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_16BIT(endian, cp) \
  15   (endian=='B' ? GET_16BIT_MSB_FIRST(cp) : GET_16BIT_LSB_FIRST(cp))
  16
  17 #define PUT_16BIT(endian, cp, val) \
  18   (endian=='B' ? PUT_16BIT_MSB_FIRST(cp, val) : PUT_16BIT_LSB_FIRST(cp, val))
  19
  20 const char *const x11_authnames[] = {
  21     "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1"
  22 };
  23
  24 struct XDMSeen {
  25     unsigned int time;
  26     unsigned char clientid[6];
  27 };
  28
  29 struct X11Auth {
  30     unsigned char fakedata[64], realdata[64];
  31     int fakeproto, realproto;
  32     int fakelen, reallen;
  33     tree234 *xdmseen;
  34 };
  35
  36 struct X11Private {
  37     const struct plug_function_table *fn;
  38     /* the above variable absolutely *must* be the first in this structure */
  39     unsigned char firstpkt[12];        /* first X data packet */
  40     struct X11Auth *auth;
  41     char *auth_protocol;
  42     unsigned char *auth_data;
  43     int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
  44     int verified;
  45     int throttled, throttle_override;
  46     unsigned long peer_ip;
  47     int peer_port;
  48     void *c;                           /* data used by ssh.c */
  49     Socket s;
  50 };
  51
  52 static int xdmseen_cmp(void *a, void *b)
  53 {
  54     struct XDMSeen *sa = a, *sb = b;
  55     return sa->time > sb->time ? 1 :
  56            sa->time < sb->time ? -1 :
  57            memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
  58 }
  59
  60 void *x11_invent_auth(char *proto, int protomaxlen,
  61                       char *data, int datamaxlen, int proto_id)
  62 {
  63     struct X11Auth *auth = snew(struct X11Auth);
  64     char ourdata[64];
  65     int i;
  66
  67     if (proto_id == X11_MIT) {
  68         auth->fakeproto = X11_MIT;
  69
  70         /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
  71         auth->fakelen = 16;
  72         for (i = 0; i < 16; i++)
  73             auth->fakedata[i] = random_byte();
  74         auth->xdmseen = NULL;
  75     } else {
  76         assert(proto_id == X11_XDM);
  77         auth->fakeproto = X11_XDM;
  78
  79         /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
  80         auth->fakelen = 16;
  81         for (i = 0; i < 16; i++)
  82             auth->fakedata[i] = (i == 8 ? 0 : random_byte());
  83         auth->xdmseen = newtree234(xdmseen_cmp);
  84     }
  85
  86     /* Now format for the recipient. */
  87     strncpy(proto, x11_authnames[auth->fakeproto], protomaxlen);
  88     ourdata[0] = '\0';
  89     for (i = 0; i < auth->fakelen; i++)
  90         sprintf(ourdata + strlen(ourdata), "%02x", auth->fakedata[i]);
  91     strncpy(data, ourdata, datamaxlen);
  92
  93     return auth;
  94 }
  95
  96 void x11_free_auth(void *authv)
  97 {
  98     struct X11Auth *auth = (struct X11Auth *)authv;
  99     struct XDMSeen *seen;
 100
 101     if (auth->xdmseen != NULL) {
 102         while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
 103             sfree(seen);
 104         freetree234(auth->xdmseen);
 105     }
 106     sfree(auth);
 107 }
 108
 109 /*
 110  * Fetch the real auth data for a given display string, and store
 111  * it in an X11Auth structure. Returns NULL on success, or an error
 112  * string.
