Add X11ForwardTimeout option to specify timeout for untrusted X11

authentication cookies to avoid fallback in X11 code to fully-trusted
implicit authentication using SO_PEERCRED described at:
http://lists.x.org/archives/xorg-devel/2010-May/008636.html

After the X11ForwardTimeout has expired the client will now refuse
incoming X11 channel opens.

based on patch from Tavis Ormandy; "nice" markus@

7 files changed, 59 insertions, 20 deletions

diff --git a/usr.bin/ssh/clientloop.c b/usr.bin/ssh/clientloop.c
index ff00211b909..be01467e9d4 100644
--- a/usr.bin/ssh/clientloop.c
+++ b/usr.bin/ssh/clientloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.220 2010/04/10 02:08:44 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.221 2010/06/25 23:15:36 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -147,11 +147,12 @@ static int stdin_eof;		/* EOF has been encountered on stderr. */
 static Buffer stdin_buffer;	/* Buffer for stdin data. */
 static Buffer stdout_buffer;	/* Buffer for stdout data. */
 static Buffer stderr_buffer;	/* Buffer for stderr data. */
-static u_int buffer_high;/* Soft max buffer size. */
+static u_int buffer_high;	/* Soft max buffer size. */
 static int connection_in;	/* Connection to server (input). */
 static int connection_out;	/* Connection to server (output). */
 static int need_rekeying;	/* Set to non-zero if rekeying is requested. */
-static int session_closed = 0;	/* In SSH2: login session closed. */
+static int session_closed;	/* In SSH2: login session closed. */
+static int x11_refuse_time;	/* If >0, refuse x11 opens after this time. */
 
 static void client_init_dispatch(void);
 int	session_ident = -1;
@@ -246,7 +247,7 @@ get_current_time(void)
 #define SSH_X11_PROTO "MIT-MAGIC-COOKIE-1"
 void
 client_x11_get_proto(const char *display, const char *xauth_path,
-    u_int trusted, char **_proto, char **_data)
+    u_int trusted, u_int timeout, char **_proto, char **_data)
 {
 	char cmd[1024];
 	char line[512];
@@ -256,6 +257,7 @@ client_x11_get_proto(const char *display, const char *xauth_path,
 	int got_data = 0, generated = 0, do_unlink = 0, i;
 	char *xauthdir, *xauthfile;
 	struct stat st;
+	u_int now;
 
 	xauthdir = xauthfile = NULL;
 	*_proto = proto;
@@ -291,11 +293,18 @@ client_x11_get_proto(const char *display, const char *xauth_path,
 				    xauthdir);
 				snprintf(cmd, sizeof(cmd),
 				    "%s -f %s generate %s " SSH_X11_PROTO
-				    " untrusted timeout 1200 2>" _PATH_DEVNULL,
-				    xauth_path, xauthfile, display);
+				    " untrusted timeout %u 2>" _PATH_DEVNULL,
+				    xauth_path, xauthfile, display, timeout);
 				debug2("x11_get_proto: %s", cmd);
 				if (system(cmd) == 0)
 					generated = 1;
+				if (x11_refuse_time == 0) {
+					now = time(NULL) + 1;
+					if (UINT_MAX - timeout < now)
+						x11_refuse_time = UINT_MAX;
+					else
+						x11_refuse_time = now + timeout;
+				}
 			}
 		}
 
@@ -1674,6 +1683,11 @@ client_request_x11(const char *request_type, int rchan)
 		    "malicious server.");
 		return NULL;
 	}
+	if (x11_refuse_time != 0 && time(NULL) >= x11_refuse_time) {
+		verbose("Rejected X11 connection after ForwardX11Timeout "
+		    "expired");
+		return NULL;
+	}
 	originator = packet_get_string(NULL);
 	if (datafellows & SSH_BUG_X11FWD) {
 		debug2("buggy server: x11 request w/o originator_port");
diff --git a/usr.bin/ssh/clientloop.h b/usr.bin/ssh/clientloop.h
index a5bc246a343..52115db6ec8 100644
--- a/usr.bin/ssh/clientloop.h
+++ b/usr.bin/ssh/clientloop.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.h,v 1.24 2010/05/16 12:55:51 markus Exp $ */
+/* $OpenBSD: clientloop.h,v 1.25 2010/06/25 23:15:36 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -39,7 +39,7 @@
 
