/* * Platform-independent bits of X11 forwarding. */ #include #include #include #include #include "putty.h" #include "ssh.h" #include "tree234.h" #define GET_16BIT(endian, cp) \ (endian=='B' ? GET_16BIT_MSB_FIRST(cp) : GET_16BIT_LSB_FIRST(cp)) #define PUT_16BIT(endian, cp, val) \ (endian=='B' ? PUT_16BIT_MSB_FIRST(cp, val) : PUT_16BIT_LSB_FIRST(cp, val)) const char *const x11_authnames[] = { "", "MIT-MAGIC-COOKIE-1", "XDM-AUTHORIZATION-1" }; struct XDMSeen { unsigned int time; unsigned char clientid[6]; }; struct X11Connection { const struct plug_function_table *fn; /* the above variable absolutely *must* be the first in this structure */ unsigned char firstpkt[12]; /* first X data packet */ struct X11Display *disp; char *auth_protocol; unsigned char *auth_data; int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize; int verified; int throttled, throttle_override; int no_data_sent_to_x_client; unsigned long peer_ip; int peer_port; struct ssh_channel *c; /* channel structure held by ssh.c */ Socket s; }; 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)); } /* Do-nothing "plug" implementation, used by x11_setup_display() when it * creates a trial connection (and then immediately closes it). * XXX: bit out of place here, could in principle live in a platform- * independent network.c or something */ static void dummy_plug_log(Plug p, int type, SockAddr addr, int port, const char *error_msg, int error_code) { } static int dummy_plug_closing (Plug p, const char *error_msg, int error_code, int calling_back) { return 1; } static int dummy_plug_receive(Plug p, int urgent, char *data, int len) { return 1; } static void dummy_plug_sent(Plug p, int bufsize) { } static int dummy_plug_accepting(Plug p, accept_fn_t constructor, accept_ctx_t ctx) { return 1; } static const struct plug_function_table dummy_plug = { dummy_plug_log, dummy_plug_closing, dummy_plug_receive, dummy_plug_sent, dummy_plug_accepting }; struct X11Display *x11_setup_display(char *display, int authtype, Conf *conf) { struct X11Display *disp = snew(struct X11Display); char *localcopy; int i; if (!display || !*display) { localcopy = platform_get_x_display(); if (!localcopy || !*localcopy) { sfree(localcopy); localcopy = dupstr(":0"); /* plausible default for any platform */ } } else localcopy = dupstr(display); /* * Parse the display name. * * We expect this to have one of the following forms: * * - the standard X format which looks like * [ [ protocol '/' ] host ] ':' displaynumber [ '.' screennumber ] * (X11 also permits a double colon to indicate DECnet, but * that's not our problem, thankfully!) * * - only seen in the wild on MacOS (so far): a pathname to a * Unix-domain socket, which will typically and confusingly * end in ":0", and which I'm currently distinguishing from * the standard scheme by noting that it starts with '/'. */ if (localcopy[0] == '/') { disp->unixsocketpath = localcopy; disp->unixdomain = TRUE; disp->hostname = NULL; disp->displaynum = -1; disp->screennum = 0; disp->addr = NULL; } else { char *colon, *dot, *slash; char *protocol, *hostname; colon = strrchr(localcopy, ':'); if (!colon) { sfree(disp); sfree(localcopy); return NULL; /* FIXME: report a specific error? */ } *colon++ = '\0'; dot = strchr(colon, '.'); if (dot) *dot++ = '\0'; disp->displaynum = atoi(colon); if (dot) disp->screennum = atoi(dot); else disp->screennum = 0; protocol = NULL; hostname = localcopy; if (colon > localcopy) { slash = strchr(localcopy, '/'); if (slash) { *slash++ = '\0'; protocol = localcopy; hostname = slash; } } disp->hostname = *hostname ? dupstr(hostname) : NULL; if (protocol) disp->unixdomain = (!strcmp(protocol, "local") || !strcmp(protocol, "unix")); else if (!