command.c

   1 /*
   2  * Copyright (C) 1997-2009 Andre Noll <maan@systemlinux.org>
   3  *
   4  * Licensed under the GPL v2. For licencing details see COPYING.
   5  */
   6
   7 /** \file command.c Client authentication and server commands. */
   8
   9 #include <signal.h>
  10 #include <sys/time.h>
  11 #include <sys/types.h>
  12 #include <dirent.h>
  13 #include <openssl/rc4.h>
  14
  15 #include "para.h"
  16 #include "error.h"
  17 #include "server.cmdline.h"
  18 #include "string.h"
  19 #include "afh.h"
  20 #include "afs.h"
  21 #include "server.h"
  22 #include "vss.h"
  23 #include "list.h"
  24 #include "send.h"
  25 #include "rc4.h"
  26 #include "net.h"
  27 #include "daemon.h"
  28 #include "fd.h"
  29 #include "ipc.h"
  30 #include "user_list.h"
  31 #include "server_command_list.h"
  32 #include "afs_command_list.h"
  33 #include "sched.h"
  34 #include "signal.h"
  35
  36 /** Commands including options must be shorter than this. */
  37 #define MAX_COMMAND_LEN 32768
  38
  39 static RC4_KEY rc4_recv_key;
  40 static RC4_KEY rc4_send_key;
  41 static unsigned char rc4_buf[2 * RC4_KEY_LEN];
  42
  43 extern int mmd_mutex;
  44 extern struct misc_meta_data *mmd;
  45 extern struct sender senders[];
  46
  47 static void dummy(__a_unused int s)
  48 {
  49 }
  50
  51 static void mmd_dup(struct misc_meta_data *new_mmd)
  52 {
  53         mutex_lock(mmd_mutex);
  54         *new_mmd = *mmd;
  55         mutex_unlock(mmd_mutex);
  56 }
  57
  58 /*
  59  * Compute human readable string containing vss status for given integer value.
  60  *
  61  * We don't want to use vss_playing() and friends here because we take a
  62  * snapshot of the mmd struct and use the copy for computing the state of the
  63  * vss. If the real data were used, we would take the mmd lock for a rather
  64  * long time or risk to get an inconsistent view.
  65  */
  66 static char *vss_status_tohuman(unsigned int flags)
  67 {
  68         if (flags & VSS_PLAYING)
  69                 return para_strdup("playing");
  70         if (flags & VSS_NEXT)
  71                 return para_strdup("stopped");
  72         return para_strdup("paused");
  73 }
  74
  75 /*
  76  * return human readable permission string. Never returns NULL.
  77  */
  78 static char *cmd_perms_itohuman(unsigned int perms)
  79 {
  80         char *msg = para_malloc(5 * sizeof(char));
  81
  82         msg[0] = perms & AFS_READ? 'a' : '-';
  83         msg[1] = perms & AFS_WRITE? 'A' : '-';
  84         msg[2] = perms & VSS_READ? 'v' : '-';
  85         msg[3] = perms & VSS_WRITE? 'V' : '-';
  86         msg[4] = '\0';
  87         return msg;
  88 }
  89
  90 /*
  91  * Never returns NULL.
