- djm@cvs.openbsd.org 2013/08/20 00:11:38

[readconf.c readconf.h ssh_config.5 sshconnect.c]
     Add a ssh_config ProxyUseFDPass option that supports the use of
     ProxyCommands that establish a connection and then pass a connected
     file descriptor back to ssh(1). This allows the ProxyCommand to exit
     rather than have to shuffle data back and forth and enables ssh to use
     getpeername, etc. to obtain address information just like it does with
     regular directly-connected sockets. ok markus@

ChangeLog

@@ -50,6 +50,14 @@
      [scp.1 ssh.1]
      some Bx/Ox conversion;
      From: Jan Stary
+   - djm@cvs.openbsd.org 2013/08/20 00:11:38
+     [readconf.c readconf.h ssh_config.5 sshconnect.c]
+     Add a ssh_config ProxyUseFDPass option that supports the use of
+     ProxyCommands that establish a connection and then pass a connected
+     file descriptor back to ssh(1). This allows the ProxyCommand to exit
+     rather than have to shuffle data back and forth and enables ssh to use
+     getpeername, etc. to obtain address information just like it does with
+     regular directly-connected sockets. ok markus@
 
 20130808
  - (dtucker) [regress/Makefile regress/test-exec.sh] Don't try to use test -nt

readconf.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.204 2013/06/10 19:19:44 dtucker Exp $ */
+/* $OpenBSD: readconf.c,v 1.205 2013/08/20 00:11:37 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -137,7 +137,7 @@ typedef enum {
 	oHashKnownHosts,
 	oTunnel, oTunnelDevice, oLocalCommand, oPermitLocalCommand,
 	oVisualHostKey, oUseRoaming, oZeroKnowledgePasswordAuthentication,
-	oKexAlgorithms, oIPQoS, oRequestTTY, oIgnoreUnknown,
+	oKexAlgorithms, oIPQoS, oRequestTTY, oIgnoreUnknown, oProxyUseFdpass,
 	oIgnoredUnknownOption, oDeprecated, oUnsupported
 } OpCodes;
 
@@ -249,6 +249,7 @@ static struct {
 	{ "kexalgorithms", oKexAlgorithms },
 	{ "ipqos", oIPQoS },
 	{ "requesttty", oRequestTTY },
+	{ "proxyusefdpass", oProxyUseFdpass },
 	{ "ignoreunknown", oIgnoreUnknown },
 
 	{ NULL, oBadOption }
@@ -1072,6 +1073,10 @@ parse_int:
 		charptr = &options->ignored_unknown;
 		goto parse_string;
 
+	case oProxyUseFdpass:
+		intptr = &options->proxy_use_fdpass;
+		goto parse_flag;
+
 	case oDeprecated:
 		debug("%s line %d: Deprecated option \"%s\"",
 		    filename, linenum, keyword);
@@ -1233,6 +1238,7 @@ initialize_options(Options * options)
 	options->ip_qos_interactive = -1;
 	options->ip_qos_bulk = -1;
 	options->request_tty = -1;
+	options->proxy_use_fdpass = -1;
 	options->ignored_unknown = NULL;
 }
 
@@ -1385,6 +1391,8 @@ fill_default_options(Options * options)
 		options->ip_qos_bulk = IPTOS_THROUGHPUT;
 	if (options->request_tty == -1)
 		options->request_tty = REQUEST_TTY_AUTO;
+	if (options->proxy_use_fdpass == -1)
+		options->proxy_use_fdpass = 0;
 	/* options->local_command should not be set by default */
 	/* options->proxy_command should not be set by default */
 	/* options->user will be set in the main program if appropriate */

readconf.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.95 2013/05/16 04:27:50 djm Exp $ */
+/* $OpenBSD: readconf.h,v 1.96 2013/08/20 00:11:38 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -138,6 +138,8 @@ typedef struct {
 
 	int	request_tty;
 
+	int	proxy_use_fdpass;
+
 	char	*ignored_unknown; /* Pattern list of unknown tokens to ignore */
 }       Options;
 

ssh_config.5

@@ -33,8 +33,8 @@
 .\" (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 1.166 2013/06/27 14:05:37 jmc Exp $
+.\" $OpenBSD: ssh_config.5,v 1.167 2013/08/20 00:11:38 djm Exp $
-.Dd $Mdocdate: June 27 2013 $
+.Dd $Mdocdate: August 20 2013 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -937,6 +937,14 @@ For example, the following directive would connect via an HTTP proxy at
 .Bd -literal -offset 3n
 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
 .Ed
+.It Cm ProxyUseFdpass
+Specifies that the a
+.Cm ProxyCommand
+will pass a connected file descriptor back to
+.Nm ssh
+instead of continuing to execute and pass data.
+The default is
+.Dq no .
 .It Cm PubkeyAuthentication
 Specifies whether to try public key authentication.
 The argument to this keyword must be

sshconnect.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect.c,v 1.238 2013/05/17 00:13:14 djm Exp $ */
+/* $OpenBSD: sshconnect.c,v 1.239 2013/08/20 00:11:38 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -59,6 +59,7 @@
 #include "misc.h"
 #include "dns.h"
 #include "roaming.h"
+#include "monitor_fdpass.h"
 #include "ssh2.h"
 #include "version.h"
 
