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);
174 return NULL; /* FIXME: report an error */
179 * Try upgrading an IP-style localhost display to a Unix-socket
180 * display (as the standard X connection libraries do).
182 if (!disp->unixdomain && sk_address_is_local(disp->addr)) {
183 SockAddr ux = platform_get_x11_unix_address(NULL, disp->displaynum);
184 const char *err = sk_addr_error(ux);
186 /* Create trial connection to see if there is a useful Unix-domain
188 const struct plug_function_table *dummy = &dummy_plug;
189 Socket s = sk_new(sk_addr_dup(ux), 0, 0, 0, 0, 0, (Plug)&dummy);
190 err = sk_socket_error(s);
196 sk_addr_free(disp->addr);
197 disp->unixdomain = TRUE;
199 /* Fill in the rest in a moment */
203 if (disp->unixdomain) {
205 disp->addr = platform_get_x11_unix_address(disp->unixsocketpath,
207 if (disp->unixsocketpath)
208 disp->realhost = dupstr(disp->unixsocketpath);
210 disp->realhost = dupprintf("unix:%d", disp->displaynum);
215 * Invent the remote authorisation details.
217 if (authtype == X11_MIT) {
218 disp->remoteauthproto = X11_MIT;
220 /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
221 disp->remoteauthdata = snewn(16, unsigned char);
222 for (i = 0; i < 16; i++)
223 disp->remoteauthdata[i] = random_byte();
224 disp->remoteauthdatalen = 16;
226 disp->xdmseen = NULL;
228 assert(authtype == X11_XDM);
229 disp->remoteauthproto = X11_XDM;
231 /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
232 disp->remoteauthdata = snewn(16, unsigned char);
233 for (i = 0; i < 16; i++)
234 disp->remoteauthdata[i] = (i == 8 ? 0 : random_byte());
235 disp->remoteauthdatalen = 16;
237 disp->xdmseen = newtree234(xdmseen_cmp);
239 disp->remoteauthprotoname = dupstr(x11_authnames[disp->remoteauthproto]);
240 disp->remoteauthdatastring = snewn(disp->remoteauthdatalen * 2 + 1, char);
241 for (i = 0; i < disp->remoteauthdatalen; i++)
242 sprintf(disp->remoteauthdatastring + i*2, "%02x",
243 disp->remoteauthdata[i]);
246 * Fetch the local authorisation details.
248 disp->localauthproto = X11_NO_AUTH;
249 disp->localauthdata = NULL;
250 disp->localauthdatalen = 0;
251 platform_get_x11_auth(disp, conf);
256 void x11_free_display(struct X11Display *disp)
258 if (disp->xdmseen != NULL) {
259 struct XDMSeen *seen;
260 while ((seen = delpos234(disp->xdmseen, 0)) != NULL)
262 freetree234(disp->xdmseen);
264 sfree(disp->hostname);
265 sfree(disp->unixsocketpath);
266 if (disp->localauthdata)
267 smemclr(disp->localauthdata, disp->localauthdatalen);
268 sfree(disp->localauthdata);
269 if (disp->remoteauthdata)
270 smemclr(disp->remoteauthdata, disp->remoteauthdatalen);
271 sfree(disp->remoteauthdata);
272 sfree(disp->remoteauthprotoname);
273 sfree(disp->remoteauthdatastring);
274 sk_addr_free(disp->addr);
278 #define XDM_MAXSKEW 20*60 /* 20 minute clock skew should be OK */
280 static char *x11_verify(unsigned long peer_ip, int peer_port,
281 struct X11Display *disp, char *proto,
282 unsigned char *data, int dlen)
284 if (strcmp(proto, x11_authnames[disp->remoteauthproto]) != 0)
285 return "wrong authorisation protocol attempted";
286 if (disp->remoteauthproto == X11_MIT) {
287 if (dlen != disp->remoteauthdatalen)
288 return "MIT-MAGIC-COOKIE-1 data was wrong length";
289 if (memcmp(disp->remoteauthdata, data, dlen) != 0)
290 return "MIT-MAGIC-COOKIE-1 data did not match";
292 if (disp->remoteauthproto == X11_XDM) {
296 struct XDMSeen *seen, *ret;
299 return "XDM-AUTHORIZATION-1 data was wrong length";
301 return "cannot do XDM-AUTHORIZATION-1 without remote address data";
302 des_decrypt_xdmauth(disp->remoteauthdata+9, data, 24);
303 if (memcmp(disp->remoteauthdata, data, 8) != 0)
304 return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
305 if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
306 return "XDM-AUTHORIZATION-1 data failed check"; /* IP wrong */