  92  */
  93 static char *vss_get_status_flags(unsigned int flags)
  94 {
  95         char *msg = para_malloc(5 * sizeof(char));
  96
  97         msg[0] = (flags & VSS_PLAYING)? 'P' : '_';
  98         msg[1] = (flags & VSS_NOMORE)? 'O' : '_';
  99         msg[2] = (flags & VSS_NEXT)? 'N' : '_';
 100         msg[3] = (flags & VSS_REPOS)? 'R' : '_';
 101         msg[4] = '\0';
 102         return msg;
 103 }
 104
 105 static char *get_status(struct misc_meta_data *nmmd)
 106 {
 107         char *ret, mtime[30] = "";
 108         char *status, *flags; /* vss status info */
 109         char *ut = uptime_str();
 110         long offset = (nmmd->offset + 500) / 1000;
 111         struct timeval current_time;
 112         struct tm mtime_tm;
 113
 114         /* report real status */
 115         status = vss_status_tohuman(nmmd->vss_status_flags);
 116         flags = vss_get_status_flags(nmmd->vss_status_flags);
 117         if (nmmd->size) { /* parent currently has an audio file open */
 118                 localtime_r(&nmmd->mtime, &mtime_tm);
 119                 strftime(mtime, 29, "%b %d %Y", &mtime_tm);
 120         }
 121         gettimeofday(&current_time, NULL);
 122         ret = make_message(
 123                 "%s: %zu\n" /* file size */
 124                 "%s: %s\n" /* mtime */
 125                 "%s: %s\n" /* status */
 126                 "%s: %s\n" /* status flags */
 127                 "%s: %li\n" /* offset */
 128                 "%s: %s\n" /* afs mode */
 129                 "%s: %lu.%lu\n" /* stream start */
 130                 "%s: %lu.%lu\n" /* current server time */
 131                 "%s", /* afs status info */
 132                 status_item_list[SI_FILE_SIZE], nmmd->size / 1024,
 133                 status_item_list[SI_MTIME], mtime,
 134                 status_item_list[SI_STATUS], status,
 135                 status_item_list[SI_STATUS_FLAGS], flags,
 136
 137                 status_item_list[SI_OFFSET], offset,
 138                 status_item_list[SI_AFS_MODE], mmd->afs_mode_string,
 139
 140                 status_item_list[SI_STREAM_START],
 141                         (long unsigned)nmmd->stream_start.tv_sec,
 142                         (long unsigned)nmmd->stream_start.tv_usec,
 143                 status_item_list[SI_CURRENT_TIME],
 144                         (long unsigned)current_time.tv_sec,
 145                         (long unsigned)current_time.tv_usec,
 146
 147                 nmmd->afd.verbose_ls_output
 148
 149         );
 150         free(flags);
 151         free(status);
 152         free(ut);
 153         return ret;
 154 }
 155
 156 static int check_sender_args(int argc, char * const * argv, struct sender_command_data *scd)
 157 {
 158         int i;
 159         /* this has to match sender.h */
 160         const char *subcmds[] = {"add", "delete", "allow", "deny", "on", "off", NULL};
 161
 162         scd->sender_num = -1;
 163         if (argc < 2)
 164                 return -E_COMMAND_SYNTAX;
 165         for (i = 0; senders[i].name; i++)
 166                 if (!strcmp(senders[i].name, argv[1]))
 167                         break;
 168         PARA_DEBUG_LOG("%d:%s\n", argc, argv[1]);
 169         if (!senders[i].name)
 170                 return -E_COMMAND_SYNTAX;
 171         scd->sender_num = i;
 172         for (i = 0; subcmds[i]; i++)
 173                 if (!strcmp(subcmds[i], argv[2]))
 174                         break;
 175         if (!subcmds[i])
 176                 return -E_COMMAND_SYNTAX;
 177         scd->cmd_num = i;
 178         if (!senders[scd->sender_num].client_cmds[scd->cmd_num])
 179                 return -E_SENDER_CMD;
 180         switch (scd->cmd_num) {
 181         case SENDER_ON:
 182         case SENDER_OFF:
 183                 if (argc != 3)
