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 extern void platform_get_x11_auth(char *display, int *proto,
  66                                   unsigned char *data, int *datalen);
  67
  68 struct X11Private {
  69     const struct plug_function_table *fn;
  70     /* the above variable absolutely *must* be the first in this structure */
  71     unsigned char firstpkt[12];        /* first X data packet */
  72     struct X11Auth *auth;
  73     char *auth_protocol;
  74     unsigned char *auth_data;
  75     int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
  76     int verified;
  77     int throttled, throttle_override;
  78     void *c;                           /* data used by ssh.c */
  79     Socket s;
  80 };
  81
  82 void *x11_invent_auth(char *proto, int protomaxlen,
  83                      char *data, int datamaxlen)
  84 {
  85     struct X11Auth *auth = smalloc(sizeof(struct X11Auth));
  86     char ourdata[64];
  87     int i;
  88
  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
  96     /* Now format for the recipient. */
  97     strncpy(proto, x11_authnames[auth->fakeproto], protomaxlen);
  98     ourdata[0] = '\0';
  99     for (i = 0; i < auth->fakelen; i++)
 100         sprintf(ourdata + strlen(ourdata), "%02x", auth->fakedata[i]);
 101     strncpy(data, ourdata, datamaxlen);
 102
 103     return auth;
 104 }
 105
 106 /*
 107  * Fetch the real auth data for a given display string, and store
 108  * it in an X11Auth structure. Returns NULL on success, or an error
 109  * string.
 110  */
 111 void x11_get_real_auth(void *authv, char *display)
 112 {
 113     struct X11Auth *auth = (struct X11Auth *)authv;
 114
 115     auth->realproto = X11_NO_AUTH;     /* in case next call does nothing */
 116
 117     auth->reallen = sizeof(auth->realdata);
 118     platform_get_x11_auth(display, &auth->realproto,
 119                           auth->realdata, &auth->reallen);
 120 }
 121
 122 static int x11_verify(struct X11Auth *auth,
 123                       char *proto, unsigned char *data, int dlen)
 124 {
 125     if (strcmp(proto, x11_authnames[auth->fakeproto]) != 0)
 126         return 0;                      /* wrong protocol attempted */
 127     if (auth->fakeproto == X11_MIT) {
 128         if (dlen != auth->fakelen)
 129             return 0;                  /* cookie was wrong length */
 130         if (memcmp(auth->fakedata, data, dlen) != 0)
 131             return 0;                  /* cookie was wrong cookie! */
 132     }
 133     /* implement other protocols here if ever required */
 134     return 1;
 135 }
 136
 137 static int x11_closing(Plug plug, char *error_msg, int error_code,
 138                        int calling_back)
 139 {
 140     struct X11Private *pr = (struct X11Private *) plug;
 141
 142     /*
 143      * We have no way to communicate down the forwarded connection,
 144      * so if an error occurred on the socket, we just ignore it
 145      * and treat it like a proper close.
 146      */
 147     sshfwd_close(pr->c);
 148     x11_close(pr->s);
 149     return 1;
 150 }
 151
 152 static int x11_receive(Plug plug, int urgent, char *data, int len)
 153 {
 154     struct X11Private *pr = (struct X11Private *) plug;
 155
 156     if (sshfwd_write(pr->c, data, len) > 0) {
 157         pr->throttled = 1;
 158         sk_set_frozen(pr->s, 1);
 159     }
 160
 161     return 1;
 162 }
 163
 164 static void x11_sent(Plug plug, int bufsize)
 165 {
 166     struct X11Private *pr = (struct X11Private *) plug;
 167
 168     sshfwd_unthrottle(pr->c, bufsize);
 169 }
 170
 171 /*
 172  * When setting up X forwarding, we should send the screen number
 173  * from the specified local display. This function extracts it from
 174  * the display string.
 175  */
 176 int x11_get_screen_number(char *display)
 177 {
 178     int n;
 179
 180     n = strcspn(display, ":");
 181     if (!display[n])
 182         return 0;
 183     n = strcspn(display, ".");
 184     if (!display[n])
 185         return 0;
 186     return atoi(display + n + 1);
 187 }
 188
 189 /*
 190  * Called to set up the raw connection.
