1 /*
2 * Platform-independent bits of X11 forwarding.
3 */
4
5 #include <stdio.h>
6 #include <stdlib.h>
7 #include <assert.h>
8 #include <time.h>
9
10 #include "putty.h"
11 #include "ssh.h"
12 #include "sshchan.h"
13 #include "tree234.h"
14
GET_16BIT_X11(char endian,const void * p)15 static inline uint16_t GET_16BIT_X11(char endian, const void *p)
16 {
17 return endian == 'B' ? GET_16BIT_MSB_FIRST(p) : GET_16BIT_LSB_FIRST(p);
18 }
19
PUT_16BIT_X11(char endian,void * p,uint16_t value)20 static inline void PUT_16BIT_X11(char endian, void *p, uint16_t value)
21 {
22 if (endian == 'B')
23 PUT_16BIT_MSB_FIRST(p, value);
24 else
25 PUT_16BIT_LSB_FIRST(p, value);
26 }
27
28 const char *const x11_authnames[] = {
29 "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1"
30 };
31
32 struct XDMSeen {
33 unsigned int time;
34 unsigned char clientid[6];
35 };
36
37 typedef struct X11Connection {
38 unsigned char firstpkt[12]; /* first X data packet */
39 tree234 *authtree;
40 struct X11Display *disp;
41 char *auth_protocol;
42 unsigned char *auth_data;
43 int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
44 bool verified;
45 bool input_wanted;
46 bool no_data_sent_to_x_client;
47 char *peer_addr;
48 int peer_port;
49 SshChannel *c; /* channel structure held by SSH backend */
50 Socket *s;
51
52 Plug plug;
53 Channel chan;
54 } X11Connection;
55
xdmseen_cmp(void * a,void * b)56 static int xdmseen_cmp(void *a, void *b)
57 {
58 struct XDMSeen *sa = a, *sb = b;
59 return sa->time > sb->time ? 1 :
60 sa->time < sb->time ? -1 :
61 memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
62 }
63
x11_invent_fake_auth(tree234 * authtree,int authtype)64 struct X11FakeAuth *x11_invent_fake_auth(tree234 *authtree, int authtype)
65 {
66 struct X11FakeAuth *auth = snew(struct X11FakeAuth);
67 int i;
68
69 /*
70 * This function has the job of inventing a set of X11 fake auth
71 * data, and adding it to 'authtree'. We must preserve the
72 * property that for any given actual authorisation attempt, _at
73 * most one_ thing in the tree can possibly match it.
74 *
75 * For MIT-MAGIC-COOKIE-1, that's not too difficult: the match
76 * criterion is simply that the entire cookie is correct, so we
77 * just have to make sure we don't make up two cookies the same.
78 * (Vanishingly unlikely, but we check anyway to be sure, and go
79 * round again inventing a new cookie if add234 tells us the one
80 * we thought of is already in use.)
81 *
82 * For XDM-AUTHORIZATION-1, it's a little more fiddly. The setup
83 * with XA1 is that half the cookie is used as a DES key with
84 * which to CBC-encrypt an assortment of stuff. Happily, the stuff
85 * encrypted _begins_ with the other half of the cookie, and the
86 * IV is always zero, which means that any valid XA1 authorisation
87 * attempt for a given cookie must begin with the same cipher
88 * block, consisting of the DES ECB encryption of the first half
89 * of the cookie using the second half as a key. So we compute
90 * that cipher block here and now, and use it as the sorting key
91 * for distinguishing XA1 entries in the tree.
92 */
93
94 if (authtype == X11_MIT) {
95 auth->proto = X11_MIT;
96
97 /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
98 auth->datalen = 16;
99 auth->data = snewn(auth->datalen, unsigned char);
100 auth->xa1_firstblock = NULL;
101
102 while (1) {
103 random_read(auth->data, auth->datalen);
104 if (add234(authtree, auth) == auth)
105 break;
106 }
107
108 auth->xdmseen = NULL;
109 } else {
110 assert(authtype == X11_XDM);
111 auth->proto = X11_XDM;
112
113 /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
114 auth->datalen = 16;
115 auth->data = snewn(auth->datalen, unsigned char);
116 auth->xa1_firstblock = snewn(8, unsigned char);
117 memset(auth->xa1_firstblock, 0, 8);
118
119 while (1) {
120 random_read(auth->data, 15);
121 auth->data[15] = auth->data[8];
122 auth->data[8] = 0;
123
124 memcpy(auth->xa1_firstblock, auth->data, 8);
125 des_encrypt_xdmauth(auth->data + 9, auth->xa1_firstblock, 8);
126 if (add234(authtree, auth) == auth)
127 break;
128 }
129
130 auth->xdmseen = newtree234(xdmseen_cmp);
131 }
132 auth->protoname = dupstr(x11_authnames[auth->proto]);
133 auth->datastring = snewn(auth->datalen * 2 + 1, char);
134 for (i = 0; i < auth->datalen; i++)
135 sprintf(auth->datastring + i*2, "%02x",
136 auth->data[i]);
137
138 auth->disp = NULL;
139 auth->share_cs = NULL;
140 auth->share_chan = NULL;
141
142 return auth;
143 }
144
x11_free_fake_auth(struct X11FakeAuth * auth)145 void x11_free_fake_auth(struct X11FakeAuth *auth)
146 {
147 if (auth->data)
148 smemclr(auth->data, auth->datalen);
149 sfree(auth->data);
150 sfree(auth->protoname);
151 sfree(auth->datastring);
152 sfree(auth->xa1_firstblock);
153 if (auth->xdmseen != NULL) {
154 struct XDMSeen *seen;
155 while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
156 sfree(seen);
157 freetree234(auth->xdmseen);
158 }
159 sfree(auth);
160 }
161
x11_authcmp(void * av,void * bv)162 int x11_authcmp(void *av, void *bv)
163 {
164 struct X11FakeAuth *a = (struct X11FakeAuth *)av;
165 struct X11FakeAuth *b = (struct X11FakeAuth *)bv;
166
167 if (a->proto < b->proto)
168 return -1;
169 else if (a->proto > b->proto)
170 return +1;
171
172 if (a->proto == X11_MIT) {
173 if (a->datalen < b->datalen)
174 return -1;
175 else if (a->datalen > b->datalen)
176 return +1;
177
178 return memcmp(a->data, b->data, a->datalen);
179 } else {
180 assert(a->proto == X11_XDM);
181
182 return memcmp(a->xa1_firstblock, b->xa1_firstblock, 8);
183 }
184 }
185
x11_setup_display(const char * display,Conf * conf,char ** error_msg)186 struct X11Display *x11_setup_display(const char *display, Conf *conf,
187 char **error_msg)
188 {
189 struct X11Display *disp = snew(struct X11Display);
190 char *localcopy;
191
192 *error_msg = NULL;
193
194 if (!display || !*display) {
195 localcopy = platform_get_x_display();
196 if (!localcopy || !*localcopy) {
197 sfree(localcopy);
198 localcopy = dupstr(":0"); /* plausible default for any platform */
199 }
200 } else
201 localcopy = dupstr(display);
202
203 /*
204 * Parse the display name.
