upstream: Add BindInterface ssh_config directive and -B

command-line argument to ssh(1) that directs it to bind its outgoing
connection to the address of the specified network interface.

BindInterface prefers to use addresses that aren't loopback or link-
local, but will fall back to those if no other addresses of the
required family are available on that interface.

Based on patch by Mike Manning in bz#2820, ok dtucker@

OpenBSD-Commit-ID: c5064d285c2851f773dd736a2c342aa384fbf713

readconf.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.281 2017/12/05 23:59:47 dtucker Exp $ */
+/* $OpenBSD: readconf.c,v 1.282 2018/02/23 02:34:33 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -156,7 +156,7 @@ typedef enum {
 	oPubkeyAuthentication,
 	oKbdInteractiveAuthentication, oKbdInteractiveDevices, oHostKeyAlias,
 	oDynamicForward, oPreferredAuthentications, oHostbasedAuthentication,
-	oHostKeyAlgorithms, oBindAddress, oPKCS11Provider,
+	oHostKeyAlgorithms, oBindAddress, oBindInterface, oPKCS11Provider,
 	oClearAllForwardings, oNoHostAuthenticationForLocalhost,
 	oEnableSSHKeysign, oRekeyLimit, oVerifyHostKeyDNS, oConnectTimeout,
 	oAddressFamily, oGssAuthentication, oGssDelegateCreds,
@@ -266,6 +266,7 @@ static struct {
 	{ "preferredauthentications", oPreferredAuthentications },
 	{ "hostkeyalgorithms", oHostKeyAlgorithms },
 	{ "bindaddress", oBindAddress },
+	{ "bindinterface", oBindInterface },
 	{ "clearallforwardings", oClearAllForwardings },
 	{ "enablesshkeysign", oEnableSSHKeysign },
 	{ "verifyhostkeydns", oVerifyHostKeyDNS },
@@ -1099,6 +1100,10 @@ parse_char_array:
 		charptr = &options->bind_address;
 		goto parse_string;
 
+	case oBindInterface:
+		charptr = &options->bind_interface;
+		goto parse_string;
+
 	case oPKCS11Provider:
 		charptr = &options->pkcs11_provider;
 		goto parse_string;
@@ -1800,6 +1805,7 @@ initialize_options(Options * options)
 	options->log_level = SYSLOG_LEVEL_NOT_SET;
 	options->preferred_authentications = NULL;
 	options->bind_address = NULL;
+	options->bind_interface = NULL;
 	options->pkcs11_provider = NULL;
 	options->enable_ssh_keysign = - 1;
 	options->no_host_authentication_for_localhost = - 1;
@@ -2509,6 +2515,7 @@ dump_client_config(Options *o, const char *host)
 
 	/* String options */
 	dump_cfg_string(oBindAddress, o->bind_address);
+	dump_cfg_string(oBindInterface, o->bind_interface);
 	dump_cfg_string(oCiphers, o->ciphers ? o->ciphers : KEX_CLIENT_ENCRYPT);
 	dump_cfg_string(oControlPath, o->control_path);
 	dump_cfg_string(oHostKeyAlgorithms, o->hostkeyalgorithms);

readconf.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.h,v 1.124 2017/10/21 23:06:24 millert Exp $ */
+/* $OpenBSD: readconf.h,v 1.125 2018/02/23 02:34:33 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -81,6 +81,7 @@ typedef struct {
 	char   *user_hostfiles[SSH_MAX_HOSTS_FILES];
 	char   *preferred_authentications;
 	char   *bind_address;	/* local socket address for connection to sshd */
+	char   *bind_interface;	/* local interface for bind address */
 	char   *pkcs11_provider; /* PKCS#11 provider */
 	int	verify_host_key_dns;	/* Verify host key using DNS */
 

