/*
* 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 "channel.h"
#include "tree234.h"
struct XDMSeen {
unsigned int time;
unsigned char clientid[6];
};
typedef struct X11Connection {
unsigned char firstpkt[12]; /* first X data packet */
tree234 *authtree;
struct X11Display *disp;
char *auth_protocol;
unsigned char *auth_data;
int data_read, auth_plen, auth_psize, auth_dlen, auth_dsize;
bool verified;
bool input_wanted;
bool no_data_sent_to_x_client;
char *peer_addr;
int peer_port;
SshChannel *c; /* channel structure held by SSH backend */
Socket *s;
Plug plug;
Channel chan;
} X11Connection;
static int xdmseen_cmp(void *a, void *b)
{
struct XDMSeen *sa = a, *sb = b;
return sa->time > sb->time ? 1 :
sa->time < sb->time ? -1 :
memcmp(sa->clientid, sb->clientid, sizeof(sa->clientid));
}
struct X11FakeAuth *x11_invent_fake_auth(tree234 *authtree, int authtype)
{
struct X11FakeAuth *auth = snew(struct X11FakeAuth);
int i;
/*
* This function has the job of inventing a set of X11 fake auth
* data, and adding it to 'authtree'. We must preserve the
* property that for any given actual authorisation attempt, _at
* most one_ thing in the tree can possibly match it.
*
* For MIT-MAGIC-COOKIE-1, that's not too difficult: the match
* criterion is simply that the entire cookie is correct, so we
* just have to make sure we don't make up two cookies the same.
* (Vanishingly unlikely, but we check anyway to be sure, and go
* round again inventing a new cookie if add234 tells us the one
* we thought of is already in use.)
*
* For XDM-AUTHORIZATION-1, it's a little more fiddly. The setup
* with XA1 is that half the cookie is used as a DES key with
* which to CBC-encrypt an assortment of stuff. Happily, the stuff
* encrypted _begins_ with the other half of the cookie, and the
* IV is always zero, which means that any valid XA1 authorisation
* attempt for a given cookie must begin with the same cipher
* block, consisting of the DES ECB encryption of the first half
* of the cookie using the second half as a key. So we compute
* that cipher block here and now, and use it as the sorting key
* for distinguishing XA1 entries in the tree.
*/
if (authtype == X11_MIT) {
auth->proto = X11_MIT;
/* MIT-MAGIC-COOKIE-1. Cookie size is 128 bits (16 bytes). */
auth->datalen = 16;
auth->data = snewn(auth->datalen, unsigned char);
auth->xa1_firstblock = NULL;
while (1) {
random_read(auth->data, auth->datalen);
if (add234(authtree, auth) == auth)
break;
}
auth->xdmseen = NULL;
} else {
assert(authtype == X11_XDM);
auth->proto = X11_XDM;
/* XDM-AUTHORIZATION-1. Cookie size is 16 bytes; byte 8 is zero. */
auth->datalen = 16;
auth->data = snewn(auth->datalen, unsigned char);
auth->xa1_firstblock = snewn(8, unsigned char);
memset(auth->xa1_firstblock, 0, 8);
while (1) {
random_read(auth->data, 15);
auth->data[15] = auth->data[8];
auth->data[8] = 0;
memcpy(auth->xa1_firstblock, auth->data, 8);
des_encrypt_xdmauth(auth->data + 9, auth->xa1_firstblock, 8);
if (add234(authtree, auth) == auth)
break;
}
auth->xdmseen = newtree234(xdmseen_cmp);
}
auth->protoname = dupstr(x11_authnames[auth->proto]);
auth->datastring = snewn(auth->datalen * 2 + 1, char);
for (i = 0; i < auth->datalen; i++)
sprintf(auth->datastring + i*2, "%02x",
auth->data[i]);
auth->disp = NULL;
