plink: updated to revision 10170 of putty

1 files changed, 1088 insertions, 796 deletions

diff --git a/tools/plink/x11fwd.c b/tools/plink/x11fwd.c
index d98908a77..7ecb4cc27 100644
--- a/tools/plink/x11fwd.c
+++ b/tools/plink/x11fwd.c
@@ -1,796 +1,1088 @@
-/*

- * Platform-independent bits of X11 forwarding.

- */

-

-#include <stdio.h>

-#include <stdlib.h>

-#include <assert.h>

-#include <time.h>

-

-#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 X11Private {

-    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;

-    unsigned long peer_ip;

-    int peer_port;

-    void *c;			       /* data used 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, OSSocket sock) { 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);

-	    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)

-	memset(disp->localauthdata, 0, disp->localauthdatalen);

-    sfree(disp->localauthdata);

-    if (disp->remoteauthdata)

-	memset(disp->remoteauthdata, 0, 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 = get_hostname();

-

-    /*

-     * 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;

-

-    /* 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);

-    memset(buf, 0, 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 int x11_closing(Plug plug, const char *error_msg, int error_code,

-		       int calling_back)

-{

-    struct X11Private *pr = (struct X11Private *) plug;

-

-    /*

-     * We have no way to communicate down the forwarded connection,

-     * so if an error occurred on the socket, we just ignore it

-     * and treat it like a proper close.

-     *

-     * FIXME: except we could initiate a full close here instead of

-     * just an outgoing EOF? ssh.c currently has no API for that, but

-     * it could.

-     */

-    sshfwd_write_eof(pr->c);

-    return 1;

-}

-

-static int x11_receive(Plug plug, int urgent, char *data, int len)

-{

-    struct X11Private *pr = (struct X11Private *) plug;

-

-    if (sshfwd_write(pr->c, data, len) > 0) {

-	pr->throttled = 1;

-	sk_set_frozen(pr->s, 1);

-    }

-

-    return 1;

-}

-

-static void x11_sent(Plug plug, int bufsize)

-{

-    struct X11Private *pr = (struct X11Private *) plug;

-

-    sshfwd_unthrottle(pr->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.

- * 

- * Returns an error message, or NULL on success.

- * also, fills the SocketsStructure

- */

-extern const char *x11_init(Socket *s, struct X11Display *disp, void *c,

-			    const char *peeraddr, int peerport, Conf *conf)

-{

-    static const struct plug_function_table fn_table = {

-	x11_log,

-	x11_closing,

-	x11_receive,

-	x11_sent,

-	NULL

-    };

-

-    const char *err;

-    struct X11Private *pr;

-

-    /*

-     * Open socket.

-     */

-    pr = snew(struct X11Private);

-    pr->fn = &fn_table;

-    pr->auth_protocol = NULL;

-    pr->disp = disp;

-    pr->verified = 0;

-    pr->data_read = 0;

-    pr->throttled = pr->throttle_override = 0;

-    pr->c = c;

-

-    pr->s = *s = new_connection(sk_addr_dup(disp->addr),

-				disp->realhost, disp->port,

-				0, 1, 0, 0, (Plug) pr, conf);

-    if ((err = sk_socket_error(*s)) != NULL) {

-	sfree(pr);

-	return err;

-    }

-

-    /*

-     * 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)) {

-	    pr->peer_ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];

-	    pr->peer_port = peerport;

-	} else {

-	    pr->peer_ip = 0;

-	    pr->peer_port = -1;

-	}

-    }

-

-    sk_set_private_ptr(*s, pr);

-    return NULL;

-}

-

-void x11_close(Socket s)

-{

-    struct X11Private *pr;

-    if (!s)

-	return;

-    pr = (struct X11Private *) sk_get_private_ptr(s);

-    if (pr->auth_protocol) {

-	sfree(pr->auth_protocol);

-	sfree(pr->auth_data);

-    }

-

-    sfree(pr);

-

-    sk_close(s);

-}

-

-void x11_unthrottle(Socket s)