 184                         return -E_COMMAND_SYNTAX;
 185                 break;
 186         case SENDER_DENY:
 187         case SENDER_ALLOW:
 188                 if (argc != 4 && argc != 5)
 189                         return -E_COMMAND_SYNTAX;
 190                 if (!is_valid_ipv4_address(argv[3]))
 191                         return -E_COMMAND_SYNTAX;
 192                 scd->netmask = 32;
 193                 if (argc == 5) {
 194                         scd->netmask = atoi(argv[4]);
 195                         if (scd->netmask < 0 || scd->netmask > 32)
 196                                 return -E_COMMAND_SYNTAX;
 197                 }
 198                 strncpy(scd->host, argv[3], sizeof(scd->host));
 199                 break;
 200         case SENDER_ADD:
 201         case SENDER_DELETE:
 202                 if (argc != 4)
 203                         return -E_COMMAND_SYNTAX;
 204                 return parse_fec_url(argv[3], scd);
 205         default:
 206                 return -E_COMMAND_SYNTAX;
 207         }
 208         return 1;
 209 }
 210
 211 int com_sender(int fd, int argc, char * const * argv)
 212 {
 213         int i, ret;
 214         struct sender_command_data scd;
 215
 216         if (argc < 2) {
 217                 char *msg = NULL;
 218                 for (i = 0; senders[i].name; i++) {
 219                         char *tmp = make_message("%s%s\n",
 220                                 msg? msg : "", senders[i].name);
 221                         free(msg);
 222                         msg = tmp;
 223                 }
 224                 ret = send_buffer(fd, msg);
 225                 free(msg);
 226                 return ret;
 227         }
 228         ret = check_sender_args(argc, argv, &scd);
 229         if (ret < 0) {
 230                 char *msg;
 231                 if (scd.sender_num < 0)
 232                         return ret;
 233                 msg = senders[scd.sender_num].help();
 234                 ret = send_buffer(fd, msg);
 235                 free(msg);
 236                 return ret;
 237         }
 238         for (i = 0; i < 10; i++) {
 239                 mutex_lock(mmd_mutex);
 240                 if (mmd->sender_cmd_data.cmd_num >= 0) {
 241                         mutex_unlock(mmd_mutex);
 242                         usleep(100 * 1000);
 243                         continue;
 244                 }
 245                 memcpy(&mmd->sender_cmd_data, &scd, sizeof(scd));
 246                 mutex_unlock(mmd_mutex);
 247                 break;
 248         }
 249         return (i < 10)? 1 : -E_LOCK;
 250 }
 251
 252 /* server info */
 253 int com_si(int fd, int argc, __a_unused char * const * argv)
 254 {
 255         int i, ret;
 256         char *ut;
 257         char *sender_info = NULL, *sender_list = NULL;
 258
 259         if (argc != 1)
 260                 return -E_COMMAND_SYNTAX;
 261         mutex_lock(mmd_mutex);
 262         for (i = 0; senders[i].name; i++) {
 263                 char *info = senders[i].info();
 264                 sender_info = para_strcat(sender_info, info);
 265                 free(info);
 266                 sender_list = para_strcat(sender_list, senders[i].name);
 267                 sender_list = para_strcat(sender_list, " ");
 268         }
 269         ut = uptime_str();
 270         ret = send_va_buffer(fd, "up: %s\nplayed: %u\n"
 271                 "server_pid: %d\n"
 272                 "afs_pid: %d\n"
 273                 "connections (active/accepted/total): %u/%u/%u\n"
 274                 "current loglevel: %s\n"
 275                 "supported audio formats: %s\n"
 276                 "supported senders: %s\n"
 277                 "%s",
 278                 ut, mmd->num_played,
 279                 (int)getppid(),
 280                 (int)mmd->afs_pid,