307 if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
308 return "XDM-AUTHORIZATION-1 data failed check"; /* port wrong */
309 t = GET_32BIT_MSB_FIRST(data+14);
310 for (i = 18; i < 24; i++)
311 if (data[i] != 0) /* zero padding wrong */
312 return "XDM-AUTHORIZATION-1 data failed check";
314 if (abs(t - tim) > XDM_MAXSKEW)
315 return "XDM-AUTHORIZATION-1 time stamp was too far out";
316 seen = snew(struct XDMSeen);
318 memcpy(seen->clientid, data+8, 6);
319 assert(disp->xdmseen != NULL);
320 ret = add234(disp->xdmseen, seen);
323 return "XDM-AUTHORIZATION-1 data replayed";
325 /* While we're here, purge entries too old to be replayed. */
327 seen = index234(disp->xdmseen, 0);
328 assert(seen != NULL);
329 if (t - seen->time <= XDM_MAXSKEW)
331 sfree(delpos234(disp->xdmseen, 0));
334 /* implement other protocols here if ever required */
338 void x11_get_auth_from_authfile(struct X11Display *disp,
339 const char *authfilename)
342 char *buf, *ptr, *str[4];
344 int family, protocol;
345 int ideal_match = FALSE;
346 char *ourhostname = get_hostname();
349 * Normally we should look for precisely the details specified in
350 * `disp'. However, there's an oddity when the display is local:
351 * displays like "localhost:0" usually have their details stored
352 * in a Unix-domain-socket record (even if there isn't actually a
353 * real Unix-domain socket available, as with OpenSSH's proxy X11
356 * This is apparently a fudge to get round the meaninglessness of
357 * "localhost" in a shared-home-directory context -- xauth entries
358 * for Unix-domain sockets already disambiguate this by storing
359 * the *local* hostname in the conveniently-blank hostname field,
360 * but IP "localhost" records couldn't do this. So, typically, an
361 * IP "localhost" entry in the auth database isn't present and if
362 * it were it would be ignored.
364 * However, we don't entirely trust that (say) Windows X servers
365 * won't rely on a straight "localhost" entry, bad idea though
366 * that is; so if we can't find a Unix-domain-socket entry we'll
367 * fall back to an IP-based entry if we can find one.
369 int localhost = !disp->unixdomain && sk_address_is_local(disp->addr);
371 authfp = fopen(authfilename, "rb");
375 /* Records in .Xauthority contain four strings of up to 64K each */
376 buf = snewn(65537 * 4, char);
378 while (!ideal_match) {
379 int c, i, j, match = FALSE;
381 #define GET do { c = fgetc(authfp); if (c == EOF) goto done; c = (unsigned char)c; } while (0)
382 /* Expect a big-endian 2-byte number giving address family */
384 GET; family = (family << 8) | c;
385 /* Then expect four strings, each composed of a big-endian 2-byte
386 * length field followed by that many bytes of data */
388 for (i = 0; i < 4; i++) {
390 GET; len[i] = (len[i] << 8) | c;
392 for (j = 0; j < len[i]; j++) {
400 * Now we have a full X authority record in memory. See
401 * whether it matches the display we're trying to
404 * The details we've just read should be interpreted as
407 * - 'family' is the network address family used to
408 * connect to the display. 0 means IPv4; 6 means IPv6;
409 * 256 means Unix-domain sockets.
411 * - str[0] is the network address itself. For IPv4 and
412 * IPv6, this is a string of binary data of the
413 * appropriate length (respectively 4 and 16 bytes)
414 * representing the address in big-endian format, e.g.
415 * 7F 00 00 01 means IPv4 localhost. For Unix-domain
416 * sockets, this is the host name of the machine on
417 * which the Unix-domain display resides (so that an
418 * .Xauthority file on a shared file system can contain
419 * authority entries for Unix-domain displays on
420 * several machines without them clashing).
422 * - str[1] is the display number. I've no idea why
423 * .Xauthority stores this as a string when it has a
424 * perfectly good integer format, but there we go.
