release/src/router/dropbear/common-session.c

   1 /*
   2  * Dropbear - a SSH2 server
   3  *
   4  * Copyright (c) 2002,2003 Matt Johnston
   5  * All rights reserved.
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy
   8  * of this software and associated documentation files (the "Software"), to deal
   9  * in the Software without restriction, including without limitation the rights
  10  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  11  * copies of the Software, and to permit persons to whom the Software is
  12  * furnished to do so, subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in
  15  * all copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  20  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  21  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  22  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  23  * SOFTWARE. */
  24
  25 #include "includes.h"
  26 #include "session.h"
  27 #include "dbutil.h"
  28 #include "packet.h"
  29 #include "algo.h"
  30 #include "buffer.h"
  31 #include "dss.h"
  32 #include "ssh.h"
  33 #include "random.h"
  34 #include "kex.h"
  35 #include "channel.h"
  36 #include "atomicio.h"
  37 #include "runopts.h"
  38
  39 static void checktimeouts();
  40 static long select_timeout();
  41 static int ident_readln(int fd, char* buf, int count);
  42
  43 struct sshsession ses; /* GLOBAL */
  44
  45 /* need to know if the session struct has been initialised, this way isn't the
  46  * cleanest, but works OK */
  47 int sessinitdone = 0; /* GLOBAL */
  48
  49 /* this is set when we get SIGINT or SIGTERM, the handler is in main.c */
  50 int exitflag = 0; /* GLOBAL */
  51
  52
  53
  54 /* called only at the start of a session, set up initial state */
  55 void common_session_init(int sock_in, int sock_out) {
  56
  57         TRACE(("enter session_init"))
  58
  59         ses.sock_in = sock_in;
  60         ses.sock_out = sock_out;
  61         ses.maxfd = MAX(sock_in, sock_out);
  62
  63         ses.connect_time = 0;
  64         ses.last_trx_packet_time = 0;
  65         ses.last_packet_time = 0;
  66
  67         if (pipe(ses.signal_pipe) < 0) {
  68                 dropbear_exit("Signal pipe failed");
  69         }
  70         setnonblocking(ses.signal_pipe[0]);
  71         setnonblocking(ses.signal_pipe[1]);
  72
  73         ses.maxfd = MAX(ses.maxfd, ses.signal_pipe[0]);
  74         ses.maxfd = MAX(ses.maxfd, ses.signal_pipe[1]);
  75
  76         kexfirstinitialise(); /* initialise the kex state */
  77
  78         ses.writepayload = buf_new(TRANS_MAX_PAYLOAD_LEN);
  79         ses.transseq = 0;
  80
  81         ses.readbuf = NULL;
  82         ses.payload = NULL;
  83         ses.recvseq = 0;
  84
  85         initqueue(&ses.writequeue);
  86
  87         ses.requirenext = SSH_MSG_KEXINIT;
  88         ses.dataallowed = 1; /* we can send data until we actually
  89                                                         send the SSH_MSG_KEXINIT */
  90         ses.ignorenext = 0;
  91         ses.lastpacket = 0;
  92         ses.reply_queue_head = NULL;
  93         ses.reply_queue_tail = NULL;
  94
  95         /* set all the algos to none */
  96         ses.keys = (struct key_context*)m_malloc(sizeof(struct key_context));
  97         ses.newkeys = NULL;
  98         ses.keys->recv.algo_crypt = &dropbear_nocipher;
  99         ses.keys->trans.algo_crypt = &dropbear_nocipher;
 100         ses.keys->recv.crypt_mode = &dropbear_mode_none;
 101         ses.keys->trans.crypt_mode = &dropbear_mode_none;
 102
 103         ses.keys->recv.algo_mac = &dropbear_nohash;
 104         ses.keys->trans.algo_mac = &dropbear_nohash;
 105
 106         ses.keys->algo_kex = -1;
 107         ses.keys->algo_hostkey = -1;
 108         ses.keys->recv.algo_comp = DROPBEAR_COMP_NONE;
 109         ses.keys->trans.algo_comp = DROPBEAR_COMP_NONE;
 110
 111 #ifndef DISABLE_ZLIB
 112         ses.keys->recv.zstream = NULL;
 113         ses.keys->trans.zstream = NULL;
 114 #endif
 115
 116         /* key exchange buffers */
 117         ses.session_id = NULL;
 118         ses.kexhashbuf = NULL;
 119         ses.transkexinit = NULL;
 120         ses.dh_K = NULL;
 121         ses.remoteident = NULL;
 122
 123         ses.chantypes = NULL;
 124