 281                 mmd->active_connections,
 282                 mmd->num_commands,
 283                 mmd->num_connects,
 284                 conf.loglevel_arg,
 285                 supported_audio_formats(),
 286                 sender_list,
 287                 sender_info
 288         );
 289         mutex_unlock(mmd_mutex);
 290         free(ut);
 291         free(sender_list);
 292         free(sender_info);
 293         return ret;
 294 }
 295
 296 /* version */
 297 int com_version(int fd, int argc, __a_unused char * const * argv)
 298 {
 299         if (argc != 1)
 300                 return -E_COMMAND_SYNTAX;
 301         return send_buffer(fd, VERSION_TEXT("server")
 302                 "built: " BUILD_DATE "\n"
 303                 UNAME_RS ", " CC_VERSION "\n"
 304         );
 305 }
 306
 307 /* stat */
 308 int com_stat(int fd, int argc, char * const * argv)
 309 {
 310         int ret, num = 0;/* status will be printed that many
 311                           * times. num <= 0 means: print forever
 312                           */
 313         struct misc_meta_data tmp, *nmmd = &tmp;
 314         char *s;
 315
 316         para_sigaction(SIGUSR1, dummy);
 317
 318         if (argc > 1)
 319                 num = atoi(argv[1]);
 320         for (;;) {
 321
 322                 mmd_dup(nmmd);
 323                 s = get_status(nmmd);
 324                 ret = send_buffer(fd, s);
 325                 free(s);
 326                 if (ret < 0)
 327                         goto out;
 328                 ret = 1;
 329                 if (num > 0 && !--num)
 330                         goto out;
 331                 sleep(50);
 332                 if (getppid() == 1)
 333                         return -E_SERVER_CRASH;
 334         }
 335 out:
 336         return ret;
 337 }
 338
 339 static int send_list_of_commands(int fd, struct server_command *cmd,
 340                 const char *handler)
 341 {
 342         int ret, i;
 343
 344         for (i = 1; cmd->name; cmd++, i++) {
 345                 char *perms = cmd_perms_itohuman(cmd->perms);
 346                 ret = send_va_buffer(fd, "%s\t%s\t%s\t%s\n", cmd->name,
 347                         handler,
 348                         perms,
 349                         cmd->description);
 350                 free(perms);
 351                 if (ret < 0)
 352                         return ret;
 353         }
 354         return 1;
 355 }
 356
 357 /* returns string that must be freed by the caller */
 358 static struct server_command *get_cmd_ptr(const char *name, char **handler)
 359 {
 360         struct server_command *cmd;
 361
 362         for (cmd = server_cmds; cmd->name; cmd++)
 363                 if (!strcmp(cmd->name, name)) {
 364                         if (handler)
 365                                 *handler = para_strdup("server"); /* server commands */
 366                         return cmd;
 367                 }
 368         /* not found, look for commands supported by afs */
 369         for (cmd = afs_cmds; cmd->name; cmd++)
 370                 if (!strcmp(cmd->name, name)) {
 371                         if (handler)
 372                                 *handler = para_strdup("afs");
 373                         return cmd;
 374                 }
 375         return NULL;
 376 }
 377
 378 /* help */
 379 int com_help(int fd, int argc, char * const * argv)
 380 {
 381         struct server_command *cmd;
 382         char *perms, *handler;
 383         int ret;
 384
 385         if (argc < 2) {
 386                 /* no argument given, print list of commands */
 387                 if ((ret = send_list_of_commands(fd, server_cmds, "server")) < 0)
 388                         return ret;
 389                 return send_list_of_commands(fd, afs_cmds, "afs");
