- markus@cvs.openbsd.org 2003/12/16 15:49:51

[clientloop.c clientloop.h readconf.c readconf.h scp.1 sftp.1 ssh.1] [ssh.c ssh_config.5] application layer keep alive (ServerAliveInterval ServerAliveCountMax) for ssh(1), similar to the sshd(8) option; ok beck@; with help from jmc and dtucker@
2003-12-17 16:33:10 +11:00 · 2003-12-17 16:33:10 +11:00 · 509b0107f0
--- a/8
+++ b/8
@ -23,6 +23,12 @@
   - markus@cvs.openbsd.org 2003/12/14 12:37:21
     [ssh_config.5]
     we don't support GSS KEX; from Simon Wilkinson
+   - markus@cvs.openbsd.org 2003/12/16 15:49:51
+     [clientloop.c clientloop.h readconf.c readconf.h scp.1 sftp.1 ssh.1]
+     [ssh.c ssh_config.5]
+     application layer keep alive (ServerAliveInterval ServerAliveCountMax)
+     for ssh(1), similar to the sshd(8) option; ok beck@; with help from
+     jmc and dtucker@

 20031209
 - (dtucker) OpenBSD CVS Sync
@ -1592,4 +1598,4 @@
 - Fix sshd BindAddress and -b options for systems using fake-getaddrinfo.
   Report from murple@murple.net, diagnosis from dtucker@zip.com.au

-$Id: ChangeLog,v 1.3145 2003/12/17 05:32:23 djm Exp $
+$Id: ChangeLog,v 1.3146 2003/12/17 05:33:10 djm Exp $
--- a/clientloop.c
+++ b/clientloop.c
@ -59,7 +59,7 @@
 */

 #include "includes.h"
-RCSID("$OpenBSD: clientloop.c,v 1.116 2003/12/09 23:45:32 dtucker Exp $");
+RCSID("$OpenBSD: clientloop.c,v 1.117 2003/12/16 15:49:51 markus Exp $");

 #include "ssh.h"
 #include "ssh1.h"
@ -127,6 +127,7 @@ 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 server_alive_timeouts = 0;

 static void client_init_dispatch(void);
 int	session_ident = -1;
@ -313,6 +314,24 @@ client_check_window_change(void)
 	}
 }

+static void
+client_global_request_reply(int type, u_int32_t seq, void *ctxt)
+{
+	server_alive_timeouts = 0;
+	client_global_request_reply_fwd(type, seq, ctxt);
+}
+
+static void
+server_alive_check(void)
+{
+	if (++server_alive_timeouts > options.server_alive_count_max)
+		packet_disconnect("Timeout, server not responding.");
+	packet_start(SSH2_MSG_GLOBAL_REQUEST);
+	packet_put_cstring("keepalive@openssh.com");
+	packet_put_char(1);     /* boolean: want reply */
+	packet_send();
+}
+
 /*
 * Waits until the client can do something (some data becomes available on
 * one of the file descriptors).
@ -322,6 +341,9 @@ static void
 client_wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp,
    int *maxfdp, int *nallocp, int rekeying)
 {
+	struct timeval tv, *tvp;
+	int ret;
+
 	/* Add any selections by the channel mechanism. */
 	channel_prepare_select(readsetp, writesetp, maxfdp, nallocp, rekeying);

@ -363,13 +385,18 @@ client_wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp,
 	/*
 	 * Wait for something to happen.  This will suspend the process until
 	 * some selected descriptor can be read, written, or has some other
-	 * event pending. Note: if you want to implement SSH_MSG_IGNORE
-	 * messages to fool traffic analysis, this might be the place to do
-	 * it: just have a random timeout for the select, and send a random
-	 * SSH_MSG_IGNORE packet when the timeout expires.
+	 * event pending.
 	 */

-	if (select((*maxfdp)+1, *readsetp, *writesetp, NULL, NULL) < 0) {
+	if (options.server_alive_interval == 0 || !compat20)
+		tvp = NULL;
+	else {  
+		tv.tv_sec = options.server_alive_interval;
+		tv.tv_usec = 0;
+		tvp = &tv;
+	}
+	ret = select((*maxfdp)+1, *readsetp, *writesetp, NULL, tvp);
+	if (ret < 0) {
 		char buf[100];