-{

-    struct X11Private *pr;

-    if (!s)

-	return;

-    pr = (struct X11Private *) sk_get_private_ptr(s);

-

-    pr->throttled = 0;

-    sk_set_frozen(s, pr->throttled || pr->throttle_override);

-}

-

-void x11_override_throttle(Socket s, int enable)

-{

-    struct X11Private *pr;

-    if (!s)

-	return;

-    pr = (struct X11Private *) sk_get_private_ptr(s);

-

-    pr->throttle_override = enable;

-    sk_set_frozen(s, pr->throttled || pr->throttle_override);

-}

-

-/*

- * Called to send data down the raw connection.

- */

-int x11_send(Socket s, char *data, int len)

-{

-    struct X11Private *pr;

-    if (!s)

-	return 0;

-    pr = (struct X11Private *) sk_get_private_ptr(s);

-

-    /*

-     * Read the first packet.

-     */

-    while (len > 0 && pr->data_read < 12)

-	pr->firstpkt[pr->data_read++] = (unsigned char) (len--, *data++);

-    if (pr->data_read < 12)

-	return 0;

-

-    /*

-     * If we have not allocated the auth_protocol and auth_data

-     * strings, do so now.

-     */

-    if (!pr->auth_protocol) {

-	pr->auth_plen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 6);

-	pr->auth_dlen = GET_16BIT(pr->firstpkt[0], pr->firstpkt + 8);

-	pr->auth_psize = (pr->auth_plen + 3) & ~3;

-	pr->auth_dsize = (pr->auth_dlen + 3) & ~3;

-	/* Leave room for a terminating zero, to make our lives easier. */

-	pr->auth_protocol = snewn(pr->auth_psize + 1, char);

-	pr->auth_data = snewn(pr->auth_dsize, unsigned char);

-    }

-

-    /*

-     * Read the auth_protocol and auth_data strings.

-     */

-    while (len > 0 && pr->data_read < 12 + pr->auth_psize)

-	pr->auth_protocol[pr->data_read++ - 12] = (len--, *data++);

-    while (len > 0 && pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)

-	pr->auth_data[pr->data_read++ - 12 -

-		      pr->auth_psize] = (unsigned char) (len--, *data++);

-    if (pr->data_read < 12 + pr->auth_psize + pr->auth_dsize)

-	return 0;

-

-    /*

-     * If we haven't verified the authorisation, do so now.

-     */

-    if (!pr->verified) {

-	char *err;

-

-	pr->auth_protocol[pr->auth_plen] = '\0';	/* ASCIZ */

-	err = x11_verify(pr->peer_ip, pr->peer_port,

-			 pr->disp, pr->auth_protocol,

-			 pr->auth_data, pr->auth_dlen);

-

-	/*

-	 * If authorisation failed, construct and send an error

-	 * packet, then terminate the connection.

-	 */

-	if (err) {

-	    char *message;

-	    int msglen, msgsize;

-	    unsigned char *reply;

-

-	    message = dupprintf("%s X11 proxy: %s", appname, err);

-	    msglen = strlen(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, pr->firstpkt + 2, 4);	/* major/minor proto vsn */

-	    PUT_16BIT(pr->firstpkt[0], reply + 6, msgsize >> 2);/* data len */

-	    memset(reply + 8, 0, msgsize);

-	    memcpy(reply + 8, message, msglen);

-	    sshfwd_write(pr->c, (char *)reply, 8 + msgsize);

-	    sshfwd_write_eof(pr->c);

-	    sfree(reply);

-	    sfree(message);

-	    return 0;

-	}

-

-	/*

-	 * Now we know we're going to accept the connection. Strip

-	 * the fake auth data, and optionally put real auth data in

-	 * instead.

