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         auth->xdmseen = NULL;
 115     } else {
 116         assert(proto_id == X11_XDM);
 117         auth->fakeproto = X11_XDM;
 118
 119         /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
 120         auth->fakelen = 16;
 121         for (i = 0; i < 16; i++)
 122             auth->fakedata[i] = (i == 8 ? 0 : random_byte());
 123         auth->xdmseen = newtree234(xdmseen_cmp);
 124     }
 125
 126     /* Now format for the recipient. */
 127     strncpy(proto, x11_authnames[auth->fakeproto], protomaxlen);
 128     ourdata[0] = '\0';
 129     for (i = 0; i < auth->fakelen; i++)
 130         sprintf(ourdata + strlen(ourdata), "%02x", auth->fakedata[i]);
 131     strncpy(data, ourdata, datamaxlen);
 132
 133     return auth;
 134 }
 135
 136 void x11_free_auth(void *authv)
 137 {
 138     struct X11Auth *auth = (struct X11Auth *)authv;
 139     struct XDMSeen *seen;
 140
 141     if (auth->xdmseen != NULL) {
 142         while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
 143             sfree(seen);
 144         freetree234(auth->xdmseen);
 145     }
 146     sfree(auth);
 147 }
 148
 149 /*
 150  * Fetch the real auth data for a given display string, and store
 151  * it in an X11Auth structure. Returns NULL on success, or an error
 152  * string.
 153  */
 154 void x11_get_real_auth(void *authv, char *display)
 155 {
 156     struct X11Auth *auth = (struct X11Auth *)authv;
 157
 158     auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */
 159
 160     auth->reallen = sizeof(auth->realdata);
 161     platform_get_x11_auth(display, &auth->realproto,
 162                           auth->realdata, &auth->reallen);
 163 }
 164
 165 #define XDM_MAXSKEW 20*60      /* 20 minute clock skew should be OK */
 166
 167 static char *x11_verify(unsigned long peer_ip, int peer_port,
 168                         struct X11Auth *auth, char *proto,
 169                         unsigned char *data, int dlen)
 170 {
 171     if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
 172         return "wrong authentication protocol attempted";
 173     if (auth->fakeproto == X11_MIT) {
 174         if (dlen != auth->fakelen)
 175             return "MIT-MAGIC-COOKIE-1 data was wrong length";
 176         if (memcmp(auth->fakedata, data, dlen) != 0)
 177             return "MIT-MAGIC-COOKIE-1 data did not match";
 178     }
 179     if (auth->fakeproto == X11_XDM) {
 180         unsigned long t;
 181         time_t tim;
 182         int i;
 183         struct XDMSeen *seen, *ret;
 184
 185         if (dlen != 24)
 186             return "XDM-AUTHORIZATION-1 data was wrong length";
 187         if (peer_port == -1)
 188             return "cannot do XDM-AUTHORIZATION-1 without remote address data";
 189         des_decrypt_xdmauth(auth->fakedata+9, data, 24);
 190         if (memcmp(auth->fakedata, data, 8) != 0)
 191             return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
 192         if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
 193             return "XDM-AUTHORIZATION-1 data failed check";   /* IP wrong */
 194         if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
 195             return "XDM-AUTHORIZATION-1 data failed check";   /* port wrong */
 196         t = GET_32BIT_MSB_FIRST(data+14);
 197         for (i = 18; i < 24; i++)
 198             if (data[i] != 0)          /* zero padding wrong */
 199                 return "XDM-AUTHORIZATION-1 data failed check";
 200         tim = time(NULL);
 201         if (abs(t - tim) > XDM_MAXSKEW)
 202             return "XDM-AUTHORIZATION-1 time stamp was too far out";
 203         seen = snew(struct XDMSeen);
 204         seen->time = t;
 205         memcpy(seen->clientid, data+8, 6);
 206         assert(auth->xdmseen != NULL);
 207         ret = add234(auth->xdmseen, seen);
 208         if (ret != seen) {
 209             sfree(seen);
 210             return "XDM-AUTHORIZATION-1 data replayed";
 211         }
 212         /* While we're here, purge entries too old to be replayed. */
 213         for (;;) {
 214             seen = index234(auth->xdmseen, 0);
 215             assert(seen != NULL);
 216             if (t - seen->time <= XDM_MAXSKEW)
 217                 break;
 218             sfree(delpos234(auth->xdmseen, 0));
 219         }
 220     }
 221     /* implement other protocols here if ever required */
 222     return NULL;
 223 }
 224
 225 static void x11_log(Plug p, int type, SockAddr addr, int port,
 226                     const char *error_msg, int error_code)
 227 {
 228     /* We have no interface to the logging module here, so we drop these. */
 229 }
 230
 231 static int x11_closing(Plug plug, const char *error_msg, int error_code,
 232                        int calling_back)
 233 {
 234     struct X11Private *pr = (struct X11Private *) plug;
 235
 236     /*
 237      * We have no way to communicate down the forwarded connection,
 238      * so if an error occurred on the socket, we just ignore it
 239      * and treat it like a proper close.
