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 "runopts.h"
  37
  38 static void checktimeouts();
  39 static long select_timeout();
  40 static int ident_readln(int fd, char* buf, int count);
  41 static void read_session_identification();
  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 /* called only at the start of a session, set up initial state */
  53 void common_session_init(int sock_in, int sock_out) {
  54
  55         TRACE(("enter session_init"))
  56
  57         ses.sock_in = sock_in;
  58         ses.sock_out = sock_out;
  59         ses.maxfd = MAX(sock_in, sock_out);
  60
  61         ses.connect_time = 0;
  62         ses.last_trx_packet_time = 0;
  63         ses.last_packet_time = 0;
  64
  65         if (pipe(ses.signal_pipe) < 0) {
  66                 dropbear_exit("Signal pipe failed");
  67         }
  68         setnonblocking(ses.signal_pipe[0]);
  69         setnonblocking(ses.signal_pipe[1]);
  70
  71         ses.maxfd = MAX(ses.maxfd, ses.signal_pipe[0]);
  72         ses.maxfd = MAX(ses.maxfd, ses.signal_pipe[1]);
  73
  74         kexfirstinitialise(); /* initialise the kex state */
  75
  76         ses.writepayload = buf_new(TRANS_MAX_PAYLOAD_LEN);
  77         ses.transseq = 0;
  78
  79         ses.readbuf = NULL;
  80         ses.payload = NULL;
  81         ses.recvseq = 0;
  82
  83         initqueue(&ses.writequeue);
  84
  85         ses.requirenext[0] = SSH_MSG_KEXINIT;
  86         ses.dataallowed = 1; /* we can send data until we actually
  87                                                         send the SSH_MSG_KEXINIT */
  88         ses.ignorenext = 0;
  89         ses.lastpacket = 0;
  90         ses.reply_queue_head = NULL;
  91         ses.reply_queue_tail = NULL;
  92
  93         /* set all the algos to none */
  94         ses.keys = (struct key_context*)m_malloc(sizeof(struct key_context));
  95         ses.newkeys = NULL;
  96         ses.keys->recv.algo_crypt = &dropbear_nocipher;
  97         ses.keys->trans.algo_crypt = &dropbear_nocipher;
  98         ses.keys->recv.crypt_mode = &dropbear_mode_none;
  99         ses.keys->trans.crypt_mode = &dropbear_mode_none;
 100
 101         ses.keys->recv.algo_mac = &dropbear_nohash;
 102         ses.keys->trans.algo_mac = &dropbear_nohash;
 103
 104         ses.keys->algo_kex = -1;
 105         ses.keys->algo_hostkey = -1;
 106         ses.keys->recv.algo_comp = DROPBEAR_COMP_NONE;
 107         ses.keys->trans.algo_comp = DROPBEAR_COMP_NONE;
 108
 109 #ifndef DISABLE_ZLIB
 110         ses.keys->recv.zstream = NULL;
 111         ses.keys->trans.zstream = NULL;
 112 #endif
 113
 114         /* key exchange buffers */
 115         ses.session_id = NULL;
 116         ses.kexhashbuf = NULL;
 117         ses.transkexinit = NULL;
 118         ses.dh_K = NULL;
 119         ses.remoteident = NULL;
 120
 121         ses.chantypes = NULL;
 122
 123         ses.allowprivport = 0;
 124
 125         TRACE(("leave session_init"))
 126 }
 127
 128 void session_loop(void(*loophandler)()) {
 129
 130         fd_set readfd, writefd;
 131         struct timeval timeout;
 132         int val;
 133
 134         /* main loop, select()s for all sockets in use */
 135         for(;;) {
 136
 137                 timeout.tv_sec = select_timeout();
 138                 timeout.tv_usec = 0;
 139                 FD_ZERO(&writefd);
 140                 FD_ZERO(&readfd);
 141                 dropbear_assert(ses.payload == NULL);
 142
 143                 /* during initial setup we flush out the KEXINIT packet before
 144                  * attempting to read the remote version string, which might block */
 145                 if (ses.sock_in != -1 && (ses.remoteident || isempty(&ses.writequeue))) {
 146                         FD_SET(ses.sock_in, &readfd);
 147                 }
 148                 if (ses.sock_out != -1 && !isempty(&ses.writequeue)) {
 149                         FD_SET(ses.sock_out, &writefd);
 150                 }
 151
 152                 /* We get woken up when signal handlers write to this pipe.