 390         }
 391         /* argument given for help */
 392         cmd = get_cmd_ptr(argv[1], &handler);
 393         if (!cmd) {
 394                 free(handler);
 395                 return -E_BAD_CMD;
 396         }
 397         perms = cmd_perms_itohuman(cmd->perms);
 398         ret = send_va_buffer(fd,
 399                 "%s - %s\n\n"
 400                 "handler: %s\n"
 401                 "permissions: %s\n"
 402                 "usage: %s\n\n"
 403                 "%s\n",
 404                 argv[1],
 405                 cmd->description,
 406                 handler,
 407                 perms,
 408                 cmd->usage,
 409                 cmd->help
 410         );
 411         free(perms);
 412         free(handler);
 413         return ret;
 414 }
 415
 416 /* hup */
 417 int com_hup(__a_unused int fd, int argc, __a_unused char * const * argv)
 418 {
 419         if (argc != 1)
 420                 return -E_COMMAND_SYNTAX;
 421         kill(getppid(), SIGHUP);
 422         return 1;
 423 }
 424
 425 /* term */
 426 int com_term(__a_unused int fd, int argc, __a_unused char * const * argv)
 427 {
 428         if (argc != 1)
 429                 return -E_COMMAND_SYNTAX;
 430         kill(getppid(), SIGTERM);
 431         return 1;
 432 }
 433
 434 int com_play(__a_unused int fd, int argc, __a_unused char * const * argv)
 435 {
 436         if (argc != 1)
 437                 return -E_COMMAND_SYNTAX;
 438         mutex_lock(mmd_mutex);
 439         mmd->new_vss_status_flags |= VSS_PLAYING;
 440         mmd->new_vss_status_flags &= ~VSS_NOMORE;
 441         mutex_unlock(mmd_mutex);
 442         return 1;
 443
 444 }
 445
 446 /* stop */
 447 int com_stop(__a_unused int fd, int argc, __a_unused char * const * argv)
 448 {
 449         if (argc != 1)
 450                 return -E_COMMAND_SYNTAX;
 451         mutex_lock(mmd_mutex);
 452         mmd->new_vss_status_flags &= ~VSS_PLAYING;
 453         mmd->new_vss_status_flags &= ~VSS_REPOS;
 454         mmd->new_vss_status_flags |= VSS_NEXT;
 455         mutex_unlock(mmd_mutex);
 456         return 1;
 457 }
 458
 459 /* pause */
 460 int com_pause(__a_unused int fd, int argc, __a_unused char * const * argv)
 461 {
 462         if (argc != 1)
 463                 return -E_COMMAND_SYNTAX;
 464         mutex_lock(mmd_mutex);
 465         if (!vss_paused() && !vss_stopped()) {
 466                 mmd->events++;
 467                 mmd->new_vss_status_flags &= ~VSS_PLAYING;
 468                 mmd->new_vss_status_flags &= ~VSS_NEXT;
 469         }
 470         mutex_unlock(mmd_mutex);
 471         return 1;
 472 }
 473
 474 /* next */
 475 int com_next(__a_unused int fd, int argc, __a_unused char * const * argv)
 476 {
 477         if (argc != 1)
 478                 return -E_COMMAND_SYNTAX;
 479         mutex_lock(mmd_mutex);
 480         mmd->events++;
 481         mmd->new_vss_status_flags |= VSS_NEXT;
 482         mutex_unlock(mmd_mutex);
 483         return 1;
 484 }
 485
 486 /* nomore */
 487 int com_nomore(__a_unused int fd, int argc, __a_unused char * const * argv)
 488 {
 489         if (argc != 1)
 490                 return -E_COMMAND_SYNTAX;
 491         mutex_lock(mmd_mutex);
 492         if (vss_playing() || vss_paused())
 493                 mmd->new_vss_status_flags |= VSS_NOMORE;
 494         mutex_unlock(mmd_mutex);
 495         return 1;
 496 }
 497
 498 /* ff */
 499 int com_ff(__a_unused int fd, int argc, char * const * argv)
 500 {
 501         long promille;
 502         int ret, backwards = 0;
 503         unsigned i;
 504         char c;
 505
 506         if (argc != 2)
 507                 return -E_COMMAND_SYNTAX;
 508         if (!(ret = sscanf(argv[1], "%u%c", &i, &c)))
 509                 return -E_COMMAND_SYNTAX;