 240      */
 241     sshfwd_close(pr->c);
 242     x11_close(pr->s);
 243     return 1;
 244 }
 245
 246 static int x11_receive(Plug plug, int urgent, char *data, int len)
 247 {
 248     struct X11Private *pr = (struct X11Private *) plug;
 249
 250     if (sshfwd_write(pr->c, data, len) > 0) {
 251         pr->throttled = 1;
 252         sk_set_frozen(pr->s, 1);
 253     }
 254
 255     return 1;
 256 }
 257
 258 static void x11_sent(Plug plug, int bufsize)
 259 {
 260     struct X11Private *pr = (struct X11Private *) plug;
 261
 262     sshfwd_unthrottle(pr->c, bufsize);
 263 }
 264
 265 /*
 266  * When setting up X forwarding, we should send the screen number
 267  * from the specified local display. This function extracts it from
 268  * the display string.
 269  */
 270 int x11_get_screen_number(char *display)
 271 {
 272     int n;
 273
 274     n = strcspn(display, ":");
 275     if (!display[n])
 276         return 0;
 277     n = strcspn(display, ".");
 278     if (!display[n])
 279         return 0;
 280     return atoi(display + n + 1);
 281 }
 282
 283 /* Find the right display, returns an allocated string */
 284 char *x11_display(const char *display) {
 285     char *ret;
 286     if(!display || !*display) {
 287         /* try to find platform-specific local display */
 288         if((ret = platform_get_x_display())==0)
 289             /* plausible default for all platforms */
 290             ret = dupstr(":0");
 291     } else
 292         ret = dupstr(display);
 293     if(ret[0] == ':') {
 294         /* no transport specified, use whatever we think is best */
 295         char *s = dupcat(platform_x11_best_transport, ret, (char *)0);
 296         sfree(ret);
 297         return s;
 298     } else
 299         return ret;
 300 }
 301
 302 /*
 303  * Called to set up the raw connection.
 304  *
 305  * Returns an error message, or NULL on success.
 306  * also, fills the SocketsStructure
 307  */
 308 const char *x11_init(Socket * s, char *display, void *c, void *auth,
 309                      const char *peeraddr, int peerport, const Config *cfg)
 310 {
 311     static const struct plug_function_table fn_table = {
 312         x11_log,
 313         x11_closing,
 314         x11_receive,
 315         x11_sent,
 316         NULL
 317     };
 318
 319     SockAddr addr;
 320     int port;
 321     const char *err;
 322     char *dummy_realhost;
 323     char host[128];
 324     int n, displaynum;
 325     struct X11Private *pr;
 326
 327     /* default display */
 328     display = x11_display(display);
 329     /*
 330      * Split up display name into host and display-number parts.