ssh.1

@@ -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.1,v 1.389 2017/11/03 02:29:17 djm Exp $
+.\" $OpenBSD: ssh.1,v 1.390 2018/02/23 02:34:33 djm Exp $
-.Dd $Mdocdate: November 3 2017 $
+.Dd $Mdocdate: February 23 2018 $
 .Dt SSH 1
 .Os
 .Sh NAME
@@ -43,6 +43,7 @@
 .Sh SYNOPSIS
 .Nm ssh
 .Op Fl 46AaCfGgKkMNnqsTtVvXxYy
+.Op Fl B Ar bind_interface
 .Op Fl b Ar bind_address
 .Op Fl c Ar cipher_spec
 .Op Fl D Oo Ar bind_address : Oc Ns Ar port
@@ -124,6 +125,12 @@ authenticate using the identities loaded into the agent.
 .It Fl a
 Disables forwarding of the authentication agent connection.
 .Pp
+.It Fl B Ar interface
+Bind to the address of
+.Ar interface
+before attempting to connect to the destination host.
+This is only useful on systems with more than one address.
+.Pp
 .It Fl b Ar bind_address
 Use
 .Ar bind_address

ssh.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.473 2018/02/13 03:36:56 djm Exp $ */
+/* $OpenBSD: ssh.c,v 1.474 2018/02/23 02:34:33 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -201,13 +201,13 @@ static void
 usage(void)
 {
 	fprintf(stderr,
-"usage: ssh [-46AaCfGgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec]\n"
+"usage: ssh [-46AaCfGgKkMNnqsTtVvXxYy] [-B bind_interface]\n"
-"           [-D [bind_address:]port] [-E log_file] [-e escape_char]\n"
+"           [-b bind_address] [-c cipher_spec] [-D [bind_address:]port]\n"
-"           [-F configfile] [-I pkcs11] [-i identity_file]\n"
+"           [-E log_file] [-e escape_char] [-F configfile] [-I pkcs11]\n"
-"           [-J [user@]host[:port]] [-L address] [-l login_name] [-m mac_spec]\n"
+"           [-i identity_file] [-J [user@]host[:port]] [-L address]\n"
-"           [-O ctl_cmd] [-o option] [-p port] [-Q query_option] [-R address]\n"
+"           [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]\n"
-"           [-S ctl_path] [-W host:port] [-w local_tun[:remote_tun]]\n"
+"           [-Q query_option] [-R address] [-S ctl_path] [-W host:port]\n"
-"           destination [command]\n"
+"           [-w local_tun[:remote_tun]] destination [command]\n"
 	);
 	exit(255);
 }
@@ -663,7 +663,7 @@ main(int ac, char **av)
 
  again:
 	while ((opt = getopt(ac, av, "1246ab:c:e:fgi:kl:m:no:p:qstvx"
-	    "ACD:E:F:GI:J:KL:MNO:PQ:R:S:TVw:W:XYy")) != -1) {
+	    "AB:CD:E:F:GI:J:KL:MNO:PQ:R:S:TVw:W:XYy")) != -1) {
 		switch (opt) {
 		case '1':
 			fatal("SSH protocol v.1 is no longer supported");
@@ -973,6 +973,9 @@ main(int ac, char **av)
 		case 'b':
 			options.bind_address = optarg;
 			break;
+		case 'B':
+			options.bind_interface = optarg;
+			break;
 		case 'F':
 			config = optarg;
 			break;

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 1.266 2018/02/16 02:40:45 djm Exp $
+.\" $OpenBSD: ssh_config.5,v 1.267 2018/02/23 02:34:33 djm Exp $
-.Dd $Mdocdate: February 16 2018 $
+.Dd $Mdocdate: February 23 2018 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -254,6 +254,13 @@ The argument must be
 or
 .Cm no
 (the default).
+.It Cm BindInterface
+Use the address of the specified interface on the local machine as the
+source address of the connection.
+Note that this option does not work if
+.Cm UsePrivilegedPort
+is set to
+.Cm yes .
 .It Cm BindAddress
 Use the specified address on the local machine as the source address of
 the connection.

sshconnect.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect.c,v 1.294 2018/02/10 09:25:35 djm Exp $ */
+/* $OpenBSD: sshconnect.c,v 1.295 2018/02/23 02:34:33 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -23,6 +23,7 @@
 # include <sys/time.h>
 #endif
 
+#include <net/if.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 
@@ -43,6 +44,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <ifaddrs.h>
 