 510         if (ret > 1 && c == '-')
 511                 backwards = 1; /* jmp backwards */
 512         mutex_lock(mmd_mutex);
 513         ret = -E_NO_AUDIO_FILE;
 514         if (!mmd->afd.afhi.chunks_total || !mmd->afd.afhi.seconds_total)
 515                 goto out;
 516         promille = (1000 * mmd->current_chunk) / mmd->afd.afhi.chunks_total;
 517         if (backwards)
 518                 promille -= 1000 * i / mmd->afd.afhi.seconds_total;
 519         else
 520                 promille += 1000 * i / mmd->afd.afhi.seconds_total;
 521         if (promille < 0)
 522                 promille = 0;
 523         if (promille >  1000) {
 524                 mmd->new_vss_status_flags |= VSS_NEXT;
 525                 goto out;
 526         }
 527         mmd->repos_request = (mmd->afd.afhi.chunks_total * promille) / 1000;
 528         mmd->new_vss_status_flags |= VSS_REPOS;
 529         mmd->new_vss_status_flags &= ~VSS_NEXT;
 530         mmd->events++;
 531         ret = 1;
 532 out:
 533         mutex_unlock(mmd_mutex);
 534         return ret;
 535 }
 536
 537 /* jmp */
 538 int com_jmp(__a_unused int fd, int argc, char * const * argv)
 539 {
 540         long unsigned int i;
 541         int ret;
 542
 543         if (argc != 2)
 544                 return -E_COMMAND_SYNTAX;
 545         if (sscanf(argv[1], "%lu", &i) <= 0)
 546                 return -E_COMMAND_SYNTAX;
 547         mutex_lock(mmd_mutex);
 548         ret = -E_NO_AUDIO_FILE;
 549         if (!mmd->afd.afhi.chunks_total)
 550                 goto out;
 551         if (i > 100)
 552                 i = 100;
 553         PARA_INFO_LOG("jumping to %lu%%\n", i);
 554         mmd->repos_request = (mmd->afd.afhi.chunks_total * i + 50)/ 100;
 555         PARA_INFO_LOG("sent: %lu,  offset before jmp: %lu\n",
 556                 mmd->chunks_sent, mmd->offset);
 557         mmd->new_vss_status_flags |= VSS_REPOS;
 558         mmd->new_vss_status_flags &= ~VSS_NEXT;
 559         ret = 1;
 560         mmd->events++;
 561 out:
 562         mutex_unlock(mmd_mutex);
 563         return ret;
 564 }
 565
 566 /*
 567  * check if perms are sufficient to exec a command having perms cmd_perms.
 568  * Returns 0 if perms are sufficient, -E_PERM otherwise.
 569  */
 570 static int check_perms(unsigned int perms, struct server_command *cmd_ptr)
 571 {
 572         PARA_DEBUG_LOG("checking permissions\n");
 573         return (cmd_ptr->perms & perms) < cmd_ptr->perms ? -E_PERM : 0;
 574 }
 575
 576 /*
 577  * Parse first string from *cmd and lookup in table of valid commands.
 578  * On error, NULL is returned.
 579  */
 580 static struct server_command *parse_cmd(const char *cmdstr)
 581 {
 582         char buf[255];
 583         int n = 0;
 584
 585         sscanf(cmdstr, "%200s%n", buf, &n);
 586         if (!n)
 587                 return NULL;
 588         buf[n] = '\0';
 589         return get_cmd_ptr(buf, NULL);
 590 }
 591
 592 static void init_rc4_keys(void)
 593 {
 594         int i;
 595
 596         for (i = 0; i < 2 * RC4_KEY_LEN; i++)
 597                 rc4_buf[i] = para_random(256);
 598         PARA_DEBUG_LOG("rc4 keys initialized (%u:%u)\n",
 599                 (unsigned char) rc4_buf[0],
 600                 (unsigned char) rc4_buf[RC4_KEY_LEN]);
 601         RC4_set_key(&rc4_recv_key, RC4_KEY_LEN, rc4_buf);
 602         RC4_set_key(&rc4_send_key, RC4_KEY_LEN, rc4_buf + RC4_KEY_LEN);
 603 }
 604
 605 static void rc4_recv(unsigned long len, const unsigned char *indata,
 606                 unsigned char *outdata, __a_unused void *private_data)
 607 {
 608         RC4(&rc4_recv_key, len, indata, outdata);
 609 }
 610
 611 static void rc4_send(unsigned long len, const unsigned char *indata,
 612                 unsigned char *outdata, __a_unused void *private_data)
 613 {