 153                    SIGCHLD in svr-chansession is the only one currently. */
 154                 FD_SET(ses.signal_pipe[0], &readfd);
 155
 156                 /* set up for channels which require reading/writing */
 157                 if (ses.dataallowed) {
 158                         setchannelfds(&readfd, &writefd);
 159                 }
 160                 val = select(ses.maxfd+1, &readfd, &writefd, NULL, &timeout);
 161
 162                 if (exitflag) {
 163                         dropbear_exit("Terminated by signal");
 164                 }
 165
 166                 if (val < 0 && errno != EINTR) {
 167                         dropbear_exit("Error in select");
 168                 }
 169
 170                 if (val <= 0) {
 171                         /* If we were interrupted or the select timed out, we still
 172                          * want to iterate over channels etc for reading, to handle
 173                          * server processes exiting etc.
 174                          * We don't want to read/write FDs. */
 175                         FD_ZERO(&writefd);
 176                         FD_ZERO(&readfd);
 177                 }
 178
 179                 /* We'll just empty out the pipe if required. We don't do
 180                 any thing with the data, since the pipe's purpose is purely to
 181                 wake up the select() above. */
 182                 if (FD_ISSET(ses.signal_pipe[0], &readfd)) {
 183                         char x;
 184                         while (read(ses.signal_pipe[0], &x, 1) > 0) {}
 185                 }
 186
 187                 /* check for auth timeout, rekeying required etc */
 188                 checktimeouts();
 189
 190                 /* process session socket's incoming/outgoing data */
 191                 if (ses.sock_out != -1) {
 192                         if (FD_ISSET(ses.sock_out, &writefd) && !isempty(&ses.writequeue)) {
 193                                 write_packet();
 194                         }
 195                 }
 196
 197                 if (ses.sock_in != -1) {
 198                         if (FD_ISSET(ses.sock_in, &readfd)) {
 199                                 if (!ses.remoteident) {
 200                                         /* blocking read of the version string */
 201                                         read_session_identification();
 202                                 } else {
 203                                         read_packet();
 204                                 }
 205                         }
 206
 207                         /* Process the decrypted packet. After this, the read buffer
 208                          * will be ready for a new packet */
 209                         if (ses.payload != NULL) {
 210                                 process_packet();
 211                         }
 212                 }
 213
 214                 /* if required, flush out any queued reply packets that
 215                 were being held up during a KEX */
 216                 maybe_flush_reply_queue();
 217
 218                 /* process pipes etc for the channels, ses.dataallowed == 0
 219                  * during rekeying ) */
 220                 if (ses.dataallowed) {
 221                         channelio(&readfd, &writefd);
 222                 }
 223
 224                 if (loophandler) {
 225                         loophandler();
 226                 }
 227
 228         } /* for(;;) */
 229
 230         /* Not reached */
 231 }
 232
 233 /* clean up a session on exit */
 234 void session_cleanup() {
 235
 236         TRACE(("enter session_cleanup"))
 237
 238         /* we can't cleanup if we don't know the session state */
 239         if (!sessinitdone) {
 240                 TRACE(("leave session_cleanup: !sessinitdone"))
 241                 return;
 242         }
 243
 244         if (ses.extra_session_cleanup) {
 245                 ses.extra_session_cleanup();
 246         }
 247
 248         m_free(ses.session_id);
 249         m_burn(ses.keys, sizeof(struct key_context));
 250         m_free(ses.keys);
 251
 252         chancleanup();
 253
 254         TRACE(("leave session_cleanup"))
 255 }
 256
 257 void send_session_identification() {
 258         buffer *writebuf = buf_new(strlen(LOCAL_IDENT "\r\n") + 1);