 /* Client side main loop for the interactive session. */
 int	 client_loop(int, int, int);
-void	 client_x11_get_proto(const char *, const char *, u_int,
+void	 client_x11_get_proto(const char *, const char *, u_int, u_int,
 	    char **, char **);
 void	 client_global_request_reply_fwd(int, u_int32_t, void *);
 void	 client_session2_setup(int, int, int, const char *, struct termios *,
diff --git a/usr.bin/ssh/mux.c b/usr.bin/ssh/mux.c
index 71557a8b37b..92de5636dab 100644
--- a/usr.bin/ssh/mux.c
+++ b/usr.bin/ssh/mux.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mux.c,v 1.20 2010/06/25 07:14:46 djm Exp $ */
+/* $OpenBSD: mux.c,v 1.21 2010/06/25 23:15:36 djm Exp $ */
 /*
  * Copyright (c) 2002-2008 Damien Miller <djm@openbsd.org>
  *
@@ -1089,11 +1089,14 @@ mux_session_confirm(int id, int success, void *arg)
 	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);
+		    options.forward_x11_trusted, options.forward_x11_timeout,
+		    &proto, &data);
 		/* Request forwarding with authentication spoofing. */
-		debug("Requesting X11 forwarding with authentication spoofing.");
+		debug("Requesting X11 forwarding with authentication "
+		    "spoofing.");
 		x11_request_forwarding_with_spoofing(id, display, proto, data);
 		/* XXX wait for reply */
 	}
diff --git a/usr.bin/ssh/readconf.c b/usr.bin/ssh/readconf.c
index c5474132f8e..da717e6462c 100644
--- a/usr.bin/ssh/readconf.c
+++ b/usr.bin/ssh/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.185 2010/06/25 07:14:46 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.186 2010/06/25 23:15:36 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -107,8 +107,8 @@
 
 typedef enum {
 	oBadOption,
-	oForwardAgent, oForwardX11, oForwardX11Trusted, oGatewayPorts,
-	oExitOnForwardFailure,
+	oForwardAgent, oForwardX11, oForwardX11Trusted, oForwardX11Timeout,
+	oGatewayPorts, oExitOnForwardFailure,
 	oPasswordAuthentication, oRSAAuthentication,
 	oChallengeResponseAuthentication, oXAuthLocation,
 	oIdentityFile, oHostName, oPort, oCipher, oRemoteForward, oLocalForward,
@@ -140,6 +140,7 @@ static struct {
 	{ "forwardagent", oForwardAgent },
 	{ "forwardx11", oForwardX11 },
 	{ "forwardx11trusted", oForwardX11Trusted },
+	{ "forwardx11timeout", oForwardX11Timeout },
 	{ "exitonforwardfailure", oExitOnForwardFailure },
 	{ "xauthlocation", oXAuthLocation },
 	{ "gatewayports", oGatewayPorts },
@@ -410,6 +411,10 @@ parse_flag:
 	case oForwardX11Trusted:
 		intptr = &options->forward_x11_trusted;
 		goto parse_flag;
+	
+	case oForwardX11Timeout:
+		intptr = &options->forward_x11_timeout;
+		goto parse_time;
 