*hostname || !strcmp(hostname, "unix")) disp->unixdomain = platform_uses_x11_unix_by_default; else disp->unixdomain = FALSE; if (!disp->hostname && !disp->unixdomain) disp->hostname = dupstr("localhost"); disp->unixsocketpath = NULL; disp->addr = NULL; sfree(localcopy); } /* * Look up the display hostname, if we need to. */ if (!disp->unixdomain) { const char *err; disp->port = 6000 + disp->displaynum; disp->addr = name_lookup(disp->hostname, disp->port, &disp->realhost, conf, ADDRTYPE_UNSPEC); if ((err = sk_addr_error(disp->addr)) != NULL) { sk_addr_free(disp->addr); sfree(disp->hostname); sfree(disp->unixsocketpath); sfree(disp); return NULL; /* FIXME: report an error */ } } /* * Try upgrading an IP-style localhost display to a Unix-socket * display (as the standard X connection libraries do). */ if (!disp->unixdomain && sk_address_is_local(disp->addr)) { SockAddr ux = platform_get_x11_unix_address(NULL, disp->displaynum); const char *err = sk_addr_error(ux); if (!err) { /* Create trial connection to see if there is a useful Unix-domain * socket */ const struct plug_function_table *dummy = &dummy_plug; Socket s = sk_new(sk_addr_dup(ux), 0, 0, 0, 0, 0, (Plug)&dummy); err = sk_socket_error(s); sk_close(s); } if (err) { sk_addr_free(ux); } else { sk_addr_free(disp->addr); disp->unixdomain = TRUE; disp->addr = ux; /* Fill in the rest in a moment */ } } if (disp->unixdomain) { if (!disp->addr) disp->addr = platform_get_x11_unix_address(disp->unixsocketpath, disp->displaynum); if (disp->unixsocketpath) disp->realhost = dupstr(disp->unixsocketpath); else disp->realhost = dupprintf("unix:%d", disp->displaynum); disp->port = 0; } /* * Invent the remote authorisation details. */ if (authtype == X11_MIT) { disp->remoteauthproto = X11_MIT; /* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */ disp->remoteauthdata = snewn(16, unsigned char); for (i = 0; i < 16; i++) disp->remoteauthdata[i] = random_byte(); disp->remoteauthdatalen = 16; disp->xdmseen = NULL; } else { assert(authtype == X11_XDM); disp->remoteauthproto = X11_XDM; /* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */ disp->remoteauthdata = snewn(16, unsigned char); for (i = 0; i < 16; i++) disp->remoteauthdata[i] = (i == 8 ? 0 : random_byte()); disp->remoteauthdatalen = 16; disp->xdmseen = newtree234(xdmseen_cmp); } disp->remoteauthprotoname = dupstr(x11_authnames[disp->remoteauthproto]); disp->remoteauthdatastring = snewn(disp->remoteauthdatalen * 2 + 1, char); for (i = 0; i < disp->remoteauthdatalen; i++) sprintf(disp->remoteauthdatastring + i*2, "%02x", disp->remoteauthdata[i]); /* * Fetch the local authorisation details. */ disp->localauthproto = X11_NO_AUTH; disp->localauthdata = NULL; disp->localauthdatalen = 0; platform_get_x11_auth(disp, conf); return disp; } void x11_free_display(struct X11Display *disp) { if (disp->xdmseen != NULL) { struct XDMSeen *seen; while ((seen = delpos234(disp->xdmseen, 0)) != NULL) sfree(seen); freetree234(disp->xdmseen); } sfree(disp->hostname); sfree(disp->unixsocketpath); if (disp->localauthdata) smemclr(disp->localauthdata, disp->localauthdatalen); sfree(disp->localauthdata); if (disp->remoteauthdata) smemclr(disp->remoteauthdata, disp->remoteauthdatalen); sfree(disp->remoteauthdata); sfree(disp->remoteauthprotoname); sfree(disp->remoteauthdatastring); sk_addr_free(disp->addr); sfree(disp); } #define XDM_MAXSKEW 20*60 /* 20 minute clock skew should be OK */ static char *x11_verify(unsigned long peer_ip, int peer_port, struct X11Display *disp, char *proto, unsigned char *data, int dlen) { if (strcmp(proto, x11_authnames[disp->remoteauthproto]) != 0) return "wrong authorisation protocol attempted"; if (disp->remoteauthproto == X11_MIT) { if (dlen != disp->remoteauthdatalen) return "MIT-MAGIC-COOKIE-1 data was wrong length"; if (memcmp(disp->remoteauthdata, data, dlen) != 0) return "MIT-MAGIC-COOKIE-1 data did not match"; } if (disp->remoteauthproto == 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(disp->remoteauthdata+9, data, 24); if (memcmp(disp->remoteauthdata, 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 (abs(t - tim) > 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(disp->xdmseen != NULL); ret = add234(disp->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(disp->xdmseen, 0); assert(seen != NULL); if (t - seen->time <= XDM_MAXSKEW) break; sfree(delpos234(disp->xdmseen, 0)); } } /* implement other protocols here if ever required */ return NULL; } void x11_get_auth_from_authfile(struct X11Display *disp, const char *authfilename) { FILE *authfp; char *buf, *ptr, *str[4]; int len[4]; int family, protocol; int ideal_match = FALSE; char *ourhostname; /* * Normally we should look for precisely the details specified in * `disp'. However, there's an oddity when the display is local: * displays like "localhost:0" usually have their details stored * in a Unix-domain-socket record (even if there isn't actually a * real Unix-domain socket available, as with OpenSSH's proxy X11 * server). * * This is apparently a fudge to get round the meaninglessness of * "localhost" in a shared-home-directory context -- xauth entries * for Unix-domain sockets already disambiguate this by storing * the *local* hostname in the conveniently-blank hostname field, * but IP "localhost" records couldn't do this. So, typically, an * IP "localhost" entry in the auth database isn't present and if * it were it would be ignored. * * However, we don't entirely trust that (say) Windows X servers * won't rely on a straight "localhost" entry, bad idea though * that is; so if we can't find a Unix-domain-socket entry we'll * fall back to an IP-based entry if we can find one. */ int localhost = !disp->unixdomain && sk_address_is_local(disp->addr); authfp = fopen(authfilename, "rb"); if (!authfp) return; ourhostname = get_hostname(); /* Records in .Xauthority contain four strings of up to 64K each */ buf = snewn(65537 * 4, char); while (!ideal_match) { int c, i, j, match = FALSE; #define GET do { c = fgetc(authfp); if (c == EOF) goto done; c = (unsigned char)c; } while (0) /* Expect a big-endian 2-byte number giving address family */ GET; family = c; GET; family = (family << 8) | c; /* Then expect four strings, each composed of a big-endian 2-byte * length field followed by that many bytes of data */ ptr = buf; for (i = 0; i < 4; i++) { GET; len[i] = c; GET; len[i] = (len[i] << 8) | c; str[i] = ptr; for (j = 0; j < len[i]; j++) { GET; *ptr++ = c; } *ptr++ = '\0'; } #undef GET /* * Now we have a full X authority record in memory. See * whether it matches the display we're trying to * authenticate to. * * The details we've just read should be interpreted as * follows: * * - 'family' is the network address family used to * connect to the display. 0 means IPv4; 6 means IPv6; * 256 means Unix-domain sockets. * * - str[0] is the network address itself. For IPv4 and * IPv6, this is a string of binary data of the * appropriate length (respectively 4 and 16 bytes) * representing the address in big-endian format, e.g. * 7F 00 00 01 means IPv4 localhost. For Unix-domain * sockets, this is the host name of the machine on * which the Unix-domain display resides (so that an * .Xauthority file on a shared file system can contain * authority entries for Unix-domain displays on * several machines without them clashing). * * - str[1] is the display number. I've no idea why * .Xauthority stores this as a string when it has a * perfectly good integer format, but there we go. * * - str[2] is the authorisation method, encoded as its * canonical string name (i.e. "MIT-MAGIC-COOKIE-1", * "XDM-AUTHORIZATION-1" or something we don't * recognise). * * - str[3] is the actual authorisation data, stored in * binary form. */ if (disp->displaynum < 0 || disp->displaynum != atoi(str[1])) continue; /* not the one */ for (protocol = 1; protocol < lenof(x11_authnames); protocol++) if (!strcmp(str[2], x11_authnames[protocol])) break; if (protocol == lenof(x11_authnames)) continue; /* don't recognise this protocol, look for another */ switch (family) { case 0: /* IPv4 */ if (!disp->unixdomain && sk_addrtype(disp->addr) == ADDRTYPE_IPV4) { char buf[4]; sk_addrcopy(disp->addr, buf); if (len[0] == 4 && !memcmp(str[0], buf, 4)) { match = TRUE; /* If this is a "localhost" entry, note it down * but carry on looking for a Unix-domain entry. */ ideal_match = !localhost; } } break; case 6: /* IPv6 */ if (!disp->unixdomain && sk_addrtype(disp->addr) == ADDRTYPE_IPV6) { char buf[16]; sk_addrcopy(disp->addr, buf); if (len[0] == 16 && !memcmp(str[0], buf, 16)) { match = TRUE; ideal_match = !localhost; } } break; case 256: /* Unix-domain / localhost */ if ((disp->unixdomain || localhost) && ourhostname && !strcmp(ourhostname, str[0])) /* A matching Unix-domain socket is always the best * match. */ match = ideal_match = TRUE; break; } if (match) { /* Current best guess -- may be overridden if !ideal_match */ disp->localauthproto = protocol; sfree(disp->localauthdata); /* free previous guess, if any */ disp->localauthdata = snewn(len[3], unsigned char); memcpy(disp->localauthdata, str[3], len[3]); disp->localauthdatalen = len[3]; } } done: fclose(authfp); smemclr(buf, 65537 * 4); sfree(buf); sfree(ourhostname); } static void x11_log(Plug p, int 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 int x11_closing(Plug plug, const char *error_msg, int error_code, int calling_back) { struct X11Connection *xconn = (struct X11Connection *) plug; if (error_msg) { /* * 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_unclean_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); } return 1; } static int x11_receive(Plug plug, int urgent, char *data, int len) { struct X11Connection *xconn = (struct X11Connection *) plug; if (sshfwd_write(xconn->c, data, len) > 0) { xconn->throttled = 1; xconn->no_data_sent_to_x_client = FALSE; sk_set_frozen(xconn->s, 1); } return 1; } static void x11_sent(Plug plug, int bufsize) { struct X11Connection *xconn = (struct X11Connection *) plug; sshfwd_unthrottle(xconn->c, bufsize); } /* * When setting up X forwarding, we should send the screen number * from the specified local display. This function extracts it from * the display string. */ int x11_get_screen_number(char *display) { int n; n = strcspn(display, ":"); if (!display[n]) return 0; n = strcspn(display, "."); if (!display[n]) return 0; return atoi(display + n + 1); } /* * Called to set up the raw connection. * * On success, returns NULL and fills in *xconnret. On error, returns * a dynamically allocated error message string. */ extern char *x11_init(struct X11Connection **xconnret, struct X11Display *disp, void *c, const char *peeraddr, int peerport) { static const struct plug_function_table fn_table = { x11_log, x11_closing, x11_receive, x11_sent, NULL }; struct X11Connection *xconn; /* * Open socket. */ xconn = *xconnret = snew(struct X11Connection); xconn->fn = &fn_table; xconn->auth_protocol = NULL; xconn->disp = disp; xconn->verified = 0; xconn->data_read = 0; xconn->throttled = xconn->throttle_override = 0; 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. * Instead, we'll wait until we see the incoming authentication * data, which may tell us we have to divert this X forwarding * channel to a connection-sharing downstream rather than handling * it ourself. */ xconn->s = NULL; /* * See if we can make sense of the peer address we were given. */ { int i[4]; if (peeraddr && 4 == sscanf(peeraddr, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) { xconn->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3]; xconn->peer_port = peerport; } else { xconn->peer_ip = 0; xconn->peer_port = -1; } } return NULL; } void x11_close(struct X11Connection *xconn) { if (!xconn) return; if (xconn->auth_protocol) { sfree(xconn->auth_protocol); sfree(xconn->auth_data); } if (xconn->s) sk_close(xconn->s); sfree(xconn); } void x11_unthrottle(struct X11Connection *xconn) { if (!xconn) return; xconn->throttled = 0; if (xconn->s) sk_set_frozen(xconn->s, xconn->throttled || xconn->throttle_override); } void x11_override_throttle(struct X11Connection *xconn, int enable) { if (!xconn) return; xconn->throttle_override = enable; if (xconn->s) sk_set_frozen(xconn->s, xconn->throttled || xconn->throttle_override); } 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(xconn->firstpkt[0], reply + 6, msgsize >> 2);/* data len */ memset(reply + 8, 0, msgsize); memcpy(reply + 8, full_message, msglen); sshfwd_write(xconn->c, (char *)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. */ int x11_send(struct X11Connection *xconn, char *data, int len) { if (!xconn) return 0; /* * 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) { xconn->auth_plen = GET_16BIT(xconn->firstpkt[0], xconn->firstpkt + 6); xconn->auth_dlen = GET_16BIT(xconn->firstpkt[0], 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; assert(!xconn->s); xconn->auth_protocol[xconn->auth_plen] = '\0'; /* ASCIZ */ err = x11_verify(xconn->peer_ip, xconn->peer_port, xconn->disp, xconn->auth_protocol, xconn->auth_data, xconn->auth_dlen); if (err) { x11_send_init_error(xconn, err); return 0; } /* * Now we know we're going to accept the connection. Actually * connect to the X server. */ xconn->s = new_connection(sk_addr_dup(xconn->disp->addr), xconn->disp->realhost, xconn->disp->port, 0, 1, 0, 0, (Plug) xconn, sshfwd_get_conf(xconn->c)); 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; } /* * Strip the fake auth data, and optionally put real auth data * in instead. */ { char realauthdata[64]; int realauthlen = 0; int authstrlen = strlen(x11_authnames[xconn->disp->localauthproto]); int buflen = 0; /* initialise to placate optimiser */ static const char zeroes[4] = { 0,0,0,0 }; void *buf; if (xconn->disp->localauthproto == X11_MIT) { assert(xconn->disp->localauthdatalen <= lenof(realauthdata)); realauthlen = xconn->disp->localauthdatalen; memcpy(realauthdata, xconn->disp->localauthdata, realauthlen); } else if (xconn->disp->localauthproto == X11_XDM && xconn->disp->localauthdatalen == 16 && ((buf = sk_getxdmdata(xconn->s, &buflen))!=0)) { time_t t; realauthlen = (buflen+12+7) & ~7; assert(realauthlen <= lenof(realauthdata)); memset(realauthdata, 0, realauthlen); memcpy(realauthdata, xconn->disp->localauthdata, 8); memcpy(realauthdata+8, buf, buflen); t = time(NULL); PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t); des_encrypt_xdmauth(xconn->disp->localauthdata+9, (unsigned char *)realauthdata, realauthlen); sfree(buf); } /* implement other auth methods here if required */ PUT_16BIT(xconn->firstpkt[0], xconn->firstpkt + 6, authstrlen); PUT_16BIT(xconn->firstpkt[0], xconn->firstpkt + 8, realauthlen); sk_write(xconn->s, (char *)xconn->firstpkt, 12); if (authstrlen) { sk_write(xconn->s, x11_authnames[xconn->disp->localauthproto], authstrlen); sk_write(xconn->s, zeroes, 3 & (-authstrlen)); } if (realauthlen) { sk_write(xconn->s, realauthdata, realauthlen); sk_write(xconn->s, zeroes, 3 & (-realauthlen)); } } xconn->verified = 1; } /* * After initialisation, just copy data simply. */ return sk_write(xconn->s, data, len); } void x11_send_eof(struct X11Connection *xconn) { 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); } }