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 = smalloc(sizeof(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 /*
 116  * Fetch the real auth data for a given display string, and store
 117  * it in an X11Auth structure. Returns NULL on success, or an error
 118  * string.
 119  */
 120 void x11_get_real_auth(void *authv, char *display)
 121 {
 122     struct X11Auth *auth = (struct X11Auth *)authv;
 123
 124     auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */
 125
 126     auth->reallen = sizeof(auth->realdata);
 127     platform_get_x11_auth(display, &auth->realproto,
 128                           auth->realdata, &auth->reallen);
 129 }
 130
 131 static char *x11_verify(unsigned long peer_ip, int peer_port,
 132                         struct X11Auth *auth, char *proto,
 133                         unsigned char *data, int dlen)
 134 {
 135     if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
 136         return "wrong authentication protocol attempted";
 137     if (auth->fakeproto == X11_MIT) {
 138         if (dlen != auth->fakelen)
 139             return "MIT-MAGIC-COOKIE-1 data was wrong length";
 140         if (memcmp(auth->fakedata, data, dlen) != 0)
 141             return "MIT-MAGIC-COOKIE-1 data did not match";
 142     }
 143     if (auth->fakeproto == X11_XDM) {
 144         unsigned long t;
 145         time_t tim;
 146         int i;
 147
 148         if (dlen != 24)
 149             return "XDM-AUTHORIZATION-1 data was wrong length";
 150         if (peer_port == -1)
 151             return "cannot do XDM-AUTHORIZATION-1 without remote address data";
 152         des_decrypt_xdmauth(auth->fakedata+9, data, 24);
 153         if (memcmp(auth->fakedata, data, 8) != 0)
 154             return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
 155         if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
 156             return "XDM-AUTHORIZATION-1 data failed check";   /* IP wrong */
 157         if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
 158             return "XDM-AUTHORIZATION-1 data failed check";   /* port wrong */
 159         t = GET_32BIT_MSB_FIRST(data+14);
 160         for (i = 18; i < 24; i++)
 161             if (data[i] != 0)          /* zero padding wrong */
 162                 return "XDM-AUTHORIZATION-1 data failed check";
 163         tim = time(NULL);
 164         if (abs(t - tim) > 20*60)      /* 20 minute clock skew should be OK */
 165             return "XDM-AUTHORIZATION-1 time stamp was too far out";
 166     }
 167     /* implement other protocols here if ever required */
 168     return NULL;
 169 }
 170
 171 static int x11_closing(Plug plug, char *error_msg, int error_code,
 172                        int calling_back)
 173 {
 174     struct X11Private *pr = (struct X11Private *) plug;
 175
 176     /*
 177      * We have no way to communicate down the forwarded connection,
 178      * so if an error occurred on the socket, we just ignore it
 179      * and treat it like a proper close.
 180      */
 181     sshfwd_close(pr->c);
 182     x11_close(pr->s);
 183     return 1;
 184 }
 185
 186 static int x11_receive(Plug plug, int urgent, char *data, int len)
 187 {
 188     struct X11Private *pr = (struct X11Private *) plug;
 189
 190     if (sshfwd_write(pr->c, data, len) > 0) {
 191         pr->throttled = 1;
 192         sk_set_frozen(pr->s, 1);
 193     }
 194
 195     return 1;
 196 }
 197
 198 static void x11_sent(Plug plug, int bufsize)
 199 {
 200     struct X11Private *pr = (struct X11Private *) plug;
 201
 202     sshfwd_unthrottle(pr->c, bufsize);
 203 }
 204
 205 /*
 206  * When setting up X forwarding, we should send the screen number
 207  * from the specified local display. This function extracts it from
 208  * the display string.
 209  */
 210 int x11_get_screen_number(char *display)
 211 {
 212     int n;
 213
 214     n = strcspn(display, ":");
 215     if (!display[n])
 216         return 0;
 217     n = strcspn(display, ".");
 218     if (!display[n])
 219         return 0;
 220     return atoi(display + n + 1);
 221 }
 222
 223 /*
 224  * Called to set up the raw connection.
 225  *
 226  * Returns an error message, or NULL on success.