 113  */
 114 void x11_get_real_auth(void *authv, char *display)
 115 {
 116     struct X11Auth *auth = (struct X11Auth *)authv;
 117
 118     auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */
 119
 120     auth->reallen = sizeof(auth->realdata);
 121     platform_get_x11_auth(display, &auth->realproto,
 122                           auth->realdata, &auth->reallen);
 123 }
 124
 125 #define XDM_MAXSKEW 20*60      /* 20 minute clock skew should be OK */
 126
 127 static char *x11_verify(unsigned long peer_ip, int peer_port,
 128                         struct X11Auth *auth, char *proto,
 129                         unsigned char *data, int dlen)
 130 {
 131     if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
 132         return "wrong authentication protocol attempted";
 133     if (auth->fakeproto == X11_MIT) {
 134         if (dlen != auth->fakelen)
 135             return "MIT-MAGIC-COOKIE-1 data was wrong length";
 136         if (memcmp(auth->fakedata, data, dlen) != 0)
 137             return "MIT-MAGIC-COOKIE-1 data did not match";
 138     }
 139     if (auth->fakeproto == X11_XDM) {
 140         unsigned long t;
 141         time_t tim;
 142         int i;
 143         struct XDMSeen *seen, *ret;
 144
 145         if (dlen != 24)
 146             return "XDM-AUTHORIZATION-1 data was wrong length";
 147         if (peer_port == -1)
 148             return "cannot do XDM-AUTHORIZATION-1 without remote address data";
 149         des_decrypt_xdmauth(auth->fakedata+9, data, 24);
 150         if (memcmp(auth->fakedata, data, 8) != 0)
 151             return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
 152         if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
 153             return "XDM-AUTHORIZATION-1 data failed check";   /* IP wrong */
 154         if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
 155             return "XDM-AUTHORIZATION-1 data failed check";   /* port wrong */
 156         t = GET_32BIT_MSB_FIRST(data+14);
 157         for (i = 18; i < 24; i++)
 158             if (data[i] != 0)          /* zero padding wrong */
 159                 return "XDM-AUTHORIZATION-1 data failed check";
 160         tim = time(NULL);
 161         if (abs(t - tim) > XDM_MAXSKEW)
 162             return "XDM-AUTHORIZATION-1 time stamp was too far out";
 163         seen = snew(struct XDMSeen);
 164         seen->time = t;
 165         memcpy(seen->clientid, data+8, 6);
 166         assert(auth->xdmseen != NULL);
 167         ret = add234(auth->xdmseen, seen);
 168         if (ret != seen) {
 169             sfree(seen);
 170             return "XDM-AUTHORIZATION-1 data replayed";
 171         }
 172         /* While we're here, purge entries too old to be replayed. */
 173         for (;;) {
 174             seen = index234(auth->xdmseen, 0);
 175             assert(seen != NULL);
 176             if (t - seen->time <= XDM_MAXSKEW)
 177                 break;
 178             sfree(delpos234(auth->xdmseen, 0));
 179         }
 180     }
 181     /* implement other protocols here if ever required */
 182     return NULL;
 183 }
 184
 185 static void x11_log(Plug p, int type, SockAddr addr, int port,
 186                     const char *error_msg, int error_code)
 187 {
 188     /* We have no interface to the logging module here, so we drop these. */
 189 }
 190
 191 static int x11_closing(Plug plug, const char *error_msg, int error_code,
 192                        int calling_back)
 193 {
 194     struct X11Private *pr = (struct X11Private *) plug;
 195
 196     /*
 197      * We have no way to communicate down the forwarded connection,
 198      * so if an error occurred on the socket, we just ignore it
 199      * and treat it like a proper close.
 200      */
 201     sshfwd_close(pr->c);
 202     x11_close(pr->s);
 203     return 1;
 204 }
 205
 206 static int x11_receive(Plug plug, int urgent, char *data, int len)
 207 {
 208     struct X11Private *pr = (struct X11Private *) plug;
 209
 210     if (sshfwd_write(pr->c, data, len) > 0) {
 211         pr->throttled = 1;
 212         sk_set_frozen(pr->s, 1);
 213     }
 214
 215     return 1;
 216 }
 217
 218 static void x11_sent(Plug plug, int bufsize)
 219 {
 220     struct X11Private *pr = (struct X11Private *) plug;
 221
 222     sshfwd_unthrottle(pr->c, bufsize);
 223 }
 224
 225 /*
 226  * When setting up X forwarding, we should send the screen number
 227  * from the specified local display. This function extracts it from
 228  * the display string.
 229  */
 230 int x11_get_screen_number(char *display)
 231 {
 232     int n;
 233
 234     n = strcspn(display, ":");
 235     if (!display[n])
 236         return 0;
 237     n = strcspn(display, ".");
 238     if (!display[n])
 239         return 0;
 240     return atoi(display + n + 1);
 241 }
 242
 243 /* Find the right display, returns an allocated string */
 244 char *x11_display(const char *display) {
 245     char *ret;
 246     if(!display || !*display) {
 247         /* try to find platform-specific local display */
 248         if((ret = platform_get_x_display())==0 || !*ret)
 249             /* plausible default for all platforms */
 250             ret = dupstr(":0");
 251     } else
 252         ret = dupstr(display);
 253     if(ret[0] == ':') {
 254         /* no transport specified, use whatever we think is best */
 255         char *s = dupcat(platform_x11_best_transport, ret, (char *)0);
 256         sfree(ret);
 257         return s;
 258     } else
 259         return ret;
 260 }
 261
 262 /*
 263  * Called to set up the raw connection.
