result = gnutls_certificate_allocate_credentials(x509_cred);
 390     if (result != GNUTLS_E_SUCCESS) {
 391         LOG(ERROR,
 392             "initialize_tls_session_client(): "
 393             "gnutls_certificate_allocate_credentials(): %s",
 394             gnutls_strerror(result));
 395         return -1;
 396     }
 397
 398     /* Load proxy CA file, this CA "list" is send to the client. */
 399     if (!use_invalid_cert) {
 400         result = gnutls_certificate_set_x509_trust_file(*x509_cred,
 401                                                         PROXY_CA_FILE,
 402                                                         GNUTLS_X509_FMT_PEM);
 403         if (result <= 0) {
 404             LOG(ERROR,
 405                 "initialize_tls_session_client(): can't read CA file: '%s'",
 406                 PROXY_CA_FILE);
 407             gnutls_certificate_free_credentials(*x509_cred);
 408             return -1;
 409         }
 410     }
 411     /* If the invalid hostname was specified do nothing, we use a self-signed
 412      * certificate in this case. */
 413
 414     /* And certificate for this website and proxy's private key. */
 415     if (!use_invalid_cert) {
 416         result = gnutls_certificate_set_x509_key_file(*x509_cred,
 417                                                       path, PROXY_KEY_FILE,
 418                                                       GNUTLS_X509_FMT_PEM);
 419     /* If the invalid hostname was specified load our special "invalid"
 420      * certificate. */
 421     } else {
 422         result = gnutls_certificate_set_x509_key_file(*x509_cred,
 423                                                       PROXY_INVALID_CERT_FILE,
 424                                                       PROXY_KEY_FILE,
 425                                                       GNUTLS_X509_FMT_PEM);
 426     }
 427     if (result != GNUTLS_E_SUCCESS) {
 428         LOG(ERROR,
 429             "initialize_tls_session_client(): "
 430             "can't read server certificate ('%s') or key file ('%s'): %s",
 431             path, PROXY_KEY_FILE, gnutls_strerror(result));
 432         gnutls_certificate_free_credentials(*x509_cred);
 433         /* Could be a missing certificate. */
 434         return -2;
 435     }
 436
 437     gnutls_certificate_set_dh_params(*x509_cred, global_tls_dh_params);
 438
 439     return initialize_tls_session_both(GNUTLS_SERVER,
 440                                        peer_socket, session, x509_cred);
 441 }
 442 static int initialize_tls_session_server(int peer_socket,
 443         gnutls_session_t *session,
 444         gnutls_certificate_credentials_t *x509_cred) {
 445     int result;
 446
 447     result = gnutls_certificate_allocate_credentials(x509_cred);
 448     if (result != GNUTLS_E_SUCCESS) {
 449         LOG(ERROR,
 450             "initialize_tls_session_server(): "
 451             "gnutls_certificate_allocate_credentials(): %s",
 452             gnutls_strerror(result));
 453         return -1;
 454     }
 455
 456     return initialize_tls_session_both(GNUTLS_CLIENT,
 457                                        peer_socket, session, x509_cred);
 458 }
 459 static int initialize_tls_session_both(int flags,
 460         int peer_socket,
 461         gnutls_session_t *session,
 462         gnutls_certificate_credentials_t *x509_cred) {
 463     int result;
 464
 465     result = gnutls_init(session, flags);
 466     if (result != GNUTLS_E_SUCCESS) {
 467         LOG(ERROR,
 468             "initialize_tls_session_both(): gnutls_init(): %s",
 469             gnutls_strerror(result));
 470         gnutls_certificate_free_credentials(*x509_cred);
 471         return -1;
 472     }
 473     result = gnutls_priority_set(*session, global_tls_priority_cache);
 474     if (result != GNUTLS_E_SUCCESS) {
 475         LOG(ERROR,
 476             "initialize_tls_session_both(): gnutls_priority_set(): %s",
 477             gnutls_strerror(result));
 478         gnutls_deinit(*session);
 479         gnutls_certificate_free_credentials(*x509_cred);
 480         return -1;
 481     }
 482     result = gnutls_credentials_set(*session,
 483                                     GNUTLS_CRD_CERTIFICATE, *x509_cred);
 484     if (result != GNUTLS_E_SUCCESS) {
 485         LOG(ERROR,
 486             "initialize_tls_session_both(): gnutls_credentials_set(): %s",
 487             gnutls_strerror(result));
 488         gnutls_deinit(*session);
 489         gnutls_certificate_free_credentials(*x509_cred);
 490         return -1;
 491     }
 492
 493     gnutls_transport_set_ptr(*session, (gnutls_transport_ptr_t)peer_socket);
 494
 495     return 0;
 496 }
 497
 498
 499 static int fdopen_read_write(int socket, FILE **read_fd, FILE **write_fd) {
 500     *read_fd = fdopen(socket, "r");
 501     if (*read_fd == NULL) {
 502         LOG_PERROR(WARNING, "fdopen_read_write(): fdopen(\"r\") failed");
 503         return -1;
 504     }
 505
 506     *write_fd = fdopen(dup(socket), "w");
 507     if (*write_fd == NULL) {
 508         LOG_PERROR(WARNING, "fdopen_read_write(): fdopen(\"w\") failed");
 509         fclose(*read_fd);
 510         *read_fd = NULL; /* "tell" caller read_fd is already closed */
 511         return -1;
 512     }
 513
 514     return 0;
 515 }
 516
 517 /* Read HTTP request line and headers (ignored).
