git.distorted.org.uk Git - u/mdw/putty/blob - ssh.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <winsock.h>
   4
   5 #include "putty.h"
   6
   7 #ifndef FALSE
   8 #define FALSE 0
   9 #endif
  10 #ifndef TRUE
  11 #define TRUE 1
  12 #endif
  13
  14 #include "ssh.h"
  15
  16 #define SSH_MSG_DISCONNECT 1
  17 #define SSH_SMSG_PUBLIC_KEY 2
  18 #define SSH_CMSG_SESSION_KEY 3
  19 #define SSH_CMSG_USER 4
  20 #define SSH_CMSG_AUTH_PASSWORD 9
  21 #define SSH_CMSG_REQUEST_PTY 10
  22 #define SSH_CMSG_EXEC_SHELL 12
  23 #define SSH_CMSG_STDIN_DATA 16
  24 #define SSH_SMSG_STDOUT_DATA 17
  25 #define SSH_SMSG_STDERR_DATA 18
  26 #define SSH_SMSG_SUCCESS 14
  27 #define SSH_SMSG_FAILURE 15
  28 #define SSH_SMSG_EXITSTATUS 20
  29 #define SSH_MSG_IGNORE 32
  30 #define SSH_CMSG_EXIT_CONFIRMATION 33
  31 #define SSH_MSG_DEBUG 36
  32 #define SSH_CMSG_AUTH_TIS 39
  33 #define SSH_SMSG_AUTH_TIS_CHALLENGE 40
  34 #define SSH_CMSG_AUTH_TIS_RESPONSE 41
  35
  36 #define SSH_AUTH_TIS              5
  37
  38 /* Coroutine mechanics for the sillier bits of the code */
  39 #define crBegin1        static int crLine = 0;
  40 #define crBegin2        switch(crLine) { case 0:;
  41 #define crBegin         crBegin1; crBegin2;
  42 #define crFinish(z)     } crLine = 0; return (z)
  43 #define crFinishV       } crLine = 0; return
  44 #define crReturn(z)     \
  45         do {\
  46             crLine=__LINE__; return (z); case __LINE__:;\
  47         } while (0)
  48 #define crReturnV       \
  49         do {\
  50             crLine=__LINE__; return; case __LINE__:;\
  51         } while (0)
  52 #define crStop(z)       do{ crLine = 0; return (z); }while(0)
  53 #define crStopV         do{ crLine = 0; return; }while(0)
  54
  55 #ifndef FALSE
  56 #define FALSE 0
  57 #endif
  58 #ifndef TRUE
  59 #define TRUE 1
  60 #endif
  61
  62 static SOCKET s = INVALID_SOCKET;
  63
  64 static unsigned char session_key[32];
  65 static struct ssh_cipher *cipher = NULL;
  66
  67 static char *savedhost;
  68
  69 static enum {
  70     SSH_STATE_BEFORE_SIZE,
  71     SSH_STATE_INTERMED,
  72     SSH_STATE_SESSION,
  73     SSH_STATE_CLOSED
  74 } ssh_state = SSH_STATE_BEFORE_SIZE;
  75
  76 static int size_needed = FALSE;
  77
  78 static void s_write (char *buf, int len) {
  79     while (len > 0) {
  80         int i = send (s, buf, len, 0);
  81         if (i > 0)
  82             len -= i, buf += i;
  83     }
  84 }
  85
  86 static int s_read (char *buf, int len) {
  87     int ret = 0;
  88     while (len > 0) {
  89         int i = recv (s, buf, len, 0);
  90         if (i > 0)
  91             len -= i, buf += i, ret += i;
  92         else
  93             return i;
  94     }
  95     return ret;
  96 }
  97
  98 static void c_write (char *buf, int len) {
  99     while (len--) {
 100         int new_head = (inbuf_head + 1) & INBUF_MASK;
 101         if (new_head != inbuf_reap) {
 102             inbuf[inbuf_head] = *buf++;
 103             inbuf_head = new_head;
 104         } else {
 105             term_out();
 106             if( inbuf_head == inbuf_reap ) len++; else break;
 107         }
 108     }
 109 }
 110
 111 struct Packet {
 112     long length;
 113     int type;
 114     unsigned long crc;
 115     unsigned char *data;
 116     unsigned char *body;
 117     long maxlen;
 118 };
 119
 120 static struct Packet pktin = { 0, 0, 0, NULL, 0 };
 121 static struct Packet pktout = { 0, 0, 0, NULL, 0 };
 122
 123 static void ssh_protocol(unsigned char *in, int inlen, int ispkt);
