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