git.distorted.org.uk Git - u/mdw/putty/blob - x11fwd.c

   1 /*
   2  * Platform-independent bits of X11 forwarding.
   3  */
   4
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7 #include <assert.h>
   8 #include <time.h>
   9
  10 #include "putty.h"
  11 #include "ssh.h"
  12 #include "tree234.h"
  13
  14 #define GET_32BIT_LSB_FIRST(cp) \
  15   (((unsigned long)(unsigned char)(cp)[0]) | \
  16   ((unsigned long)(unsigned char)(cp)[1] << 8) | \
  17   ((unsigned long)(unsigned char)(cp)[2] << 16) | \
  18   ((unsigned long)(unsigned char)(cp)[3] << 24))
  19
  20 #define PUT_32BIT_LSB_FIRST(cp, value) ( \
  21   (cp)[0] = (char)(value), \
  22   (cp)[1] = (char)((value) >> 8), \
  23   (cp)[2] = (char)((value) >> 16), \
  24   (cp)[3] = (char)((value) >> 24) )
  25
  26 #define GET_16BIT_LSB_FIRST(cp) \
  27   (((unsigned long)(unsigned char)(cp)[0]) | \
  28   ((unsigned long)(unsigned char)(cp)[1] << 8))
  29
  30 #define PUT_16BIT_LSB_FIRST(cp, value) ( \
  31   (cp)[0] = (char)(value), \
  32   (cp)[1] = (char)((value) >> 8) )
  33
  34 #define GET_32BIT_MSB_FIRST(cp) \
  35   (((unsigned long)(unsigned char)(cp)[0] << 24) | \
  36   ((unsigned long)(unsigned char)(cp)[1] << 16) | \
  37   ((unsigned long)(unsigned char)(cp)[2] << 8) | \
  38   ((unsigned long)(unsigned char)(cp)[3]))
  39
  40 #define PUT_32BIT_MSB_FIRST(cp, value) ( \
  41   (cp)[0] = (char)((value) >> 24), \
  42   (cp)[1] = (char)((value) >> 16), \
  43   (cp)[2] = (char)((value) >> 8), \
  44   (cp)[3] = (char)(value) )
  45
  46 #define GET_16BIT_MSB_FIRST(cp) \
  47   (((unsigned long)(unsigned char)(cp)[0] << 8) | \
  48   ((unsigned long)(unsigned char)(cp)[1]))
  49
  50 #define PUT_16BIT_MSB_FIRST(cp, value) ( \
  51   (cp)[0] = (char)((value) >> 8), \
  52   (cp)[1] = (char)(value) )
  53
  54 #define GET_16BIT(endian, cp) \
  55   (endian=='B' ? GET_16BIT_MSB_FIRST(cp) : GET_16BIT_LSB_FIRST(cp))
  56
  57 #define PUT_16BIT(endian, cp, val) \
  58   (endian=='B' ? PUT_16BIT_MSB_FIRST(cp, val) : PUT_16BIT_LSB_FIRST(cp, val))
  59
  60 const char *const x11_authnames[] = {
  61     "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1"
  62 };
  63
  64 struct XDMSeen {
  65     unsigned int time;
  66     unsigned char clientid[6];
  67 };
  68
  69 struct X11Auth {
  70     unsigned char fakedata[64], realdata[64];
  71     int fakeproto, realproto;
  72     int fakelen, reallen;
  73     tree234 *xdmseen;
  74 };
  75
  76 struct X11Private {
  77     const struct plug_function_table *fn;
  78     /* the above variable absolutely *must* be the first in this structure */
  79     unsigned char firstpkt[12];        /* first X data packet */
  80     struct X11Auth *auth;
  81     char *auth_protocol;
  82     unsigned char *auth_data;
  83     int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
  84     int verified;
  85     int throttled, throttle_override;
  86     unsigned long peer_ip;
  87     int peer_port;
  88     void *c;                           /* data used by ssh.c */
  89     Socket s;
  90 };
  91
  92 static int xdmseen_cmp(void *a, void *b)
  93 {
  94     struct XDMSeen *sa = a, *sb = b;
  95     return sa->time > sb->time ? 1 :
  96            sa->time < sb->time ? -1 :
  97            memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
  98 }
  99
 100 void *x11_invent_auth(char *proto, int protomaxlen,
 101                       char *data, int datamaxlen, int proto_id)
 102 {
 103     struct X11Auth *auth = snew(struct X11Auth);
 104     char ourdata[64];
 105     int i;
 106
 107     if (proto_id == X11_MIT) {
 108         auth->fakeproto = X11_MIT;
 109
 110         /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
 111         auth->fakelen = 16;
 112         for (i = 0; i < 16; i++)
 113             auth->fakedata[i] = random_byte();