-	 */

-        {

-            char realauthdata[64];

-            int realauthlen = 0;

-            int authstrlen = strlen(x11_authnames[pr->disp->localauthproto]);

-	    int buflen = 0;	       /* initialise to placate optimiser */

-            static const char zeroes[4] = { 0,0,0,0 };

-	    void *buf;

-

-            if (pr->disp->localauthproto == X11_MIT) {

-                assert(pr->disp->localauthdatalen <= lenof(realauthdata));

-                realauthlen = pr->disp->localauthdatalen;

-                memcpy(realauthdata, pr->disp->localauthdata, realauthlen);

-            } else if (pr->disp->localauthproto == X11_XDM &&

-		       pr->disp->localauthdatalen == 16 &&

-		       ((buf = sk_getxdmdata(s, &buflen))!=0)) {

-		time_t t;

-                realauthlen = (buflen+12+7) & ~7;

-		assert(realauthlen <= lenof(realauthdata));

-		memset(realauthdata, 0, realauthlen);

-		memcpy(realauthdata, pr->disp->localauthdata, 8);

-		memcpy(realauthdata+8, buf, buflen);

-		t = time(NULL);

-		PUT_32BIT_MSB_FIRST(realauthdata+8+buflen, t);

-		des_encrypt_xdmauth(pr->disp->localauthdata+9,

-				    (unsigned char *)realauthdata,

-				    realauthlen);

-		sfree(buf);

-	    }

-            /* implement other auth methods here if required */

-

-            PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 6, authstrlen);

-            PUT_16BIT(pr->firstpkt[0], pr->firstpkt + 8, realauthlen);

-        

-            sk_write(s, (char *)pr->firstpkt, 12);

-

-            if (authstrlen) {

-                sk_write(s, x11_authnames[pr->disp->localauthproto],

-			 authstrlen);

-                sk_write(s, zeroes, 3 & (-authstrlen));

-            }

-            if (realauthlen) {

-                sk_write(s, realauthdata, realauthlen);

-                sk_write(s, zeroes, 3 & (-realauthlen));

-            }

-        }

-	pr->verified = 1;

-    }

-

-    /*

-     * After initialisation, just copy data simply.

-     */

-

-    return sk_write(s, data, len);

-}

-

-void x11_send_eof(Socket s)

-{

-    sk_write_eof(s);