 227  * also, fills the SocketsStructure
 228  */
 229 char *x11_init(Socket * s, char *display, void *c, void *auth,
 230                const char *peeraddr, int peerport)
 231 {
 232     static const struct plug_function_table fn_table = {
 233         x11_closing,
 234         x11_receive,
 235         x11_sent,
 236         NULL
 237     };
 238
 239     SockAddr addr;
 240     int port;
 241     char *err, *dummy_realhost;
 242     char host[128];
 243     int n, displaynum;
 244     struct X11Private *pr;
 245
 246     /*
 247      * Split up display name into host and display-number parts.
 248      */
 249     n = strcspn(display, ":");
 250     if (display[n])
 251         displaynum = atoi(display + n + 1);
 252     else
 253         displaynum = 0;                /* sensible default */
 254     if (n > sizeof(host) - 1)
 255         n = sizeof(host) - 1;
 256     if (n > 0) {
 257         strncpy(host, display, n);
 258         host[n] = '\0';
 259     } else {
 260         /*
 261          * Local display numbers, particularly on Unix, often omit
 262          * the display part completely.
 263          */
 264         strcpy(host, "localhost");
 265     }
 266
 267     port = 6000 + displaynum;
 268
 269     /*
 270      * Try to find host.
 271      */
 272     addr = name_lookup(host, port, &dummy_realhost);
 273     if ((err = sk_addr_error(addr)) != NULL)
 274         return err;
 275
 276     /*
 277      * Open socket.
 278      */
 279     pr = (struct X11Private *) smalloc(sizeof(struct X11Private));
 280     pr->fn = &fn_table;
 281     pr->auth_protocol = NULL;
 282     pr->auth = (struct X11Auth *)auth;
 283     pr->verified = 0;
 284     pr->data_read = 0;
 285     pr->throttled = pr->throttle_override = 0;
 286     pr->c = c;
 287
 288     pr->s = *s = new_connection(addr, dummy_realhost, port, 0, 1, 0, (Plug) pr);
 289     if ((err = sk_socket_error(*s)) != NULL) {
 290         sfree(pr);
 291         return err;
 292     }
 293
 294     /*
 295      * See if we can make sense of the peer address we were given.
 296      */
 297     {
 298         int i[4];
 299         if (peeraddr &&
 300             4 == sscanf(peeraddr, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
 301             pr->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
 302             pr->peer_port = peerport;
 303         } else {
 304             pr->peer_ip = 0;
 305             pr->peer_port = -1;
 306         }
 307     }
 308
 309     sk_set_private_ptr(*s, pr);
 310     sk_addr_free(addr);
 311     return NULL;
 312 }
 313
 314 void x11_close(Socket s)
 315 {
 316     struct X11Private *pr;
 317     if (!s)
 318         return;
 319     pr = (struct X11Private *) sk_get_private_ptr(s);
 320     if (pr->auth_protocol) {
 321         sfree(pr->auth_protocol);
 322         sfree(pr->auth_data);
 323     }
 324
 325     sfree(pr);
 326
 327     sk_close(s);
 328 }
 329
 330 void x11_unthrottle(Socket s)
 331 {
 332     struct X11Private *pr;
 333     if (!s)
 334         return;
 335     pr = (struct X11Private *) sk_get_private_ptr(s);
 336
 337     pr->throttled = 0;
 338     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 339 }
 340
 341 void x11_override_throttle(Socket s, int enable)
 342 {
 343     struct X11Private *pr;
 344     if (!s)
 345         return;
 346     pr = (struct X11Private *) sk_get_private_ptr(s);
 347
 348     pr->throttle_override = enable;
 349     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 350 }
 351
 352 /*
 353  * Called to send data down the raw connection.
 354  */
 355 int x11_send(Socket s, char *data, int len)
 356 {
 357     struct X11Private *pr = (struct X11Private *) sk_get_private_ptr(s);
 358
 359     if (s == NULL)
 360         return 0;
 361
 362     /*
 363      * Read the first packet.
 364      */
 365     while (len > 0 && pr->data_read < 12)
 366         pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
 367     if (pr->data_read < 12)
 368         return 0;
 369
 370     /*
 371      * If we have not allocated the auth_protocol and auth_data
 372      * strings, do so now.