 114     } else {
 115         assert(proto_id == X11_XDM);
 116         auth->fakeproto = X11_XDM;
 117
 118         /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
 119         auth->fakelen = 16;
 120         for (i = 0; i < 16; i++)
 121             auth->fakedata[i] = (i == 8 ? 0 : random_byte());
 122         auth->xdmseen = newtree234(xdmseen_cmp);
 123     }
 124
 125     /* Now format for the recipient. */
 126     strncpy(proto, x11_authnames[auth->fakeproto], protomaxlen);
 127     ourdata[0] = '\0';
 128     for (i = 0; i < auth->fakelen; i++)
 129         sprintf(ourdata + strlen(ourdata), "%02x", auth->fakedata[i]);
 130     strncpy(data, ourdata, datamaxlen);
 131
 132     return auth;
 133 }
 134
 135 void x11_free_auth(void *authv)
 136 {
 137     struct X11Auth *auth = (struct X11Auth *)authv;
 138     struct XDMSeen *seen;
 139
 140     if (auth->xdmseen != NULL) {
 141         while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
 142             sfree(seen);
 143         freetree234(auth->xdmseen);
 144     }
 145     sfree(auth);
 146 }
 147
 148 /*
 149  * Fetch the real auth data for a given display string, and store
 150  * it in an X11Auth structure. Returns NULL on success, or an error
 151  * string.
 152  */
 153 void x11_get_real_auth(void *authv, char *display)
 154 {
 155     struct X11Auth *auth = (struct X11Auth *)authv;
 156
 157     auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */
 158
 159     auth->reallen = sizeof(auth->realdata);
 160     platform_get_x11_auth(display, &auth->realproto,
 161                           auth->realdata, &auth->reallen);
 162 }
 163
 164 #define XDM_MAXSKEW 20*60      /* 20 minute clock skew should be OK */
 165
 166 static char *x11_verify(unsigned long peer_ip, int peer_port,
 167                         struct X11Auth *auth, char *proto,
 168                         unsigned char *data, int dlen)
 169 {
 170     if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
 171         return "wrong authentication protocol attempted";
 172     if (auth->fakeproto == X11_MIT) {
 173         if (dlen != auth->fakelen)
 174             return "MIT-MAGIC-COOKIE-1 data was wrong length";
 175         if (memcmp(auth->fakedata, data, dlen) != 0)
 176             return "MIT-MAGIC-COOKIE-1 data did not match";
 177     }
 178     if (auth->fakeproto == X11_XDM) {
 179         unsigned long t;
 180         time_t tim;
 181         int i;
 182         struct XDMSeen *seen, *ret;
 183
 184         if (dlen != 24)
 185             return "XDM-AUTHORIZATION-1 data was wrong length";
 186         if (peer_port == -1)
 187             return "cannot do XDM-AUTHORIZATION-1 without remote address data";
 188         des_decrypt_xdmauth(auth->fakedata+9, data, 24);
 189         if (memcmp(auth->fakedata, data, 8) != 0)
 190             return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
 191         if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
 192             return "XDM-AUTHORIZATION-1 data failed check";   /* IP wrong */
 193         if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
 194             return "XDM-AUTHORIZATION-1 data failed check";   /* port wrong */
 195         t = GET_32BIT_MSB_FIRST(data+14);
 196         for (i = 18; i < 24; i++)
 197             if (data[i] != 0)          /* zero padding wrong */
 198                 return "XDM-AUTHORIZATION-1 data failed check";
 199         tim = time(NULL);
 200         if (abs(t - tim) > XDM_MAXSKEW)
 201             return "XDM-AUTHORIZATION-1 time stamp was too far out";
 202         seen = snew(struct XDMSeen);
 203         seen->time = t;
 204         memcpy(seen->clientid, data+8, 6);
 205         assert(auth->xdmseen != NULL);
 206         ret = add234(auth->xdmseen, seen);
 207         if (ret != seen) {