205 *
206 * We expect this to have one of the following forms:
207 *
208 * - the standard X format which looks like
209 * [ [ protocol '/' ] host ] ':' displaynumber [ '.' screennumber ]
210 * (X11 also permits a double colon to indicate DECnet, but
211 * that's not our problem, thankfully!)
212 *
213 * - only seen in the wild on MacOS (so far): a pathname to a
214 * Unix-domain socket, which will typically and confusingly
215 * end in ":0", and which I'm currently distinguishing from
216 * the standard scheme by noting that it starts with '/'.
217 */
218 if (localcopy[0] == '/') {
219 disp->unixsocketpath = localcopy;
220 disp->unixdomain = true;
221 disp->hostname = NULL;
222 disp->displaynum = -1;
223 disp->screennum = 0;
224 disp->addr = NULL;
225 } else {
226 char *colon, *dot, *slash;
227 char *protocol, *hostname;
228
229 colon = host_strrchr(localcopy, ':');
230 if (!colon) {
231 *error_msg = dupprintf("display name '%s' has no ':number'"
232 " suffix", localcopy);
233
234 sfree(disp);
235 sfree(localcopy);
236 return NULL;
237 }
238
239 *colon++ = '\0';
240 dot = strchr(colon, '.');
241 if (dot)
242 *dot++ = '\0';
243
244 disp->displaynum = atoi(colon);
245 if (dot)
246 disp->screennum = atoi(dot);
247 else
248 disp->screennum = 0;
249
250 protocol = NULL;
251 hostname = localcopy;
252 if (colon > localcopy) {
253 slash = strchr(localcopy, '/');
254 if (slash) {
255 *slash++ = '\0';
256 protocol = localcopy;
257 hostname = slash;
258 }
259 }
260
261 disp->hostname = *hostname ? dupstr(hostname) : NULL;
262
263 if (protocol)
264 disp->unixdomain = (!strcmp(protocol, "local") ||
265 !strcmp(protocol, "unix"));
266 else if (!*hostname || !strcmp(hostname, "unix"))
267 disp->unixdomain = platform_uses_x11_unix_by_default;
268 else
269 disp->unixdomain = false;
270
271 if (!disp->hostname && !disp->unixdomain)
272 disp->hostname = dupstr("localhost");
273
274 disp->unixsocketpath = NULL;
275 disp->addr = NULL;
276
277 sfree(localcopy);
278 }
279
280 /*
281 * Look up the display hostname, if we need to.
282 */
283 if (!disp->unixdomain) {
284 const char *err;
285
286 disp->port = 6000 + disp->displaynum;
287 disp->addr = name_lookup(disp->hostname, disp->port,
288 &disp->realhost, conf, ADDRTYPE_UNSPEC,
289 NULL, NULL);
290
291 if ((err = sk_addr_error(disp->addr)) != NULL) {
292 *error_msg = dupprintf("unable to resolve host name '%s' in "
293 "display name", disp->hostname);
294
295 sk_addr_free(disp->addr);
296 sfree(disp->hostname);
297 sfree(disp->unixsocketpath);
298 sfree(disp);
299 return NULL;
300 }
301 }
302
303 /*
304 * Try upgrading an IP-style localhost display to a Unix-socket
305 * display (as the standard X connection libraries do).
306 */
307 if (!disp->unixdomain && sk_address_is_local(disp->addr)) {
308 SockAddr *ux = platform_get_x11_unix_address(NULL, disp->displaynum);
309 const char *err = sk_addr_error(ux);
310 if (!err) {
311 /* Create trial connection to see if there is a useful Unix-domain
312 * socket */
313 Socket *s = sk_new(sk_addr_dup(ux), 0, false, false,
314 false, false, nullplug);
315 err = sk_socket_error(s);
316 sk_close(s);
317 }
318 if (err) {
319 sk_addr_free(ux);
320 } else {
321 sk_addr_free(disp->addr);
322 disp->unixdomain = true;
323 disp->addr = ux;
324 /* Fill in the rest in a moment */
325 }
326 }
327
328 if (disp->unixdomain) {
329 if (!disp->addr)
330 disp->addr = platform_get_x11_unix_address(disp->unixsocketpath,
331 disp->displaynum);
332 if (disp->unixsocketpath)
333 disp->realhost = dupstr(disp->unixsocketpath);
334 else
335 disp->realhost = dupprintf("unix:%d", disp->displaynum);
336 disp->port = 0;
337 }
338
339 /*
340 * Fetch the local authorisation details.