 264  *
 265  * Returns an error message, or NULL on success.
 266  * also, fills the SocketsStructure
 267  */
 268 const char *x11_init(Socket * s, char *display, void *c, void *auth,
 269                      const char *peeraddr, int peerport, const Config *cfg)
 270 {
 271     static const struct plug_function_table fn_table = {
 272         x11_log,
 273         x11_closing,
 274         x11_receive,
 275         x11_sent,
 276         NULL
 277     };
 278
 279     SockAddr addr;
 280     int port;
 281     const char *err;
 282     char *dummy_realhost;
 283     char host[128];
 284     int n, displaynum;
 285     struct X11Private *pr;
 286
 287     /* default display */
 288     display = x11_display(display);
 289     /*
 290      * Split up display name into host and display-number parts.
 291      */
 292     n = strcspn(display, ":");
 293     assert(n != 0);             /* x11_display() promises this */
 294     if (display[n])
 295         displaynum = atoi(display + n + 1);
 296     else
 297         displaynum = 0;                /* sensible default */
 298     if (n > sizeof(host) - 1)
 299         n = sizeof(host) - 1;
 300     strncpy(host, display, n);
 301     host[n] = '\0';
 302     sfree(display);
 303
 304     if(!strcmp(host, "unix")) {
 305         /* use AF_UNIX sockets (doesn't make sense on all platforms) */
 306         addr = platform_get_x11_unix_address(displaynum,
 307                                              &dummy_realhost);
 308         port = 0;               /* to show we are not confused */
 309     } else {
 310         port = 6000 + displaynum;
 311
 312         /*
 313          * Try to find host.
 314          */
 315         addr = name_lookup(host, port, &dummy_realhost, cfg, ADDRTYPE_UNSPEC);
 316         if ((err = sk_addr_error(addr)) != NULL) {
 317             sk_addr_free(addr);
 318             return err;
 319         }
 320     }
 321
 322     /*
 323      * Open socket.
 324      */
 325     pr = snew(struct X11Private);
 326     pr->fn = &fn_table;
 327     pr->auth_protocol = NULL;
 328     pr->auth = (struct X11Auth *)auth;
 329     pr->verified = 0;
 330     pr->data_read = 0;
 331     pr->throttled = pr->throttle_override = 0;
 332     pr->c = c;
 333
 334     pr->s = *s = new_connection(addr, dummy_realhost, port,
 335                                 0, 1, 0, 0, (Plug) pr, cfg);
 336     if ((err = sk_socket_error(*s)) != NULL) {
 337         sfree(pr);
 338         return err;
 339     }
 340
 341     /*
 342      * See if we can make sense of the peer address we were given.
 343      */
 344     {
 345         int i[4];
 346         if (peeraddr &&
 347             4 == sscanf(peeraddr, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
 348             pr->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
 349             pr->peer_port = peerport;
 350         } else {
 351             pr->peer_ip = 0;
 352             pr->peer_port = -1;
 353         }
 354     }
 355
 356     sk_set_private_ptr(*s, pr);
 357     return NULL;
 358 }
 359
 360 void x11_close(Socket s)
 361 {
 362     struct X11Private *pr;
 363     if (!s)
 364         return;
 365     pr = (struct X11Private *) sk_get_private_ptr(s);
 366     if (pr->auth_protocol) {
 367         sfree(pr->auth_protocol);
 368         sfree(pr->auth_data);
 369     }
 370
 371     sfree(pr);
 372
 373     sk_close(s);
 374 }
 375
 376 void x11_unthrottle(Socket s)
 377 {
 378     struct X11Private *pr;
 379     if (!s)
 380         return;
 381     pr = (struct X11Private *) sk_get_private_ptr(s);
 382
 383     pr->throttled = 0;
 384     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 385 }
 386
 387 void x11_override_throttle(Socket s, int enable)
 388 {
 389     struct X11Private *pr;
 390     if (!s)
 391         return;
 392     pr = (struct X11Private *) sk_get_private_ptr(s);
 393
 394     pr->throttle_override = enable;
 395     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 396 }
 397
 398 /*
 399  * Called to send data down the raw connection.
 400  */
 401 int x11_send(Socket s, char *data, int len)
 402 {
 403     struct X11Private *pr;
 404     if (!s)
 405         return 0;
 406     pr = (struct X11Private *) sk_get_private_ptr(s);
 407
 408     /*
 409      * Read the first packet.