auth->share_cs = NULL;
auth->share_chan = NULL;
return auth;
}
void x11_free_fake_auth(struct X11FakeAuth *auth)
{
if (auth->data)
smemclr(auth->data, auth->datalen);
sfree(auth->data);
sfree(auth->protoname);
sfree(auth->datastring);
sfree(auth->xa1_firstblock);
if (auth->xdmseen != NULL) {
struct XDMSeen *seen;
while ((seen = delpos234(auth->xdmseen, 0)) != NULL)
sfree(seen);
freetree234(auth->xdmseen);
}
sfree(auth);
}
int x11_authcmp(void *av, void *bv)
{
struct X11FakeAuth *a = (struct X11FakeAuth *)av;
struct X11FakeAuth *b = (struct X11FakeAuth *)bv;
if (a->proto < b->proto)
return -1;
else if (a->proto > b->proto)
return +1;
if (a->proto == X11_MIT) {
if (a->datalen < b->datalen)
return -1;
else if (a->datalen > b->datalen)
return +1;
return memcmp(a->data, b->data, a->datalen);
} else {
assert(a->proto == X11_XDM);
return memcmp(a->xa1_firstblock, b->xa1_firstblock, 8);
}
}
#define XDM_MAXSKEW 20*60 /* 20 minute clock skew should be OK */
static 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 if (!proto[0]) {
/*
* If the user has attempted to connect to the forwarded X
* display with no authority at all, we can give a better
* error message than the generic "unsupported protocol". We
* at least _recognise_ the null auth protocol, even if we
* don't _accept_ it.
*/
return dupstr("No authorisation provided");
} else {
return dupprintf("Unsupported authorisation protocol '%s'", proto);
}
if ((auth = find234(authtree, &match_dummy, 0)) == NULL)
return dupstr("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 dupprintf("XDM-AUTHORIZATION-1 data was wrong length "
"(%d, expected 24)", dlen);
if (peer_port == -1)
return dupstr("cannot do XDM-AUTHORIZATION-1 without remote "
"address data");
des_decrypt_xdmauth(auth->data+9, data, 24);
/* Bitwise-OR together any mismatches in the fixed parts of
* the data, to allow checking it all at once */
uint32_t mismatches = 0;
/* Check non-key half of auth cookie */
for (i = 0; i < 8; i++)
mismatches |= auth->data[i] ^ data[i];
/* Check IP address and port */
mismatches |= GET_32BIT_MSB_FIRST(data+8) ^ peer_ip;
mismatches |= (unsigned short)(GET_16BIT_MSB_FIRST(data+12) ^
peer_port);
/* Check zero padding */
for (i = 18; i < 24; i++)
mismatches |= data[i];
if (mismatches)
return dupstr("XDM-AUTHORIZATION-1 data failed check");
t = GET_32BIT_MSB_FIRST(data+14);
tim = time(NULL);
if (((unsigned long)t - (unsigned long)tim
+ XDM_MAXSKEW) > 2*XDM_MAXSKEW)
return dupstr("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 dupstr("XDM-AUTHORIZATION-1 data replayed");
}
/* While we're here, purge entries too old to be replayed. */
for (;;) {
seen = index234(auth->xdmseen, 0);
assert(seen != NULL);
if (t - seen->time <= XDM_MAXSKEW)
break;
sfree(delpos234(auth->xdmseen, 0));
}
}
/* implement other protocols here if ever required */
*auth_ret = auth;
return NULL;
}
static void x11_send_init_error(struct X11Connection *conn,
const char *err_message);
static void x11_closing(Plug *plug, PlugCloseType type, const char *error_msg)
{
struct X11Connection *xconn = container_of(
plug, struct X11Connection, plug);
if (type != PLUGCLOSE_NORMAL) {
/*
* Socket error. If we're still at the connection setup stage,
* construct an X11 error packet passing on the problem.