341 */
342 disp->localauthproto = X11_NO_AUTH;
343 disp->localauthdata = NULL;
344 disp->localauthdatalen = 0;
345 platform_get_x11_auth(disp, conf);
346
347 return disp;
348 }
349
x11_free_display(struct X11Display * disp)350 void x11_free_display(struct X11Display *disp)
351 {
352 sfree(disp->hostname);
353 sfree(disp->unixsocketpath);
354 if (disp->localauthdata)
355 smemclr(disp->localauthdata, disp->localauthdatalen);
356 sfree(disp->localauthdata);
357 sk_addr_free(disp->addr);
358 sfree(disp);
359 }
360
361 #define XDM_MAXSKEW 20*60 /* 20 minute clock skew should be OK */
362
x11_verify(unsigned long peer_ip,int peer_port,tree234 * authtree,char * proto,unsigned char * data,int dlen,struct X11FakeAuth ** auth_ret)363 static const char *x11_verify(unsigned long peer_ip, int peer_port,
364 tree234 *authtree, char *proto,
365 unsigned char *data, int dlen,
366 struct X11FakeAuth **auth_ret)
367 {
368 struct X11FakeAuth match_dummy; /* for passing to find234 */
369 struct X11FakeAuth *auth;
370
371 /*
372 * First, do a lookup in our tree to find the only authorisation
373 * record that _might_ match.
374 */
375 if (!strcmp(proto, x11_authnames[X11_MIT])) {
376 /*
377 * Just look up the whole cookie that was presented to us,
378 * which x11_authcmp will compare against the cookies we
379 * currently believe in.
380 */
381 match_dummy.proto = X11_MIT;
382 match_dummy.datalen = dlen;
383 match_dummy.data = data;
384 } else if (!strcmp(proto, x11_authnames[X11_XDM])) {
385 /*
386 * Look up the first cipher block, against the stored first
387 * cipher blocks for the XDM-AUTHORIZATION-1 cookies we
388 * currently know. (See comment in x11_invent_fake_auth.)
389 */
390 match_dummy.proto = X11_XDM;
391 match_dummy.xa1_firstblock = data;
392 } else {
393 return "Unsupported authorisation protocol";
394 }
395
396 if ((auth = find234(authtree, &match_dummy, 0)) == NULL)
397 return "Authorisation not recognised";
398
399 /*
400 * If we're using MIT-MAGIC-COOKIE-1, that was all we needed. If
401 * we're doing XDM-AUTHORIZATION-1, though, we have to check the
402 * rest of the auth data.
403 */
404 if (auth->proto == X11_XDM) {
405 unsigned long t;
406 time_t tim;
407 int i;
408 struct XDMSeen *seen, *ret;
409
410 if (dlen != 24)
411 return "XDM-AUTHORIZATION-1 data was wrong length";
412 if (peer_port == -1)
413 return "cannot do XDM-AUTHORIZATION-1 without remote address data";
414 des_decrypt_xdmauth(auth->data+9, data, 24);
415 if (memcmp(auth->data, data, 8) != 0)
416 return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */
417 if (GET_32BIT_MSB_FIRST(data+8) != peer_ip)
418 return "XDM-AUTHORIZATION-1 data failed check"; /* IP wrong */
419 if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port)
420 return "XDM-AUTHORIZATION-1 data failed check"; /* port wrong */
421 t = GET_32BIT_MSB_FIRST(data+14);
422 for (i = 18; i < 24; i++)
423 if (data[i] != 0) /* zero padding wrong */
424 return "XDM-AUTHORIZATION-1 data failed check";
425 tim = time(NULL);
426 if (((unsigned long)t - (unsigned long)tim
427 + XDM_MAXSKEW) > 2*XDM_MAXSKEW)
428 return "XDM-AUTHORIZATION-1 time stamp was too far out";
429 seen = snew(struct XDMSeen);
430 seen->time = t;
431 memcpy(seen->clientid, data+8, 6);
432 assert(auth->xdmseen != NULL);
433 ret = add234(auth->xdmseen, seen);
434 if (ret != seen) {
435 sfree(seen);
436 return "XDM-AUTHORIZATION-1 data replayed";
437 }
438 /* While we're here, purge entries too old to be replayed. */
439 for (;;) {
440 seen = index234(auth->xdmseen, 0);
441 assert(seen != NULL);
442 if (t - seen->time <= XDM_MAXSKEW)
443 break;
444 sfree(delpos234(auth->xdmseen, 0));
445 }
446 }
447 /* implement other protocols here if ever required */
448
449 *auth_ret = auth;
450 return NULL;
451 }
452
BinarySource_get_string_xauth(BinarySource * src)453 ptrlen BinarySource_get_string_xauth(BinarySource *src)
454 {
455 size_t len = get_uint16(src);
456 return get_data(src, len);
457 }
458 #define get_string_xauth(src) \
459 BinarySource_get_string_xauth(BinarySource_UPCAST(src))
460
BinarySink_put_stringpl_xauth(BinarySink * bs,ptrlen pl)461 void BinarySink_put_stringpl_xauth(BinarySink *bs, ptrlen pl)
462 {
463 assert((pl.len >> 16) == 0);
464 put_uint16(bs, pl.len);
465 put_datapl(bs, pl);
466 }
467 #define put_stringpl_xauth(bs, ptrlen) \
468 BinarySink_put_stringpl_xauth(BinarySink_UPCAST(bs),ptrlen)
469
x11_get_auth_from_authfile(struct X11Display * disp,const char * authfilename)470 void x11_get_auth_from_authfile(struct X11Display *disp,
471 const char *authfilename)
472 {
473 FILE *authfp;
474 char *buf;
475 int size;
476 BinarySource src[1];
477 int family, protocol;
478 ptrlen addr, protoname, data;
479 char *displaynum_string;
480 int displaynum;
481 bool ideal_match = false;
482 char *ourhostname;
483
484 /* A maximally sized (wildly implausible) .Xauthority record
485 * consists of a 16-bit integer to start with, then four strings,
486 * each of which has a 16-bit length field followed by that many
487 * bytes of data (i.e. up to 0xFFFF bytes). */
488 const size_t MAX_RECORD_SIZE = 2 + 4 * (2+0xFFFF);
489
490 /* We'll want a buffer of twice that size (see below). */
491 const size_t BUF_SIZE = 2 * MAX_RECORD_SIZE;
492
493 /*
494 * Normally we should look for precisely the details specified in
495 * `disp'. However, there's an oddity when the display is local:
496 * displays like "localhost:0" usually have their details stored
497 * in a Unix-domain-socket record (even if there isn't actually a
498 * real Unix-domain socket available, as with OpenSSH's proxy X11
499 * server).
