- djm@cvs.openbsd.org 2005/07/04 00:58:43

[channels.c clientloop.c clientloop.h misc.c misc.h ssh.c ssh_config.5] implement support for X11 and agent forwarding over multiplex slave connections. Because of protocol limitations, the slave connections inherit the master's DISPLAY and SSH_AUTH_SOCK rather than distinctly forwarding their own. ok dtucker@ "put it in" deraadt@
2005-07-06 09:44:19 +10:00 · 2005-07-06 09:44:19 +10:00 · 1339002e8b
--- a/9
+++ b/9
@ -3,6 +3,13 @@
   - markus@cvs.openbsd.org 2005/07/01 13:19:47
     [channels.c]
     don't free() if getaddrinfo() fails; report mpech@
+   - djm@cvs.openbsd.org 2005/07/04 00:58:43
+     [channels.c clientloop.c clientloop.h misc.c misc.h ssh.c ssh_config.5]
+     implement support for X11 and agent forwarding over multiplex slave
+     connections. Because of protocol limitations, the slave connections inherit
+     the master's DISPLAY and SSH_AUTH_SOCK rather than distinctly forwarding
+     their own.
+     ok dtucker@ "put it in" deraadt@

 20050626
 - (djm) OpenBSD CVS Sync
@ -2769,4 +2776,4 @@
   - (djm) Trim deprecated options from INSTALL. Mention UsePAM
   - (djm) Fix quote handling in sftp; Patch from admorten AT umich.edu

-$Id: ChangeLog,v 1.3832 2005/07/05 23:36:05 djm Exp $
+$Id: ChangeLog,v 1.3833 2005/07/05 23:44:19 djm Exp $
--- a/channels.c
+++ b/channels.c
@ -39,7 +39,7 @@
 */

 #include "includes.h"
-RCSID("$OpenBSD: channels.c,v 1.218 2005/07/01 13:19:47 markus Exp $");
+RCSID("$OpenBSD: channels.c,v 1.219 2005/07/04 00:58:42 djm Exp $");

 #include "ssh.h"
 #include "ssh1.h"
@ -111,6 +111,9 @@ static int all_opens_permitted = 0;
 /* Maximum number of fake X11 displays to try. */
 #define MAX_DISPLAYS  1000

+/* Saved X11 local (client) display. */
+static char *x11_saved_display = NULL;
+
 /* Saved X11 authentication protocol name. */
 static char *x11_saved_proto = NULL;

@ -2955,12 +2958,18 @@ x11_request_forwarding_with_spoofing(int client_session_id, const char *disp,
    const char *proto, const char *data)
 {
 	u_int data_len = (u_int) strlen(data) / 2;
-	u_int i, value, len;
+	u_int i, value;
 	char *new_data;
 	int screen_number;
 	const char *cp;
 	u_int32_t rnd = 0;

+	if (x11_saved_display && strcmp(disp, x11_saved_display) != 0) {
+		error("x11_request_forwarding_with_spoofing: different "
+		    "$DISPLAY already forwarded");
+		return;
+	}
+
 	cp = disp;
 	if (disp)
 		cp = strchr(disp, ':');
@ -2971,33 +2980,31 @@ x11_request_forwarding_with_spoofing(int client_session_id, const char *disp,
 	else
 		screen_number = 0;

-	/* Save protocol name. */
-	x11_saved_proto = xstrdup(proto);
-
-	/*
-	 * Extract real authentication data and generate fake data of the
-	 * same length.
-	 */
-	x11_saved_data = xmalloc(data_len);
-	x11_fake_data = xmalloc(data_len);
-	for (i = 0; i < data_len; i++) {
-		if (sscanf(data + 2 * i, "%2x", &value) != 1)
-			fatal("x11_request_forwarding: bad authentication data: %.100s", data);
-		if (i % 4 == 0)
-			rnd = arc4random();
-		x11_saved_data[i] = value;
-		x11_fake_data[i] = rnd & 0xff;
-		rnd >>= 8;
+	if (x11_saved_proto == NULL) {
+		/* Save protocol name. */
+		x11_saved_proto = xstrdup(proto);
+		/*
+		 * Extract real authentication data and generate fake data 
+		 * of the same length.
+		 */
+		x11_saved_data = xmalloc(data_len);
+		x11_fake_data = xmalloc(data_len);
+		for (i = 0; i < data_len; i++) {
+			if (sscanf(data + 2 * i, "%2x", &value) != 1)
+				fatal("x11_request_forwarding: bad "
+				    "authentication data: %.100s", data);
+			if (i % 4 == 0)
+				rnd = arc4random();
+			x11_saved_data[i] = value;
+			x11_fake_data[i] = rnd & 0xff;
+			rnd >>= 8;
+		}
+		x11_saved_data_len = data_len;
+		x11_fake_data_len = data_len;
 	}
-	x11_saved_data_len = data_len;
-	x11_fake_data_len = data_len;