 		/*
@ -386,7 +413,8 @@ client_wait_until_can_do_something(fd_set **readsetp, fd_set **writesetp,
 		snprintf(buf, sizeof buf, "select: %s\r\n", strerror(errno));
 		buffer_append(&stderr_buffer, buf, strlen(buf));
 		quit_pending = 1;
-	}
+	} else if (ret == 0)
+		server_alive_check();
 }

 static void
@ -1365,7 +1393,8 @@ client_input_global_request(int type, u_int32_t seq, void *ctxt)

 	rtype = packet_get_string(NULL);
 	want_reply = packet_get_char();
-	debug("client_input_global_request: rtype %s want_reply %d", rtype, want_reply);
+	debug("client_input_global_request: rtype %s want_reply %d",
+	    rtype, want_reply);
 	if (want_reply) {
 		packet_start(success ?
 		    SSH2_MSG_REQUEST_SUCCESS : SSH2_MSG_REQUEST_FAILURE);
--- a/clientloop.h
+++ b/clientloop.h
@ -1,4 +1,4 @@
-/*	$OpenBSD: clientloop.h,v 1.7 2002/04/22 21:04:52 markus Exp $	*/
+/*	$OpenBSD: clientloop.h,v 1.8 2003/12/16 15:49:51 markus Exp $	*/

 /*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -37,4 +37,4 @@

 /* Client side main loop for the interactive session. */
 int	 client_loop(int, int, int);
-void	 client_global_request_reply(int type, u_int32_t seq, void *ctxt);
+void	 client_global_request_reply_fwd(int, u_int32_t, void *);
--- a/readconf.c
+++ b/readconf.c
@ -12,7 +12,7 @@
 */

 #include "includes.h"
-RCSID("$OpenBSD: readconf.c,v 1.126 2003/12/09 21:53:36 markus Exp $");
+RCSID("$OpenBSD: readconf.c,v 1.127 2003/12/16 15:49:51 markus Exp $");

 #include "ssh.h"
 #include "xmalloc.h"
@ -105,6 +105,7 @@ typedef enum {
 	oClearAllForwardings, oNoHostAuthenticationForLocalhost,
 	oEnableSSHKeysign, oRekeyLimit, oVerifyHostKeyDNS, oConnectTimeout,
 	oAddressFamily, oGssAuthentication, oGssDelegateCreds,
+	oServerAliveInterval, oServerAliveCountMax,
 	oDeprecated, oUnsupported
 } OpCodes;

@ -189,6 +190,8 @@ static struct {
 	{ "rekeylimit", oRekeyLimit },
 	{ "connecttimeout", oConnectTimeout },
 	{ "addressfamily", oAddressFamily },
+	{ "serveraliveinterval", oServerAliveInterval },
+	{ "serveralivecountmax", oServerAliveCountMax },
 	{ NULL, oBadOption }
 };

@ -307,7 +310,7 @@ process_config_line(Options *options, const char *host,
 		/* NOTREACHED */
 	case oConnectTimeout:
 		intptr = &options->connection_timeout;
-/* parse_time: */
+parse_time:
 		arg = strdelim(&s);
 		if (!arg || *arg == '\0')
 			fatal("%s line %d: missing time value.",
@ -733,6 +736,14 @@ parse_int:
 		intptr = &options->enable_ssh_keysign;
 		goto parse_flag;

+	case oServerAliveInterval:
+		intptr = &options->server_alive_interval;
+		goto parse_time;
+
+	case oServerAliveCountMax:
+		intptr = &options->server_alive_count_max;
+		goto parse_int;
+
 	case oDeprecated:
 		debug("%s line %d: Deprecated option \"%s\"",
 		    filename, linenum, keyword);
@ -860,6 +871,8 @@ initialize_options(Options * options)
 	options->no_host_authentication_for_localhost = - 1;
 	options->rekey_limit = - 1;
 	options->verify_host_key_dns = -1;
+	options->server_alive_interval = -1;
+	options->server_alive_count_max = -1;
 }

 /*
@ -974,6 +987,10 @@ fill_default_options(Options * options)
 		options->rekey_limit = 0;
 	if (options->verify_host_key_dns == -1)
 		options->verify_host_key_dns = 0;
+	if (options->server_alive_interval == -1)
+		options->server_alive_interval = 0;
+	if (options->server_alive_count_max == -1)
+		options->server_alive_count_max = 3;
 	/* options->proxy_command should not be set by default */
 	/* options->user will be set in the main program if appropriate */
 	/* options->hostname will be set in the main program if appropriate */
--- a/readconf.h
+++ b/readconf.h
@ -1,4 +1,4 @@
-/*	$OpenBSD: readconf.h,v 1.58 2003/12/09 21:53:36 markus Exp $	*/
+/*	$OpenBSD: readconf.h,v 1.59 2003/12/16 15:49:51 markus Exp $	*/

 /*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -100,6 +100,8 @@ typedef struct {
 	int	enable_ssh_keysign;
 	int	rekey_limit;
 	int	no_host_authentication_for_localhost;
+	int	server_alive_interval; 
+	int	server_alive_count_max;
 }       Options;