 125         ses.allowprivport = 0;
 126
 127         TRACE(("leave session_init"))
 128 }
 129
 130 void session_loop(void(*loophandler)()) {
 131
 132         fd_set readfd, writefd;
 133         struct timeval timeout;
 134         int val;
 135
 136         /* main loop, select()s for all sockets in use */
 137         for(;;) {
 138
 139                 timeout.tv_sec = select_timeout();
 140                 timeout.tv_usec = 0;
 141                 FD_ZERO(&writefd);
 142                 FD_ZERO(&readfd);
 143                 dropbear_assert(ses.payload == NULL);
 144                 if (ses.sock_in != -1) {
 145                         FD_SET(ses.sock_in, &readfd);
 146                 }
 147                 if (ses.sock_out != -1 && !isempty(&ses.writequeue)) {
 148                         FD_SET(ses.sock_out, &writefd);
 149                 }
 150
 151                 /* We get woken up when signal handlers write to this pipe.
 152                    SIGCHLD in svr-chansession is the only one currently. */
 153                 FD_SET(ses.signal_pipe[0], &readfd);
 154
 155                 /* set up for channels which require reading/writing */
 156                 if (ses.dataallowed) {
 157                         setchannelfds(&readfd, &writefd);
 158                 }
 159                 val = select(ses.maxfd+1, &readfd, &writefd, NULL, &timeout);
 160
 161                 if (exitflag) {
 162                         dropbear_exit("Terminated by signal");
 163                 }
 164
 165                 if (val < 0 && errno != EINTR) {
 166                         dropbear_exit("Error in select");
 167                 }
 168
 169                 if (val <= 0) {
 170                         /* If we were interrupted or the select timed out, we still
 171                          * want to iterate over channels etc for reading, to handle
 172                          * server processes exiting etc.
 173                          * We don't want to read/write FDs. */
 174                         FD_ZERO(&writefd);
 175                         FD_ZERO(&readfd);
 176                 }
 177
 178                 /* We'll just empty out the pipe if required. We don't do
 179                 any thing with the data, since the pipe's purpose is purely to
 180                 wake up the select() above. */
 181                 if (FD_ISSET(ses.signal_pipe[0], &readfd)) {
 182                         char x;
 183                         while (read(ses.signal_pipe[0], &x, 1) > 0) {}
 184                 }
 185
 186                 /* check for auth timeout, rekeying required etc */
 187                 checktimeouts();
 188
 189                 /* process session socket's incoming/outgoing data */
 190                 if (ses.sock_out != -1) {
 191                         if (FD_ISSET(ses.sock_out, &writefd) && !isempty(&ses.writequeue)) {
 192                                 write_packet();
 193                         }
 194                 }
 195
 196                 if (ses.sock_in != -1) {
 197                         if (FD_ISSET(ses.sock_in, &readfd)) {
 198                                 read_packet();
 199                         }
 200
 201                         /* Process the decrypted packet. After this, the read buffer
 202                          * will be ready for a new packet */
 203                         if (ses.payload != NULL) {
 204                                 process_packet();
 205                         }
 206                 }
 207
 208                 /* if required, flush out any queued reply packets that
 209                 were being held up during a KEX */
 210                 maybe_flush_reply_queue();
 211
 212                 /* process pipes etc for the channels, ses.dataallowed == 0
 213                  * during rekeying ) */
 214                 if (ses.dataallowed) {
 215                         channelio(&readfd, &writefd);
 216                 }
 217
 218                 if (loophandler) {
 219                         loophandler();
 220                 }
 221
 222         } /* for(;;) */
 223
 224         /* Not reached */
 225 }
 226
 227 /* clean up a session on exit */
 228 void common_session_cleanup() {
 229
 230         TRACE(("enter session_cleanup"))
 231