 124 static void ssh_size(void);
 125
 126 static void ssh_gotdata(unsigned char *data, int datalen) {
 127     static long len, biglen, to_read;
 128     static unsigned char *p;
 129     static int i, pad;
 130
 131     crBegin;
 132     while (1) {
 133         for (i = len = 0; i < 4; i++) {
 134             while (datalen == 0)
 135                 crReturnV;
 136             len = (len << 8) + *data;
 137             data++, datalen--;
 138         }
 139
 140 #ifdef FWHACK
 141         if (len == 0x52656d6f) {       /* "Remo"te server has closed ... */
 142             len = 0x300;               /* big enough to carry to end */
 143         }
 144 #endif
 145
 146         pad = 8 - (len%8);
 147
 148         biglen = len + pad;
 149
 150         len -= 5;                      /* type and CRC */
 151
 152         pktin.length = len;
 153         if (pktin.maxlen < biglen) {
 154             pktin.maxlen = biglen;
 155             pktin.data = (pktin.data == NULL ? malloc(biglen) :
 156                         realloc(pktin.data, biglen));
 157             if (!pktin.data)
 158                 fatalbox("Out of memory");
 159         }
 160
 161         p = pktin.data, to_read = biglen;
 162         while (to_read > 0) {
 163             static int chunk;
 164             chunk = to_read;
 165             while (datalen == 0)
 166                 crReturnV;
 167             if (chunk > datalen)
 168                 chunk = datalen;
 169             memcpy(p, data, chunk);
 170             data += chunk;
 171             datalen -= chunk;
 172             p += chunk;
 173             to_read -= chunk;
 174         }
 175
 176         if (cipher)
 177             cipher->decrypt(pktin.data, biglen);
 178
 179         pktin.type = pktin.data[pad];
 180         pktin.body = pktin.data+pad+1;
 181
 182         if (pktin.type == SSH_MSG_DEBUG) {
 183             /* FIXME: log it */
 184         } else if (pktin.type == SSH_MSG_IGNORE) {
 185             /* do nothing */;
 186         } else
 187             ssh_protocol(NULL, 0, 1);
 188     }
 189     crFinishV;
 190 }
 191
 192 static void s_wrpkt_start(int type, int len) {
 193     int pad, biglen;
 194
 195     len += 5;                          /* type and CRC */
 196     pad = 8 - (len%8);
 197     biglen = len + pad;
 198
 199     pktout.length = len-5;
 200     if (pktout.maxlen < biglen) {
 201         pktout.maxlen = biglen;
 202         pktout.data = (pktout.data == NULL ? malloc(biglen+4) :
 203                        realloc(pktout.data, biglen+4));
 204         if (!pktout.data)
 205             fatalbox("Out of memory");
 206     }
 207
 208     pktout.type = type;
 209     pktout.body = pktout.data+4+pad+1;
 210 }
 211
 212 static void s_wrpkt(void) {
 213     int pad, len, biglen, i;
 214     unsigned long crc;
 215
 216     len = pktout.length + 5;           /* type and CRC */
 217     pad = 8 - (len%8);
 218     biglen = len + pad;
 219
 220     pktout.body[-1] = pktout.type;
 221     for (i=0; i<pad; i++)
 222         pktout.data[i+4] = random_byte();
 223     crc = crc32(pktout.data+4, biglen-4);
 224
 225     pktout.data[biglen+0] = (unsigned char) ((crc >> 24) & 0xFF);
 226     pktout.data[biglen+1] = (unsigned char) ((crc >> 16) & 0xFF);
 227     pktout.data[biglen+2] = (unsigned char) ((crc >> 8) & 0xFF);
 228     pktout.data[biglen+3] = (unsigned char) (crc & 0xFF);
 229
 230     pktout.data[0] = (len >> 24) & 0xFF;
 231     pktout.data[1] = (len >> 16) & 0xFF;
 232     pktout.data[2] = (len >> 8) & 0xFF;