 191  *
 192  * Returns an error message, or NULL on success.
 193  * also, fills the SocketsStructure
 194  */
 195 char *x11_init(Socket * s, char *display, void *c, void *auth)
 196 {
 197     static const struct plug_function_table fn_table = {
 198         x11_closing,
 199         x11_receive,
 200         x11_sent,
 201         NULL
 202     };
 203
 204     SockAddr addr;
 205     int port;
 206     char *err, *dummy_realhost;
 207     char host[128];
 208     int n, displaynum;
 209     struct X11Private *pr;
 210
 211     /*
 212      * Split up display name into host and display-number parts.
 213      */
 214     n = strcspn(display, ":");
 215     if (display[n])
 216         displaynum = atoi(display + n + 1);
 217     else
 218         displaynum = 0;                /* sensible default */
 219     if (n > sizeof(host) - 1)
 220         n = sizeof(host) - 1;
 221     if (n > 0) {
 222         strncpy(host, display, n);
 223         host[n] = '\0';
 224     } else {
 225         /*
 226          * Local display numbers, particularly on Unix, often omit
 227          * the display part completely.
 228          */
 229         strcpy(host, "localhost");
 230     }
 231
 232     port = 6000 + displaynum;
 233
 234     /*
 235      * Try to find host.
 236      */
 237     addr = name_lookup(host, port, &dummy_realhost);
 238     if ((err = sk_addr_error(addr)) != NULL)
 239         return err;
 240
 241     /*
 242      * Open socket.
 243      */
 244     pr = (struct X11Private *) smalloc(sizeof(struct X11Private));
 245     pr->fn = &fn_table;
 246     pr->auth_protocol = NULL;
 247     pr->auth = (struct X11Auth *)auth;
 248     pr->verified = 0;
 249     pr->data_read = 0;
 250     pr->throttled = pr->throttle_override = 0;
 251     pr->c = c;
 252
 253     pr->s = *s = new_connection(addr, dummy_realhost, port, 0, 1, 0, (Plug) pr);
 254     if ((err = sk_socket_error(*s)) != NULL) {
 255         sfree(pr);
 256         return err;
 257     }
 258
 259     sk_set_private_ptr(*s, pr);
 260     sk_addr_free(addr);
 261     return NULL;
 262 }
 263
 264 void x11_close(Socket s)
 265 {
 266     struct X11Private *pr;
 267     if (!s)
 268         return;
 269     pr = (struct X11Private *) sk_get_private_ptr(s);
 270     if (pr->auth_protocol) {
 271         sfree(pr->auth_protocol);
 272         sfree(pr->auth_data);
 273     }
 274
 275     sfree(pr);
 276
 277     sk_close(s);
 278 }
 279
 280 void x11_unthrottle(Socket s)
 281 {
 282     struct X11Private *pr;
 283     if (!s)
 284         return;
 285     pr = (struct X11Private *) sk_get_private_ptr(s);
 286
 287     pr->throttled = 0;
 288     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 289 }
 290
 291 void x11_override_throttle(Socket s, int enable)
 292 {
 293     struct X11Private *pr;
 294     if (!s)
 295         return;
 296     pr = (struct X11Private *) sk_get_private_ptr(s);
 297
 298     pr->throttle_override = enable;
 299     sk_set_frozen(s, pr->throttled || pr->throttle_override);
 300 }
 301
 302 /*
 303  * Called to send data down the raw connection.
 304  */
 305 int x11_send(Socket s, char *data, int len)
 306 {
 307     struct X11Private *pr = (struct X11Private *) sk_get_private_ptr(s);
 308
 309     if (s == NULL)
 310         return 0;
 311
 312     /*
 313      * Read the first packet.
 314      */
 315     while (len > 0 && pr->data_read < 12)
 316         pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
 317     if (pr->data_read < 12)
 318         return 0;
 319
 320     /*
 321      * If we have not allocated the auth_protocol and auth_data
 322      * strings, do so now.