 	/* Convert the fake data into hex. */
-	len = 2 * data_len + 1;
-	new_data = xmalloc(len);
-	for (i = 0; i < data_len; i++)
-		snprintf(new_data + 2 * i, len - 2 * i,
-		    "%02x", (u_char) x11_fake_data[i]);
+	new_data = tohex(x11_fake_data, data_len);

 	/* Send the request packet. */
 	if (compat20) {
--- a/clientloop.c
+++ b/clientloop.c
@ -59,7 +59,7 @@
 */

 #include "includes.h"
-RCSID("$OpenBSD: clientloop.c,v 1.139 2005/06/17 02:44:32 djm Exp $");
+RCSID("$OpenBSD: clientloop.c,v 1.140 2005/07/04 00:58:43 djm Exp $");

 #include "ssh.h"
 #include "ssh1.h"
@ -140,6 +140,8 @@ int	session_ident = -1;
 struct confirm_ctx {
 	int want_tty;
 	int want_subsys;
+	int want_x_fwd;
+	int want_agent_fwd;
 	Buffer cmd;
 	char *term;
 	struct termios tio;
@ -631,6 +633,7 @@ static void
 client_extra_session2_setup(int id, void *arg)
 {
 	struct confirm_ctx *cctx = arg;
+	const char *display;
 	Channel *c;
 	int i;

@ -639,6 +642,24 @@ client_extra_session2_setup(int id, void *arg)
 	if ((c = channel_lookup(id)) == NULL)
 		fatal("%s: no channel for id %d", __func__, id);

+	display = getenv("DISPLAY");	
+	if (cctx->want_x_fwd && options.forward_x11 && display != NULL) {
+		char *proto, *data;
+		/* Get reasonable local authentication information. */
+		client_x11_get_proto(display, options.xauth_location,
+		    options.forward_x11_trusted, &proto, &data);
+		/* Request forwarding with authentication spoofing. */
+		debug("Requesting X11 forwarding with authentication spoofing.");
+		x11_request_forwarding_with_spoofing(id, display, proto, data);
+		/* XXX wait for reply */
+	}
+
+	if (cctx->want_agent_fwd && options.forward_agent) {
+		debug("Requesting authentication agent forwarding.");
+		channel_request_start(id, "auth-agent-req@openssh.com", 0);
+		packet_send();
+	}
+
 	client_session2_setup(id, cctx->want_tty, cctx->want_subsys,
 	    cctx->term, &cctx->tio, c->rfd, &cctx->cmd, cctx->env,
 	    client_subsystem_reply);
@ -704,7 +725,7 @@ client_process_control(fd_set * readset)
 		buffer_free(&m);
 		return;
 	}
-	if ((ver = buffer_get_char(&m)) != 1) {
+	if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
 		error("%s: wrong client version %d", __func__, ver);
 		buffer_free(&m);
 		close(client_fd);
@ -738,7 +759,7 @@ client_process_control(fd_set * readset)
 		buffer_clear(&m);
 		buffer_put_int(&m, allowed);
 		buffer_put_int(&m, getpid());
-		if (ssh_msg_send(client_fd, /* version */1, &m) == -1) {
+		if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 			error("%s: client msg_send failed", __func__);
 			close(client_fd);
 			buffer_free(&m);
@ -758,7 +779,7 @@ client_process_control(fd_set * readset)
 	buffer_clear(&m);
 	buffer_put_int(&m, allowed);
 	buffer_put_int(&m, getpid());
-	if (ssh_msg_send(client_fd, /* version */1, &m) == -1) {
+	if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 		error("%s: client msg_send failed", __func__);
 		close(client_fd);
 		buffer_free(&m);
@ -779,7 +800,7 @@ client_process_control(fd_set * readset)
 		buffer_free(&m);
 		return;
 	}
-	if ((ver = buffer_get_char(&m)) != 1) {
+	if ((ver = buffer_get_char(&m)) != SSHMUX_VER) {
 		error("%s: wrong client version %d", __func__, ver);
 		buffer_free(&m);
 		close(client_fd);
@ -790,6 +811,8 @@ client_process_control(fd_set * readset)
 	memset(cctx, 0, sizeof(*cctx));
 	cctx->want_tty = (flags & SSHMUX_FLAG_TTY) != 0;
 	cctx->want_subsys = (flags & SSHMUX_FLAG_SUBSYS) != 0;
+	cctx->want_x_fwd = (flags & SSHMUX_FLAG_X11_FWD) != 0;
+	cctx->want_agent_fwd = (flags & SSHMUX_FLAG_AGENT_FWD) != 0;
 	cctx->term = buffer_get_string(&m, &len);