 233     pktout.data[3] = len & 0xFF;
 234
 235     if (cipher)
 236         cipher->encrypt(pktout.data+4, biglen);
 237
 238     s_write(pktout.data, biglen+4);
 239 }
 240
 241 static int ssh_versioncmp(char *a, char *b) {
 242     char *ae, *be;
 243     unsigned long av, bv;
 244
 245     av = strtoul(a, &ae, 10);
 246     bv = strtoul(b, &be, 10);
 247     if (av != bv) return (av < bv ? -1 : +1);
 248     if (*ae == '.') ae++;
 249     if (*be == '.') be++;
 250     av = strtoul(ae, &ae, 10);
 251     bv = strtoul(be, &be, 10);
 252     if (av != bv) return (av < bv ? -1 : +1);
 253     return 0;
 254 }
 255
 256 static int do_ssh_init(void) {
 257     char c, *vsp;
 258     char version[10];
 259     char vstring[80];
 260     char vlog[sizeof(vstring)+20];
 261     int i;
 262
 263 #ifdef FWHACK
 264     i = 0;
 265     while (s_read(&c, 1) == 1) {
 266         if (c == 'S' && i < 2) i++;
 267         else if (c == 'S' && i == 2) i = 2;
 268         else if (c == 'H' && i == 2) break;
 269         else i = 0;
 270     }
 271 #else
 272     if (s_read(&c,1) != 1 || c != 'S') return 0;
 273     if (s_read(&c,1) != 1 || c != 'S') return 0;
 274     if (s_read(&c,1) != 1 || c != 'H') return 0;
 275 #endif
 276     strcpy(vstring, "SSH-");
 277     vsp = vstring+4;
 278     if (s_read(&c,1) != 1 || c != '-') return 0;
 279     i = 0;
 280     while (1) {
 281         if (s_read(&c,1) != 1)
 282             return 0;
 283         if (vsp < vstring+sizeof(vstring)-1)
 284             *vsp++ = c;
 285         if (i >= 0) {
 286             if (c == '-') {
 287                 version[i] = '\0';
 288                 i = -1;
 289             } else if (i < sizeof(version)-1)
 290                 version[i++] = c;
 291         }
 292         else if (c == '\n')
 293             break;
 294     }
 295
 296     *vsp = 0;
 297     sprintf(vlog, "Server version: %s", vstring);
 298     vlog[strcspn(vlog, "\r\n")] = '\0';
 299     logevent(vlog);
 300
 301     sprintf(vstring, "SSH-%s-PuTTY\n",
 302             (ssh_versioncmp(version, "1.5") <= 0 ? version : "1.5"));
 303     sprintf(vlog, "We claim version: %s", vstring);
 304     vlog[strcspn(vlog, "\r\n")] = '\0';
 305     logevent(vlog);
 306     s_write(vstring, strlen(vstring));
 307     return 1;
 308 }
 309
 310 static void ssh_protocol(unsigned char *in, int inlen, int ispkt) {
 311     int i, j, len;
 312     unsigned char session_id[16];
 313     unsigned char *rsabuf, *keystr1, *keystr2;
 314     unsigned char cookie[8];
 315     struct RSAKey servkey, hostkey;
 316     struct MD5Context md5c;
 317     static unsigned long supported_ciphers_mask, supported_auths_mask;
 318     int cipher_type;
 319
 320     extern struct ssh_cipher ssh_3des;
 321     extern struct ssh_cipher ssh_des;
 322     extern struct ssh_cipher ssh_blowfish;
 323
 324     crBegin;
 325
 326     random_init();
 327
 328     while (!ispkt)
 329         crReturnV;
 330
 331     if (pktin.type != SSH_SMSG_PUBLIC_KEY)
 332         fatalbox("Public key packet not received");
 333
 334     logevent("Received public keys");
 335
 336     memcpy(cookie, pktin.body, 8);
 337
 338     i = makekey(pktin.body+8, &servkey, &keystr1);
 339
 340     j = makekey(pktin.body+8+i, &hostkey, &keystr2);
 341
 342     /*
 343      * Hash the host key and print the hash in the log box. Just as
 344      * a last resort in case the registry's host key checking is
 345      * compromised, we'll allow the user some ability to verify
 346      * host keys by eye.