 208             sfree(seen);
 209             return "XDM-AUTHORIZATION-1 data replayed";
 210         }
 211         /* While we're here, purge entries too old to be replayed. */
 212         for (;;) {
 213             seen = index234(auth->xdmseen, 0);
 214             assert(seen != NULL);
 215             if (t - seen->time <= XDM_MAXSKEW)
 216                 break;
 217             sfree(delpos234(auth->xdmseen, 0));
 218         }
 219     }
 220     /* implement other protocols here if ever required */
 221     return NULL;
 222 }
 223
 224 static void x11_log(Plug p, int type, SockAddr addr, int port,
 225                     const char *error_msg, int error_code)
 226 {
 227     /* We have no interface to the logging module here, so we drop these. */
 228 }
 229
 230 static int x11_closing(Plug plug, const char *error_msg, int error_code,
 231                        int calling_back)
 232 {
 233     struct X11Private *pr = (struct X11Private *) plug;
 234
 235     /*
 236      * We have no way to communicate down the forwarded connection,
 237      * so if an error occurred on the socket, we just ignore it
 238      * and treat it like a proper close.
 239      */
 240     sshfwd_close(pr->c);
 241     x11_close(pr->s);
 242     return 1;
 243 }
 244
 245 static int x11_receive(Plug plug, int urgent, char *data, int len)
 246 {
 247     struct X11Private *pr = (struct X11Private *) plug;
 248
 249     if (sshfwd_write(pr->c, data, len) > 0) {
 250         pr->throttled = 1;
 251         sk_set_frozen(pr->s, 1);
 252     }
 253
 254     return 1;
 255 }
 256
 257 static void x11_sent(Plug plug, int bufsize)
 258 {
 259     struct X11Private *pr = (struct X11Private *) plug;
 260
 261     sshfwd_unthrottle(pr->c, bufsize);
 262 }
 263
 264 /*
 265  * When setting up X forwarding, we should send the screen number
 266  * from the specified local display. This function extracts it from
 267  * the display string.
 268  */
 269 int x11_get_screen_number(char *display)
 270 {
 271     int n;
 272
 273     n = strcspn(display, ":");
 274     if (!display[n])
 275         return 0;
 276     n = strcspn(display, ".");
 277     if (!display[n])
 278         return 0;
 279     return atoi(display + n + 1);
 280 }
 281
 282 /* Find the right display, returns an allocated string */
 283 char *x11_display(const char *display) {
 284     char *ret;
 285     if(!display || !*display) {
 286         /* try to find platform-specific local display */
 287         if((ret = platform_get_x_display())==0)
 288             /* plausible default for all platforms */
 289             ret = dupstr(":0");
 290     } else
 291         ret = dupstr(display);
 292     if(ret[0] == ':') {
 293         /* no transport specified, use whatever we think is best */
 294         char *s = dupcat(platform_x11_best_transport, ret, (char *)0);
 295         sfree(ret);
 296         return s;
 297     } else
 298         return ret;
 299 }
 300
 301 /*
 302  * Called to set up the raw connection.
 303  *
 304  * Returns an error message, or NULL on success.
 305  * also, fills the SocketsStructure
 306  */
 307 const char *x11_init(Socket * s, char *display, void *c, void *auth,
 308                      const char *peeraddr, int peerport, const Config *cfg)
 309 {
 310     static const struct plug_function_table fn_table = {
 311         x11_log,
 312         x11_closing,
 313         x11_receive,
 314         x11_sent,
 315         NULL
 316     };
 317
 318     SockAddr addr;
 319     int port;
 320     const char *err;
 321     char *dummy_realhost;
 322     char host[128];
 323     int n, displaynum;
 324     struct X11Private *pr;
 325
 326     /* default display */
 327     display = x11_display(display);
 328     /*
 329      * Split up display name into host and display-number parts.