 518  *
 519  * On success 0 is returned, -1 on client error, -2 on unexpected EOF.
 520  */
 521 static int read_http_request(FILE *client_fd, char *request, size_t length) {
 522     char buffer[MAX_REQUEST_LINE];
 523     int found_proxy_authorization;
 524
 525     assert(length <= INT_MAX);
 526     if (fgets(request, (int)length, client_fd) == NULL) {
 527         if (ferror(client_fd)) {
 528             LOG_PERROR(WARNING, "read_http_request(): fgets()");
 529             return -1;
 530         }
 531         /* EOF */
 532         return -2;
 533     }
 534
 535     found_proxy_authorization = 0;
 536     while (fgets(buffer, sizeof(buffer), client_fd) != NULL) {
 537         const char *authentication = "Proxy-Authorization: Basic ";
 538
 539         if (http_digest_authorization != NULL
 540                 && !strncmp(buffer, authentication, strlen(authentication))) {
 541             found_proxy_authorization = 1;
 542
 543             /* Check if the passphrase matches. */
 544             strtok(buffer, "\r\n");
 545             if (strcmp(buffer + strlen(authentication),
 546                        http_digest_authorization)) {
 547                 return -3;
 548             }
 549         }
 550
 551         /* End of header. */
 552         if (!strcmp(buffer, "\n") || !strcmp(buffer, "\r\n")) {
 553             break;
 554         }
 555     }
 556     if (ferror(client_fd)) {
 557         LOG_PERROR(WARNING, "read_http_request(): fgets()");
 558         return -1;
 559     }
 560
 561     if (http_digest_authorization != NULL && !found_proxy_authorization) {
 562         return -3;
 563     }
 564
 565     return 0;
 566 }
 567
 568 static void send_bad_request(FILE *client_fd) {
 569     const char error[] = "400 Bad Request";
 570     const char msg[]   = "Your browser sent an invalid request.";
 571     fprintf(client_fd, HTTP_RESPONSE_FORMAT, error, "", error, error, msg);
 572     fflush(client_fd);
 573 }
 574 static void send_authentication_required(FILE *client_fd) {
 575     const char error[] = "407 Proxy Authentication Required";
 576     const char auth[]  = "Proxy-Authenticate: Basic realm=\"tlsproxy\"\r\n";
 577     const char msg[]   = "TODO";
 578     fprintf(client_fd, HTTP_RESPONSE_FORMAT, error, auth, error, error, msg);
 579     fflush(client_fd);
 580 }
 581 static void send_forwarding_failure(FILE *client_fd) {
 582     const char error[] = "503 Forwarding failure";
 583     const char msg[]   = "Failed to connect to server, check logs.";
 584     fprintf(client_fd, HTTP_RESPONSE_FORMAT, error, "", error, error, msg);
 585     fflush(client_fd);
 586 }
 587 static void tls_send_invalid_cert_message(gnutls_session_t session) {
 588     const char error[] = "500 Internal Server Error";
 589     const char msg[]   = "Server certificate validation failed, check logs.";
 590
 591     int result;
 592     char buffer[sizeof(HTTP_RESPONSE_FORMAT)
 593                 + 3 * sizeof(error) + sizeof(msg)];
 594
 595     result = snprintf(buffer, sizeof(buffer), HTTP_RESPONSE_FORMAT,
 596                                               error, "", error, error, msg);
 597     assert(result > 0 && (size_t)result < sizeof(buffer));
 598
 599     gnutls_record_send(session, buffer, strlen(buffer));
 600 }
 601
 602
 603 /* Transfer data between client and server sockets until one closes the
 604  * connection. */
 605 static void transfer_data(int client, int server) {
 606     struct pollfd fds[2];
 607     fds[0].fd      = client;
 608     fds[0].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 609     fds[0].revents = 0;
 610     fds[1].fd      = server;
 611     fds[1].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 612     fds[1].revents = 0;
 613
 614     LOG(DEBUG1, "transfer_data(): %d -> %d", client, server);
 615
 616     for (;;) {
 617         int result = poll(fds, 2 /* fd count */, -1 /* no timeout */);
 618         if (result < 0) {
 619             LOG_PERROR(ERROR, "transfer_data(): poll()");
 620             return;
 621         }
 622
 623         /* Data available from client. */
 624         if (fds[0].revents & POLLIN || fds[0].revents & POLLPRI) {
 625             if (read_from_write_to(client, server) != 0) {
 626                 /* EOF (or other error) */
 627                 break;
 628             }
 629         }
 630         /* Data available from server. */
 631         if (fds[1].revents & POLLIN || fds[1].revents & POLLPRI) {