426 * - str[2] is the authorisation method, encoded as its
427 * canonical string name (i.e. "MIT-MAGIC-COOKIE-1",
428 * "XDM-AUTHORIZATION-1" or something we don't
431 * - str[3] is the actual authorisation data, stored in
435 if (disp->displaynum < 0 || disp->displaynum != atoi(str[1]))
436 continue; /* not the one */
438 for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
439 if (!strcmp(str[2], x11_authnames[protocol]))
441 if (protocol == lenof(x11_authnames))
442 continue; /* don't recognise this protocol, look for another */
446 if (!disp->unixdomain &&
447 sk_addrtype(disp->addr) == ADDRTYPE_IPV4) {
449 sk_addrcopy(disp->addr, buf);
450 if (len[0] == 4 && !memcmp(str[0], buf, 4)) {
452 /* If this is a "localhost" entry, note it down
453 * but carry on looking for a Unix-domain entry. */
454 ideal_match = !localhost;
459 if (!disp->unixdomain &&
460 sk_addrtype(disp->addr) == ADDRTYPE_IPV6) {
462 sk_addrcopy(disp->addr, buf);
463 if (len[0] == 16 && !memcmp(str[0], buf, 16)) {
465 ideal_match = !localhost;
469 case 256: /* Unix-domain / localhost */
470 if ((disp->unixdomain || localhost)
471 && ourhostname && !strcmp(ourhostname, str[0]))
472 /* A matching Unix-domain socket is always the best
474 match = ideal_match = TRUE;
479 /* Current best guess -- may be overridden if !ideal_match */
480 disp->localauthproto = protocol;
481 sfree(disp->localauthdata); /* free previous guess, if any */
482 disp->localauthdata = snewn(len[3], unsigned char);
483 memcpy(disp->localauthdata, str[3], len[3]);
484 disp->localauthdatalen = len[3];
490 smemclr(buf, 65537 * 4);
495 static void x11_log(Plug p, int type, SockAddr addr, int port,
496 const char *error_msg, int error_code)
498 /* We have no interface to the logging module here, so we drop these. */
501 static int x11_closing(Plug plug, const char *error_msg, int error_code,
504 struct X11Private *pr = (struct X11Private *) plug;
508 * Socket error. Slam the connection instantly shut.
510 sshfwd_unclean_close(pr->c);
513 * Ordinary EOF received on socket. Send an EOF on the SSH
517 sshfwd_write_eof(pr->c);
523 static int x11_receive(Plug plug, int urgent, char *data, int len)
525 struct X11Private *pr = (struct X11Private *) plug;
527 if (sshfwd_write(pr->c, data, len) > 0) {
529 sk_set_frozen(pr->s, 1);
535 static void x11_sent(Plug plug, int bufsize)
537 struct X11Private *pr = (struct X11Private *) plug;
539 sshfwd_unthrottle(pr->c, bufsize);
543 * When setting up X forwarding, we should send the screen number
544 * from the specified local display. This function extracts it from
545 * the display string.
547 int x11_get_screen_number(char *display)
551 n = strcspn(display, ":");
554 n = strcspn(display, ".");
557 return atoi(display + n + 1);
561 * Called to set up the raw connection.
563 * Returns an error message, or NULL on success.
564 * also, fills the SocketsStructure
566 extern const char *x11_init(Socket *s, struct X11Display *disp, void *c,
567 const char *peeraddr, int peerport, Conf *conf)
569 static const struct plug_function_table fn_table = {
578 struct X11Private *pr;
583 pr = snew(struct X11Private);
585 pr->auth_protocol = NULL;
589 pr->throttled = pr->throttle_override = 0;
592 pr->s = *s = new_connection(sk_addr_dup(disp->addr),
593 disp->realhost, disp->port,
594 0, 1, 0, 0, (Plug) pr, conf);
595 if ((err = sk_socket_error(*s)) != NULL) {
601 * See if we can make sense of the peer address we were given.
606 4 == sscanf(peeraddr, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
607 pr->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
608 pr->peer_port = peerport;
615 sk_set_private_ptr(*s, pr);
619 void x11_close(Socket s)
621 struct X11Private *pr;
624 pr = (struct X11Private *) sk_get_private_ptr(s);
625 if (pr->auth_protocol) {
626 sfree(pr->auth_protocol);
627 sfree(pr->auth_data);
635 void x11_unthrottle(Socket s)
637 struct X11Private *pr;
640 pr = (struct X11Private *) sk_get_private_ptr(s);
643 sk_set_frozen(s, pr->throttled || pr->throttle_override);
646 void x11_override_throttle(Socket s, int enable)
648 struct X11Private *pr;
651 pr = (struct X11Private *) sk_get_private_ptr(s);
653 pr->throttle_override = enable;
654 sk_set_frozen(s, pr->throttled || pr->throttle_override);
658 * Called to send data down the raw connection.