 331      */
 332     n = strcspn(display, ":");
 333     assert(n != 0);             /* x11_display() promises this */
 334     if (display[n])
 335         displaynum = atoi(display + n + 1);
 336     else
 337         displaynum = 0;                /* sensible default */
 338     if (n > sizeof(host) - 1)
 339         n = sizeof(host) - 1;
 340     strncpy(host, display, n);
 341     host[n] = '\0';
 342     sfree(display);
 343
 344     if(!strcmp(host, "unix")) {
 345         /* use AF_UNIX sockets (doesn't make sense on all platforms) */
 346         addr = platform_get_x11_unix_address(displaynum,
 347                                              &dummy_realhost);
 348         port = 0;               /* to show we are not confused */
 349     } else {
 350         port = 6000 + displaynum;
 351
 352         /*
 353          * Try to find host.
 354          */
 355         addr = name_lookup(host, port, &dummy_realhost, cfg, ADDRTYPE_UNSPEC);
 356         if ((err = sk_addr_error(addr)) != NULL) {
 357             sk_addr_free(addr);
 358             return err;
 359         }
 360     }
 361
 362     /*
 363      * Open socket.
 364      */
 365     pr = snew(struct X11Private);
 366     pr->fn = &fn_table;
 367     pr->auth_protocol = NULL;
 368     pr->auth = (struct X11Auth *)auth;
 369     pr->verified = 0;
 370     pr->data_read = 0;
 371     pr->throttled = pr->throttle_override = 0;
 372     pr->c = c;
 373
 374     pr->s = *s = new_connection(addr, dummy_realhost, port,
 375                                 0, 1, 0, 0, (Plug) pr, cfg);
 376     if ((err = sk_socket_error(*s)) != NULL) {
 377         sfree(pr);
 378         return err;
 379     }
 380
 381     /*
 382      * See if we can make sense of the peer address we were given.
 383      */
 384     {
 385         int i[4];
 386         if (peeraddr &&
 387             4 == sscanf(peeraddr, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
 388             pr->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
 389             pr->peer_port = peerport;
 390         } else {
 391             pr->peer_ip = 0;
 392             pr->peer_port = -1;
 393         }
 394     }
 395
 396     sk_set_private_ptr(*s, pr);
 397     return NULL;
 398 }
 399
 400 void x11_close(Socket s)
 401 {
 402     struct X11Private *pr;
 403     if (!s)
 404         return;
 405     pr = (struct X11Private *) sk_get_private_ptr(s);
 406     if (pr->auth_protocol) {
 407         sfree(pr->auth_protocol);
 408         sfree(pr->auth_data);
 409     }
 410
 411     sfree(pr);
 412
 413     sk_close(s);
 414 }
 415
 416 void x11_unthrottle(Socket s)
 417 {
 418     struct X11Private *pr;
 419     if (!s)
 420         return;
 421     pr = (struct X11Private *) sk_get_private_ptr(s);
 422
 423     pr->throttled = 0;
 424     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 425 }
 426
 427 void x11_override_throttle(Socket s, int enable)
 428 {
 429     struct X11Private *pr;
 430     if (!s)
 431         return;
 432     pr = (struct X11Private *) sk_get_private_ptr(s);
 433
 434     pr->throttle_override = enable;
 435     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 436 }
 437
 438 /*
 439  * Called to send data down the raw connection.
 440  */
 441 int x11_send(Socket s, char *data, int len)
 442 {
 443     struct X11Private *pr;
 444     if (!s)
 445         return 0;
 446     pr = (struct X11Private *) sk_get_private_ptr(s);
 447
 448     /*
 449      * Read the first packet.
 450      */
 451     while (len > 0 && pr->data_read < 12)
 452         pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
 453     if (pr->data_read < 12)
 454         return 0;
 455
 456     /*
 457      * If we have not allocated the auth_protocol and auth_data
 458      * strings, do so now.
 459      */
 460     if (!pr->auth_protocol) {
 461         pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
 462         pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
 463         pr->auth_psize = (pr->auth_plen + 3) & ~3;
 464         pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
 465         /* Leave room for a terminating zero, to make our lives easier. */
 466         pr->auth_protocol = snewn(pr->auth_psize + 1, char);
 467         pr->auth_data = snewn(pr->auth_dsize, unsigned char);
 468     }
 469
 470     /*
 471      * Read the auth_protocol and auth_data strings.
