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

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