500 *
501 * This is apparently a fudge to get round the meaninglessness of
502 * "localhost" in a shared-home-directory context -- xauth entries
503 * for Unix-domain sockets already disambiguate this by storing
504 * the *local* hostname in the conveniently-blank hostname field,
505 * but IP "localhost" records couldn't do this. So, typically, an
506 * IP "localhost" entry in the auth database isn't present and if
507 * it were it would be ignored.
508 *
509 * However, we don't entirely trust that (say) Windows X servers
510 * won't rely on a straight "localhost" entry, bad idea though
511 * that is; so if we can't find a Unix-domain-socket entry we'll
512 * fall back to an IP-based entry if we can find one.
513 */
514 bool localhost = !disp->unixdomain && sk_address_is_local(disp->addr);
515
516 authfp = fopen(authfilename, "rb");
517 if (!authfp)
518 return;
519
520 ourhostname = get_hostname();
521
522 /*
523 * Allocate enough space to hold two maximally sized records, so
524 * that a full record can start anywhere in the first half. That
525 * way we avoid the accidentally-quadratic algorithm that would
526 * arise if we moved everything to the front of the buffer after
527 * consuming each record; instead, we only move everything to the
528 * front after our current position gets past the half-way mark.
529 * Before then, there's no need to move anyway; so this guarantees
530 * linear time, in that every byte written into this buffer moves
531 * at most once (because every move is from the second half of the
532 * buffer to the first half).
533 */
534 buf = snewn(BUF_SIZE, char);
535 size = fread(buf, 1, BUF_SIZE, authfp);
536 BinarySource_BARE_INIT(src, buf, size);
537
538 while (!ideal_match) {
539 bool match = false;
540
541 if (src->pos >= MAX_RECORD_SIZE) {
542 size -= src->pos;
543 memcpy(buf, buf + src->pos, size);
544 size += fread(buf + size, 1, BUF_SIZE - size, authfp);
545 BinarySource_BARE_INIT(src, buf, size);
546 }
547
548 family = get_uint16(src);
549 addr = get_string_xauth(src);
550 displaynum_string = mkstr(get_string_xauth(src));
551 displaynum = displaynum_string[0] ? atoi(displaynum_string) : -1;
552 sfree(displaynum_string);
553 protoname = get_string_xauth(src);
554 data = get_string_xauth(src);
555 if (get_err(src))
556 break;
557
558 /*
559 * Now we have a full X authority record in memory. See
560 * whether it matches the display we're trying to
561 * authenticate to.
562 *
563 * The details we've just read should be interpreted as
564 * follows:
565 *
566 * - 'family' is the network address family used to
567 * connect to the display. 0 means IPv4; 6 means IPv6;
568 * 256 means Unix-domain sockets.
569 *
570 * - 'addr' is the network address itself. For IPv4 and
571 * IPv6, this is a string of binary data of the
572 * appropriate length (respectively 4 and 16 bytes)
573 * representing the address in big-endian format, e.g.
574 * 7F 00 00 01 means IPv4 localhost. For Unix-domain
575 * sockets, this is the host name of the machine on
576 * which the Unix-domain display resides (so that an
577 * .Xauthority file on a shared file system can contain
578 * authority entries for Unix-domain displays on
579 * several machines without them clashing).
580 *
581 * - 'displaynum' is the display number. An empty display
582 * number is a wildcard for any display number.
583 *
584 * - 'protoname' is the authorisation protocol, encoded as
585 * its canonical string name (i.e. "MIT-MAGIC-COOKIE-1",
586 * "XDM-AUTHORIZATION-1" or something we don't recognise).
587 *
588 * - 'data' is the actual authorisation data, stored in
589 * binary form.