 323      */
 324     if (!pr->auth_protocol) {
 325         pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
 326         pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
 327         pr->auth_psize = (pr->auth_plen + 3) & ~3;
 328         pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
 329         /* Leave room for a terminating zero, to make our lives easier. */
 330         pr->auth_protocol = (char *) smalloc(pr->auth_psize + 1);
 331         pr->auth_data = (unsigned char *) smalloc(pr->auth_dsize);
 332     }
 333
 334     /*
 335      * Read the auth_protocol and auth_data strings.
 336      */
 337     while (len > 0 && pr->data_read < 12 + pr->auth_psize)
 338         pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
 339     while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 340         pr->auth_data[pr->data_read++ - 12 -
 341                       pr->auth_psize] = (unsigned char) (len--, *data++);
 342     if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
 343         return 0;
 344
 345     /*
 346      * If we haven't verified the authentication, do so now.
 347      */
 348     if (!pr->verified) {
 349         int ret;
 350
 351         pr->auth_protocol[pr->auth_plen] = '\0';        /* ASCIZ */
 352         ret = x11_verify(pr->auth, pr->auth_protocol,
 353                          pr->auth_data, pr->auth_dlen);
 354
 355         /*
 356          * If authentication failed, construct and send an error
 357          * packet, then terminate the connection.
 358          */
 359         if (!ret) {
 360             char message[] = "Authentication failed at PuTTY X11 proxy";
 361             unsigned char reply[8 + sizeof(message) + 4];
 362             int msglen = sizeof(message) - 1;   /* skip zero byte */
 363             int msgsize = (msglen + 3) & ~3;
 364             reply[0] = 0;              /* failure */
 365             reply[1] = msglen;         /* length of reason string */
 366             memcpy(reply + 2, pr->firstpkt + 2, 4);     /* major/minor proto vsn */
 367             PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
 368             memset(reply + 8, 0, msgsize);
 369             memcpy(reply + 8, message, msglen);
 370             sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
 371             sshfwd_close(pr->c);
 372             x11_close(s);
 373             return 0;
 374         }
 375
 376         /*
 377          * Now we know we're going to accept the connection. Strip
 378          * the fake auth data, and optionally put real auth data in
 379          * instead.
 380          */
 381         {
 382             char realauthdata[64];
 383             int realauthlen = 0;
 384             int authstrlen = strlen(x11_authnames[pr->auth->realproto]);
 385             unsigned long ip;
 386             int port;
 387             static const char zeroes[4] = { 0,0,0,0 };
 388
 389             if (pr->auth->realproto == X11_MIT) {
 390                 assert(pr->auth->reallen <= lenof(realauthdata));
 391                 realauthlen = pr->auth->reallen;
 392                 memcpy(realauthdata, pr->auth->realdata, realauthlen);
 393             } else if (pr->auth->realproto == X11_XDM &&
 394                        pr->auth->reallen == 16 &&
 395                        sk_getxdmdata(s, &ip, &port)) {
 396                 time_t t;
 397                 realauthlen = 24;
 398                 memset(realauthdata, 0, 24);
 399                 memcpy(realauthdata, pr->auth->realdata, 8);
 400                 PUT_32BIT_MSB_FIRST(realauthdata+8, ip);
 401                 PUT_16BIT_MSB_FIRST(realauthdata+12, port);
 402                 t = time(NULL);
 403                 PUT_32BIT_MSB_FIRST(realauthdata+14, t);
 404                 des_encrypt_xdmauth(pr->auth->realdata+9, realauthdata, 24);
 405             }
 406             /* implement other auth methods here if required */
 407
 408             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
 409             PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
 410
 411             sk_write(s, (char *)pr->firstpkt, 12);
 412
 413             if (authstrlen) {
 414                 sk_write(s, x11_authnames[pr->auth->realproto], authstrlen);
 415                 sk_write(s, zeroes, 3 & (-authstrlen));
 416             }
 417             if (realauthlen) {
 418                 sk_write(s, realauthdata, realauthlen);
 419                 sk_write(s, zeroes, 3 & (-realauthlen));
 420             }
 421         }
 422         pr->verified = 1;
 423     }
 424
 425     /*
 426      * After initialisation, just copy data simply.
 427      */
 428
 429     return sk_write(s, data, len);
 430 }