 373      */
 374     if (!pr->auth_protocol) {
 375         pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
 376         pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
 377         pr->auth_psize = (pr->auth_plen + 3) & ~3;
 378         pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
 379         /* Leave room for a terminating zero, to make our lives easier. */
 380         pr->auth_protocol = (char *) smalloc(pr->auth_psize + 1);
 381         pr->auth_data = (unsigned char *) smalloc(pr->auth_dsize);
 382     }
 383
 384     /*
 385      * Read the auth_protocol and auth_data strings.
 386      */
 387     while (len > 0 && pr->data_read < 12 + pr->auth_psize)
 388         pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
 389     while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 390         pr->auth_data[pr->data_read++ - 12 -
 391                       pr->auth_psize] = (unsigned char) (len--, *data++);
 392     if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 393         return 0;
 394
 395     /*
 396      * If we haven't verified the authentication, do so now.
 397      */
 398     if (!pr->verified) {
 399         char *err;
 400
 401         pr->auth_protocol[pr->auth_plen] = '\0';        /* ASCIZ */
 402         err = x11_verify(pr->peer_ip, pr->peer_port,
 403                          pr->auth, pr->auth_protocol,
 404                          pr->auth_data, pr->auth_dlen);
 405
 406         /*
 407          * If authentication failed, construct and send an error
 408          * packet, then terminate the connection.
 409          */
 410         if (err) {
 411             char *message;
 412             int msglen, msgsize;
 413             unsigned char *reply;
 414
 415             message = dupprintf("PuTTY X11 proxy: %s", err);
 416             msglen = strlen(message);
 417             reply = smalloc(8 + msglen+1 + 4);   /* include zero byte */
 418             msgsize = (msglen + 3) & ~3;
 419             reply[0] = 0;              /* failure */
 420             reply[1] = msglen;         /* length of reason string */
 421             memcpy(reply + 2, pr->firstpkt + 2, 4);     /* major/minor proto vsn */
 422             PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
 423             memset(reply + 8, 0, msgsize);
 424             memcpy(reply + 8, message, msglen);
 425             sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
 426             sshfwd_close(pr->c);
 427             x11_close(s);
 428             sfree(reply);
 429             sfree(message);
 430             return 0;
 431         }
 432
 433         /*
 434          * Now we know we're going to accept the connection. Strip
 435          * the fake auth data, and optionally put real auth data in
 436          * instead.
 437          */
 438         {
 439             char realauthdata[64];
 440             int realauthlen = 0;
 441             int authstrlen = strlen(x11_authnames[pr->auth->realproto]);
 442             unsigned long ip;
 443             int port;
 444             static const char zeroes[4] = { 0,0,0,0 };
 445
 446             if (pr->auth->realproto == X11_MIT) {
 447                 assert(pr->auth->reallen <= lenof(realauthdata));
 448                 realauthlen = pr->auth->reallen;
 449                 memcpy(realauthdata, pr->auth->realdata, realauthlen);
 450             } else if (pr->auth->realproto == X11_XDM &&
 451                        pr->auth->reallen == 16 &&
 452                        sk_getxdmdata(s, &ip, &port)) {
 453                 time_t t;
 454                 realauthlen = 24;
 455                 memset(realauthdata, 0, 24);
 456                 memcpy(realauthdata, pr->auth->realdata, 8);
 457                 PUT_32BIT_MSB_FIRST(realauthdata+8, ip);
 458                 PUT_16BIT_MSB_FIRST(realauthdata+12, port);
 459                 t = time(NULL);
 460                 PUT_32BIT_MSB_FIRST(realauthdata+14, t);
 461                 des_encrypt_xdmauth(pr->auth->realdata+9,
 462                                     (unsigned char *)realauthdata, 24);
 463             }
 464             /* implement other auth methods here if required */
 465
 466             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
 467             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
 468
 469             sk_write(s, (char *)pr->firstpkt, 12);
 470
 471             if (authstrlen) {
 472                 sk_write(s, x11_authnames[pr->auth->realproto], authstrlen);
 473                 sk_write(s, zeroes, 3 & (-authstrlen));
 474             }
 475             if (realauthlen) {
 476                 sk_write(s, realauthdata, realauthlen);
 477                 sk_write(s, zeroes, 3 & (-realauthlen));
 478             }
 479         }
 480         pr->verified = 1;
 481     }
 482
 483     /*
 484      * After initialisation, just copy data simply.
 485      */
 486
 487     return sk_write(s, data, len);
 488 }