 614         RC4(&rc4_send_key, len, indata, outdata);
 615 }
 616
 617 static int read_command(int fd, char **result)
 618 {
 619         int ret;
 620         char buf[4096];
 621         char *command = NULL;
 622
 623         for (;;) {
 624                 size_t numbytes;
 625                 char *p;
 626
 627                 ret = recv_buffer(fd, buf, sizeof(buf));
 628                 if (ret < 0)
 629                         goto out;
 630                 if (!ret)
 631                         break;
 632                 numbytes = ret;
 633                 ret = -E_COMMAND_SYNTAX;
 634                 if (command && numbytes + strlen(command) > MAX_COMMAND_LEN) /* DOS */
 635                         goto out;
 636                 command = para_strcat(command, buf);
 637                 p = strstr(command, EOC_MSG);
 638                 if (p) {
 639                         *p = '\0';
 640                         break;
 641                 }
 642         }
 643         ret = command? 1 : -E_COMMAND_SYNTAX;
 644 out:
 645         if (ret < 0)
 646                 free(command);
 647         else
 648                 *result = command;
 649         return ret;
 650
 651 }
 652
 653 static void reset_signals(void)
 654 {
 655         para_sigaction(SIGCHLD, SIG_IGN);
 656         para_sigaction(SIGINT, SIG_DFL);
 657         para_sigaction(SIGTERM, SIG_DFL);
 658         para_sigaction(SIGHUP, SIG_DFL);
 659 }
 660
 661 /**
 662  * Perform user authentication and execute a command.
 663  *
 664  * \param fd The file descriptor to send output to.
 665  * \param peername Identifies the connecting peer.
 666  *
 667  * Whenever para_server accepts an incoming tcp connection on
 668  * the port it listens on, it forks and the resulting child
 669  * calls this function.
 670  *
 671  * An RSA-based challenge/response is used to authenticate
 672  * the peer. It that authentication succeeds, a random RC4
 673  * session key is generated and sent back to the peer,
 674  * encrypted with its RSA public key.  From this point on,
 675  * all transfers are crypted with this session key.
 676  *
 677  * Next it is checked if the peer supplied  a valid server command or a command
 678  * for the audio file selector.  If yes, and if the user has sufficient
 679  * permissions to execute that command, the function calls the corresponding
 680  * command handler which does argument checking and further processing.
 681  *
 682  * In order to cope with a DOS attacks, a timeout is set up
 683  * which terminates the function if the connection was not
 684  * authenticated when the timeout expires.
 685  *
 686  * \sa alarm(2), rc4(3), crypt.c, crypt.h
 687  */
 688 __noreturn void handle_connect(int fd, const char *peername)
 689 {
 690         int ret, argc, use_rc4 = 0;
 691         char buf[4096];
 692         unsigned char crypt_buf[MAXLINE];
 693         struct user *u;
 694         struct server_command *cmd = NULL;
 695         long unsigned challenge_nr, chall_response;
 696         char **argv = NULL;
 697         char *p, *command = NULL;
 698         size_t numbytes;
 699
 700         reset_signals();
 701         /* we need a blocking fd here as recv() might return EAGAIN otherwise. */
 702         ret = mark_fd_blocking(fd);
 703         if (ret < 0)
 704                 goto err_out;
 705         challenge_nr = random();
 706         /* send Welcome message */
 707         ret = send_va_buffer(fd, "This is para_server, version "
 708                 PACKAGE_VERSION  ".\n" );
 709         if (ret < 0)
 710                 goto err_out;
 711         /* recv auth request line */
 712         ret = recv_buffer(fd, buf, sizeof(buf));
 713         if (ret < 0)
 714                 goto err_out;
 715         if (ret <= 6) {
 716                 ret = -E_AUTH;