*/
if (xconn->no_data_sent_to_x_client) {
char *err_message = dupprintf("unable to connect to forwarded "
"X server: %s", error_msg);
x11_send_init_error(xconn, err_message);
sfree(err_message);
}
/*
* Whether we did that or not, now we slam the connection
* shut.
*/
sshfwd_initiate_close(xconn->c, error_msg);
} else {
/*
* Ordinary EOF received on socket. Send an EOF on the SSH
* channel.
*/
if (xconn->c)
sshfwd_write_eof(xconn->c);
}
}
static void x11_receive(Plug *plug, int urgent, const char *data, size_t len)
{
struct X11Connection *xconn = container_of(
plug, struct X11Connection, plug);
xconn->no_data_sent_to_x_client = false;
sshfwd_write(xconn->c, data, len);
}
static void x11_sent(Plug *plug, size_t bufsize)
{
struct X11Connection *xconn = container_of(
plug, struct X11Connection, plug);
sshfwd_unthrottle(xconn->c, bufsize);
}
static const PlugVtable X11Connection_plugvt = {
.log = nullplug_log,
.closing = x11_closing,
.receive = x11_receive,
.sent = x11_sent,
};
static void x11_chan_free(Channel *chan);
static size_t x11_send(
Channel *chan, bool is_stderr, const void *vdata, size_t len);
static void x11_send_eof(Channel *chan);
static void x11_set_input_wanted(Channel *chan, bool wanted);
static char *x11_log_close_msg(Channel *chan);
static const ChannelVtable X11Connection_channelvt = {
.free = x11_chan_free,
.open_confirmation = chan_remotely_opened_confirmation,
.open_failed = chan_remotely_opened_failure,
.send = x11_send,
.send_eof = x11_send_eof,
.set_input_wanted = x11_set_input_wanted,
.log_close_msg = x11_log_close_msg,
.want_close = chan_default_want_close,
.rcvd_exit_status = chan_no_exit_status,
.rcvd_exit_signal = chan_no_exit_signal,
.rcvd_exit_signal_numeric = chan_no_exit_signal_numeric,
.run_shell = chan_no_run_shell,
.run_command = chan_no_run_command,
.run_subsystem = chan_no_run_subsystem,
.enable_x11_forwarding = chan_no_enable_x11_forwarding,
.enable_agent_forwarding = chan_no_enable_agent_forwarding,
.allocate_pty = chan_no_allocate_pty,
.set_env = chan_no_set_env,
.send_break = chan_no_send_break,
.send_signal = chan_no_send_signal,
.change_window_size = chan_no_change_window_size,
.request_response = chan_no_request_response,
};
/*
* Called to set up the X11Connection structure, though this does not
* yet connect to an actual server.
*/
Channel *x11_new_channel(tree234 *authtree, SshChannel *c,
const char *peeraddr, int peerport,
bool connection_sharing_possible)
{
struct X11Connection *xconn;
/*
* Open socket.
*/
xconn = snew(struct X11Connection);
xconn->plug.vt = &X11Connection_plugvt;
xconn->chan.vt = &X11Connection_channelvt;
xconn->chan.initial_fixed_window_size =
(connection_sharing_possible ? 128 : 0);
xconn->auth_protocol = NULL;
xconn->authtree = authtree;
xconn->verified = false;
xconn->data_read = 0;
xconn->input_wanted = true;
xconn->no_data_sent_to_x_client = true;
xconn->c = c;
/*
* We don't actually open a local socket to the X server just yet,
* because we don't know which one it is. Instead, we'll wait
* until we see the incoming authentication data, which may tell
* us what display to connect to, or whether we have to divert
* this X forwarding channel to a connection-sharing downstream
* rather than handling it ourself.
*/
xconn->disp = NULL;
xconn->s = NULL;
/*
* Stash the peer address we were given in its original text form.
