2 * Platform-independent bits of X11 forwarding.
14 #define GET_16BIT(endian, cp) \
15 (endian=='B' ? GET_16BIT_MSB_FIRST(cp) : GET_16BIT_LSB_FIRST(cp))
17 #define PUT_16BIT(endian, cp, val) \
18 (endian=='B' ? PUT_16BIT_MSB_FIRST(cp, val) : PUT_16BIT_LSB_FIRST(cp, val))
20 const char *const x11_authnames[] = {
21 "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1"
26 unsigned char clientid[6];
30 const struct plug_function_table *fn;
31 /* the above variable absolutely *must* be the first in this structure */
32 unsigned char firstpkt[12]; /* first X data packet */
33 struct X11Display *disp;
35 unsigned char *auth_data;
36 int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
38 int throttled, throttle_override;
39 unsigned long peer_ip;
41 void *c; /* data used by ssh.c */
45 static int xdmseen_cmp(void *a, void *b)
47 struct XDMSeen *sa = a, *sb = b;
48 return sa->time > sb->time ? 1 :
49 sa->time < sb->time ? -1 :
50 memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
53 /* Do-nothing "plug" implementation, used by x11_setup_display() when it
54 * creates a trial connection (and then immediately closes it).
55 * XXX: bit out of place here, could in principle live in a platform-
56 * independent network.c or something */
57 static void dummy_plug_log(Plug p, int type, SockAddr addr, int port,
58 const char *error_msg, int error_code) { }
59 static int dummy_plug_closing
60 (Plug p, const char *error_msg, int error_code, int calling_back)
62 static int dummy_plug_receive(Plug p, int urgent, char *data, int len)
64 static void dummy_plug_sent(Plug p, int bufsize) { }
65 static int dummy_plug_accepting(Plug p, OSSocket sock) { return 1; }
66 static const struct plug_function_table dummy_plug = {
67 dummy_plug_log, dummy_plug_closing, dummy_plug_receive,
68 dummy_plug_sent, dummy_plug_accepting
71 struct X11Display *x11_setup_display(char *display, int authtype, Conf *conf)
73 struct X11Display *disp = snew(struct X11Display);
77 if (!display || !*display) {
78 localcopy = platform_get_x_display();
79 if (!localcopy || !*localcopy) {
81 localcopy = dupstr(":0"); /* plausible default for any platform */
84 localcopy = dupstr(display);
87 * Parse the display name.
89 * We expect this to have one of the following forms:
91 * - the standard X format which looks like
92 * [ [ protocol '/' ] host ] ':' displaynumber [ '.' screennumber ]
93 * (X11 also permits a double colon to indicate DECnet, but
94 * that's not our problem, thankfully!)
96 * - only seen in the wild on MacOS (so far): a pathname to a
97 * Unix-domain socket, which will typically and confusingly
98 * end in ":0", and which I'm currently distinguishing from
99 * the standard scheme by noting that it starts with '/'.
101 if (localcopy[0] == '/') {
102 disp->unixsocketpath = localcopy;
103 disp->unixdomain = TRUE;
104 disp->hostname = NULL;
105 disp->displaynum = -1;
109 char *colon, *dot, *slash;
110 char *protocol, *hostname;
112 colon = strrchr(localcopy, ':');
116 return NULL; /* FIXME: report a specific error? */
120 dot = strchr(colon, '.');
124 disp->displaynum = atoi(colon);
126 disp->screennum = atoi(dot);
131 hostname = localcopy;
132 if (colon > localcopy) {
133 slash = strchr(localcopy, '/');
136 protocol = localcopy;
141 disp->hostname = *hostname ? dupstr(hostname) : NULL;
144 disp->unixdomain = (!strcmp(protocol, "local") ||
145 !strcmp(protocol, "unix"));
146 else if (!*hostname || !strcmp(hostname, "unix"))
147 disp->unixdomain = platform_uses_x11_unix_by_default;
149 disp->unixdomain = FALSE;
151 if (!disp->hostname && !disp->unixdomain)
152 disp->hostname = dupstr("localhost");
154 disp->unixsocketpath = NULL;
161 * Look up the display hostname, if we need to.
