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] = (value), \
  17   (cp)[1] = (value) >> 8, \
  18   (cp)[2] = (value) >> 16, \
  19   (cp)[3] = (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] = (value), \
  27   (cp)[1] = (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] = (value) >> 24, \
  37   (cp)[1] = (value) >> 16, \
  38   (cp)[2] = (value) >> 8, \
  39   (cp)[3] = (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] = (value) >> 8, \
  47   (cp)[1] = (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     void *c;                           /* data used by ssh.c */
  76     Socket s;
  77 };
  78
  79 void *x11_invent_auth(char *proto, int protomaxlen,
  80                      char *data, int datamaxlen)
  81 {
  82     struct X11Auth *auth = smalloc(sizeof(struct X11Auth));
  83     char ourdata[64];
  84     int i;
  85
  86     auth->fakeproto = X11_MIT;
  87
  88     /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
  89     auth->fakelen = 16;
  90     for (i = 0; i < 16; i++)
  91         auth->fakedata[i] = random_byte();
  92
  93     /* Now format for the recipient. */
  94     strncpy(proto, x11_authnames[auth->fakeproto], protomaxlen);
  95     ourdata[0] = '\0';
  96     for (i = 0; i < auth->fakelen; i++)
  97         sprintf(ourdata + strlen(ourdata), "%02x", auth->fakedata[i]);
  98     strncpy(data, ourdata, datamaxlen);
  99
 100     return auth;
 101 }
 102
 103 /*
 104  * Fetch the real auth data for a given display string, and store
 105  * it in an X11Auth structure. Returns NULL on success, or an error
 106  * string.
 107  */
 108 void x11_get_real_auth(void *authv, char *display)
 109 {
 110     struct X11Auth *auth = (struct X11Auth *)authv;
 111
 112     auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */
 113
 114     auth->reallen = sizeof(auth->realdata);
 115     platform_get_x11_auth(display, &auth->realproto,
 116                           auth->realdata, &auth->reallen);
 117 }
 118
 119 static int x11_verify(struct X11Auth *auth,
 120                       char *proto, unsigned char *data, int dlen)
 121 {
 122     if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
 123         return 0;                      /* wrong protocol attempted */
 124     if (auth->fakeproto == X11_MIT) {
 125         if (dlen != auth->fakelen)
 126             return 0;                  /* cookie was wrong length */
 127         if (memcmp(auth->fakedata, data, dlen) != 0)
 128             return 0;                  /* cookie was wrong cookie! */
 129     }
 130     /* implement other protocols here if ever required */
 131     return 1;
 132 }
 133
 134 static int x11_closing(Plug plug, char *error_msg, int error_code,
 135                        int calling_back)
 136 {
 137     struct X11Private *pr = (struct X11Private *) plug;
 138
 139     /*
 140      * We have no way to communicate down the forwarded connection,
 141      * so if an error occurred on the socket, we just ignore it
 142      * and treat it like a proper close.
 143      */
 144     sshfwd_close(pr->c);
 145     x11_close(pr->s);
 146     return 1;
 147 }
 148
 149 static int x11_receive(Plug plug, int urgent, char *data, int len)
 150 {
 151     struct X11Private *pr = (struct X11Private *) plug;
 152
 153     if (sshfwd_write(pr->c, data, len) > 0) {
 154         pr->throttled = 1;
 155         sk_set_frozen(pr->s, 1);
 156     }
 157
 158     return 1;
 159 }
 160
 161 static void x11_sent(Plug plug, int bufsize)
 162 {
 163     struct X11Private *pr = (struct X11Private *) plug;
 164
 165     sshfwd_unthrottle(pr->c, bufsize);
 166 }
 167
 168 /*
 169  * When setting up X forwarding, we should send the screen number
 170  * from the specified local display. This function extracts it from
 171  * the display string.
 172  */
 173 int x11_get_screen_number(char *display)
 174 {
 175     int n;
 176
 177     n = strcspn(display, ":");
 178     if (!display[n])
 179         return 0;
 180     n = strcspn(display, ".");
 181     if (!display[n])
 182         return 0;
 183     return atoi(display + n + 1);
 184 }
 185
 186 /*
 187  * Called to set up the raw connection.