590 */
591
592 if (disp->displaynum < 0 ||
593 (displaynum >= 0 && disp->displaynum != displaynum))
594 continue; /* not the one */
595
596 for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
597 if (ptrlen_eq_string(protoname, x11_authnames[protocol]))
598 break;
599 if (protocol == lenof(x11_authnames))
600 continue; /* don't recognise this protocol, look for another */
601
602 switch (family) {
603 case 0: /* IPv4 */
604 if (!disp->unixdomain &&
605 sk_addrtype(disp->addr) == ADDRTYPE_IPV4) {
606 char buf[4];
607 sk_addrcopy(disp->addr, buf);
608 if (addr.len == 4 && !memcmp(addr.ptr, buf, 4)) {
609 match = true;
610 /* If this is a "localhost" entry, note it down
611 * but carry on looking for a Unix-domain entry. */
612 ideal_match = !localhost;
613 }
614 }
615 break;
616 case 6: /* IPv6 */
617 if (!disp->unixdomain &&
618 sk_addrtype(disp->addr) == ADDRTYPE_IPV6) {
619 char buf[16];
620 sk_addrcopy(disp->addr, buf);
621 if (addr.len == 16 && !memcmp(addr.ptr, buf, 16)) {
622 match = true;
623 ideal_match = !localhost;
624 }
625 }
626 break;
627 case 256: /* Unix-domain / localhost */
628 if ((disp->unixdomain || localhost)
629 && ourhostname && ptrlen_eq_string(addr, ourhostname)) {
630 /* A matching Unix-domain socket is always the best
631 * match. */
632 match = true;
633 ideal_match = true;
634 }
635 break;
636 }
637
638 if (match) {
639 /* Current best guess -- may be overridden if !ideal_match */
640 disp->localauthproto = protocol;
641 sfree(disp->localauthdata); /* free previous guess, if any */
642 disp->localauthdata = snewn(data.len, unsigned char);
643 memcpy(disp->localauthdata, data.ptr, data.len);
644 disp->localauthdatalen = data.len;
645 }
646 }
647
648 fclose(authfp);
649 smemclr(buf, 2 * MAX_RECORD_SIZE);
650 sfree(buf);
651 sfree(ourhostname);
652 }
653
x11_format_auth_for_authfile(BinarySink * bs,SockAddr * addr,int display_no,ptrlen authproto,ptrlen authdata)654 void x11_format_auth_for_authfile(
655 BinarySink *bs, SockAddr *addr, int display_no,
656 ptrlen authproto, ptrlen authdata)
657 {
658 if (sk_address_is_special_local(addr)) {
659 char *ourhostname = get_hostname();
660 put_uint16(bs, 256); /* indicates Unix-domain socket */
661 put_stringpl_xauth(bs, ptrlen_from_asciz(ourhostname));
662 sfree(ourhostname);
663 } else if (sk_addrtype(addr) == ADDRTYPE_IPV4) {
664 char ipv4buf[4];
665 sk_addrcopy(addr, ipv4buf);
666 put_uint16(bs, 0); /* indicates IPv4 */
667 put_stringpl_xauth(bs, make_ptrlen(ipv4buf, 4));
668 } else if (sk_addrtype(addr) == ADDRTYPE_IPV6) {
669 char ipv6buf[16];
670 sk_addrcopy(addr, ipv6buf);
671 put_uint16(bs, 6); /* indicates IPv6 */
672 put_stringpl_xauth(bs, make_ptrlen(ipv6buf, 16));
673 } else {
674 unreachable("Bad address type in x11_format_auth_for_authfile");
675 }
676
677 {
678 char *numberbuf = dupprintf("%d", display_no);
679 put_stringpl_xauth(bs, ptrlen_from_asciz(numberbuf));
680 sfree(numberbuf);
681 }
682
683 put_stringpl_xauth(bs, authproto);
684 put_stringpl_xauth(bs, authdata);
685 }
686
x11_log(Plug * p,PlugLogType type,SockAddr * addr,int port,const char * error_msg,int error_code)687 static void x11_log(Plug *p, PlugLogType type, SockAddr *addr, int port,
688 const char *error_msg, int error_code)
689 {
690 /* We have no interface to the logging module here, so we drop these. */
691 }
692
693 static void x11_send_init_error(struct X11Connection *conn,
694 const char *err_message);
695
x11_closing(Plug * plug,const char * error_msg,int error_code,bool calling_back)696 static void x11_closing(Plug *plug, const char *error_msg, int error_code,
697 bool calling_back)
698 {
699 struct X11Connection *xconn = container_of(
700 plug, struct X11Connection, plug);
701
702 if (error_msg) {
703 /*
704 * Socket error. If we're still at the connection setup stage,
705 * construct an X11 error packet passing on the problem.
706 */
707 if (xconn->no_data_sent_to_x_client) {
708 char *err_message = dupprintf("unable to connect to forwarded "
709 "X server: %s", error_msg);
710 x11_send_init_error(xconn, err_message);
711 sfree(err_message);
712 }
713
714 /*
715 * Whether we did that or not, now we slam the connection
716 * shut.
717 */
718 sshfwd_initiate_close(xconn->c, error_msg);
719 } else {
720 /*
721 * Ordinary EOF received on socket. Send an EOF on the SSH
722 * channel.
723 */
724 if (xconn->c)
725 sshfwd_write_eof(xconn->c);
726 }
727 }
728
x11_receive(Plug * plug,int urgent,const char * data,size_t len)729 static void x11_receive(Plug *plug, int urgent, const char *data, size_t len)
730 {
731 struct X11Connection *xconn = container_of(
732 plug, struct X11Connection, plug);
733
734 xconn->no_data_sent_to_x_client = false;
735 sshfwd_write(xconn->c, data, len);
736 }
737
x11_sent(Plug * plug,size_t bufsize)738 static void x11_sent(Plug *plug, size_t bufsize)
739 {
740 struct X11Connection *xconn = container_of(
741 plug, struct X11Connection, plug);
742
743 sshfwd_unthrottle(xconn->c, bufsize);
744 }
745
746 /*
747 * When setting up X forwarding, we should send the screen number
748 * from the specified local display. This function extracts it from
749 * the display string.