163 if (!disp->unixdomain) {
166 disp->port = 6000 + disp->displaynum;
167 disp->addr = name_lookup(disp->hostname, disp->port,
168 &disp->realhost, conf, ADDRTYPE_UNSPEC);
170 if ((err = sk_addr_error(disp->addr)) != NULL) {
171 sk_addr_free(disp->addr);
172 sfree(disp->hostname);
173 sfree(disp->unixsocketpath);
175 return NULL; /* FIXME: report an error */
180 * Try upgrading an IP-style localhost display to a Unix-socket
181 * display (as the standard X connection libraries do).
183 if (!disp->unixdomain && sk_address_is_local(disp->addr)) {
184 SockAddr ux = platform_get_x11_unix_address(NULL, disp->displaynum);
185 const char *err = sk_addr_error(ux);
187 /* Create trial connection to see if there is a useful Unix-domain
189 const struct plug_function_table *dummy = &dummy_plug;
190 Socket s = sk_new(sk_addr_dup(ux), 0, 0, 0, 0, 0, (Plug)&dummy);
191 err = sk_socket_error(s);
197 sk_addr_free(disp->addr);
198 disp->unixdomain = TRUE;
200 /* Fill in the rest in a moment */
204 if (disp->unixdomain) {
206 disp->addr = platform_get_x11_unix_address(disp->unixsocketpath,
208 if (disp->unixsocketpath)
209 disp->realhost = dupstr(disp->unixsocketpath);
211 disp->realhost = dupprintf("unix:%d", disp->displaynum);
216 * Invent the remote authorisation details.
218 if (authtype == X11_MIT) {
219 disp->remoteauthproto = X11_MIT;
221 /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
222 disp->remoteauthdata = snewn(16, unsigned char);
223 for (i = 0; i < 16; i++)
224 disp->remoteauthdata[i] = random_byte();
225 disp->remoteauthdatalen = 16;
227 disp->xdmseen = NULL;
229 assert(authtype == X11_XDM);
230 disp->remoteauthproto = X11_XDM;
232 /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
233 disp->remoteauthdata = snewn(16, unsigned char);
234 for (i = 0; i < 16; i++)
235 disp->remoteauthdata[i] = (i == 8 ? 0 : random_byte());
236 disp->remoteauthdatalen = 16;
238 disp->xdmseen = newtree234(xdmseen_cmp);
240 disp->remoteauthprotoname = dupstr(x11_authnames[disp->remoteauthproto]);
241 disp->remoteauthdatastring = snewn(disp->remoteauthdatalen * 2 + 1, char);
242 for (i = 0; i < disp->remoteauthdatalen; i++)
243 sprintf(disp->remoteauthdatastring + i*2, "%02x",
244 disp->remoteauthdata[i]);
247 * Fetch the local authorisation details.
249 disp->localauthproto = X11_NO_AUTH;
250 disp->localauthdata = NULL;
251 disp->localauthdatalen = 0;
252 platform_get_x11_auth(disp, conf);
257 void x11_free_display(struct X11Display *disp)
259 if (disp->xdmseen != NULL) {
260 struct XDMSeen *seen;
261 while ((seen = delpos234(disp->xdmseen, 0)) != NULL)
263 freetree234(disp->xdmseen);
265 sfree(disp->hostname);
266 sfree(disp->unixsocketpath);
267 if (disp->localauthdata)
268 smemclr(disp->localauthdata, disp->localauthdatalen);
269 sfree(disp->localauthdata);
270 if (disp->remoteauthdata)
271 smemclr(disp->remoteauthdata, disp->remoteauthdatalen);
272 sfree(disp->remoteauthdata);
273 sfree(disp->remoteauthprotoname);
274 sfree(disp->remoteauthdatastring);
275 sk_addr_free(disp->addr);
279 #define XDM_MAXSKEW 20*60 /* 20 minute clock skew should be OK */
281 static char *x11_verify(unsigned long peer_ip, int peer_port,
282 struct X11Display *disp, char *proto,
283 unsigned char *data, int dlen)
285 if (strcmp(proto, x11_authnames[disp->remoteauthproto]) != 0)
286 return "wrong authorisation protocol attempted";
287 if (disp->remoteauthproto == X11_MIT) {
288 if (dlen != disp->remoteauthdatalen)
289 return "MIT-MAGIC-COOKIE-1 data was wrong length";
290 if (memcmp(disp->remoteauthdata, data, dlen) != 0)
291 return "MIT-MAGIC-COOKIE-1 data did not match";
293 if (disp->remoteauthproto == X11_XDM) {
297 struct XDMSeen *seen, *ret;
300 return "XDM-AUTHORIZATION-1 data was wrong length";
302 return "cannot do XDM-AUTHORIZATION-1 without remote address data";
303 des_decrypt_xdmauth(disp->remoteauthdata+9, data, 24);
304 if (memcmp(disp->remoteauthdata, data, 8) != 0)
305 return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