 347      */
 348     MD5Init(&md5c);
 349     MD5Update(&md5c, keystr2, hostkey.bytes);
 350     MD5Final(session_id, &md5c);
 351     {
 352         char logmsg[80];
 353         int i;
 354         logevent("Host key MD5 is:");
 355         strcpy(logmsg, "      ");
 356         for (i = 0; i < 16; i++)
 357             sprintf(logmsg+strlen(logmsg), "%02x", session_id[i]);
 358         logevent(logmsg);
 359     }
 360
 361     supported_ciphers_mask = ((pktin.body[12+i+j] << 24) |
 362                               (pktin.body[13+i+j] << 16) |
 363                               (pktin.body[14+i+j] << 8) |
 364                               (pktin.body[15+i+j]));
 365
 366     supported_auths_mask = ((pktin.body[16+i+j] << 24) |
 367                             (pktin.body[17+i+j] << 16) |
 368                             (pktin.body[18+i+j] << 8) |
 369                             (pktin.body[19+i+j]));
 370
 371     MD5Init(&md5c);
 372
 373     MD5Update(&md5c, keystr2, hostkey.bytes);
 374     MD5Update(&md5c, keystr1, servkey.bytes);
 375     MD5Update(&md5c, pktin.body, 8);
 376
 377     MD5Final(session_id, &md5c);
 378
 379     for (i=0; i<32; i++)
 380         session_key[i] = random_byte();
 381
 382     len = (hostkey.bytes > servkey.bytes ? hostkey.bytes : servkey.bytes);
 383
 384     rsabuf = malloc(len);
 385     if (!rsabuf)
 386         fatalbox("Out of memory");
 387
 388     /*
 389      * Verify the host key.
 390      */
 391     {
 392         /*
 393          * First format the key into a string.
 394          */
 395         int len = rsastr_len(&hostkey);
 396         char *keystr = malloc(len);
 397         if (!keystr)
 398             fatalbox("Out of memory");
 399         rsastr_fmt(keystr, &hostkey);
 400         verify_ssh_host_key(savedhost, keystr);
 401         free(keystr);
 402     }
 403
 404     for (i=0; i<32; i++) {
 405         rsabuf[i] = session_key[i];
 406         if (i < 16)
 407             rsabuf[i] ^= session_id[i];
 408     }
 409
 410     if (hostkey.bytes > servkey.bytes) {
 411         rsaencrypt(rsabuf, 32, &servkey);
 412         rsaencrypt(rsabuf, servkey.bytes, &hostkey);
 413     } else {
 414         rsaencrypt(rsabuf, 32, &hostkey);
 415         rsaencrypt(rsabuf, hostkey.bytes, &servkey);
 416     }
 417
 418     logevent("Encrypted session key");
 419
 420     cipher_type = cfg.cipher == CIPHER_BLOWFISH ? SSH_CIPHER_BLOWFISH :
 421                   cfg.cipher == CIPHER_DES ? SSH_CIPHER_DES :
 422                   SSH_CIPHER_3DES;
 423     if ((supported_ciphers_mask & (1 << cipher_type)) == 0) {
 424         c_write("Selected cipher not supported, falling back to 3DES\r\n", 53);
 425         cipher_type = SSH_CIPHER_3DES;
 426     }
 427     switch (cipher_type) {
 428       case SSH_CIPHER_3DES: logevent("Using 3DES encryption"); break;
 429       case SSH_CIPHER_DES: logevent("Using single-DES encryption"); break;
 430       case SSH_CIPHER_BLOWFISH: logevent("Using Blowfish encryption"); break;
 431     }
 432
 433     s_wrpkt_start(SSH_CMSG_SESSION_KEY, len+15);
 434     pktout.body[0] = cipher_type;
 435     memcpy(pktout.body+1, cookie, 8);
 436     pktout.body[9] = (len*8) >> 8;
 437     pktout.body[10] = (len*8) & 0xFF;
 438     memcpy(pktout.body+11, rsabuf, len);
 439     pktout.body[len+11] = pktout.body[len+12] = 0;   /* protocol flags */
 440     pktout.body[len+13] = pktout.body[len+14] = 0;
 441     s_wrpkt();
 442     logevent("Trying to enable encryption...");
 443
 444     free(rsabuf);
 445
 446     cipher = cipher_type == SSH_CIPHER_BLOWFISH ? &ssh_blowfish :
 447              cipher_type == SSH_CIPHER_DES ? &ssh_des :
 448              &ssh_3des;
 449     cipher->sesskey(session_key);
 450
 451     do { crReturnV; } while (!ispkt);
 452
 453     if (pktin.type != SSH_SMSG_SUCCESS)
 454         fatalbox("Encryption not successfully enabled");
 455
 456     logevent("Successfully started encryption");
 457
 458     fflush(stdout);
 459     {
 460         static char username[100];
 461         static int pos = 0;
 462         static char c;
 463         if (!*cfg.username) {
 464             c_write("login as: ", 10);
 465             while (pos >= 0) {
 466                 do { crReturnV; } while (ispkt);