 	cmd = buffer_get_string(&m, &len);
@ -823,7 +846,7 @@ client_process_control(fd_set * readset)

 	/* This roundtrip is just for synchronisation of ttymodes */
 	buffer_clear(&m);
-	if (ssh_msg_send(client_fd, /* version */1, &m) == -1) {
+	if (ssh_msg_send(client_fd, SSHMUX_VER, &m) == -1) {
 		error("%s: client msg_send failed", __func__);
 		close(client_fd);
 		close(new_fd[0]);
--- a/clientloop.h
+++ b/clientloop.h
@ -1,4 +1,4 @@
-/*	$OpenBSD: clientloop.h,v 1.13 2005/06/16 03:38:36 djm Exp $	*/
+/*	$OpenBSD: clientloop.h,v 1.14 2005/07/04 00:58:43 djm Exp $	*/

 /*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -43,6 +43,9 @@ void	 client_global_request_reply_fwd(int, u_int32_t, void *);
 void	 client_session2_setup(int, int, int, const char *, struct termios *,
 	    int, Buffer *, char **, dispatch_fn *);

+/* Multiplexing protocol version */
+#define SSHMUX_VER			1
+
 /* Multiplexing control protocol flags */
 #define SSHMUX_COMMAND_OPEN		1	/* Open new connection */
 #define SSHMUX_COMMAND_ALIVE_CHECK	2	/* Check master is alive */
@ -50,3 +53,5 @@ void	 client_session2_setup(int, int, int, const char *, struct termios *,

 #define SSHMUX_FLAG_TTY			(1)	/* Request tty on open */
 #define SSHMUX_FLAG_SUBSYS		(1<<1)	/* Subsystem request on open */
+#define SSHMUX_FLAG_X11_FWD		(1<<2)	/* Request X11 forwarding */
+#define SSHMUX_FLAG_AGENT_FWD		(1<<3)	/* Request agent forwarding */
--- a/misc.c
+++ b/misc.c
@ -24,7 +24,7 @@
 */

 #include "includes.h"
-RCSID("$OpenBSD: misc.c,v 1.32 2005/06/17 02:44:32 djm Exp $");
+RCSID("$OpenBSD: misc.c,v 1.33 2005/07/04 00:58:43 djm Exp $");

 #include "misc.h"
 #include "log.h"
@ -506,3 +506,20 @@ read_keyfile_line(FILE *f, const char *filename, char *buf, size_t bufsz,
 	}
 	return -1;
 }
+
+char *
+tohex(const u_char *d, u_int l)
+{
+	char b[3], *r;
+	u_int i, hl;
+
+	hl = l * 2 + 1;
+	r = xmalloc(hl);
+	*r = '\0';
+	for (i = 0; i < l; i++) {
+		snprintf(b, sizeof(b), "%02x", d[i]);
+		strlcat(r, b, hl);
+	}
+	return (r);
+}
+
--- a/misc.h
+++ b/misc.h
@ -1,4 +1,4 @@
-/*	$OpenBSD: misc.h,v 1.23 2005/06/06 11:20:36 djm Exp $	*/
+/*	$OpenBSD: misc.h,v 1.24 2005/07/04 00:58:43 djm Exp $	*/

 /*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -26,6 +26,7 @@ char	*colon(char *);
 long	 convtime(const char *);
 char	*tilde_expand_filename(const char *, uid_t);
 char	*percent_expand(const char *, ...) __attribute__((sentinel));
+char	*tohex(const u_char *, u_int);

 struct passwd *pwcopy(struct passwd *);

--- a/ssh.c
+++ b/ssh.c
@ -40,7 +40,7 @@
 */

 #include "includes.h"
-RCSID("$OpenBSD: ssh.c,v 1.246 2005/06/25 22:47:49 djm Exp $");
+RCSID("$OpenBSD: ssh.c,v 1.247 2005/07/04 00:58:43 djm Exp $");