*/
xconn->peer_addr = peeraddr ? dupstr(peeraddr) : NULL;
xconn->peer_port = peerport;
return &xconn->chan;
}
static void x11_chan_free(Channel *chan)
{
assert(chan->vt == &X11Connection_channelvt);
X11Connection *xconn = container_of(chan, X11Connection, chan);
if (xconn->auth_protocol) {
sfree(xconn->auth_protocol);
sfree(xconn->auth_data);
}
if (xconn->s)
sk_close(xconn->s);
sfree(xconn->peer_addr);
sfree(xconn);
}
static void x11_set_input_wanted(Channel *chan, bool wanted)
{
assert(chan->vt == &X11Connection_channelvt);
X11Connection *xconn = container_of(chan, X11Connection, chan);
xconn->input_wanted = wanted;
if (xconn->s)
sk_set_frozen(xconn->s, !xconn->input_wanted);
}
static void x11_send_init_error(struct X11Connection *xconn,
const char *err_message)
{
char *full_message;
int msglen, msgsize;
unsigned char *reply;
full_message = dupprintf("%s X11 proxy: %s\n", appname, err_message);
msglen = strlen(full_message);
reply = snewn(8 + msglen+1 + 4, unsigned char); /* include zero */
msgsize = (msglen + 3) & ~3;
reply[0] = 0; /* failure */
reply[1] = msglen; /* length of reason string */
memcpy(reply + 2, xconn->firstpkt + 2, 4); /* major/minor proto vsn */
PUT_16BIT_X11(xconn->firstpkt[0], reply + 6, msgsize >> 2);/* data len */
memset(reply + 8, 0, msgsize);
memcpy(reply + 8, full_message, msglen);
sshfwd_write(xconn->c, reply, 8 + msgsize);
sshfwd_write_eof(xconn->c);
xconn->no_data_sent_to_x_client = false;
sfree(reply);
sfree(full_message);
}
/*
* Called to send data down the raw connection.
*/
static size_t x11_send(
Channel *chan, bool is_stderr, const void *vdata, size_t len)
{
assert(chan->vt == &X11Connection_channelvt);
X11Connection *xconn = container_of(chan, X11Connection, chan);
const char *data = (const char *)vdata;
/*
* Read the first packet.
*/
while (len > 0 && xconn->data_read < 12)
xconn->firstpkt[xconn->data_read++] = (unsigned char) (len--, *data++);
if (xconn->data_read < 12)
return 0;
/*
* If we have not allocated the auth_protocol and auth_data
* strings, do so now.
*/
if (!xconn->auth_protocol) {
char endian = xconn->firstpkt[0];
xconn->auth_plen = GET_16BIT_X11(endian, xconn->firstpkt + 6);
xconn->auth_dlen = GET_16BIT_X11(endian, xconn->firstpkt + 8);
xconn->auth_psize = (xconn->auth_plen + 3) & ~3;
xconn->auth_dsize = (xconn->auth_dlen + 3) & ~3;
/* Leave room for a terminating zero, to make our lives easier. */
xconn->auth_protocol = snewn(xconn->auth_psize + 1, char);
xconn->auth_data = snewn(xconn->auth_dsize, unsigned char);
}
/*
* Read the auth_protocol and auth_data strings.
*/
while (len > 0 &&
xconn->data_read < 12 + xconn->auth_psize)
xconn->auth_protocol[xconn->data_read++ - 12] = (len--, *data++);
while (len > 0 &&
xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize)
xconn->auth_data[xconn->data_read++ - 12 -
xconn->auth_psize] = (unsigned char) (len--, *data++);
if (xconn->data_read < 12 + xconn->auth_psize + xconn->auth_dsize)
return 0;
/*
* If we haven't verified the authorisation, do so now.