 467                 while (inlen--) switch (c = *in++) {
 468                   case 10: case 13:
 469                     username[pos] = 0;
 470                     pos = -1;
 471                     break;
 472                   case 8: case 127:
 473                     if (pos > 0) {
 474                         c_write("\b \b", 3);
 475                         pos--;
 476                     }
 477                     break;
 478                   case 21: case 27:
 479                     while (pos > 0) {
 480                         c_write("\b \b", 3);
 481                         pos--;
 482                     }
 483                     break;
 484                   case 3: case 4:
 485                     random_save_seed();
 486                     exit(0);
 487                     break;
 488                   default:
 489                     if (c >= ' ' && c <= '~' && pos < 40) {
 490                         username[pos++] = c;
 491                         c_write(&c, 1);
 492                     }
 493                     break;
 494                 }
 495             }
 496             c_write("\r\n", 2);
 497             username[strcspn(username, "\n\r")] = '\0';
 498         } else {
 499             char stuff[200];
 500             strncpy(username, cfg.username, 99);
 501             username[99] = '\0';
 502             sprintf(stuff, "Sent username \"%s\".\r\n", username);
 503             c_write(stuff, strlen(stuff));
 504         }
 505         s_wrpkt_start(SSH_CMSG_USER, 4+strlen(username));
 506         {
 507             char userlog[20+sizeof(username)];
 508             sprintf(userlog, "Sent username \"%s\"", username);
 509             logevent(userlog);
 510         }
 511         pktout.body[0] = pktout.body[1] = pktout.body[2] = 0;
 512         pktout.body[3] = strlen(username);
 513         memcpy(pktout.body+4, username, strlen(username));
 514         s_wrpkt();
 515     }
 516
 517     do { crReturnV; } while (!ispkt);
 518
 519     while (pktin.type == SSH_SMSG_FAILURE) {
 520         static char password[100];
 521         static int pos;
 522         static char c;
 523         static int pwpkt_type;
 524
 525         /*
 526          * Show password prompt, having first obtained it via a TIS
 527          * exchange if we're doing TIS authentication.
 528          */
 529         pwpkt_type = SSH_CMSG_AUTH_PASSWORD;
 530         if (pktin.type == SSH_SMSG_FAILURE &&
 531             cfg.try_tis_auth &&
 532             (supported_auths_mask & (1<<SSH_AUTH_TIS))) {
 533             pwpkt_type = SSH_CMSG_AUTH_TIS_RESPONSE;
 534             logevent("Requested TIS authentication");
 535             s_wrpkt_start(SSH_CMSG_AUTH_TIS, 0);
 536             s_wrpkt();
 537             do { crReturnV; } while (!ispkt);
 538             if (pktin.type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
 539                 logevent("TIS authentication declined");
 540                 c_write("TIS authentication refused.\r\n", 29);
 541             } else {
 542                 int challengelen = ((pktin.body[0] << 24) |
 543                                     (pktin.body[1] << 16) |
 544                                     (pktin.body[2] << 8) |
 545                                     (pktin.body[3]));
 546                 logevent("Received TIS challenge");
 547                 c_write(pktin.body+4, challengelen);
 548             }
 549         }
 550         if (pwpkt_type == SSH_CMSG_AUTH_PASSWORD)
 551             c_write("password: ", 10);
 552
 553         pos = 0;
 554         while (pos >= 0) {
 555             do { crReturnV; } while (ispkt);
 556             while (inlen--) switch (c = *in++) {
 557               case 10: case 13:
 558                 password[pos] = 0;
 559                 pos = -1;
 560                 break;
 561               case 8: case 127:
 562                 if (pos > 0)
 563                     pos--;
 564                 break;
 565               case 21: case 27:
 566                 pos = 0;
 567                 break;
 568               case 3: case 4:
 569                 random_save_seed();
 570                 exit(0);
 571                 break;
 572               default:
 573                 if (c >= ' ' && c <= '~' && pos < 40)
 574                     password[pos++] = c;
 575                 break;
 576             }
 577         }
 578         c_write("\r\n", 2);
 579         s_wrpkt_start(pwpkt_type, 4+strlen(password));
 580         pktout.body[0] = pktout.body[1] = pktout.body[2] = 0;
 581         pktout.body[3] = strlen(password);
 582         memcpy(pktout.body+4, password, strlen(password));
 583         s_wrpkt();
 584         logevent("Sent password");
 585         memset(password, 0, strlen(password));
 586         do { crReturnV; } while (!ispkt);
 587         if (pktin.type == 15) {
 588             c_write("Access denied\r\n", 15);
 589             logevent("Authentication refused");
 590         } else if (pktin.type != 14) {
 591             fatalbox("Strange packet received, type %d", pktin.type);
 592         }
 593     }
 594
 595     logevent("Authentication successful");
 596
 597     if (!cfg.nopty) {
 598         i = strlen(cfg.termtype);
 599         s_wrpkt_start(SSH_CMSG_REQUEST_PTY, i+5*4+1);
 600         pktout.body[0] = (i >> 24) & 0xFF;
 601         pktout.body[1] = (i >> 16) & 0xFF;
 602         pktout.body[2] = (i >> 8) & 0xFF;
 603         pktout.body[3] = i & 0xFF;
 604         memcpy(pktout.body+4, cfg.termtype, i);
 605         i += 4;
 606         pktout.body[i++] = (rows >> 24) & 0xFF;
 607         pktout.body[i++] = (rows >> 16) & 0xFF;
 608         pktout.body[i++] = (rows >> 8) & 0xFF;
 609         pktout.body[i++] = rows & 0xFF;
 610         pktout.body[i++] = (cols >> 24) & 0xFF;
 611         pktout.body[i++] = (cols >> 16) & 0xFF;
 612         pktout.body[i++] = (cols >> 8) & 0xFF;
 613         pktout.body[i++] = cols & 0xFF;
 614         memset(pktout.body+i, 0, 9);       /* 0 pixwidth, 0 pixheight, 0.b endofopt */
 615         s_wrpkt();
 616         ssh_state = SSH_STATE_INTERMED;
 617         do { crReturnV; } while (!ispkt);
 618         if (pktin.type != SSH_SMSG_SUCCESS && pktin.type != SSH_SMSG_FAILURE) {
 619             fatalbox("Protocol confusion");
 620         } else if (pktin.type == SSH_SMSG_FAILURE) {
 621             c_write("Server refused to allocate pty\r\n", 32);
 622         }
 623         logevent("Allocated pty");
 624     }
 625
 626     s_wrpkt_start(SSH_CMSG_EXEC_SHELL, 0);
 627     s_wrpkt();
 628     logevent("Started session");
 629
 630     ssh_state = SSH_STATE_SESSION;
 631     if (size_needed)
 632         ssh_size();
 633
 634     while (1) {
 635         crReturnV;
 636         if (ispkt) {
 637             if (pktin.type == SSH_SMSG_STDOUT_DATA ||
 638                 pktin.type == SSH_SMSG_STDERR_DATA) {
 639                 long len = 0;
 640                 for (i = 0; i < 4; i++)
 641                     len = (len << 8) + pktin.body[i];
 642                 c_write(pktin.body+4, len);
 643             } else if (pktin.type == SSH_MSG_DISCONNECT) {
 644                 ssh_state = SSH_STATE_CLOSED;
 645                 logevent("Received disconnect request");
 646             } else if (pktin.type == SSH_SMSG_SUCCESS) {
 647                 /* may be from EXEC_SHELL on some servers */
 648             } else if (pktin.type == SSH_SMSG_FAILURE) {
 649                 /* may be from EXEC_SHELL on some servers
 650                  * if no pty is available or in other odd cases. Ignore */
 651             } else if (pktin.type == SSH_SMSG_EXITSTATUS) {
 652                 s_wrpkt_start(SSH_CMSG_EXIT_CONFIRMATION, 0);
 653                 s_wrpkt();
 654             } else {
 655                 fatalbox("Strange packet received: type %d", pktin.type);
 656             }
 657         } else {
 658             s_wrpkt_start(SSH_CMSG_STDIN_DATA, 4+inlen);
 659             pktout.body[0] = (inlen >> 24) & 0xFF;
 660             pktout.body[1] = (inlen >> 16) & 0xFF;
 661             pktout.body[2] = (inlen >> 8) & 0xFF;
 662             pktout.body[3] = inlen & 0xFF;
 663             memcpy(pktout.body+4, in, inlen);
 664             s_wrpkt();
 665         }
 666     }
 667
 668     crFinishV;
 669 }
 670
 671 /*
 672  * Called to set up the connection. Will arrange for WM_NETEVENT
 673  * messages to be passed to the specified window, whose window
 674  * procedure should then call telnet_msg().