 	case oGatewayPorts:
 		intptr = &options->gateway_ports;
@@ -1014,6 +1019,7 @@ initialize_options(Options * options)
 	options->forward_agent = -1;
 	options->forward_x11 = -1;
 	options->forward_x11_trusted = -1;
+	options->forward_x11_timeout = -1;
 	options->exit_on_forward_failure = -1;
 	options->xauth_location = NULL;
 	options->gateway_ports = -1;
@@ -1100,6 +1106,8 @@ fill_default_options(Options * options)
 		options->forward_x11 = 0;
 	if (options->forward_x11_trusted == -1)
 		options->forward_x11_trusted = 0;
+	if (options->forward_x11_timeout == -1)
+		options->forward_x11_timeout = 1200;
 	if (options->exit_on_forward_failure == -1)
 		options->exit_on_forward_failure = 0;
 	if (options->xauth_location == NULL)
diff --git a/usr.bin/ssh/readconf.h b/usr.bin/ssh/readconf.h
index 3c8eae9d2d4..66acafdefa1 100644
--- a/usr.bin/ssh/readconf.h
+++ b/usr.bin/ssh/readconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.84 2010/06/25 07:14:46 djm Exp $ */
+/* $OpenBSD: readconf.h,v 1.85 2010/06/25 23:15:36 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -32,6 +32,7 @@ typedef struct {
 typedef struct {
 	int     forward_agent;	/* Forward authentication agent. */
 	int     forward_x11;	/* Forward X11 display. */
+	int     forward_x11_timeout;	/* Expiration for Cookies */
 	int     forward_x11_trusted;	/* Trust Forward X11 display. */
 	int     exit_on_forward_failure;	/* Exit if bind(2) fails for -L/-R */
 	char   *xauth_location;	/* Location for xauth program */
diff --git a/usr.bin/ssh/ssh.c b/usr.bin/ssh/ssh.c
index c9f87053a57..b6aa87c40f9 100644
--- a/usr.bin/ssh/ssh.c
+++ b/usr.bin/ssh/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.339 2010/06/25 23:10:30 djm Exp $ */
+/* $OpenBSD: ssh.c,v 1.340 2010/06/25 23:15:36 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1084,7 +1084,9 @@ ssh_session(void)
 		char *proto, *data;
 		/* Get reasonable local authentication information. */
 		client_x11_get_proto(display, options.xauth_location,
-		    options.forward_x11_trusted, &proto, &data);
+		    options.forward_x11_trusted, 
+		    options.forward_x11_timeout,
+		    &proto, &data);
 		/* Request forwarding with authentication spoofing. */
 		debug("Requesting X11 forwarding with authentication "
 		    "spoofing.");
@@ -1180,7 +1182,8 @@ ssh_session2_setup(int id, int success, void *arg)
 		char *proto, *data;
 		/* Get reasonable local authentication information. */
 		client_x11_get_proto(display, options.xauth_location,
-		    options.forward_x11_trusted, &proto, &data);
+		    options.forward_x11_trusted,
+		    options.forward_x11_timeout, &proto, &data);
 		/* Request forwarding with authentication spoofing. */
 		debug("Requesting X11 forwarding with authentication "
 		    "spoofing.");
diff --git a/usr.bin/ssh/ssh_config.5 b/usr.bin/ssh/ssh_config.5
index 2df948e62ae..6968a4488c6 100644
--- a/usr.bin/ssh/ssh_config.5
+++ b/usr.bin/ssh/ssh_config.5
@@ -34,8 +34,8 @@
 .\" (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 1.133 2010/04/16 06:45:01 jmc Exp $
-.Dd $Mdocdate: April 16 2010 $
+.\" $OpenBSD: ssh_config.5,v 1.134 2010/06/25 23:15:36 djm Exp $
+.Dd $Mdocdate: June 25 2010 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -432,6 +432,16 @@ An attacker may then be able to perform activities such as keystroke monitoring
 if the
 .Cm ForwardX11Trusted
 option is also enabled.
+.It Cm ForwardX11Timeout
+Specify a timeout for untrusted X11 forwarding using the format described in
+.Sx TIME FORMATS
+section of
+.Xr sshd_config 5 .
+X11 connections received by
+.Xr ssh 1
+after this time will be refused.
+The default is to disable untrusted X11 forwarding after twenty minutes has
+elapsed.
 .It Cm ForwardX11Trusted
 If this option is set to
 .Dq yes ,