/* * Platform-independent bits of X11 forwarding. */ #include #include #include #include #include "putty.h" #include "ssh.h" #include "channel.h" #include "tree234.h" struct XDMSeen { unsigned int time; unsigned char clientid[6]; }; typedef struct X11Connection { unsigned char firstpkt[12]; /* first X data packet */ tree234 *authtree; struct X11Display *disp; char *auth_protocol; unsigned char *auth_data; int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize; bool verified; bool input_wanted; bool no_data_sent_to_x_client; char *peer_addr; int peer_port; SshChannel *c; /* channel structure held by SSH backend */ Socket *s; Plug plug; Channel chan; } X11Connection; static int xdmseen_cmp(void *a, void *b) { struct XDMSeen *sa = a, *sb = b; return sa->time > sb->time ? 1 : sa->time < sb->time ? -1 : memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid)); } struct X11FakeAuth *x11_invent_fake_auth(tree234 *authtree, int authtype) { struct X11FakeAuth *auth = snew(struct X11FakeAuth); int i; /* * This function has the job of inventing a set of X11 fake auth * data, and adding it to 'authtree'. We must preserve the * property that for any given actual authorisation attempt, _at * most one_ thing in the tree can possibly match it. * * For MIT-MAGIC-COOKIE-1, that's not too difficult: the match * criterion is simply that the entire cookie is correct, so we * just have to make sure we don't make up two cookies the same. * (Vanishingly unlikely, but we check anyway to be sure, and go * round again inventing a new cookie if add234 tells us the one * we thought of is already in use.) * * For XDM-AUTHORIZATION-1, it's a little more fiddly. The setup * with XA1 is that half the cookie is used as a DES key with * which to CBC-encrypt an assortment of stuff. Happily, the stuff * encrypted _begins_ with the other half of the cookie, and the * IV is always zero, which means that any valid XA1 authorisation * attempt for a given cookie must begin with the same cipher * block, consisting of the DES ECB encryption of the first half * of the cookie using the second half as a key. So we compute * that cipher block here and now, and use it as the sorting key * for distinguishing XA1 entries in the tree. */ if (authtype == X11_MIT) { auth->proto = X11_MIT; /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */ auth->datalen = 16; auth->data = snewn(auth->datalen, unsigned char); auth->xa1_firstblock = NULL; while (1) { random_read(auth->data, auth->datalen); if (add234(authtree, auth) == auth) break; } auth->xdmseen = NULL; } else { assert(authtype == X11_XDM); auth->proto = X11_XDM; /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */ auth->datalen = 16; auth->data = snewn(auth->datalen, unsigned char); auth->xa1_firstblock = snewn(8, unsigned char); memset(auth->xa1_firstblock, 0, 8); while (1) { random_read(auth->data, 15); auth->data[15] = auth->data[8]; auth->data[8] = 0; memcpy(auth->xa1_firstblock, auth->data, 8); des_encrypt_xdmauth(auth->data + 9, auth->xa1_firstblock, 8); if (add234(authtree, auth) == auth) break; } auth->xdmseen = newtree234(xdmseen_cmp); } auth->protoname = dupstr(x11_authnames[auth->proto]); auth->datastring = snewn(auth->datalen * 2 + 1, char); for (i = 0; i < auth->datalen; i++) sprintf(auth->datastring + i*2, "%02x", auth->data[i]); auth->disp = NULL; auth->share_cs = NULL; auth->share_chan = NULL; return auth; } void x11_free_fake_auth(struct X11FakeAuth *auth) { if (auth->data) smemclr(auth->data, auth->datalen); sfree(auth->data); sfree(auth->protoname); sfree(auth->datastring); sfree(auth->xa1_firstblock); if (auth->xdmseen != NULL) { struct XDMSeen *seen; while ((seen = delpos234(auth->xdmseen, 0)) != NULL) sfree(seen); freetree234(auth->xdmseen); } sfree(auth); } int x11_authcmp(void *av, void *bv) { struct X11FakeAuth *a = (struct X11FakeAuth *)av; struct X11FakeAuth *b = (struct X11FakeAuth *)bv; if (a->proto < b->proto) return -1; else if (a->proto > b->proto) return +1; if (a->proto == X11_MIT) { if (a->datalen < b->datalen) return -1; else if (a->datalen > b->datalen) return +1; return memcmp(a->data, b->data, a->datalen); } else { assert(a->proto == X11_XDM); return memcmp(a->xa1_firstblock, b->xa1_firstblock, 8); } } #define XDM_MAXSKEW 20*60 /* 20 minute clock skew should be OK */ static const char *x11_verify(unsigned long peer_ip, int peer_port, tree234 *authtree, char *proto, unsigned char *data, int dlen, struct X11FakeAuth **auth_ret) { struct X11FakeAuth match_dummy; /* for passing to find234 */ struct X11FakeAuth *auth; /* * First, do a lookup in our tree to find the only authorisation * record that _might_ match. */ if (!strcmp(proto, x11_authnames[X11_MIT])) { /* * Just look up the whole cookie that was presented to us, * which x11_authcmp will compare against the cookies we * currently believe in. */ match_dummy.proto = X11_MIT; match_dummy.datalen = dlen; match_dummy.data = data; } else if (!strcmp(proto, x11_authnames[X11_XDM])) { /* * Look up the first cipher block, against the stored first * cipher blocks for the XDM-AUTHORIZATION-1 cookies we * currently know. (See comment in x11_invent_fake_auth.) */ match_dummy.proto = X11_XDM; match_dummy.xa1_firstblock = data; } else { return "Unsupported authorisation protocol"; } if ((auth = find234(authtree, &match_dummy, 0)) == NULL) return "Authorisation not recognised"; /* * If we're using MIT-MAGIC-COOKIE-1, that was all we needed. If * we're doing XDM-AUTHORIZATION-1, though, we have to check the * rest of the auth data. */ if (auth->proto == X11_XDM) { unsigned long t; time_t tim; int i; struct XDMSeen *seen, *ret; if (dlen != 24) return "XDM-AUTHORIZATION-1 data was wrong length"; if (peer_port == -1) return "cannot do XDM-AUTHORIZATION-1 without remote address data"; des_decrypt_xdmauth(auth->data+9, data, 24); if (memcmp(auth->data, data, 8) != 0) return "XDM-AUTHORIZATION-1 data failed check"; /* cookie wrong */ if (GET_32BIT_MSB_FIRST(data+8) != peer_ip) return "XDM-AUTHORIZATION-1 data failed check"; /* IP wrong */ if ((int)GET_16BIT_MSB_FIRST(data+12) != peer_port) return "XDM-AUTHORIZATION-1 data failed check"; /* port wrong */ t = GET_32BIT_MSB_FIRST(data+14); for (i = 18; i < 24; i++) if (data[i] != 0) /* zero padding wrong */ return "XDM-AUTHORIZATION-1 data failed check"; tim = time(NULL); if (((unsigned long)t - (unsigned long)tim + XDM_MAXSKEW) > 2*XDM_MAXSKEW) return "XDM-AUTHORIZATION-1 time stamp was too far out"; seen = snew(struct XDMSeen); seen->time = t; memcpy(seen->clientid, data+8, 6); assert(auth->xdmseen != NULL); ret = add234(auth->xdmseen, seen); if (ret != seen) { sfree(seen); return "XDM-AUTHORIZATION-1 data replayed"; } /* While we're here, purge entries too old to be replayed. */ for (;;) { seen = index234(auth->xdmseen, 0); assert(seen != NULL); if (t - seen->time <= XDM_MAXSKEW) break; sfree(delpos234(auth->xdmseen, 0)); } } /* implement other protocols here if ever required */ *auth_ret = auth; return NULL; } static void x11_log(Plug *p, PlugLogType type, SockAddr *addr, int port, const char *error_msg, int error_code) { /* We have no interface to the logging module here, so we drop these. */ } static void x11_send_init_error(struct X11Connection *conn, const char *err_message); static void x11_closing(Plug *plug, PlugCloseType type, const char *error_msg) { struct X11Connection *xconn = container_of( plug, struct X11Connection, plug); if (type != PLUGCLOSE_NORMAL) { /* * Socket error. If we're still at the connection setup stage, * construct an X11 error packet passing on the problem. */ if (xconn->no_data_sent_to_x_client) { char *err_message = dupprintf("unable to connect to forwarded " "X server: %s", error_msg); x11_send_init_error(xconn, err_message); sfree(err_message); } /* * Whether we did that or not, now we slam the connection * shut. */ sshfwd_initiate_close(xconn->c, error_msg); } else { /* * Ordinary EOF received on socket. Send an EOF on the SSH * channel. */ if (xconn->c) sshfwd_write_eof(xconn->c); } } static void x11_receive(Plug *plug, int urgent, const char *data, size_t len) { struct X11Connection *xconn = container_of( plug, struct X11Connection, plug); xconn->no_data_sent_to_x_client = false; sshfwd_write(xconn->c, data, len); } static void x11_sent(Plug *plug, size_t bufsize) { struct X11Connection *xconn = container_of( plug, struct X11Connection, plug); sshfwd_unthrottle(xconn->c, bufsize); } static const PlugVtable X11Connection_plugvt = { .log = x11_log, .closing = x11_closing, .receive = x11_receive, .sent = x11_sent, }; static void x11_chan_free(Channel *chan); static size_t x11_send( Channel *chan, bool is_stderr, const