660 int x11_send(Socket s, char *data, int len)
662 struct X11Private *pr;
665 pr = (struct X11Private *) sk_get_private_ptr(s);
668 * Read the first packet.
670 while (len > 0 && pr->data_read < 12)
671 pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);
672 if (pr->data_read < 12)
676 * If we have not allocated the auth_protocol and auth_data
677 * strings, do so now.
679 if (!pr->auth_protocol) {
680 pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);
681 pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);
682 pr->auth_psize = (pr->auth_plen + 3) & ~3;
683 pr->auth_dsize = (pr->auth_dlen + 3) & ~3;
684 /* Leave room for a terminating zero, to make our lives easier. */
685 pr->auth_protocol = snewn(pr->auth_psize + 1, char);
686 pr->auth_data = snewn(pr->auth_dsize, unsigned char);
690 * Read the auth_protocol and auth_data strings.
692 while (len > 0 && pr->data_read < 12 + pr->auth_psize)
693 pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);
694 while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
695 pr->auth_data[pr->data_read++ - 12 -
696 pr->auth_psize] = (unsigned char) (len--, *data++);
697 if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)
701 * If we haven't verified the authorisation, do so now.
706 pr->auth_protocol[pr->auth_plen] = '\0'; /* ASCIZ */
707 err = x11_verify(pr->peer_ip, pr->peer_port,
708 pr->disp, pr->auth_protocol,
709 pr->auth_data, pr->auth_dlen);
712 * If authorisation failed, construct and send an error
713 * packet, then terminate the connection.
718 unsigned char *reply;
720 message = dupprintf("%s X11 proxy: %s", appname, err);
721 msglen = strlen(message);
722 reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */
723 msgsize = (msglen + 3) & ~3;
724 reply[0] = 0; /* failure */
725 reply[1] = msglen; /* length of reason string */
726 memcpy(reply + 2, pr->firstpkt + 2, 4); /* major/minor proto vsn */
727 PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
728 memset(reply + 8, 0, msgsize);
729 memcpy(reply + 8, message, msglen);
730 sshfwd_write(pr->c, (char *)reply, 8 + msgsize);
731 sshfwd_write_eof(pr->c);
738 * Now we know we're going to accept the connection. Strip
739 * the fake auth data, and optionally put real auth data in
743 char realauthdata[64];
745 int authstrlen = strlen(x11_authnames[pr->disp->localauthproto]);
746 int buflen = 0; /* initialise to placate optimiser */
747 static const char zeroes[4] = { 0,0,0,0 };
750 if (pr->disp->localauthproto == X11_MIT) {
751 assert(pr->disp->localauthdatalen <= lenof(realauthdata));
752 realauthlen = pr->disp->localauthdatalen;
753 memcpy(realauthdata, pr->disp->localauthdata, realauthlen);
754 } else if (pr->disp->localauthproto == X11_XDM &&
755 pr->disp->localauthdatalen == 16 &&
756 ((buf = sk_getxdmdata(s, &buflen))!=0)) {
758 realauthlen = (buflen+12+7) & ~7;
759 assert(realauthlen <= lenof(realauthdata));
760 memset(realauthdata, 0, realauthlen);
761 memcpy(realauthdata, pr->disp->localauthdata, 8);
762 memcpy(realauthdata+8, buf, buflen);
764 PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t);
765 des_encrypt_xdmauth(pr->disp->localauthdata+9,
766 (unsigned char *)realauthdata,
770 /* implement other auth methods here if required */
772 PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);
773 PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);
775 sk_write(s, (char *)pr->firstpkt, 12);
778 sk_write(s, x11_authnames[pr->disp->localauthproto],
780 sk_write(s, zeroes, 3 & (-authstrlen));
783 sk_write(s, realauthdata, realauthlen);
784 sk_write(s, zeroes, 3 & (-realauthlen));
791 * After initialisation, just copy data simply.
794 return sk_write(s, data, len);
797 void x11_send_eof(Socket s)