 #include <openssl/evp.h>
 #include <openssl/err.h>
@ -1250,41 +1250,44 @@ control_client(const char *path)
 	 		error("Control socket connect(%.100s): %s", path,
 			    strerror(errno));
 		}
-		close(sock);
-		return;
-	}
+ 		close(sock);
+ 		return;
+ 	}
 
-	if (stdin_null_flag) {
-		if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
-			fatal("open(/dev/null): %s", strerror(errno));
-		if (dup2(fd, STDIN_FILENO) == -1)
-			fatal("dup2: %s", strerror(errno));
-		if (fd > STDERR_FILENO)
-			close(fd);
-	}
+ 	if (stdin_null_flag) {
+ 		if ((fd = open(_PATH_DEVNULL, O_RDONLY)) == -1)
+ 			fatal("open(/dev/null): %s", strerror(errno));
+ 		if (dup2(fd, STDIN_FILENO) == -1)
+ 			fatal("dup2: %s", strerror(errno));
+ 		if (fd > STDERR_FILENO)
+ 			close(fd);
+ 	}
  
-	if ((term = getenv("TERM")) == NULL)
-		term = "";
+	term = getenv("TERM");

 	flags = 0;
 	if (tty_flag)
 		flags |= SSHMUX_FLAG_TTY;
 	if (subsystem_flag)
 		flags |= SSHMUX_FLAG_SUBSYS;
+	if (options.forward_x11)
+		flags |= SSHMUX_FLAG_X11_FWD;
+	if (options.forward_agent)
+		flags |= SSHMUX_FLAG_AGENT_FWD;

 	buffer_init(&m);

 	/* Send our command to server */
 	buffer_put_int(&m, mux_command);
 	buffer_put_int(&m, flags);
-	if (ssh_msg_send(sock, /* version */1, &m) == -1)
+	if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1)
 		fatal("%s: msg_send", __func__);
 	buffer_clear(&m);

 	/* Get authorisation status and PID of controlee */
 	if (ssh_msg_recv(sock, &m) == -1)
 		fatal("%s: msg_recv", __func__);
-	if (buffer_get_char(&m) != 1)
+	if (buffer_get_char(&m) != SSHMUX_VER)
 		fatal("%s: wrong version", __func__);
 	if (buffer_get_int(&m) != 1)
 		fatal("Connection to master denied");
@ -1308,7 +1311,7 @@ control_client(const char *path)
 	}

 	/* SSHMUX_COMMAND_OPEN */
-	buffer_put_cstring(&m, term);
+	buffer_put_cstring(&m, term ? term : "");
 	buffer_append(&command, "\0", 1);
 	buffer_put_cstring(&m, buffer_ptr(&command));

@ -1330,7 +1333,7 @@ control_client(const char *path)
 			}
 	}

-	if (ssh_msg_send(sock, /* version */1, &m) == -1)
+	if (ssh_msg_send(sock, SSHMUX_VER, &m) == -1)
 		fatal("%s: msg_send", __func__);

 	mm_send_fd(sock, STDIN_FILENO);
@ -1341,7 +1344,7 @@ control_client(const char *path)
 	buffer_clear(&m);
 	if (ssh_msg_recv(sock, &m) == -1)
 		fatal("%s: msg_recv", __func__);
-	if (buffer_get_char(&m) != 1)
+	if (buffer_get_char(&m) != SSHMUX_VER)
 		fatal("%s: wrong version", __func__);
 	buffer_free(&m);

--- a/ssh_config.5
+++ b/ssh_config.5
@ -34,7 +34,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.57 2005/06/18 04:30:36 djm Exp $
+.\" $OpenBSD: ssh_config.5,v 1.58 2005/07/04 00:58:43 djm Exp $
 .Dd September 25, 1999
 .Dt SSH_CONFIG 5
 .Os
@ -279,6 +279,12 @@ can not be opened,
 .Nm ssh
 will continue without connecting to a master instance.
 .Pp
+X11 and
+.Xr ssh-agent 4
+forwarding is supported over these multiplexed connections, however the
+display and agent fowarded will be the one belonging to the master
+connection. I.e. it is not possible to forward multiple displays or agents.
+.Pp
 Two additional options allow for opportunistic multiplexing: try to use a
 master connection but fall back to creating a new one if one does not already
 exist.