 232         /* we can't cleanup if we don't know the session state */
 233         if (!sessinitdone) {
 234                 TRACE(("leave session_cleanup: !sessinitdone"))
 235                 return;
 236         }
 237
 238         m_free(ses.session_id);
 239         m_burn(ses.keys, sizeof(struct key_context));
 240         m_free(ses.keys);
 241
 242         chancleanup();
 243
 244         TRACE(("leave session_cleanup"))
 245 }
 246
 247
 248 void session_identification() {
 249
 250         /* max length of 255 chars */
 251         char linebuf[256];
 252         int len = 0;
 253         char done = 0;
 254         int i;
 255
 256         /* write our version string, this blocks */
 257         if (atomicio(write, ses.sock_out, LOCAL_IDENT "\r\n",
 258                                 strlen(LOCAL_IDENT "\r\n")) == DROPBEAR_FAILURE) {
 259                 ses.remoteclosed();
 260         }
 261
 262         /* If they send more than 50 lines, something is wrong */
 263         for (i = 0; i < 50; i++) {
 264                 len = ident_readln(ses.sock_in, linebuf, sizeof(linebuf));
 265
 266                 if (len < 0 && errno != EINTR) {
 267                         /* It failed */
 268                         break;
 269                 }
 270
 271                 if (len >= 4 && memcmp(linebuf, "SSH-", 4) == 0) {
 272                         /* start of line matches */
 273                         done = 1;
 274                         break;
 275                 }
 276         }
 277
 278         if (!done) {
 279                 TRACE(("err: %s for '%s'\n", strerror(errno), linebuf))
 280                 ses.remoteclosed();
 281         } else {
 282                 /* linebuf is already null terminated */
 283                 ses.remoteident = m_malloc(len);
 284                 memcpy(ses.remoteident, linebuf, len);
 285         }
 286
 287         /* Shall assume that 2.x will be backwards compatible. */
 288         if (strncmp(ses.remoteident, "SSH-2.", 6) != 0
 289                         && strncmp(ses.remoteident, "SSH-1.99-", 9) != 0) {
 290                 dropbear_exit("Incompatible remote version '%s'", ses.remoteident);
 291         }
 292
 293         TRACE(("remoteident: %s", ses.remoteident))
 294
 295 }
 296
 297 /* returns the length including null-terminating zero on success,
 298  * or -1 on failure */
 299 static int ident_readln(int fd, char* buf, int count) {
 300
 301         char in;
 302         int pos = 0;
 303         int num = 0;
 304         fd_set fds;
 305         struct timeval timeout;
 306
 307         TRACE(("enter ident_readln"))
 308
 309         if (count < 1) {
 310                 return -1;
 311         }
 312
 313         FD_ZERO(&fds);
 314
 315         /* select since it's a non-blocking fd */
 316
 317         /* leave space to null-terminate */
 318         while (pos < count-1) {
 319
 320                 FD_SET(fd, &fds);
 321
 322                 timeout.tv_sec = 1;
 323                 timeout.tv_usec = 0;
 324                 if (select(fd+1, &fds, NULL, NULL, &timeout) < 0) {
 325                         if (errno == EINTR) {
 326                                 continue;
 327                         }
 328                         TRACE(("leave ident_readln: select error"))
 329                         return -1;
 330                 }
 331
 332                 checktimeouts();
 333
 334                 /* Have to go one byte at a time, since we don't want to read past
 335                  * the end, and have to somehow shove bytes back into the normal
 336                  * packet reader */
 337                 if (FD_ISSET(fd, &fds)) {
 338                         num = read(fd, &in, 1);
 339                         /* a "\n" is a newline, "\r" we want to read in and keep going
 340                          * so that it won't be read as part of the next line */
 341                         if (num < 0) {
 342                                 /* error */
 343                                 if (errno == EINTR) {
 344                                         continue; /* not a real error */
 345                                 }
 346                                 TRACE(("leave ident_readln: read error"))
 347                                 return -1;