 330      */
 331     n = strcspn(display, ":");
 332     assert(n != 0);             /* x11_display() promises this */
 333     if (display[n])
 334         displaynum = atoi(display + n + 1);
 335     else
 336         displaynum = 0;                /* sensible default */
 337     if (n > sizeof(host) - 1)
 338         n = sizeof(host) - 1;
 339     strncpy(host, display, n);
 340     host[n] = '\0';
 341     sfree(display);
 342
 343     if(!strcmp(host, "unix")) {
 344         /* use AF_UNIX sockets (doesn't make sense on all platforms) */
 345         addr = platform_get_x11_unix_address(displaynum,
 346                                              &dummy_realhost);
 347         port = 0;               /* to show we are not confused */
 348     } else {
 349         port = 6000 + displaynum;
 350
 351         /*
 352          * Try to find host.
 353          */
 354         addr = name_lookup(host, port, &dummy_realhost, cfg, ADDRTYPE_UNSPEC);
 355         if ((err = sk_addr_error(addr)) != NULL) {
 356             sk_addr_free(addr);
 357             return err;
 358         }
 359     }
 360
 361     /*
 362      * Open socket.
 363      */
 364     pr = snew(struct X11Private);
 365     pr->fn = &fn_table;
 366     pr->auth_protocol = NULL;
 367     pr->auth = (struct X11Auth *)auth;
 368     pr->verified = 0;
 369     pr->data_read = 0;
 370     pr->throttled = pr->throttle_override = 0;
 371     pr->c = c;
 372
 373     pr->s = *s = new_connection(addr, dummy_realhost, port,
 374                                 0, 1, 0, 0, (Plug) pr, cfg);
 375     if ((err = sk_socket_error(*s)) != NULL) {
 376         sfree(pr);
 377         return err;
 378     }
 379
 380     /*
 381      * See if we can make sense of the peer address we were given.
 382      */
 383     {
 384         int i[4];
 385         if (peeraddr &&
 386             4 == sscanf(peeraddr, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
 387             pr->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
 388             pr->peer_port = peerport;
 389         } else {
 390             pr->peer_ip = 0;
 391             pr->peer_port = -1;
 392         }
 393     }
 394
 395     sk_set_private_ptr(*s, pr);
 396     return NULL;
 397 }
 398
 399 void x11_close(Socket s)
 400 {
 401     struct X11Private *pr;
 402     if (!s)
 403         return;
 404     pr = (struct X11Private *) sk_get_private_ptr(s);
 405     if (pr->auth_protocol) {
 406         sfree(pr->auth_protocol);
 407         sfree(pr->auth_data);
 408     }
 409
 410     sfree(pr);
 411
 412     sk_close(s);
 413 }
 414
 415 void x11_unthrottle(Socket s)
 416 {
 417     struct X11Private *pr;
 418     if (!s)
 419         return;
 420     pr = (struct X11Private *) sk_get_private_ptr(s);
 421
 422     pr->throttled = 0;
 423     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 424 }
 425
 426 void x11_override_throttle(Socket s, int enable)
 427 {
 428     struct X11Private *pr;
 429     if (!s)
 430         return;
 431     pr = (struct X11Private *) sk_get_private_ptr(s);
 432
 433     pr->throttle_override = enable;
 434     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 435 }
 436
 437 /*
 438  * Called to send data down the raw connection.
 439  */
 440 int x11_send(Socket s, char *data, int len)
 441 {
 442     struct X11Private *pr;
 443     if (!s)
 444         return 0;
 445     pr = (struct X11Private *) sk_get_private_ptr(s);
 446
 447     /*
 448      * Read the first packet.
 449      */
 450     while (len > 0 && pr->data_read < 12)
 451         pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
 452     if (pr->data_read < 12)
 453         return 0;
 454
 455     /*
 456      * If we have not allocated the auth_protocol and auth_data
 457      * strings, do so now.