 188  *
 189  * Returns an error message, or NULL on success.
 190  * also, fills the SocketsStructure
 191  */
 192 char *x11_init(Socket * s, char *display, void *c, void *auth)
 193 {
 194     static const struct plug_function_table fn_table = {
 195         x11_closing,
 196         x11_receive,
 197         x11_sent,
 198         NULL
 199     };
 200
 201     SockAddr addr;
 202     int port;
 203     char *err, *dummy_realhost;
 204     char host[128];
 205     int n, displaynum;
 206     struct X11Private *pr;
 207
 208     /*
 209      * Split up display name into host and display-number parts.
 210      */
 211     n = strcspn(display, ":");
 212     if (display[n])
 213         displaynum = atoi(display + n + 1);
 214     else
 215         displaynum = 0;                /* sensible default */
 216     if (n > sizeof(host) - 1)
 217         n = sizeof(host) - 1;
 218     if (n > 0) {
 219         strncpy(host, display, n);
 220         host[n] = '\0';
 221     } else {
 222         /*
 223          * Local display numbers, particularly on Unix, often omit
 224          * the display part completely.
 225          */
 226         strcpy(host, "localhost");
 227     }
 228
 229     port = 6000 + displaynum;
 230
 231     /*
 232      * Try to find host.
 233      */
 234     addr = name_lookup(host, port, &dummy_realhost);
 235     if ((err = sk_addr_error(addr)) != NULL)
 236         return err;
 237
 238     /*
 239      * Open socket.
 240      */
 241     pr = (struct X11Private *) smalloc(sizeof(struct X11Private));
 242     pr->fn = &fn_table;
 243     pr->auth_protocol = NULL;
 244     pr->auth = (struct X11Auth *)auth;
 245     pr->verified = 0;
 246     pr->data_read = 0;
 247     pr->throttled = pr->throttle_override = 0;
 248     pr->c = c;
 249
 250     pr->s = *s = new_connection(addr, dummy_realhost, port, 0, 1, 0, (Plug) pr);
 251     if ((err = sk_socket_error(*s)) != NULL) {
 252         sfree(pr);
 253         return err;
 254     }
 255
 256     sk_set_private_ptr(*s, pr);
 257     sk_addr_free(addr);
 258     return NULL;
 259 }
 260
 261 void x11_close(Socket s)
 262 {
 263     struct X11Private *pr;
 264     if (!s)
 265         return;
 266     pr = (struct X11Private *) sk_get_private_ptr(s);
 267     if (pr->auth_protocol) {
 268         sfree(pr->auth_protocol);
 269         sfree(pr->auth_data);
 270     }
 271
 272     sfree(pr);
 273
 274     sk_close(s);
 275 }
 276
 277 void x11_unthrottle(Socket s)
 278 {
 279     struct X11Private *pr;
 280     if (!s)
 281         return;
 282     pr = (struct X11Private *) sk_get_private_ptr(s);
 283
 284     pr->throttled = 0;
 285     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 286 }
 287
 288 void x11_override_throttle(Socket s, int enable)
 289 {
 290     struct X11Private *pr;
 291     if (!s)
 292         return;
 293     pr = (struct X11Private *) sk_get_private_ptr(s);
 294
 295     pr->throttle_override = enable;
 296     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 297 }
 298
 299 /*
 300  * Called to send data down the raw connection.
 301  */
 302 int x11_send(Socket s, char *data, int len)
 303 {
 304     struct X11Private *pr = (struct X11Private *) sk_get_private_ptr(s);
 305
 306     if (s == NULL)
 307         return 0;
 308
 309     /*
 310      * Read the first packet.
 311      */
 312     while (len > 0 && pr->data_read < 12)
 313         pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
 314     if (pr->data_read < 12)
 315         return 0;
 316
 317     /*
 318      * If we have not allocated the auth_protocol and auth_data
 319      * strings, do so now.