306 if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
307 return "XDM-AUTHORIZATION-1 data failed check"; /* IP wrong */
308 if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
309 return "XDM-AUTHORIZATION-1 data failed check"; /* port wrong */
310 t = GET_32BIT_MSB_FIRST(data+14);
311 for (i = 18; i < 24; i++)
312 if (data[i] != 0) /* zero padding wrong */
313 return "XDM-AUTHORIZATION-1 data failed check";
315 if (abs(t - tim) > XDM_MAXSKEW)
316 return "XDM-AUTHORIZATION-1 time stamp was too far out";
317 seen = snew(struct XDMSeen);
319 memcpy(seen->clientid, data+8, 6);
320 assert(disp->xdmseen != NULL);
321 ret = add234(disp->xdmseen, seen);
324 return "XDM-AUTHORIZATION-1 data replayed";
326 /* While we're here, purge entries too old to be replayed. */
328 seen = index234(disp->xdmseen, 0);
329 assert(seen != NULL);
330 if (t - seen->time <= XDM_MAXSKEW)
332 sfree(delpos234(disp->xdmseen, 0));
335 /* implement other protocols here if ever required */
339 void x11_get_auth_from_authfile(struct X11Display *disp,
340 const char *authfilename)
343 char *buf, *ptr, *str[4];
345 int family, protocol;
346 int ideal_match = FALSE;
350 * Normally we should look for precisely the details specified in
351 * `disp'. However, there's an oddity when the display is local:
352 * displays like "localhost:0" usually have their details stored
353 * in a Unix-domain-socket record (even if there isn't actually a
354 * real Unix-domain socket available, as with OpenSSH's proxy X11
357 * This is apparently a fudge to get round the meaninglessness of
358 * "localhost" in a shared-home-directory context -- xauth entries
359 * for Unix-domain sockets already disambiguate this by storing
360 * the *local* hostname in the conveniently-blank hostname field,
361 * but IP "localhost" records couldn't do this. So, typically, an
362 * IP "localhost" entry in the auth database isn't present and if
363 * it were it would be ignored.
365 * However, we don't entirely trust that (say) Windows X servers
366 * won't rely on a straight "localhost" entry, bad idea though
367 * that is; so if we can't find a Unix-domain-socket entry we'll
368 * fall back to an IP-based entry if we can find one.
370 int localhost = !disp->unixdomain && sk_address_is_local(disp->addr);
372 authfp = fopen(authfilename, "rb");
376 ourhostname = get_hostname();
378 /* Records in .Xauthority contain four strings of up to 64K each */
379 buf = snewn(65537 * 4, char);
381 while (!ideal_match) {
382 int c, i, j, match = FALSE;
384 #define GET do { c = fgetc(authfp); if (c == EOF) goto done; c = (unsigned char)c; } while (0)
385 /* Expect a big-endian 2-byte number giving address family */
387 GET; family = (family << 8) | c;
388 /* Then expect four strings, each composed of a big-endian 2-byte
389 * length field followed by that many bytes of data */
391 for (i = 0; i < 4; i++) {
393 GET; len[i] = (len[i] << 8) | c;
395 for (j = 0; j < len[i]; j++) {
403 * Now we have a full X authority record in memory. See
404 * whether it matches the display we're trying to
407 * The details we've just read should be interpreted as
410 * - 'family' is the network address family used to
411 * connect to the display. 0 means IPv4; 6 means IPv6;
412 * 256 means Unix-domain sockets.
414 * - str[0] is the network address itself. For IPv4 and
415 * IPv6, this is a string of binary data of the
416 * appropriate length (respectively 4 and 16 bytes)
417 * representing the address in big-endian format, e.g.
418 * 7F 00 00 01 means IPv4 localhost. For Unix-domain
419 * sockets, this is the host name of the machine on
420 * which the Unix-domain display resides (so that an
421 * .Xauthority file on a shared file system can contain
422 * authority entries for Unix-domain displays on
423 * several machines without them clashing).
425 * - str[1] is the display number. I've no idea why
426 * .Xauthority stores this as a string when it has a
427 * perfectly good integer format, but there we go.