750 */
x11_get_screen_number(char * display)751 int x11_get_screen_number(char *display)
752 {
753 int n;
754
755 n = host_strcspn(display, ":");
756 if (!display[n])
757 return 0;
758 n = strcspn(display, ".");
759 if (!display[n])
760 return 0;
761 return atoi(display + n + 1);
762 }
763
764 static const PlugVtable X11Connection_plugvt = {
765 .log = x11_log,
766 .closing = x11_closing,
767 .receive = x11_receive,
768 .sent = x11_sent,
769 };
770
771 static void x11_chan_free(Channel *chan);
772 static size_t x11_send(
773 Channel *chan, bool is_stderr, const void *vdata, size_t len);
774 static void x11_send_eof(Channel *chan);
775 static void x11_set_input_wanted(Channel *chan, bool wanted);
776 static char *x11_log_close_msg(Channel *chan);
777
778 static const ChannelVtable X11Connection_channelvt = {
779 .free = x11_chan_free,
780 .open_confirmation = chan_remotely_opened_confirmation,
781 .open_failed = chan_remotely_opened_failure,
782 .send = x11_send,
783 .send_eof = x11_send_eof,
784 .set_input_wanted = x11_set_input_wanted,
785 .log_close_msg = x11_log_close_msg,
786 .want_close = chan_default_want_close,
787 .rcvd_exit_status = chan_no_exit_status,
788 .rcvd_exit_signal = chan_no_exit_signal,
789 .rcvd_exit_signal_numeric = chan_no_exit_signal_numeric,
790 .run_shell = chan_no_run_shell,
791 .run_command = chan_no_run_command,
792 .run_subsystem = chan_no_run_subsystem,
793 .enable_x11_forwarding = chan_no_enable_x11_forwarding,
794 .enable_agent_forwarding = chan_no_enable_agent_forwarding,
795 .allocate_pty = chan_no_allocate_pty,
796 .set_env = chan_no_set_env,
797 .send_break = chan_no_send_break,
798 .send_signal = chan_no_send_signal,
799 .change_window_size = chan_no_change_window_size,
800 .request_response = chan_no_request_response,
801 };
802
803 /*
804 * Called to set up the X11Connection structure, though this does not
805 * yet connect to an actual server.
806 */
x11_new_channel(tree234 * authtree,SshChannel * c,const char * peeraddr,int peerport,bool connection_sharing_possible)807 Channel *x11_new_channel(tree234 *authtree, SshChannel *c,
808 const char *peeraddr, int peerport,
809 bool connection_sharing_possible)
810 {
811 struct X11Connection *xconn;
812
813 /*
814 * Open socket.
815 */
816 xconn = snew(struct X11Connection);
817 xconn->plug.vt = &X11Connection_plugvt;
818 xconn->chan.vt = &X11Connection_channelvt;
819 xconn->chan.initial_fixed_window_size =
820 (connection_sharing_possible ? 128 : 0);
821 xconn->auth_protocol = NULL;
822 xconn->authtree = authtree;
823 xconn->verified = false;
824 xconn->data_read = 0;
825 xconn->input_wanted = true;
826 xconn->no_data_sent_to_x_client = true;
827 xconn->c = c;
828
829 /*
830 * We don't actually open a local socket to the X server just yet,
831 * because we don't know which one it is. Instead, we'll wait
832 * until we see the incoming authentication data, which may tell
833 * us what display to connect to, or whether we have to divert
834 * this X forwarding channel to a connection-sharing downstream
835 * rather than handling it ourself.
836 */
837 xconn->disp = NULL;
838 xconn->s = NULL;
839
840 /*
841 * Stash the peer address we were given in its original text form.
842 */
843 xconn->peer_addr = peeraddr ? dupstr(peeraddr) : NULL;
844 xconn->peer_port = peerport;
845
846 return &xconn->chan;
847 }
848
x11_chan_free(Channel * chan)849 static void x11_chan_free(Channel *chan)
850 {
851 assert(chan->vt == &X11Connection_channelvt);
852 X11Connection *xconn = container_of(chan, X11Connection, chan);
853
854 if (xconn->auth_protocol) {
855 sfree(xconn->auth_protocol);
856 sfree(xconn->auth_data);
857 }
858
859 if (xconn->s)
860 sk_close(xconn->s);
861
862 sfree(xconn->peer_addr);
863 sfree(xconn);
864 }
865
x11_set_input_wanted(Channel * chan,bool wanted)866 static void x11_set_input_wanted(Channel *chan, bool wanted)
867 {
868 assert(chan->vt == &X11Connection_channelvt);
869 X11Connection *xconn = container_of(chan, X11Connection, chan);
870
871 xconn->input_wanted = wanted;
872 if (xconn->s)
873 sk_set_frozen(xconn->s, !xconn->input_wanted);
874 }
875
x11_send_init_error(struct X11Connection * xconn,const char * err_message)876 static void x11_send_init_error(struct X11Connection *xconn,
877 const char *err_message)
878 {
879 char *full_message;
880 int msglen, msgsize;
881 unsigned char *reply;
882
883 full_message = dupprintf("%s X11 proxy: %s\n", appname, err_message);
884
885 msglen = strlen(full_message);
886 reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */
887 msgsize = (msglen + 3) & ~3;
888 reply[0] = 0; /* failure */
889 reply[1] = msglen; /* length of reason string */
890 memcpy(reply + 2, xconn->firstpkt + 2, 4); /* major/minor proto vsn */
891 PUT_16BIT_X11(xconn->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
892 memset(reply + 8, 0, msgsize);
893 memcpy(reply + 8, full_message, msglen);
894 sshfwd_write(xconn->c, reply, 8 + msgsize);
895 sshfwd_write_eof(xconn->c);
896 xconn->no_data_sent_to_x_client = false;
897 sfree(reply);
898 sfree(full_message);
899 }
900
x11_parse_ip(const char * addr_string,unsigned long * ip)901 static bool x11_parse_ip(const char *addr_string, unsigned long *ip)
902 {
903
904 /*
905 * See if we can make sense of this string as an IPv4 address, for
906 * XDM-AUTHORIZATION-1 purposes.