void *vdata, size_t len); static void x11_send_eof(Channel *chan); static void x11_set_input_wanted(Channel *chan, bool wanted); static char *x11_log_close_msg(Channel *chan); static const ChannelVtable X11Connection_channelvt = { .free = x11_chan_free, .open_confirmation = chan_remotely_opened_confirmation, .open_failed = chan_remotely_opened_failure, .send = x11_send, .send_eof = x11_send_eof, .set_input_wanted = x11_set_input_wanted, .log_close_msg = x11_log_close_msg, .want_close = chan_default_want_close, .rcvd_exit_status = chan_no_exit_status, .rcvd_exit_signal = chan_no_exit_signal, .rcvd_exit_signal_numeric = chan_no_exit_signal_numeric, .run_shell = chan_no_run_shell, .run_command = chan_no_run_command, .run_subsystem = chan_no_run_subsystem, .enable_x11_forwarding = chan_no_enable_x11_forwarding, .enable_agent_forwarding = chan_no_enable_agent_forwarding, .allocate_pty = chan_no_allocate_pty, .set_env = chan_no_set_env, .send_break = chan_no_send_break, .send_signal = chan_no_send_signal, .change_window_size = chan_no_change_window_size, .request_response = chan_no_request_response, }; /* * Called to set up the X11Connection structure, though this does not * yet connect to an actual server. */ Channel *x11_new_channel(tree234 *authtree, SshChannel *c, const char *peeraddr, int peerport, bool connection_sharing_possible) { struct X11Connection *xconn; /* * Open socket. */ xconn = snew(struct X11Connection); xconn->plug.vt = &X11Connection_plugvt; xconn->chan.vt = &X11Connection_channelvt; xconn->chan.initial_fixed_window_size = (connection_sharing_possible ? 128 : 0); xconn->auth_protocol = NULL; xconn->authtree = authtree; xconn->verified = false; xconn->data_read = 0; xconn->input_wanted = true; xconn->no_data_sent_to_x_client = true; xconn->c = c; /* * We don't actually open a local socket to the X server just yet, * because we don't know which one it is. Instead, we'll wait * until we see the incoming authentication data, which may tell * us what display to connect to, or whether we have to divert * this X forwarding channel to a connection-sharing downstream * rather than handling it ourself. */ xconn->disp = NULL; xconn->s = NULL; /* * Stash the peer address we were given in its original text form. */ xconn->peer_addr = peeraddr ? dupstr(peeraddr) : NULL; xconn->peer_port = peerport; return &xconn->chan; } static void x11_chan_free(Channel *chan) { assert(chan->vt == &X11Connection_channelvt); X11Connection *xconn = container_of(chan, X11Connection, chan); if (xconn->auth_protocol) { sfree(xconn->auth_protocol); sfree(xconn->auth_data); } if (xconn->s) sk_close(xconn->s); sfree(xconn->peer_addr); sfree(xconn); } static void x11_set_input_wanted(Channel *chan, bool wanted) { assert(chan->vt == &X11Connection_channelvt); X11Connection *xconn = container_of(chan, X11Connection, chan); xconn->input_wanted = wanted; if (xconn->s) sk_set_frozen(xconn->s, !xconn->input_wanted); } static void x11_send_init_error(struct X11Connection *xconn, const char *err_message) { char *full_message; int msglen, msgsize; unsigned char *reply; full_message = dupprintf("%s X11 proxy: %s\n", appname, err_message); msglen = strlen(full_message); reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */ msgsize = (msglen + 3) & ~3; reply[0] = 0; /* failure */ reply[1] = msglen; /* length of reason string */ memcpy(reply + 2, xconn->firstpkt + 2, 4); /* major/minor proto vsn */ PUT_16BIT_X11(xconn->firstpkt[0], reply + 6, msgsize >> 2);/* data len */ memset(reply + 8, 0, msgsize); memcpy(reply + 8, full_message, msglen); sshfwd_write(xconn->c, reply, 8 + msgsize); sshfwd_write_eof(xconn->c); xconn->no_data_sent_to_x_client = false; sfree(reply); sfree(full_message); } /* * Called to send data down the raw connection. */ static size_t x11_send( Channel *chan, bool is_stderr, const void *vdata, size_t len) { assert(chan->vt == &X11Connection_channelvt); X11Connection *xconn = container_of(chan, X11Connection, chan); const char *data = (const char *)vdata; /* * Read the first packet. */ while (len > 0 && xconn->data_read < 12) xconn->firstpkt[xconn->data_read++] = (unsigned char) (len--, *data++); if (xconn->data_read < 12) return 0; /* * If we have not allocated the auth_protocol and auth_data * strings, do so now. */ if (!xconn->auth_protocol) { char