429 * - str[2] is the authorisation method, encoded as its
430 * canonical string name (i.e. "MIT-MAGIC-COOKIE-1",
431 * "XDM-AUTHORIZATION-1" or something we don't
434 * - str[3] is the actual authorisation data, stored in
438 if (disp->displaynum < 0 || disp->displaynum != atoi(str[1]))
439 continue; /* not the one */
441 for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
442 if (!strcmp(str[2], x11_authnames[protocol]))
444 if (protocol == lenof(x11_authnames))
445 continue; /* don't recognise this protocol, look for another */
449 if (!disp->unixdomain &&
450 sk_addrtype(disp->addr) == ADDRTYPE_IPV4) {
452 sk_addrcopy(disp->addr, buf);
453 if (len[0] == 4 && !memcmp(str[0], buf, 4)) {
455 /* If this is a "localhost" entry, note it down
456 * but carry on looking for a Unix-domain entry. */
457 ideal_match = !localhost;
462 if (!disp->unixdomain &&
463 sk_addrtype(disp->addr) == ADDRTYPE_IPV6) {
465 sk_addrcopy(disp->addr, buf);
466 if (len[0] == 16 && !memcmp(str[0], buf, 16)) {
468 ideal_match = !localhost;
472 case 256: /* Unix-domain / localhost */
473 if ((disp->unixdomain || localhost)
474 && ourhostname && !strcmp(ourhostname, str[0]))
475 /* A matching Unix-domain socket is always the best
477 match = ideal_match = TRUE;
482 /* Current best guess -- may be overridden if !ideal_match */
483 disp->localauthproto = protocol;
484 sfree(disp->localauthdata); /* free previous guess, if any */
485 disp->localauthdata = snewn(len[3], unsigned char);
486 memcpy(disp->localauthdata, str[3], len[3]);
487 disp->localauthdatalen = len[3];
493 smemclr(buf, 65537 * 4);
498 static void x11_log(Plug p, int type, SockAddr addr, int port,
499 const char *error_msg, int error_code)
501 /* We have no interface to the logging module here, so we drop these. */
504 static int x11_closing(Plug plug, const char *error_msg, int error_code,
507 struct X11Private *pr = (struct X11Private *) plug;
511 * Socket error. Slam the connection instantly shut.
513 sshfwd_unclean_close(pr->c);
516 * Ordinary EOF received on socket. Send an EOF on the SSH
520 sshfwd_write_eof(pr->c);
526 static int x11_receive(Plug plug, int urgent, char *data, int len)
528 struct X11Private *pr = (struct X11Private *) plug;
530 if (sshfwd_write(pr->c, data, len) > 0) {
532 sk_set_frozen(pr->s, 1);
538 static void x11_sent(Plug plug, int bufsize)
540 struct X11Private *pr = (struct X11Private *) plug;
542 sshfwd_unthrottle(pr->c, bufsize);
546 * When setting up X forwarding, we should send the screen number
547 * from the specified local display. This function extracts it from
548 * the display string.
550 int x11_get_screen_number(char *display)
554 n = strcspn(display, ":");
557 n = strcspn(display, ".");
560 return atoi(display + n + 1);
564 * Called to set up the raw connection.
566 * Returns an error message, or NULL on success.
567 * also, fills the SocketsStructure
569 extern const char *x11_init(Socket *s, struct X11Display *disp, void *c,
570 const char *peeraddr, int peerport, Conf *conf)
572 static const struct plug_function_table fn_table = {
581 struct X11Private *pr;
586 pr = snew(struct X11Private);
588 pr->auth_protocol = NULL;
592 pr->throttled = pr->throttle_override = 0;
595 pr->s = *s = new_connection(sk_addr_dup(disp->addr),
596 disp->realhost, disp->port,
597 0, 1, 0, 0, (Plug) pr, conf);
598 if ((err = sk_socket_error(*s)) != NULL) {
604 * See if we can make sense of the peer address we were given.