 472      */
 473     while (len > 0 && pr->data_read < 12 + pr->auth_psize)
 474         pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
 475     while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 476         pr->auth_data[pr->data_read++ - 12 -
 477                       pr->auth_psize] = (unsigned char) (len--, *data++);
 478     if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 479         return 0;
 480
 481     /*
 482      * If we haven't verified the authentication, do so now.
 483      */
 484     if (!pr->verified) {
 485         char *err;
 486
 487         pr->auth_protocol[pr->auth_plen] = '\0';        /* ASCIZ */
 488         err = x11_verify(pr->peer_ip, pr->peer_port,
 489                          pr->auth, pr->auth_protocol,
 490                          pr->auth_data, pr->auth_dlen);
 491
 492         /*
 493          * If authentication failed, construct and send an error
 494          * packet, then terminate the connection.
 495          */
 496         if (err) {
 497             char *message;
 498             int msglen, msgsize;
 499             unsigned char *reply;
 500
 501             message = dupprintf("PuTTY X11 proxy: %s", err);
 502             msglen = strlen(message);
 503             reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */
 504             msgsize = (msglen + 3) & ~3;
 505             reply[0] = 0;              /* failure */
 506             reply[1] = msglen;         /* length of reason string */
 507             memcpy(reply + 2, pr->firstpkt + 2, 4);     /* major/minor proto vsn */
 508             PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
 509             memset(reply + 8, 0, msgsize);
 510             memcpy(reply + 8, message, msglen);
 511             sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
 512             sshfwd_close(pr->c);
 513             x11_close(s);
 514             sfree(reply);
 515             sfree(message);
 516             return 0;
 517         }
 518
 519         /*
 520          * Now we know we're going to accept the connection. Strip
 521          * the fake auth data, and optionally put real auth data in
 522          * instead.
 523          */
 524         {
 525             char realauthdata[64];
 526             int realauthlen = 0;
 527             int authstrlen = strlen(x11_authnames[pr->auth->realproto]);
 528             int buflen;
 529             static const char zeroes[4] = { 0,0,0,0 };
 530             void *buf;
 531
 532             if (pr->auth->realproto == X11_MIT) {
 533                 assert(pr->auth->reallen <= lenof(realauthdata));
 534                 realauthlen = pr->auth->reallen;
 535                 memcpy(realauthdata, pr->auth->realdata, realauthlen);
 536             } else if (pr->auth->realproto == X11_XDM &&
 537                        pr->auth->reallen == 16 &&
 538                        ((buf = sk_getxdmdata(s, &buflen))!=0)) {
 539                 time_t t;
 540                 realauthlen = (buflen+12+7) & ~7;
 541                 assert(realauthlen <= lenof(realauthdata));
 542                 memset(realauthdata, 0, realauthlen);
 543                 memcpy(realauthdata, pr->auth->realdata, 8);
 544                 memcpy(realauthdata+8, buf, buflen);
 545                 t = time(NULL);
 546                 PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t);
 547                 des_encrypt_xdmauth(pr->auth->realdata+9,
 548                                     (unsigned char *)realauthdata,
 549                                     realauthlen);
 550                 sfree(buf);
 551             }
 552             /* implement other auth methods here if required */
 553
 554             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
 555             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
 556
 557             sk_write(s, (char *)pr->firstpkt, 12);
 558
 559             if (authstrlen) {
 560                 sk_write(s, x11_authnames[pr->auth->realproto], authstrlen);
 561                 sk_write(s, zeroes, 3 & (-authstrlen));
 562             }
 563             if (realauthlen) {
 564                 sk_write(s, realauthdata, realauthlen);
 565                 sk_write(s, zeroes, 3 & (-realauthlen));
 566             }
 567         }
 568         pr->verified = 1;
 569     }
 570
 571     /*
 572      * After initialisation, just copy data simply.
 573      */
 574
 575     return sk_write(s, data, len);
 576 }