endian = xconn->firstpkt[0]; xconn->auth_plen = GET_16BIT_X11(endian, xconn->firstpkt + 6); xconn->auth_dlen = GET_16BIT_X11(endian, xconn->firstpkt + 8); xconn->auth_psize = (xconn->auth_plen + 3) & ~3; xconn->auth_dsize = (xconn->auth_dlen + 3) & ~3; /* Leave room for a terminating zero, to make our lives easier. */ xconn->auth_protocol = snewn(xconn->auth_psize + 1, char); xconn->auth_data = snewn(xconn->auth_dsize, unsigned char); } /* * Read the auth_protocol and auth_data strings. */ while (len > 0 && xconn->data_read < 12 + xconn->auth_psize) xconn->auth_protocol[xconn->data_read++ - 12] = (len--, *data++); while (len > 0 && xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize) xconn->auth_data[xconn->data_read++ - 12 - xconn->auth_psize] = (unsigned char) (len--, *data++); if (xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize) return 0; /* * If we haven't verified the authorisation, do so now. */ if (!xconn->verified) { const char *err; struct X11FakeAuth *auth_matched = NULL; unsigned long peer_ip; int peer_port; int protomajor, protominor; void *greeting; int greeting_len; unsigned char *socketdata; int socketdatalen; char new_peer_addr[32]; int new_peer_port; char endian = xconn->firstpkt[0]; protomajor = GET_16BIT_X11(endian, xconn->firstpkt + 2); protominor = GET_16BIT_X11(endian, xconn->firstpkt + 4); assert(!xconn->s); xconn->auth_protocol[xconn->auth_plen] = '\0'; /* ASCIZ */ peer_ip = 0; /* placate optimiser */ if (x11_parse_ip(xconn->peer_addr, &peer_ip)) peer_port = xconn->peer_port; else peer_port = -1; /* signal no peer address data available */ err = x11_verify(peer_ip, peer_port, xconn->authtree, xconn->auth_protocol, xconn->auth_data, xconn->auth_dlen, &auth_matched); if (err) { x11_send_init_error(xconn, err); return 0; } assert(auth_matched); /* * If this auth points to a connection-sharing downstream * rather than an X display we know how to connect to * directly, pass it off to the sharing module now. (This will * have the side effect of freeing xconn.) */ if (auth_matched->share_cs) { sshfwd_x11_sharing_handover(xconn->c, auth_matched->share_cs, auth_matched->share_chan, xconn->peer_addr, xconn->peer_port, xconn->firstpkt[0], protomajor, protominor, data, len); return 0; } /* * Now we know we're going to accept the connection, and what * X display to connect to. Actually connect to it. */ xconn->chan.initial_fixed_window_size = 0; sshfwd_window_override_removed(xconn->c); xconn->disp = auth_matched->disp; xconn->s = new_connection(sk_addr_dup(xconn->disp->addr), xconn->disp->realhost, xconn->disp->port, false, true, false, false, &xconn->plug, sshfwd_get_conf(xconn->c), NULL); if ((err = sk_socket_error(xconn->s)) != NULL) { char *err_message = dupprintf("unable to connect to" " forwarded X server: %s", err); x11_send_init_error(xconn, err_message); sfree(err_message); return 0; } /* * Write a new connection header containing our replacement * auth data. */ socketdatalen = 0; /* placate compiler warning */ socketdata = sk_getxdmdata(xconn->s, &socketdatalen); if (socketdata && socketdatalen==6) { sprintf(new_peer_addr, "%d.%d.%d.%d", socketdata[0], socketdata[1], socketdata[2], socketdata[3]); new_peer_port = GET_16BIT_MSB_FIRST(socketdata + 4); } else { strcpy(new_peer_addr, "0.0.0.0"); new_peer_port = 0; } greeting = x11_make_greeting(xconn->firstpkt[0], protomajor, protominor, xconn->disp->localauthproto, xconn->disp->localauthdata, xconn->disp->localauthdatalen, new_peer_addr, new_peer_port, &greeting_len); sk_write(xconn->s, greeting, greeting_len); smemclr(greeting, greeting_len); sfree(greeting); /* * Now we're done. */ xconn->verified = true; } /* * After initialisation, just copy data simply. */ return sk_write(xconn->s, data, len); } static void x11_send_eof(Channel *chan) { assert(chan->vt == &X11Connection_channelvt); X11Connection *xconn = container_of(chan, X11Connection, chan); if (xconn->s) { sk_write_eof(xconn->s); } else { /* * If EOF is received from the X client before we've got to * the point of actually connecting to an X server, then we * should send an EOF back to the client so that the * forwarded channel will be terminated. */ if (xconn->c) sshfwd_write_eof(xconn->c); } } static char *x11_log_close_msg(Channel *chan) { return dupstr("Forwarded X11 connection terminated"); }