 717                 goto err_out;
 718         }
 719         numbytes = ret;
 720         ret = -E_AUTH;
 721         if (strncmp(buf, "auth ", 5))
 722                 goto err_out;
 723
 724         if (numbytes < 9 || strncmp(buf, "auth rc4 ", 9))
 725                 p = buf + 5; /* client version < 0.2.6 */
 726         else {
 727                 p = buf + 9; /* client version >= 0.2.6 */
 728                 use_rc4 = 1;
 729         }
 730         PARA_DEBUG_LOG("received %s request for user %s\n",
 731                 use_rc4? "rc4" : "auth", p);
 732         ret = -E_BAD_USER;
 733         u = lookup_user(p);
 734         if (!u)
 735                 goto err_out;
 736         ret = para_encrypt_challenge(u->rsa, challenge_nr, crypt_buf);
 737         if (ret <= 0)
 738                 goto err_out;
 739         numbytes = ret;
 740         PARA_DEBUG_LOG("sending %zu byte challenge\n", numbytes);
 741         /* We can't use send_buffer here since buf may contain null bytes */
 742         ret = send_bin_buffer(fd,(char *) crypt_buf, numbytes);
 743         if (ret < 0)
 744                 goto net_err;
 745         /* recv decrypted number */
 746         ret = recv_buffer(fd, buf, sizeof(buf));
 747         if (ret < 0)
 748                 goto net_err;
 749         numbytes = ret;
 750         ret = -E_AUTH;
 751         if (!numbytes)
 752                 goto net_err;
 753         if (sscanf(buf, CHALLENGE_RESPONSE_MSG "%lu", &chall_response) < 1
 754                         || chall_response != challenge_nr)
 755                 goto err_out;
 756         /* auth successful, send 'Proceed' message */
 757         PARA_INFO_LOG("good auth for %s (%lu)\n", u->name, challenge_nr);
 758         sprintf(buf, "%s", PROCEED_MSG);
 759         if (use_rc4) {
 760                 init_rc4_keys();
 761                 ret = para_encrypt_buffer(u->rsa, rc4_buf, 2 * RC4_KEY_LEN,
 762                         (unsigned char *)buf + PROCEED_MSG_LEN + 1);
 763                 if (ret <= 0)
 764                         goto err_out;
 765                 numbytes = ret + strlen(PROCEED_MSG) + 1;
 766         } else
 767                 numbytes = strlen(buf);
 768         ret = send_bin_buffer(fd, buf, numbytes);
 769         if (ret < 0)
 770                 goto net_err;
 771         if (use_rc4)
 772                 enable_crypt(fd, rc4_recv, rc4_send, NULL);
 773         ret = read_command(fd, &command);
 774         if (ret == -E_COMMAND_SYNTAX)
 775                 goto err_out;
 776         if (ret < 0)
 777                 goto net_err;
 778         ret = -E_BAD_CMD;
 779         cmd = parse_cmd(command);
 780         if (!cmd)
 781                 goto err_out;
 782         /* valid command, check permissions */
 783         ret = check_perms(u->perms, cmd);
 784         if (ret < 0)
 785                 goto err_out;
 786         /* valid command and sufficient perms */
 787         alarm(0);
 788         argc = split_args(command, &argv, "\n");
 789         PARA_NOTICE_LOG("calling com_%s() for %s@%s\n", cmd->name, u->name,
 790                         peername);
 791         ret = cmd->handler(fd, argc, argv);
 792         mutex_lock(mmd_mutex);
 793         mmd->num_commands++;
 794         mutex_unlock(mmd_mutex);
 795         if (ret >= 0)
 796                 goto out;
 797 err_out:
 798         send_va_buffer(fd, "%s\n", para_strerror(-ret));
 799 net_err:
 800         PARA_NOTICE_LOG("%s\n", para_strerror(-ret));
 801 out:
 802         free(command);
 803         free(argv);
 804         mutex_lock(mmd_mutex);
 805         if (cmd && (cmd->perms & AFS_WRITE) && ret >= 0)
 806                 mmd->events++;
 807         mmd->active_connections--;
 808         mutex_unlock(mmd_mutex);
 809         exit(ret < 0? EXIT_FAILURE : EXIT_SUCCESS);
 810 }