-}

+/*
+ * Platform-independent bits of X11 forwarding.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <time.h>
+
+#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 */
+    tree234 *authtree;
+    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;
+    char *peer_addr;
+    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 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) {
+            for (i = 0; i < auth->datalen; i++)
+                auth->data[i] = random_byte();
+            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) {
+            for (i = 0; i < auth->datalen; i++)
+                auth->data[i] = (i == 8 ? 0 : random_byte());
+            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 = 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);
+    }
+}
+
+struct X11Display *x11_setup_display(char *display, Conf *conf)
+{
+    struct X11Display *disp = snew(struct X11Display);
+    char *localcopy;
+
+    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 = host_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;
+    }
+
+    /*
+     * 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)
+{
+    sfree(disp->hostname);
+    sfree(disp->unixsocketpath);
+    if (disp->localauthdata)
+	smemclr(disp->localauthdata, disp->localauthdatalen);
+    sfree(disp->localauthdata);
+    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,
+			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 (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(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;
+}
+
+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 = host_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 X11Connection structure, though this does not
+ * yet connect to an actual server.
+ */
+struct X11Connection *x11_init(tree234 *authtree, 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 = snew(struct X11Connection);
+    xconn->fn = &fn_table;
+    xconn->auth_protocol = NULL;
+    xconn->authtree = authtree;
+    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,
+     * 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;
+}
+
+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->peer_addr);
+    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);
+}
+
+static int x11_parse_ip(const char *addr_string, unsigned long *ip)
+{
+
+    /*
+     * See if we can make sense of this string as an IPv4 address, for
+     * XDM-AUTHORIZATION-1 purposes.
+     */
+    int i[4];
+    if (addr_string &&
+        4 == sscanf(addr_string, "%d.%d.%d.%d", i+0, i+1, i+2, i+3)) {
+        *ip = (i[0] << 24) | (i[1] << 16) | (i[2] << 8) | i[3];
+        return TRUE;
+    } else {
+        return FALSE;
+    }
+}
+
+/*
+ * 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;
+        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;
+
+        protomajor = GET_16BIT(xconn->firstpkt[0], xconn->firstpkt + 2);
+        protominor = GET_16BIT(xconn->firstpkt[0], 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.
+         */
+        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.
+         */
+        sshfwd_x11_is_local(xconn->c);
+        xconn->disp = auth_matched->disp;
+        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;
+        }
+
+        /*
+         * Write a new connection header containing our replacement
+         * auth data.
+	 */
+
+        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 = 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);
+    }
+}
+
+/*
+ * Utility functions used by connection sharing to convert textual
+ * representations of an X11 auth protocol name + hex cookie into our
+ * usual integer protocol id and binary auth data.
+ */
+int x11_identify_auth_proto(const char *protoname)
+{
+    int protocol;
+
+    for (protocol = 1; protocol < lenof(x11_authnames); protocol++)
+        if (!strcmp(protoname, x11_authnames[protocol]))
+            return protocol;
+    return -1;
+}
+
+void *x11_dehexify(const char *hex, int *outlen)
+{
+    int len, i;
+    unsigned char *ret;
+
+    len = strlen(hex) / 2;
+    ret = snewn(len, unsigned char);
+
+    for (i = 0; i < len; i++) {
+        char bytestr[3];
+        unsigned val = 0;
+        bytestr[0] = hex[2*i];
+        bytestr[1] = hex[2*i+1];
+        bytestr[2] = '\0';
+        sscanf(bytestr, "%x", &val);
+        ret[i] = val;
+    }
+
+    *outlen = len;
+    return ret;
+}
+
+/*
+ * Construct an X11 greeting packet, including making up the right
+ * authorisation data.
+ */
+void *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)
+{
+    unsigned char *greeting;
+    unsigned char realauthdata[64];
+    const char *authname;
+    const unsigned char *authdata;
+    int authnamelen, authnamelen_pad;
+    int authdatalen, authdatalen_pad;
+    int greeting_len;
+
+    authname = x11_authnames[auth_proto];
+    authnamelen = strlen(authname);
+    authnamelen_pad = (authnamelen + 3) & ~3;
+
+    if (auth_proto == X11_MIT) {
+        authdata = auth_data;
+        authdatalen = auth_len;
+    } else if (auth_proto == X11_XDM && auth_len == 16) {
+        time_t t;
+        unsigned long peer_ip = 0;
+
+        x11_parse_ip(peer_addr, &peer_ip);
+
+        authdata = realauthdata;
+        authdatalen = 24;
+        memset(realauthdata, 0, authdatalen);
+        memcpy(realauthdata, auth_data, 8);
+        PUT_32BIT_MSB_FIRST(realauthdata+8, peer_ip);
+        PUT_16BIT_MSB_FIRST(realauthdata+12, peer_port);
+        t = time(NULL);
+        PUT_32BIT_MSB_FIRST(realauthdata+14, t);
+
+        des_encrypt_xdmauth((const unsigned char *)auth_data + 9,
+                            realauthdata, authdatalen);
+    } else {
+        authdata = realauthdata;
+        authdatalen = 0;
+    }
+
+    authdatalen_pad = (authdatalen + 3) & ~3;
+    greeting_len = 12 + authnamelen_pad + authdatalen_pad;
+
+    greeting = snewn(greeting_len, unsigned char);
+    memset(greeting, 0, greeting_len);
+    greeting[0] = endian;
+    PUT_16BIT(endian, greeting+2, protomajor);
+    PUT_16BIT(endian, greeting+4, protominor);
+    PUT_16BIT(endian, greeting+6, authnamelen);
+    PUT_16BIT(endian, greeting+8, authdatalen);
+    memcpy(greeting+12, authname, authnamelen);
+    memcpy(greeting+12+authnamelen_pad, authdata, authdatalen);
+
+    smemclr(realauthdata, sizeof(realauthdata));
+
+    *outlen = greeting_len;
+    return greeting;
+}