 632             if (read_from_write_to(server, client) != 0) {
 633                 /* EOF (or other error) */
 634                 break;
 635             }
 636         }
 637
 638         /* Client closed connection. */
 639         if (fds[0].revents & POLLERR || fds[0].revents & POLLHUP) {
 640             break;
 641         }
 642         /* Server closed connection. */
 643         if (fds[1].revents & POLLERR || fds[1].revents & POLLHUP) {
 644             break;
 645         }
 646     }
 647 }
 648
 649 /* Read available data from socket from and write it to socket to. At maximum
 650  * 4096 bytes are read/written. */
 651 static int read_from_write_to(int from, int to) {
 652     ssize_t size_read;
 653     ssize_t size_written;
 654     char buffer[4096];
 655
 656     size_read = read(from, buffer, sizeof(buffer));
 657     if (size_read < 0) {
 658         LOG_PERROR(WARNING, "read_from_write_to(): read()");
 659         return -1;
 660     /* EOF */
 661     } else if (size_read == 0) {
 662         return -1;
 663     }
 664
 665     size_written = write(to, buffer, (size_t)size_read);
 666     if (size_written < 0) {
 667         LOG_PERROR(WARNING, "read_from_write_to(): write()");
 668         return -1;
 669     }
 670     if (size_read != size_written) {
 671         LOG(ERROR, "read_from_write_to(): only written %ld of %ld bytes!",
 672                    (long int)size_written, (long int)size_read);
 673         return -1;
 674     }
 675
 676     return 0;
 677 }
 678
 679 /* Transfer data between client and server TLS connection until one closes the
 680  * connection. */
 681 static void transfer_data_tls(int client, int server,
 682                               gnutls_session_t client_session,
 683                               gnutls_session_t server_session) {
 684     size_t buffer_size;
 685
 686     struct pollfd fds[2];
 687     fds[0].fd      = client;
 688     fds[0].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 689     fds[0].revents = 0;
 690     fds[1].fd      = server;
 691     fds[1].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
 692     fds[1].revents = 0;
 693
 694     /* Get maximum possible buffer size. */
 695     buffer_size = gnutls_record_get_max_size(client_session);
 696     if (gnutls_record_get_max_size(server_session) < buffer_size) {
 697         buffer_size = gnutls_record_get_max_size(server_session);
 698     }
 699     LOG(DEBUG1, "transfer_data_tls(): suggested buffer size: %ld",
 700                 (long int)buffer_size);
 701
 702     for (;;) {
 703         int result = poll(fds, 2 /* fd count */, -1 /* no timeout */);
 704         if (result < 0) {
 705             LOG_PERROR(ERROR, "transfer_data(): poll()");
 706             return;
 707         }
 708
 709         /* Data available from client. */
 710         if (fds[0].revents & POLLIN || fds[0].revents & POLLPRI) {
 711             if (read_from_write_to_tls(client_session, server_session,
 712                                        buffer_size) != 0) {
 713                 /* EOF (or other error) */
 714                 break;
 715             }
 716         }
 717         /* Data available from server. */
 718         if (fds[1].revents & POLLIN || fds[1].revents & POLLPRI) {
 719             if (read_from_write_to_tls(server_session, client_session,
 720                                        buffer_size) != 0) {
 721                 /* EOF (or other error) */
 722                 break;
 723             }
 724         }
 725
 726         /* Client closed connection. */
 727         if (fds[0].revents & POLLERR || fds[0].revents & POLLHUP) {
 728             break;
 729         }
 730         /* Server closed connection. */
 731         if (fds[1].revents & POLLERR || fds[1].revents & POLLHUP) {
 732             break;
 733         }
 734     }
 735 }
 736
 737 /* Read available data from session from and write to session to. */
 738 static int read_from_write_to_tls(gnutls_session_t from,
 739                                   gnutls_session_t to,
 740                                   size_t buffer_size) {
 741     ssize_t size_read;
 742     ssize_t size_written;
 743     char buffer[16384];
 744
 745     if (buffer_size > sizeof(buffer)) {
 746         LOG(WARNING, "read_from_write_to_tls(): reduced buffer size to %ld",
 747                      (long int)(sizeof(buffer)));
 748         buffer_size = sizeof(buffer);
 749     }
 750
 751     size_read = gnutls_record_recv(from, buffer, buffer_size);