 320      */
 321     if (!pr->auth_protocol) {
 322         pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
 323         pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
 324         pr->auth_psize = (pr->auth_plen + 3) & ~3;
 325         pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
 326         /* Leave room for a terminating zero, to make our lives easier. */
 327         pr->auth_protocol = (char *) smalloc(pr->auth_psize + 1);
 328         pr->auth_data = (unsigned char *) smalloc(pr->auth_dsize);
 329     }
 330
 331     /*
 332      * Read the auth_protocol and auth_data strings.
 333      */
 334     while (len > 0 && pr->data_read < 12 + pr->auth_psize)
 335         pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
 336     while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 337         pr->auth_data[pr->data_read++ - 12 -
 338                       pr->auth_psize] = (unsigned char) (len--, *data++);
 339     if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 340         return 0;
 341
 342     /*
 343      * If we haven't verified the authentication, do so now.
 344      */
 345     if (!pr->verified) {
 346         int ret;
 347
 348         pr->auth_protocol[pr->auth_plen] = '\0';        /* ASCIZ */
 349         ret = x11_verify(pr->auth, pr->auth_protocol,
 350                          pr->auth_data, pr->auth_dlen);
 351
 352         /*
 353          * If authentication failed, construct and send an error
 354          * packet, then terminate the connection.
 355          */
 356         if (!ret) {
 357             char message[] = "Authentication failed at PuTTY X11 proxy";
 358             unsigned char reply[8 + sizeof(message) + 4];
 359             int msglen = sizeof(message) - 1;   /* skip zero byte */
 360             int msgsize = (msglen + 3) & ~3;
 361             reply[0] = 0;              /* failure */
 362             reply[1] = msglen;         /* length of reason string */
 363             memcpy(reply + 2, pr->firstpkt + 2, 4);     /* major/minor proto vsn */
 364             PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
 365             memset(reply + 8, 0, msgsize);
 366             memcpy(reply + 8, message, msglen);
 367             sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
 368             sshfwd_close(pr->c);
 369             x11_close(s);
 370             return 0;
 371         }
 372
 373         /*
 374          * Now we know we're going to accept the connection. Strip
 375          * the fake auth data, and optionally put real auth data in
 376          * instead.
 377          */
 378         {
 379             char realauthdata[64];
 380             int realauthlen = 0;
 381             int authstrlen = strlen(x11_authnames[pr->auth->realproto]);
 382             unsigned long ip;
 383             int port;
 384             static const char zeroes[4] = { 0,0,0,0 };
 385
 386             if (pr->auth->realproto == X11_MIT) {
 387                 assert(pr->auth->reallen <= lenof(realauthdata));
 388                 realauthlen = pr->auth->reallen;
 389                 memcpy(realauthdata, pr->auth->realdata, realauthlen);
 390             } else if (pr->auth->realproto == X11_XDM &&
 391                        pr->auth->reallen == 16 &&
 392                        sk_getxdmdata(s, &ip, &port)) {
 393                 time_t t;
 394                 realauthlen = 24;
 395                 memset(realauthdata, 0, 24);
 396                 memcpy(realauthdata, pr->auth->realdata, 8);
 397                 PUT_32BIT_MSB_FIRST(realauthdata+8, ip);
 398                 PUT_16BIT_MSB_FIRST(realauthdata+12, port);
 399                 t = time(NULL);
 400                 PUT_32BIT_MSB_FIRST(realauthdata+14, t);
 401                 des_encrypt_xdmauth(pr->auth->realdata+9,
 402                                     (unsigned char *)realauthdata, 24);
 403             }
 404             /* implement other auth methods here if required */
 405
 406             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
 407             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
 408
 409             sk_write(s, (char *)pr->firstpkt, 12);
 410
 411             if (authstrlen) {
 412                 sk_write(s, x11_authnames[pr->auth->realproto], authstrlen);
 413                 sk_write(s, zeroes, 3 & (-authstrlen));
 414             }
 415             if (realauthlen) {
 416                 sk_write(s, realauthdata, realauthlen);
 417                 sk_write(s, zeroes, 3 & (-realauthlen));
 418             }
 419         }
 420         pr->verified = 1;
 421     }
 422
 423     /*
 424      * After initialisation, just copy data simply.
 425      */
 426
 427     return sk_write(s, data, len);
 428 }