--- a/scp.1
+++ b/scp.1
@ -9,7 +9,7 @@
 .\"
 .\" Created: Sun May  7 00:14:37 1995 ylo
 .\"
-.\" $OpenBSD: scp.1,v 1.31 2003/12/09 21:53:36 markus Exp $
+.\" $OpenBSD: scp.1,v 1.32 2003/12/16 15:49:51 markus Exp $
 .\"
 .Dd September 25, 1999
 .Dt SCP 1
@ -149,6 +149,8 @@ For full details of the options listed below, and their possible values, see
 .It PubkeyAuthentication
 .It RhostsRSAAuthentication
 .It RSAAuthentication
+.It ServerAliveInterval
+.It ServerAliveCountMax
 .It SmartcardDevice
 .It StrictHostKeyChecking
 .It TCPKeepAlive
--- a/sftp.1
+++ b/sftp.1
@ -1,4 +1,4 @@
-.\" $OpenBSD: sftp.1,v 1.48 2003/12/09 21:53:37 markus Exp $
+.\" $OpenBSD: sftp.1,v 1.49 2003/12/16 15:49:51 markus Exp $
 .\"
 .\" Copyright (c) 2001 Damien Miller.  All rights reserved.
 .\"
@ -170,6 +170,8 @@ For full details of the options listed below, and their possible values, see
 .It PubkeyAuthentication
 .It RhostsRSAAuthentication
 .It RSAAuthentication
+.It ServerAliveInterval
+.It ServerAliveCountMax
 .It SmartcardDevice
 .It StrictHostKeyChecking
 .It TCPKeepAlive
--- a/ssh.1
+++ b/ssh.1
@ -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.1,v 1.180 2003/12/09 21:53:37 markus Exp $
+.\" $OpenBSD: ssh.1,v 1.181 2003/12/16 15:49:51 markus Exp $
 .Dd September 25, 1999
 .Dt SSH 1
 .Os
@ -648,6 +648,8 @@ For full details of the options listed below, and their possible values, see
 .It RemoteForward
 .It RhostsRSAAuthentication
 .It RSAAuthentication
+.It ServerAliveInterval
+.It ServerAliveCountMax
 .It SmartcardDevice
 .It StrictHostKeyChecking
 .It TCPKeepAlive
--- a/ssh.c
+++ b/ssh.c
@ -40,7 +40,7 @@
 */

 #include "includes.h"
-RCSID("$OpenBSD: ssh.c,v 1.205 2003/12/09 17:30:05 markus Exp $");
+RCSID("$OpenBSD: ssh.c,v 1.206 2003/12/16 15:49:51 markus Exp $");

 #include <openssl/evp.h>
 #include <openssl/err.h>
@ -1029,16 +1029,13 @@ client_subsystem_reply(int type, u_int32_t seq, void *ctxt)
 }

 void
-client_global_request_reply(int type, u_int32_t seq, void *ctxt)
+client_global_request_reply_fwd(int type, u_int32_t seq, void *ctxt)
 {
 	int i;

 	i = client_global_request_id++;
-	if (i >= options.num_remote_forwards) {
-		debug("client_global_request_reply: too many replies %d > %d",
-		    i, options.num_remote_forwards);
+	if (i >= options.num_remote_forwards)
 		return;
-	}
 	debug("remote forward %s for: listen %d, connect %s:%d",
 	    type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
 	    options.remote_forwards[i].port,
--- 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 1.27 2003/12/14 12:37:21 markus Exp $
+.\" $OpenBSD: ssh_config.5,v 1.28 2003/12/16 15:49:51 markus Exp $
 .Dd September 25, 1999
 .Dt SSH_CONFIG 5
 .Os
@ -552,6 +552,42 @@ running.
 The default is
 .Dq yes .
 Note that this option applies to protocol version 1 only.
+.It Cm ServerAliveInterval
+Sets a timeout interval in seconds after which if no data has been received
+from the server,
+.Nm ssh
+will send a message through the encrypted
+channel to request a response from the server.
+The default
+is 0, indicating that these messages will not be sent to the server.
+This option applies to protocol version 2 only.
+.It Cm ServerAliveCountMax
+Sets the number of server alive messages (see above) which may be
+sent without
+.Nm ssh
+receiving any messages back from the server.
+If this threshold is reached while server alive messages are being sent,
+.Nm ssh
+will disconnect from the server, terminating the session.
+It is important to note that the use of server alive messages is very
+different from
+.Cm TCPKeepAlive
+(below).
+The server alive messages are sent through the encrypted channel
+and therefore will not be spoofable.
+The TCP keepalive option enabled by
+.Cm TCPKeepAlive
+is spoofable.
+The server alive mechanism is valuable when the client or
+server depend on knowing when a connection has become inactive.
+.Pp
+The default value is 3.
+If, for example,
+.Cm ServerAliveInterval
+(above) is set to 15, and
+.Cm ServerAliveCountMax
+is left at the default, if the server becomes unresponsive ssh
+will disconnect after approximately 45 seconds.
 .It Cm SmartcardDevice
 Specifies which smartcard device to use.
 The argument to this keyword is the device