 752     if (size_read < 0) {
 753         LOG(WARNING, "read_from_write_to_tls(): gnutls_record_recv(): %s",
 754                      gnutls_strerror((int)size_read));
 755         return -1;
 756     /* EOF */
 757     } else if (size_read == 0) {
 758         return -1;
 759     }
 760
 761     size_written = gnutls_record_send(to, buffer, (size_t)size_read);
 762     if (size_written < 0) {
 763         LOG(WARNING, "read_from_write_to_tls(): gnutls_record_send(): %s",
 764                      gnutls_strerror((int)size_written));
 765         return -1;
 766     }
 767     if (size_read != size_written) {
 768         LOG(ERROR, "read_from_write_to_tls(): only written %ld of %ld bytes!",
 769                    (long int)size_written, (long int)size_read);
 770         return -1;
 771     }
 772
 773     return 0;
 774 }
 775
 776
 777 static int connect_to_host(const char *hostname, const char *port) {
 778     struct addrinfo gai_hints;
 779     struct addrinfo *gai_result;
 780     int gai_return;
 781
 782     int server_socket;
 783     struct addrinfo *server;
 784
 785     if (hostname == NULL || port == NULL) {
 786         return -1;
 787     }
 788
 789     /* Get IP of hostname server. */
 790     memset(&gai_hints, 0, sizeof(gai_hints));
 791     gai_hints.ai_family   = AF_UNSPEC;
 792     gai_hints.ai_socktype = SOCK_STREAM;
 793     gai_hints.ai_protocol = 0;
 794     gai_hints.ai_flags    = AI_NUMERICSERV /* given port is numeric */
 795                           | AI_ADDRCONFIG  /* supported by this computer */
 796                           | AI_V4MAPPED;   /* support IPv4 through IPv6 */
 797     gai_return = getaddrinfo(hostname, port, &gai_hints, &gai_result);
 798     if (gai_return != 0) {
 799         if (gai_return == EAI_SYSTEM) {
 800             LOG_PERROR(WARNING, "connect_to_host(): getaddrinfo()");
 801         } else {
 802             LOG(WARNING, "connect_to_host(): getaddrinfo(): %s",
 803                          gai_strerror(gai_return));
 804         }
 805         return -1;
 806     }
 807
 808     /* Now try to connect to each server returned by getaddrinfo(), use the
 809      * first successful connect. */
 810     for (server = gai_result; server != NULL; server = server->ai_next) {
 811         server_socket = socket(server->ai_family,
 812                                server->ai_socktype,
 813                                server->ai_protocol);
 814         if (server_socket < 0) {
 815             LOG_PERROR(DEBUG1, "connect_to_host(): socket(), trying next");
 816             continue;
 817         }
 818
 819         if (connect(server_socket, server->ai_addr, server->ai_addrlen) == 0) {
 820             break;
 821         }
 822         LOG_PERROR(DEBUG1, "connect_to_host(): connect(), trying next");
 823
 824         close(server_socket);
 825     }
 826     /* Make sure we free the result from getaddrinfo(). */
 827     freeaddrinfo(gai_result);
 828
 829     if (server == NULL) {
 830         LOG_PERROR(WARNING, "connect_to_host(): no server found, abort");
 831         return -1;
 832     }
 833
 834     return server_socket;
 835 }
 836
 837
 838 /* Parse HTTP CONNECT request string and save its parameters.
 839  *
 840  * The following format is expected: "CONNECT host:port HTTP/1.x".
 841  *
 842  * request and host must have the same size! port must be at least 6 bytes
 843  * long (5 + '\0').
 844  */
 845 static int parse_request(const char *request, char *host, char *port,
 846                                               int *version_minor) {
 847     int port_unused; /* just used to verify the port is numeric */
 848     char *position;
 849
 850     /* scanf() doesn't check spaces. */
 851     if (strncmp(request, "CONNECT ", 8)) {
 852         return -1;
 853     }
 854     /* Check request and extract data, "host:port" is not yet separated. */
 855     if (sscanf(request, "CONNECT %s HTTP/1.%d", host, version_minor) != 2) {
 856         return -1;
 857     }
 858     /* Make sure ":port" is there. */
 859     if ((position = strchr(host, ':')) == NULL) {
 860         return -1;
 861     }
 862     /* Make sure port is numeric. */
 863     if (sscanf(position + 1, "%d", &port_unused) != 1) {
 864         return -1;
 865     }
 866     /* Store it in *port. */
 867     strncpy(port, position + 1, 5);
 868     port[5] = '\0';
 869     /* And remove port from host. */
 870     *position = '\0';
 871
 872     return 0;
 873 }