 675  *
 676  * Returns an error message, or NULL on success.
 677  *
 678  * Also places the canonical host name into `realhost'.
 679  */
 680 static char *ssh_init (HWND hwnd, char *host, int port, char **realhost) {
 681     SOCKADDR_IN addr;
 682     struct hostent *h;
 683     unsigned long a;
 684 #ifdef FWHACK
 685     char *FWhost;
 686     int FWport;
 687 #endif
 688
 689     savedhost = malloc(1+strlen(host));
 690     if (!savedhost)
 691         fatalbox("Out of memory");
 692     strcpy(savedhost, host);
 693
 694 #ifdef FWHACK
 695     FWhost = host;
 696     FWport = port;
 697     host = FWSTR;
 698     port = 23;
 699 #endif
 700
 701     /*
 702      * Try to find host.
 703      */
 704     if ( (a = inet_addr(host)) == (unsigned long) INADDR_NONE) {
 705         if ( (h = gethostbyname(host)) == NULL)
 706             switch (WSAGetLastError()) {
 707               case WSAENETDOWN: return "Network is down";
 708               case WSAHOST_NOT_FOUND: case WSANO_DATA:
 709                 return "Host does not exist";
 710               case WSATRY_AGAIN: return "Host not found";
 711               default: return "gethostbyname: unknown error";
 712             }
 713         memcpy (&a, h->h_addr, sizeof(a));
 714         *realhost = h->h_name;
 715     } else
 716         *realhost = host;
 717 #ifdef FWHACK
 718     *realhost = FWhost;
 719 #endif
 720     a = ntohl(a);
 721
 722     if (port < 0)
 723         port = 22;                     /* default ssh port */
 724
 725     /*
 726      * Open socket.
 727      */
 728     s = socket(AF_INET, SOCK_STREAM, 0);
 729     if (s == INVALID_SOCKET)
 730         switch (WSAGetLastError()) {
 731           case WSAENETDOWN: return "Network is down";
 732           case WSAEAFNOSUPPORT: return "TCP/IP support not present";
 733           default: return "socket(): unknown error";
 734         }
 735
 736     /*
 737      * Bind to local address.
 738      */
 739     addr.sin_family = AF_INET;
 740     addr.sin_addr.s_addr = htonl(INADDR_ANY);
 741     addr.sin_port = htons(0);
 742     if (bind (s, (struct sockaddr *)&addr, sizeof(addr)) == SOCKET_ERROR)
 743         switch (WSAGetLastError()) {
 744           case WSAENETDOWN: return "Network is down";
 745           default: return "bind(): unknown error";
 746         }
 747
 748     /*
 749      * Connect to remote address.