 410      */
 411     while (len > 0 && pr->data_read < 12)
 412         pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
 413     if (pr->data_read < 12)
 414         return 0;
 415
 416     /*
 417      * If we have not allocated the auth_protocol and auth_data
 418      * strings, do so now.
 419      */
 420     if (!pr->auth_protocol) {
 421         pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
 422         pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
 423         pr->auth_psize = (pr->auth_plen + 3) & ~3;
 424         pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
 425         /* Leave room for a terminating zero, to make our lives easier. */
 426         pr->auth_protocol = snewn(pr->auth_psize + 1, char);
 427         pr->auth_data = snewn(pr->auth_dsize, unsigned char);
 428     }
 429
 430     /*
 431      * Read the auth_protocol and auth_data strings.
 432      */
 433     while (len > 0 && pr->data_read < 12 + pr->auth_psize)
 434         pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
 435     while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 436         pr->auth_data[pr->data_read++ - 12 -
 437                       pr->auth_psize] = (unsigned char) (len--, *data++);
 438     if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 439         return 0;
 440
 441     /*
 442      * If we haven't verified the authentication, do so now.
 443      */
 444     if (!pr->verified) {
 445         char *err;
 446
 447         pr->auth_protocol[pr->auth_plen] = '\0';        /* ASCIZ */
 448         err = x11_verify(pr->peer_ip, pr->peer_port,
 449                          pr->auth, pr->auth_protocol,
 450                          pr->auth_data, pr->auth_dlen);
 451
 452         /*
 453          * If authentication failed, construct and send an error
 454          * packet, then terminate the connection.
 455          */
 456         if (err) {
 457             char *message;
 458             int msglen, msgsize;
 459             unsigned char *reply;
 460
 461             message = dupprintf("PuTTY X11 proxy: %s", err);
 462             msglen = strlen(message);
 463             reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */
 464             msgsize = (msglen + 3) & ~3;
 465             reply[0] = 0;              /* failure */
 466             reply[1] = msglen;         /* length of reason string */
 467             memcpy(reply + 2, pr->firstpkt + 2, 4);     /* major/minor proto vsn */
 468             PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
 469             memset(reply + 8, 0, msgsize);
 470             memcpy(reply + 8, message, msglen);
 471             sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
 472             sshfwd_close(pr->c);
 473             x11_close(s);
 474             sfree(reply);
 475             sfree(message);
 476             return 0;
 477         }
 478
 479         /*
 480          * Now we know we're going to accept the connection. Strip
 481          * the fake auth data, and optionally put real auth data in
 482          * instead.
 483          */
 484         {
 485             char realauthdata[64];
 486             int realauthlen = 0;
 487             int authstrlen = strlen(x11_authnames[pr->auth->realproto]);
 488             int buflen;
 489             static const char zeroes[4] = { 0,0,0,0 };
 490             void *buf;
 491
 492             if (pr->auth->realproto == X11_MIT) {
 493                 assert(pr->auth->reallen <= lenof(realauthdata));
 494                 realauthlen = pr->auth->reallen;
 495                 memcpy(realauthdata, pr->auth->realdata, realauthlen);
 496             } else if (pr->auth->realproto == X11_XDM &&
 497                        pr->auth->reallen == 16 &&
 498                        ((buf = sk_getxdmdata(s, &buflen))!=0)) {
 499                 time_t t;
 500                 realauthlen = (buflen+12+7) & ~7;
 501                 assert(realauthlen <= lenof(realauthdata));
 502                 memset(realauthdata, 0, realauthlen);
 503                 memcpy(realauthdata, pr->auth->realdata, 8);
 504                 memcpy(realauthdata+8, buf, buflen);
 505                 t = time(NULL);
 506                 PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t);
 507                 des_encrypt_xdmauth(pr->auth->realdata+9,
 508                                     (unsigned char *)realauthdata,
 509                                     realauthlen);
 510                 sfree(buf);
 511             }
 512             /* implement other auth methods here if required */
 513
 514             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
 515             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
 516
 517             sk_write(s, (char *)pr->firstpkt, 12);
 518
 519             if (authstrlen) {
 520                 sk_write(s, x11_authnames[pr->auth->realproto], authstrlen);
 521                 sk_write(s, zeroes, 3 & (-authstrlen));
 522             }
 523             if (realauthlen) {
 524                 sk_write(s, realauthdata, realauthlen);
 525                 sk_write(s, zeroes, 3 & (-realauthlen));
 526             }
 527         }
 528         pr->verified = 1;
 529     }
 530
 531     /*
 532      * After initialisation, just copy data simply.
 533      */
 534
 535     return sk_write(s, data, len);
 536 }