907 */
908 int i[4];
909 if (addr_string &&
910 4 == sscanf(addr_string, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
911 *ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
912 return true;
913 } else {
914 return false;
915 }
916 }
917
918 /*
919 * Called to send data down the raw connection.
920 */
x11_send(Channel * chan,bool is_stderr,const void * vdata,size_t len)921 static size_t x11_send(
922 Channel *chan, bool is_stderr, const void *vdata, size_t len)
923 {
924 assert(chan->vt == &X11Connection_channelvt);
925 X11Connection *xconn = container_of(chan, X11Connection, chan);
926 const char *data = (const char *)vdata;
927
928 /*
929 * Read the first packet.
930 */
931 while (len > 0 && xconn->data_read < 12)
932 xconn->firstpkt[xconn->data_read++] = (unsigned char) (len--, *data++);
933 if (xconn->data_read < 12)
934 return 0;
935
936 /*
937 * If we have not allocated the auth_protocol and auth_data
938 * strings, do so now.
939 */
940 if (!xconn->auth_protocol) {
941 char endian = xconn->firstpkt[0];
942 xconn->auth_plen = GET_16BIT_X11(endian, xconn->firstpkt + 6);
943 xconn->auth_dlen = GET_16BIT_X11(endian, xconn->firstpkt + 8);
944 xconn->auth_psize = (xconn->auth_plen + 3) & ~3;
945 xconn->auth_dsize = (xconn->auth_dlen + 3) & ~3;
946 /* Leave room for a terminating zero, to make our lives easier. */
947 xconn->auth_protocol = snewn(xconn->auth_psize + 1, char);
948 xconn->auth_data = snewn(xconn->auth_dsize, unsigned char);
949 }
950
951 /*
952 * Read the auth_protocol and auth_data strings.
953 */
954 while (len > 0 &&
955 xconn->data_read < 12 + xconn->auth_psize)
956 xconn->auth_protocol[xconn->data_read++ - 12] = (len--, *data++);
957 while (len > 0 &&
958 xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize)
959 xconn->auth_data[xconn->data_read++ - 12 -
960 xconn->auth_psize] = (unsigned char) (len--, *data++);
961 if (xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize)
962 return 0;
963
964 /*
965 * If we haven't verified the authorisation, do so now.
966 */
967 if (!xconn->verified) {
968 const char *err;
969 struct X11FakeAuth *auth_matched = NULL;
970 unsigned long peer_ip;
971 int peer_port;
972 int protomajor, protominor;
973 void *greeting;
974 int greeting_len;
975 unsigned char *socketdata;
976 int socketdatalen;
977 char new_peer_addr[32];
978 int new_peer_port;
979 char endian = xconn->firstpkt[0];
980
981 protomajor = GET_16BIT_X11(endian, xconn->firstpkt + 2);
982 protominor = GET_16BIT_X11(endian, xconn->firstpkt + 4);
983
984 assert(!xconn->s);
985
986 xconn->auth_protocol[xconn->auth_plen] = '\0'; /* ASCIZ */
987
988 peer_ip = 0; /* placate optimiser */
989 if (x11_parse_ip(xconn->peer_addr, &peer_ip))
990 peer_port = xconn->peer_port;
991 else
992 peer_port = -1; /* signal no peer address data available */
993
994 err = x11_verify(peer_ip, peer_port,
995 xconn->authtree, xconn->auth_protocol,
996 xconn->auth_data, xconn->auth_dlen, &auth_matched);
997 if (err) {
998 x11_send_init_error(xconn, err);
999 return 0;
1000 }
1001 assert(auth_matched);
1002
1003 /*
1004 * If this auth points to a connection-sharing downstream
1005 * rather than an X display we know how to connect to
1006 * directly, pass it off to the sharing module now. (This will
1007 * have the side effect of freeing xconn.)
1008 */
1009 if (auth_matched->share_cs) {
1010 sshfwd_x11_sharing_handover(xconn->c, auth_matched->share_cs,
1011 auth_matched->share_chan,
1012 xconn->peer_addr, xconn->peer_port,
1013 xconn->firstpkt[0],
1014 protomajor, protominor, data, len);
1015 return 0;
1016 }
1017
1018 /*
1019 * Now we know we're going to accept the connection, and what
1020 * X display to connect to. Actually connect to it.
1021 */
1022 xconn->chan.initial_fixed_window_size = 0;
1023 sshfwd_window_override_removed(xconn->c);
1024 xconn->disp = auth_matched->disp;
1025 xconn->s = new_connection(sk_addr_dup(xconn->disp->addr),
1026 xconn->disp->realhost, xconn->disp->port,
1027 false, true, false, false, &xconn->plug,
1028 sshfwd_get_conf(xconn->c));
1029 if ((err = sk_socket_error(xconn->s)) != NULL) {
1030 char *err_message = dupprintf("unable to connect to"
1031 " forwarded X server: %s", err);
1032 x11_send_init_error(xconn, err_message);
1033 sfree(err_message);
1034 return 0;
1035 }
1036
1037 /*
1038 * Write a new connection header containing our replacement
1039 * auth data.
1040 */
1041 socketdatalen = 0; /* placate compiler warning */
1042 socketdata = sk_getxdmdata(xconn->s, &socketdatalen);
1043 if (socketdata && socketdatalen==6) {
1044 sprintf(new_peer_addr, "%d.%d.%d.%d", socketdata[0],
1045 socketdata[1], socketdata[2], socketdata[3]);
1046 new_peer_port = GET_16BIT_MSB_FIRST(socketdata + 4);
1047 } else {
1048 strcpy(new_peer_addr, "0.0.0.0");
1049 new_peer_port = 0;
1050 }
1051
1052 greeting = x11_make_greeting(xconn->firstpkt[0],
1053 protomajor, protominor,
1054 xconn->disp->localauthproto,
1055 xconn->disp->localauthdata,
1056 xconn->disp->localauthdatalen,
1057 new_peer_addr, new_peer_port,
1058 &greeting_len);
1059
1060 sk_write(xconn->s, greeting, greeting_len);
1061
1062 smemclr(greeting, greeting_len);
1063 sfree(greeting);
1064
1065 /*
1066 * Now we're done.
