Copied tools directory from trunk. Here the original versions will be checked in, so that we can update them and merge the changes back in.

1 files changed, 791 insertions, 0 deletions

diff --git a/tools/plink/x11fwd.c b/tools/plink/x11fwd.c
new file mode 100644
index 000000000..9f22a2364
--- /dev/null
+++ b/tools/plink/x11fwd.c
@@ -0,0 +1,791 @@
+/*

+ * 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,

+				     const Config *cfg)

+{

+    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, cfg, 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, cfg);

+

+    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.

+     */

+    sshfwd_close(pr->c);

+    x11_close(pr->s);

+    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,

+			    const Config *cfg)

+{

+    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, cfg);

+    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_close(pr->c);

+	    x11_close(s);

+	    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);

+}