609 4 == sscanf(peeraddr, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
610 pr->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
611 pr->peer_port = peerport;
618 sk_set_private_ptr(*s, pr);
622 void x11_close(Socket s)
624 struct X11Private *pr;
627 pr = (struct X11Private *) sk_get_private_ptr(s);
628 if (pr->auth_protocol) {
629 sfree(pr->auth_protocol);
630 sfree(pr->auth_data);
638 void x11_unthrottle(Socket s)
640 struct X11Private *pr;
643 pr = (struct X11Private *) sk_get_private_ptr(s);
646 sk_set_frozen(s, pr->throttled || pr->throttle_override);
649 void x11_override_throttle(Socket s, int enable)
651 struct X11Private *pr;
654 pr = (struct X11Private *) sk_get_private_ptr(s);
656 pr->throttle_override = enable;
657 sk_set_frozen(s, pr->throttled || pr->throttle_override);
661 * Called to send data down the raw connection.
663 int x11_send(Socket s, char *data, int len)
665 struct X11Private *pr;
668 pr = (struct X11Private *) sk_get_private_ptr(s);
671 * Read the first packet.
673 while (len > 0 && pr->data_read < 12)
674 pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
675 if (pr->data_read < 12)
679 * If we have not allocated the auth_protocol and auth_data
680 * strings, do so now.
682 if (!pr->auth_protocol) {
683 pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
684 pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
685 pr->auth_psize = (pr->auth_plen + 3) & ~3;
686 pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
687 /* Leave room for a terminating zero, to make our lives easier. */
688 pr->auth_protocol = snewn(pr->auth_psize + 1, char);
689 pr->auth_data = snewn(pr->auth_dsize, unsigned char);
693 * Read the auth_protocol and auth_data strings.
695 while (len > 0 && pr->data_read < 12 + pr->auth_psize)
696 pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
697 while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
698 pr->auth_data[pr->data_read++ - 12 -
699 pr->auth_psize] = (unsigned char) (len--, *data++);
700 if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
704 * If we haven't verified the authorisation, do so now.
709 pr->auth_protocol[pr->auth_plen] = '\0'; /* ASCIZ */
710 err = x11_verify(pr->peer_ip, pr->peer_port,
711 pr->disp, pr->auth_protocol,
712 pr->auth_data, pr->auth_dlen);
715 * If authorisation failed, construct and send an error
716 * packet, then terminate the connection.
721 unsigned char *reply;
723 message = dupprintf("%s X11 proxy: %s", appname, err);
724 msglen = strlen(message);
725 reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */
726 msgsize = (msglen + 3) & ~3;
727 reply[0] = 0; /* failure */
728 reply[1] = msglen; /* length of reason string */
729 memcpy(reply + 2, pr->firstpkt + 2, 4); /* major/minor proto vsn */
730 PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
731 memset(reply + 8, 0, msgsize);
732 memcpy(reply + 8, message, msglen);
733 sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
734 sshfwd_write_eof(pr->c);
741 * Now we know we're going to accept the connection. Strip
742 * the fake auth data, and optionally put real auth data in
746 char realauthdata[64];
748 int authstrlen = strlen(x11_authnames[pr->disp->localauthproto]);
749 int buflen = 0; /* initialise to placate optimiser */
750 static const char zeroes[4] = { 0,0,0,0 };
753 if (pr->disp->localauthproto == X11_MIT) {
754 assert(pr->disp->localauthdatalen <= lenof(realauthdata));
755 realauthlen = pr->disp->localauthdatalen;
756 memcpy(realauthdata, pr->disp->localauthdata, realauthlen);
757 } else if (pr->disp->localauthproto == X11_XDM &&
758 pr->disp->localauthdatalen == 16 &&
759 ((buf = sk_getxdmdata(s, &buflen))!=0)) {
761 realauthlen = (buflen+12+7) & ~7;
762 assert(realauthlen <= lenof(realauthdata));
763 memset(realauthdata, 0, realauthlen);
764 memcpy(realauthdata, pr->disp->localauthdata, 8);
765 memcpy(realauthdata+8, buf, buflen);
767 PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t);
768 des_encrypt_xdmauth(pr->disp->localauthdata+9,
769 (unsigned char *)realauthdata,
773 /* implement other auth methods here if required */
775 PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
776 PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
778 sk_write(s, (char *)pr->firstpkt, 12);
781 sk_write(s, x11_authnames[pr->disp->localauthproto],
783 sk_write(s, zeroes, 3 & (-authstrlen));
786 sk_write(s, realauthdata, realauthlen);
787 sk_write(s, zeroes, 3 & (-realauthlen));
794 * After initialisation, just copy data simply.
797 return sk_write(s, data, len);
800 void x11_send_eof(Socket s)