@@ -78,16 +79,113 @@ extern uid_t original_effective_uid;
 static int show_other_keys(struct hostkeys *, Key *);
 static void warn_changed_key(Key *);
 
+/* Expand a proxy command */
+static char *
+expand_proxy_command(const char *proxy_command, const char *user,
+    const char *host, int port)
+{
+	char *tmp, *ret, strport[NI_MAXSERV];
+
+	snprintf(strport, sizeof strport, "%hu", port);
+	xasprintf(&tmp, "exec %s", proxy_command);
+	ret = percent_expand(tmp, "h", host, "p", strport,
+	    "r", options.user, (char *)NULL);
+	free(tmp);
+	return ret;
+}
+
+/*
+ * Connect to the given ssh server using a proxy command that passes a
+ * a connected fd back to us.
+ */
+static int
+ssh_proxy_fdpass_connect(const char *host, u_short port,
+    const char *proxy_command)
+{
+	char *command_string;
+	int sp[2], sock;
+	pid_t pid;
+	char *shell;
+
+	if ((shell = getenv("SHELL")) == NULL)
+		shell = _PATH_BSHELL;
+
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp) < 0)
+		fatal("Could not create socketpair to communicate with "
+		    "proxy dialer: %.100s", strerror(errno));
+
+	command_string = expand_proxy_command(proxy_command, options.user,
+	    host, port);
+	debug("Executing proxy dialer command: %.500s", command_string);
+
+	/* Fork and execute the proxy command. */
+	if ((pid = fork()) == 0) {
+		char *argv[10];
+
+		/* Child.  Permanently give up superuser privileges. */
+		permanently_drop_suid(original_real_uid);
+
+		close(sp[1]);
+		/* Redirect stdin and stdout. */
+		if (sp[0] != 0) {
+			if (dup2(sp[0], 0) < 0)
+				perror("dup2 stdin");
+		}
+		if (sp[0] != 1) {
+			if (dup2(sp[0], 1) < 0)
+				perror("dup2 stdout");
+		}
+		if (sp[0] >= 2)
+			close(sp[0]);
+
+		/*
+		 * Stderr is left as it is so that error messages get
+		 * printed on the user's terminal.
+		 */
+		argv[0] = shell;
+		argv[1] = "-c";
+		argv[2] = command_string;
+		argv[3] = NULL;
+
+		/*
+		 * Execute the proxy command.
+		 * Note that we gave up any extra privileges above.
+		 */
+		execv(argv[0], argv);
+		perror(argv[0]);
+		exit(1);
+	}
+	/* Parent. */
+	if (pid < 0)
+		fatal("fork failed: %.100s", strerror(errno));
+	close(sp[0]);
+	free(command_string);
+
+	if ((sock = mm_receive_fd(sp[1])) == -1)
+		fatal("proxy dialer did not pass back a connection");
+
+	while (waitpid(pid, NULL, 0) == -1)
+		if (errno != EINTR)
+			fatal("Couldn't wait for child: %s", strerror(errno));
+
+	/* Set the connection file descriptors. */
+	packet_set_connection(sock, sock);
+	packet_set_timeout(options.server_alive_interval,
+	    options.server_alive_count_max);
+
+	return 0;
+}
+
 /*
  * Connect to the given ssh server using a proxy command.
  */
 static int
 ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
 {
-	char *command_string, *tmp;
+	char *command_string;
 	int pin[2], pout[2];
 	pid_t pid;
-	char *shell, strport[NI_MAXSERV];
+	char *shell;
 
 	if (!strcmp(proxy_command, "-")) {
 		packet_set_connection(STDIN_FILENO, STDOUT_FILENO);
@@ -96,29 +194,19 @@ ssh_proxy_connect(const char *host, u_short port, const char *proxy_command)
 		return 0;
 	}
 
+	if (options.proxy_use_fdpass)
+		return ssh_proxy_fdpass_connect(host, port, proxy_command);
+
 	if ((shell = getenv("SHELL")) == NULL || *shell == '\0')
 		shell = _PATH_BSHELL;
 
-	/* Convert the port number into a string. */
-	snprintf(strport, sizeof strport, "%hu", port);
-
-	/*
-	 * Build the final command string in the buffer by making the
-	 * appropriate substitutions to the given proxy command.
-	 *
-	 * Use "exec" to avoid "sh -c" processes on some platforms
-	 * (e.g. Solaris)
-	 */
-	xasprintf(&tmp, "exec %s", proxy_command);
-	command_string = percent_expand(tmp, "h", host, "p", strport,
-	    "r", options.user, (char *)NULL);
-	free(tmp);
-
 	/* Create pipes for communicating with the proxy. */
 	if (pipe(pin) < 0 || pipe(pout) < 0)
 		fatal("Could not create pipes to communicate with the proxy: %.100s",
 		    strerror(errno));
 
+	command_string = expand_proxy_command(proxy_command, options.user,
+	    host, port);
 	debug("Executing proxy command: %.500s", command_string);
 
 	/* Fork and execute the proxy command. */