 259         buf_putbytes(writebuf, LOCAL_IDENT "\r\n", strlen(LOCAL_IDENT "\r\n"));
 260         buf_putbyte(writebuf, 0x0); // packet type
 261         buf_setpos(writebuf, 0);
 262         enqueue(&ses.writequeue, writebuf);
 263 }
 264
 265 static void read_session_identification() {
 266         /* max length of 255 chars */
 267         char linebuf[256];
 268         int len = 0;
 269         char done = 0;
 270         int i;
 271         /* If they send more than 50 lines, something is wrong */
 272         for (i = 0; i < 50; i++) {
 273                 len = ident_readln(ses.sock_in, linebuf, sizeof(linebuf));
 274
 275                 if (len < 0 && errno != EINTR) {
 276                         /* It failed */
 277                         break;
 278                 }
 279
 280                 if (len >= 4 && memcmp(linebuf, "SSH-", 4) == 0) {
 281                         /* start of line matches */
 282                         done = 1;
 283                         break;
 284                 }
 285         }
 286
 287         if (!done) {
 288                 TRACE(("err: %s for '%s'\n", strerror(errno), linebuf))
 289                 ses.remoteclosed();
 290         } else {
 291                 /* linebuf is already null terminated */
 292                 ses.remoteident = m_malloc(len);
 293                 memcpy(ses.remoteident, linebuf, len);
 294         }
 295
 296         /* Shall assume that 2.x will be backwards compatible. */
 297         if (strncmp(ses.remoteident, "SSH-2.", 6) != 0
 298                         && strncmp(ses.remoteident, "SSH-1.99-", 9) != 0) {
 299                 dropbear_exit("Incompatible remote version '%s'", ses.remoteident);
 300         }
 301
 302         TRACE(("remoteident: %s", ses.remoteident))
 303
 304 }
 305
 306 /* returns the length including null-terminating zero on success,
 307  * or -1 on failure */
 308 static int ident_readln(int fd, char* buf, int count) {
 309
 310         char in;
 311         int pos = 0;
 312         int num = 0;
 313         fd_set fds;
 314         struct timeval timeout;
 315
 316         TRACE(("enter ident_readln"))
 317
 318         if (count < 1) {
 319                 return -1;
 320         }
 321
 322         FD_ZERO(&fds);
 323
 324         /* select since it's a non-blocking fd */
 325
 326         /* leave space to null-terminate */
 327         while (pos < count-1) {
 328
 329                 FD_SET(fd, &fds);
 330
 331                 timeout.tv_sec = 1;
 332                 timeout.tv_usec = 0;
 333                 if (select(fd+1, &fds, NULL, NULL, &timeout) < 0) {
 334                         if (errno == EINTR) {
 335                                 continue;
 336                         }
 337                         TRACE(("leave ident_readln: select error"))
 338                         return -1;
 339                 }
 340
 341                 checktimeouts();
 342
 343                 /* Have to go one byte at a time, since we don't want to read past
 344                  * the end, and have to somehow shove bytes back into the normal
 345                  * packet reader */
 346                 if (FD_ISSET(fd, &fds)) {
 347                         num = read(fd, &in, 1);
 348                         /* a "\n" is a newline, "\r" we want to read in and keep going
 349                          * so that it won't be read as part of the next line */
 350                         if (num < 0) {
 351                                 /* error */
 352                                 if (errno == EINTR) {
 353                                         continue; /* not a real error */
 354                                 }
 355                                 TRACE(("leave ident_readln: read error"))
 356                                 return -1;
 357                         }
 358                         if (num == 0) {
 359                                 /* EOF */
 360                                 TRACE(("leave ident_readln: EOF"))
 361                                 return -1;
 362                         }
 363                         if (in == '\n') {
 364                                 /* end of ident string */
 365                                 break;
 366                         }
 367                         /* we don't want to include '\r's */