 750      */
 751     addr.sin_addr.s_addr = htonl(a);
 752     addr.sin_port = htons((short)port);
 753     if (connect (s, (struct sockaddr *)&addr, sizeof(addr)) == SOCKET_ERROR)
 754         switch (WSAGetLastError()) {
 755           case WSAENETDOWN: return "Network is down";
 756           case WSAECONNREFUSED: return "Connection refused";
 757           case WSAENETUNREACH: return "Network is unreachable";
 758           case WSAEHOSTUNREACH: return "No route to host";
 759           default: return "connect(): unknown error";
 760         }
 761
 762 #ifdef FWHACK
 763     send(s, "connect ", 8, 0);
 764     send(s, FWhost, strlen(FWhost), 0);
 765     {
 766         char buf[20];
 767         sprintf(buf, " %d\n", FWport);
 768         send (s, buf, strlen(buf), 0);
 769     }
 770 #endif
 771
 772     if (!do_ssh_init())
 773         return "Protocol initialisation error";
 774
 775     if (WSAAsyncSelect (s, hwnd, WM_NETEVENT, FD_READ | FD_CLOSE) == SOCKET_ERROR)
 776         switch (WSAGetLastError()) {
 777           case WSAENETDOWN: return "Network is down";
 778           default: return "WSAAsyncSelect(): unknown error";
 779         }
 780
 781     return NULL;
 782 }
 783
 784 /*
 785  * Process a WM_NETEVENT message. Will return 0 if the connection
 786  * has closed, or <0 for a socket error.
 787  */
 788 static int ssh_msg (WPARAM wParam, LPARAM lParam) {
 789     int ret;
 790     char buf[256];
 791
 792     /*
 793      * Because reading less than the whole of the available pending
 794      * data can generate an FD_READ event, we need to allow for the
 795      * possibility that FD_READ may arrive with FD_CLOSE already in
 796      * the queue; so it's possible that we can get here even with s
 797      * invalid. If so, we return 1 and don't worry about it.
 798      */
 799     if (s == INVALID_SOCKET)
 800         return 1;
 801
 802     if (WSAGETSELECTERROR(lParam) != 0)
 803         return -WSAGETSELECTERROR(lParam);
 804
 805     switch (WSAGETSELECTEVENT(lParam)) {
 806       case FD_READ:
 807       case FD_CLOSE:
 808         ret = recv(s, buf, sizeof(buf), 0);
 809         if (ret < 0 && WSAGetLastError() == WSAEWOULDBLOCK)
 810             return 1;
 811         if (ret < 0)                   /* any _other_ error */
 812             return -10000-WSAGetLastError();
 813         if (ret == 0) {
 814             s = INVALID_SOCKET;
 815             return 0;
 816         }
 817         ssh_gotdata (buf, ret);
 818         return 1;
 819     }
 820     return 1;                          /* shouldn't happen, but WTF */
 821 }
 822
 823 /*
 824  * Called to send data down the Telnet connection.
 825  */
 826 static void ssh_send (char *buf, int len) {
 827     if (s == INVALID_SOCKET)
 828         return;
 829
 830     ssh_protocol(buf, len, 0);
 831 }
 832
 833 /*
 834  * Called to set the size of the window from Telnet's POV.
 835  */
 836 static void ssh_size(void) {
 837     switch (ssh_state) {
 838       case SSH_STATE_BEFORE_SIZE:
 839       case SSH_STATE_CLOSED:
 840         break;                         /* do nothing */
 841       case SSH_STATE_INTERMED:
 842         size_needed = TRUE;            /* buffer for later */
 843         break;
 844       case SSH_STATE_SESSION:
 845         if (!cfg.nopty) {
 846             s_wrpkt_start(11, 16);
 847             pktout.body[0] = (rows >> 24) & 0xFF;
 848             pktout.body[1] = (rows >> 16) & 0xFF;
 849             pktout.body[2] = (rows >> 8) & 0xFF;
 850             pktout.body[3] = rows & 0xFF;
 851             pktout.body[4] = (cols >> 24) & 0xFF;
 852             pktout.body[5] = (cols >> 16) & 0xFF;
 853             pktout.body[6] = (cols >> 8) & 0xFF;
 854             pktout.body[7] = cols & 0xFF;
 855             memset(pktout.body+8, 0, 8);
 856             s_wrpkt();
 857         }
 858     }
 859 }
 860
 861 /*
 862  * (Send Telnet special codes)
 863  */
 864 static void ssh_special (Telnet_Special code) {
 865     /* do nothing */
 866 }
 867
 868 Backend ssh_backend = {
 869     ssh_init,
 870     ssh_msg,
 871     ssh_send,
 872     ssh_size,
 873     ssh_special
 874 };