 458      */
 459     if (!pr->auth_protocol) {
 460         pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
 461         pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
 462         pr->auth_psize = (pr->auth_plen + 3) & ~3;
 463         pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
 464         /* Leave room for a terminating zero, to make our lives easier. */
 465         pr->auth_protocol = snewn(pr->auth_psize + 1, char);
 466         pr->auth_data = snewn(pr->auth_dsize, unsigned char);
 467     }
 468
 469     /*
 470      * Read the auth_protocol and auth_data strings.
 471      */
 472     while (len > 0 && pr->data_read < 12 + pr->auth_psize)
 473         pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
 474     while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 475         pr->auth_data[pr->data_read++ - 12 -
 476                       pr->auth_psize] = (unsigned char) (len--, *data++);
 477     if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 478         return 0;
 479
 480     /*
 481      * If we haven't verified the authentication, do so now.
 482      */
 483     if (!pr->verified) {
 484         char *err;
 485
 486         pr->auth_protocol[pr->auth_plen] = '\0';        /* ASCIZ */
 487         err = x11_verify(pr->peer_ip, pr->peer_port,
 488                          pr->auth, pr->auth_protocol,
 489                          pr->auth_data, pr->auth_dlen);
 490
 491         /*
 492          * If authentication failed, construct and send an error
 493          * packet, then terminate the connection.
 494          */
 495         if (err) {
 496             char *message;
 497             int msglen, msgsize;
 498             unsigned char *reply;
 499
 500             message = dupprintf("PuTTY X11 proxy: %s", err);
 501             msglen = strlen(message);
 502             reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */
 503             msgsize = (msglen + 3) & ~3;
 504             reply[0] = 0;              /* failure */
 505             reply[1] = msglen;         /* length of reason string */
 506             memcpy(reply + 2, pr->firstpkt + 2, 4);     /* major/minor proto vsn */
 507             PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
 508             memset(reply + 8, 0, msgsize);
 509             memcpy(reply + 8, message, msglen);
 510             sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
 511             sshfwd_close(pr->c);
 512             x11_close(s);
 513             sfree(reply);
 514             sfree(message);
 515             return 0;
 516         }
 517
 518         /*
 519          * Now we know we're going to accept the connection. Strip
 520          * the fake auth data, and optionally put real auth data in
 521          * instead.
 522          */
 523         {
 524             char realauthdata[64];
 525             int realauthlen = 0;
 526             int authstrlen = strlen(x11_authnames[pr->auth->realproto]);
 527             int buflen;
 528             static const char zeroes[4] = { 0,0,0,0 };
 529             void *buf;
 530
 531             if (pr->auth->realproto == X11_MIT) {
 532                 assert(pr->auth->reallen <= lenof(realauthdata));
 533                 realauthlen = pr->auth->reallen;
 534                 memcpy(realauthdata, pr->auth->realdata, realauthlen);
 535             } else if (pr->auth->realproto == X11_XDM &&
 536                        pr->auth->reallen == 16 &&
 537                        ((buf = sk_getxdmdata(s, &buflen))!=0)) {
 538                 time_t t;
 539                 realauthlen = (buflen+12+7) & ~7;
 540                 assert(realauthlen <= lenof(realauthdata));
 541                 memset(realauthdata, 0, realauthlen);
 542                 memcpy(realauthdata, pr->auth->realdata, 8);
 543                 memcpy(realauthdata+8, buf, buflen);
 544                 t = time(NULL);
 545                 PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t);
 546                 des_encrypt_xdmauth(pr->auth->realdata+9,
 547                                     (unsigned char *)realauthdata,
 548                                     realauthlen);
 549                 sfree(buf);
 550             }
 551             /* implement other auth methods here if required */
 552
 553             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
 554             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
 555
 556             sk_write(s, (char *)pr->firstpkt, 12);
 557
 558             if (authstrlen) {
 559                 sk_write(s, x11_authnames[pr->auth->realproto], authstrlen);
 560                 sk_write(s, zeroes, 3 & (-authstrlen));
 561             }
 562             if (realauthlen) {
 563                 sk_write(s, realauthdata, realauthlen);
 564                 sk_write(s, zeroes, 3 & (-realauthlen));
 565             }
 566         }
 567         pr->verified = 1;
 568     }
 569
 570     /*
 571      * After initialisation, just copy data simply.
 572      */
 573
 574     return sk_write(s, data, len);
 575 }