*/
if (!xconn->verified) {
const char *err;
char *errmut;
struct X11FakeAuth *auth_matched = NULL;
unsigned long peer_ip;
int peer_port;
int protomajor, protominor;
void *greeting;
int greeting_len;
unsigned char *socketdata;
int socketdatalen;
char new_peer_addr[32];
int new_peer_port;
char endian = xconn->firstpkt[0];
protomajor = GET_16BIT_X11(endian, xconn->firstpkt + 2);
protominor = GET_16BIT_X11(endian, xconn->firstpkt + 4);
assert(!xconn->s);
xconn->auth_protocol[xconn->auth_plen] = '\0'; /* ASCIZ */
peer_ip = 0; /* placate optimiser */
if (x11_parse_ip(xconn->peer_addr, &peer_ip))
peer_port = xconn->peer_port;
else
peer_port = -1; /* signal no peer address data available */
errmut = x11_verify(peer_ip, peer_port,
xconn->authtree, xconn->auth_protocol,
xconn->auth_data, xconn->auth_dlen, &auth_matched);
if (errmut) {
x11_send_init_error(xconn, errmut);
sfree(errmut);
return 0;
}
assert(auth_matched);
/*
* If this auth points to a connection-sharing downstream
* rather than an X display we know how to connect to
* directly, pass it off to the sharing module now. (This will
* have the side effect of freeing xconn.)
*/
if (auth_matched->share_cs) {
sshfwd_x11_sharing_handover(xconn->c, auth_matched->share_cs,
auth_matched->share_chan,
xconn->peer_addr, xconn->peer_port,
xconn->firstpkt[0],
protomajor, protominor, data, len);
return 0;
}
/*
* Now we know we're going to accept the connection, and what
* X display to connect to. Actually connect to it.
*/
xconn->chan.initial_fixed_window_size = 0;
sshfwd_window_override_removed(xconn->c);
xconn->disp = auth_matched->disp;
xconn->s = new_connection(sk_addr_dup(xconn->disp->addr),
xconn->disp->realhost, xconn->disp->port,
false, true, false, false, &xconn->plug,
sshfwd_get_conf(xconn->c), NULL);
if ((err = sk_socket_error(xconn->s)) != NULL) {
char *err_message = dupprintf("unable to connect to"
" forwarded X server: %s", err);
x11_send_init_error(xconn, err_message);
sfree(err_message);
return 0;
}
/*
* Write a new connection header containing our replacement
* auth data.
*/
socketdatalen = 0; /* placate compiler warning */
socketdata = sk_getxdmdata(xconn->s, &socketdatalen);
if (socketdata && socketdatalen==6) {
sprintf(new_peer_addr, "%d.%d.%d.%d", socketdata[0],
socketdata[1], socketdata[2], socketdata[3]);
new_peer_port = GET_16BIT_MSB_FIRST(socketdata + 4);
} else {
strcpy(new_peer_addr, "0.0.0.0");
new_peer_port = 0;
}
greeting = x11_make_greeting(xconn->firstpkt[0],
protomajor, protominor,
xconn->disp->localauthproto,
xconn->disp->localauthdata,
xconn->disp->localauthdatalen,
new_peer_addr, new_peer_port,
&greeting_len);
sk_write(xconn->s, greeting, greeting_len);
smemclr(greeting, greeting_len);
sfree(greeting);
/*
* Now we're done.
*/
xconn->verified = true;
}
/*
* After initialisation, just copy data simply.
*/
return sk_write(xconn->s, data, len);
}
static void x11_send_eof(Channel *chan)
{
assert(chan->vt == &X11Connection_channelvt);
X11Connection *xconn = container_of(chan, X11Connection, chan);
if (xconn->s) {
sk_write_eof(xconn->s);
} else {
/*
* If EOF is received from the X client before we've got to
* the point of actually connecting to an X server, then we
* should send an EOF back to the client so that the
* forwarded channel will be terminated.
*/
if (xconn->c)
sshfwd_write_eof(xconn->c);
}
}
static char *x11_log_close_msg(Channel *chan)
{
return dupstr("Forwarded X11 connection terminated");
}