1067 */
1068 xconn->verified = true;
1069 }
1070
1071 /*
1072 * After initialisation, just copy data simply.
1073 */
1074
1075 return sk_write(xconn->s, data, len);
1076 }
1077
x11_send_eof(Channel * chan)1078 static void x11_send_eof(Channel *chan)
1079 {
1080 assert(chan->vt == &X11Connection_channelvt);
1081 X11Connection *xconn = container_of(chan, X11Connection, chan);
1082
1083 if (xconn->s) {
1084 sk_write_eof(xconn->s);
1085 } else {
1086 /*
1087 * If EOF is received from the X client before we've got to
1088 * the point of actually connecting to an X server, then we
1089 * should send an EOF back to the client so that the
1090 * forwarded channel will be terminated.
1091 */
1092 if (xconn->c)
1093 sshfwd_write_eof(xconn->c);
1094 }
1095 }
1096
x11_log_close_msg(Channel * chan)1097 static char *x11_log_close_msg(Channel *chan)
1098 {
1099 return dupstr("Forwarded X11 connection terminated");
1100 }
1101
1102 /*
1103 * Utility functions used by connection sharing to convert textual
1104 * representations of an X11 auth protocol name + hex cookie into our
1105 * usual integer protocol id and binary auth data.
1106 */
x11_identify_auth_proto(ptrlen protoname)1107 int x11_identify_auth_proto(ptrlen protoname)
1108 {
1109 int protocol;
1110
1111 for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
1112 if (ptrlen_eq_string(protoname, x11_authnames[protocol]))
1113 return protocol;
1114 return -1;
1115 }
1116
x11_dehexify(ptrlen hexpl,int * outlen)1117 void *x11_dehexify(ptrlen hexpl, int *outlen)
1118 {
1119 int len, i;
1120 unsigned char *ret;
1121
1122 len = hexpl.len / 2;
1123 ret = snewn(len, unsigned char);
1124
1125 for (i = 0; i < len; i++) {
1126 char bytestr[3];
1127 unsigned val = 0;
1128 bytestr[0] = ((const char *)hexpl.ptr)[2*i];
1129 bytestr[1] = ((const char *)hexpl.ptr)[2*i+1];
1130 bytestr[2] = '\0';
1131 sscanf(bytestr, "%x", &val);
1132 ret[i] = val;
1133 }
1134
1135 *outlen = len;
1136 return ret;
1137 }
1138
1139 /*
1140 * Construct an X11 greeting packet, including making up the right
1141 * authorisation data.
1142 */
x11_make_greeting(int endian,int protomajor,int protominor,int auth_proto,const void * auth_data,int auth_len,const char * peer_addr,int peer_port,int * outlen)1143 void *x11_make_greeting(int endian, int protomajor, int protominor,
1144 int auth_proto, const void *auth_data, int auth_len,
1145 const char *peer_addr, int peer_port,
1146 int *outlen)
1147 {
1148 unsigned char *greeting;
1149 unsigned char realauthdata[64];
1150 const char *authname;
1151 const unsigned char *authdata;
1152 int authnamelen, authnamelen_pad;
1153 int authdatalen, authdatalen_pad;
1154 int greeting_len;
1155
1156 authname = x11_authnames[auth_proto];
1157 authnamelen = strlen(authname);
1158 authnamelen_pad = (authnamelen + 3) & ~3;
1159
1160 if (auth_proto == X11_MIT) {
1161 authdata = auth_data;
1162 authdatalen = auth_len;
1163 } else if (auth_proto == X11_XDM && auth_len == 16) {
1164 time_t t;
1165 unsigned long peer_ip = 0;
1166
1167 x11_parse_ip(peer_addr, &peer_ip);
1168
1169 authdata = realauthdata;
1170 authdatalen = 24;
1171 memset(realauthdata, 0, authdatalen);
1172 memcpy(realauthdata, auth_data, 8);
1173 PUT_32BIT_MSB_FIRST(realauthdata+8, peer_ip);
1174 PUT_16BIT_MSB_FIRST(realauthdata+12, peer_port);
1175 t = time(NULL);
1176 PUT_32BIT_MSB_FIRST(realauthdata+14, t);
1177
1178 des_encrypt_xdmauth((char *)auth_data + 9, realauthdata, authdatalen);
1179 } else {
1180 authdata = realauthdata;
1181 authdatalen = 0;
1182 }
1183
1184 authdatalen_pad = (authdatalen + 3) & ~3;
1185 greeting_len = 12 + authnamelen_pad + authdatalen_pad;
1186
1187 greeting = snewn(greeting_len, unsigned char);
1188 memset(greeting, 0, greeting_len);
1189 greeting[0] = endian;
1190 PUT_16BIT_X11(endian, greeting+2, protomajor);
1191 PUT_16BIT_X11(endian, greeting+4, protominor);
1192 PUT_16BIT_X11(endian, greeting+6, authnamelen);
1193 PUT_16BIT_X11(endian, greeting+8, authdatalen);
1194 memcpy(greeting+12, authname, authnamelen);
1195 memcpy(greeting+12+authnamelen_pad, authdata, authdatalen);
1196
1197 smemclr(realauthdata, sizeof(realauthdata));
1198
1199 *outlen = greeting_len;
1200 return greeting;
1201 }
1202