 348                         }
 349                         if (num == 0) {
 350                                 /* EOF */
 351                                 TRACE(("leave ident_readln: EOF"))
 352                                 return -1;
 353                         }
 354                         if (in == '\n') {
 355                                 /* end of ident string */
 356                                 break;
 357                         }
 358                         /* we don't want to include '\r's */
 359                         if (in != '\r') {
 360                                 buf[pos] = in;
 361                                 pos++;
 362                         }
 363                 }
 364         }
 365
 366         buf[pos] = '\0';
 367         TRACE(("leave ident_readln: return %d", pos+1))
 368         return pos+1;
 369 }
 370
 371 void send_msg_ignore() {
 372         CHECKCLEARTOWRITE();
 373         buf_putbyte(ses.writepayload, SSH_MSG_IGNORE);
 374         buf_putstring(ses.writepayload, "", 0);
 375         encrypt_packet();
 376 }
 377
 378 /* Check all timeouts which are required. Currently these are the time for
 379  * user authentication, and the automatic rekeying. */
 380 static void checktimeouts() {
 381
 382         time_t now;
 383
 384         now = time(NULL);
 385
 386         if (ses.connect_time != 0 && now - ses.connect_time >= AUTH_TIMEOUT) {
 387                         dropbear_close("Timeout before auth");
 388         }
 389
 390         /* we can't rekey if we haven't done remote ident exchange yet */
 391         if (ses.remoteident == NULL) {
 392                 return;
 393         }
 394
 395         if (!ses.kexstate.sentkexinit
 396                         && (now - ses.kexstate.lastkextime >= KEX_REKEY_TIMEOUT
 397                         || ses.kexstate.datarecv+ses.kexstate.datatrans >= KEX_REKEY_DATA)) {
 398                 TRACE(("rekeying after timeout or max data reached"))
 399                 send_msg_kexinit();
 400         }
 401
 402         if (opts.keepalive_secs > 0
 403                         && now - ses.last_trx_packet_time >= opts.keepalive_secs) {
 404                 send_msg_ignore();
 405         }
 406
 407         if (opts.idle_timeout_secs > 0 && ses.last_packet_time > 0
 408                         && now - ses.last_packet_time >= opts.idle_timeout_secs) {
 409                 dropbear_close("Idle timeout");
 410         }
 411 }
 412
 413 static long select_timeout() {
 414         /* determine the minimum timeout that might be required, so
 415         as to avoid waking when unneccessary */
 416         long ret = LONG_MAX;
 417         if (KEX_REKEY_TIMEOUT > 0)
 418                 ret = MIN(KEX_REKEY_TIMEOUT, ret);
 419         if (AUTH_TIMEOUT > 0)
 420                 ret = MIN(AUTH_TIMEOUT, ret);
 421         if (opts.keepalive_secs > 0)
 422                 ret = MIN(opts.keepalive_secs, ret);
 423     if (opts.idle_timeout_secs > 0)
 424         ret = MIN(opts.idle_timeout_secs, ret);
 425         return ret;
 426 }
 427
 428 const char* get_user_shell() {
 429         /* an empty shell should be interpreted as "/bin/sh" */
 430         if (ses.authstate.pw_shell[0] == '\0') {
 431                 return "/bin/sh";
 432         } else {
 433                 return ses.authstate.pw_shell;
 434         }
 435 }
 436 void fill_passwd(const char* username) {
 437         struct passwd *pw = NULL;
 438         if (ses.authstate.pw_name)
 439                 m_free(ses.authstate.pw_name);
 440         if (ses.authstate.pw_dir)
 441                 m_free(ses.authstate.pw_dir);
 442         if (ses.authstate.pw_shell)
 443                 m_free(ses.authstate.pw_shell);
 444         if (ses.authstate.pw_passwd)
 445                 m_free(ses.authstate.pw_passwd);
 446
 447         pw = getpwnam(username);
 448         if (!pw) {
 449                 return;
 450         }
 451         ses.authstate.pw_uid = pw->pw_uid;
 452         ses.authstate.pw_gid = pw->pw_gid;
 453         ses.authstate.pw_name = m_strdup(pw->pw_name);
 454         ses.authstate.pw_dir = m_strdup(pw->pw_dir);
 455         ses.authstate.pw_shell = m_strdup(pw->pw_shell);
 456         ses.authstate.pw_passwd = m_strdup(pw->pw_passwd);
 457 }
 458