 368                         if (in != '\r') {
 369                                 buf[pos] = in;
 370                                 pos++;
 371                         }
 372                 }
 373         }
 374
 375         buf[pos] = '\0';
 376         TRACE(("leave ident_readln: return %d", pos+1))
 377         return pos+1;
 378 }
 379
 380 void send_msg_ignore() {
 381         CHECKCLEARTOWRITE();
 382         buf_putbyte(ses.writepayload, SSH_MSG_IGNORE);
 383         buf_putstring(ses.writepayload, "", 0);
 384         encrypt_packet();
 385 }
 386
 387 /* Check all timeouts which are required. Currently these are the time for
 388  * user authentication, and the automatic rekeying. */
 389 static void checktimeouts() {
 390
 391         time_t now;
 392
 393         now = time(NULL);
 394
 395         if (ses.connect_time != 0 && now - ses.connect_time >= AUTH_TIMEOUT) {
 396                         dropbear_close("Timeout before auth");
 397         }
 398
 399         /* we can't rekey if we haven't done remote ident exchange yet */
 400         if (ses.remoteident == NULL) {
 401                 return;
 402         }
 403
 404         if (!ses.kexstate.sentkexinit
 405                         && (now - ses.kexstate.lastkextime >= KEX_REKEY_TIMEOUT
 406                         || ses.kexstate.datarecv+ses.kexstate.datatrans >= KEX_REKEY_DATA)) {
 407                 TRACE(("rekeying after timeout or max data reached"))
 408                 send_msg_kexinit();
 409         }
 410
 411         if (opts.keepalive_secs > 0
 412                         && now - ses.last_trx_packet_time >= opts.keepalive_secs) {
 413                 send_msg_ignore();
 414         }
 415
 416         if (opts.idle_timeout_secs > 0 && ses.last_packet_time > 0
 417                         && now - ses.last_packet_time >= opts.idle_timeout_secs) {
 418                 dropbear_close("Idle timeout");
 419         }
 420 }
 421
 422 static long select_timeout() {
 423         /* determine the minimum timeout that might be required, so
 424         as to avoid waking when unneccessary */
 425         long ret = LONG_MAX;
 426         if (KEX_REKEY_TIMEOUT > 0)
 427                 ret = MIN(KEX_REKEY_TIMEOUT, ret);
 428         if (AUTH_TIMEOUT > 0)
 429                 ret = MIN(AUTH_TIMEOUT, ret);
 430         if (opts.keepalive_secs > 0)
 431                 ret = MIN(opts.keepalive_secs, ret);
 432     if (opts.idle_timeout_secs > 0)
 433         ret = MIN(opts.idle_timeout_secs, ret);
 434         return ret;
 435 }
 436
 437 const char* get_user_shell() {
 438         /* an empty shell should be interpreted as "/bin/sh" */
 439         if (ses.authstate.pw_shell[0] == '\0') {
 440                 return "/bin/sh";
 441         } else {
 442                 return ses.authstate.pw_shell;
 443         }
 444 }
 445 void fill_passwd(const char* username) {
 446         struct passwd *pw = NULL;
 447         if (ses.authstate.pw_name)
 448                 m_free(ses.authstate.pw_name);
 449         if (ses.authstate.pw_dir)
 450                 m_free(ses.authstate.pw_dir);
 451         if (ses.authstate.pw_shell)
 452                 m_free(ses.authstate.pw_shell);
 453         if (ses.authstate.pw_passwd)
 454                 m_free(ses.authstate.pw_passwd);
 455
 456         pw = getpwnam(username);
 457         if (!pw) {
 458                 return;
 459         }
 460         ses.authstate.pw_uid = pw->pw_uid;
 461         ses.authstate.pw_gid = pw->pw_gid;
 462         ses.authstate.pw_name = m_strdup(pw->pw_name);
 463         ses.authstate.pw_dir = m_strdup(pw->pw_dir);
 464         ses.authstate.pw_shell = m_strdup(pw->pw_shell);
 465         {
 466                 char *passwd_crypt = pw->pw_passwd;
 467 #ifdef HAVE_SHADOW_H
 468                 /* get the shadow password if possible */
 469                 struct spwd *spasswd = getspnam(ses.authstate.pw_name);
 470                 if (spasswd && spasswd->sp_pwdp) {
 471                         passwd_crypt = spasswd->sp_pwdp;
 472                 }
 473 #endif
 474                 if (!passwd_crypt) {
 475                         /* android supposedly returns NULL */
 476                         passwd_crypt = "!!";
 477                 }
 478                 ses.authstate.pw_passwd = m_strdup(passwd_crypt);
 479         }
 480 }
 481