 #include "xmalloc.h"
 #include "key.h"
@@ -270,14 +272,79 @@ ssh_kill_proxy_command(void)
 		kill(proxy_command_pid, SIGHUP);
 }
 
+/*
+ * Search a interface address list (returned from getifaddrs(3)) for an
+ * address that matches the desired address family on the specifed interface.
+ * Returns 0 and fills in *resultp and *rlenp on success. Returns -1 on failure.
+ */
+static int
+check_ifaddrs(const char *ifname, int af, const struct ifaddrs *ifaddrs,
+    struct sockaddr_storage *resultp, socklen_t *rlenp)
+{
+	struct sockaddr_in6 *sa6;
+	struct sockaddr_in *sa;
+	struct in6_addr *v6addr;
+	const struct ifaddrs *ifa;
+	int allow_local;
+
+	/*
+	 * Prefer addresses that are not loopback or linklocal, but use them
+	 * if nothing else matches.
+	 */
+	for (allow_local = 0; allow_local < 2; allow_local++) {
+		for (ifa = ifaddrs; ifa != NULL; ifa = ifa->ifa_next) {
+			if (ifa->ifa_addr == NULL || ifa->ifa_name == NULL ||
+			    (ifa->ifa_flags & IFF_UP) == 0 ||
+			    ifa->ifa_addr->sa_family != af ||
+			    strcmp(ifa->ifa_name, options.bind_interface) != 0)
+				continue;
+			switch (ifa->ifa_addr->sa_family) {
+			case AF_INET:
+				sa = (struct sockaddr_in *)ifa->ifa_addr;
+				if (!allow_local && sa->sin_addr.s_addr ==
+				    htonl(INADDR_LOOPBACK))
+					continue;
+				if (*rlenp < sizeof(struct sockaddr_in)) {
+					error("%s: v4 addr doesn't fit",
+					    __func__);
+					return -1;
+				}
+				*rlenp = sizeof(struct sockaddr_in);
+				memcpy(resultp, sa, *rlenp);
+				return 0;
+			case AF_INET6:
+				sa6 = (struct sockaddr_in6 *)ifa->ifa_addr;
+				v6addr = &sa6->sin6_addr;
+				if (!allow_local &&
+				    (IN6_IS_ADDR_LINKLOCAL(v6addr) ||
+				    IN6_IS_ADDR_LOOPBACK(v6addr)))
+					continue;
+				if (*rlenp < sizeof(struct sockaddr_in6)) {
+					error("%s: v6 addr doesn't fit",
+					    __func__);
+					return -1;
+				}
+				*rlenp = sizeof(struct sockaddr_in6);
+				memcpy(resultp, sa6, *rlenp);
+				return 0;
+			}
+		}
+	}
+	return -1;
+}
+
 /*
  * Creates a (possibly privileged) socket for use as the ssh connection.
  */
 static int
 ssh_create_socket(int privileged, struct addrinfo *ai)
 {
-	int sock, r, gaierr;
+	int sock, r, oerrno;
+	struct sockaddr_storage bindaddr;
+	socklen_t bindaddrlen = 0;
 	struct addrinfo hints, *res = NULL;
+	struct ifaddrs *ifaddrs = NULL;
+	char ntop[NI_MAXHOST];
 
 	sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
 	if (sock < 0) {
@@ -287,22 +354,50 @@ ssh_create_socket(int privileged, struct addrinfo *ai)
 	fcntl(sock, F_SETFD, FD_CLOEXEC);
 
 	/* Bind the socket to an alternative local IP address */
-	if (options.bind_address == NULL && !privileged)
+	if (options.bind_address == NULL && options.bind_interface == NULL &&
+	    !privileged)
 		return sock;
 
-	if (options.bind_address) {
+	if (options.bind_address != NULL) {
 		memset(&hints, 0, sizeof(hints));
 		hints.ai_family = ai->ai_family;
 		hints.ai_socktype = ai->ai_socktype;
 		hints.ai_protocol = ai->ai_protocol;
 		hints.ai_flags = AI_PASSIVE;
-		gaierr = getaddrinfo(options.bind_address, NULL, &hints, &res);
+		if ((r = getaddrinfo(options.bind_address, NULL,
-		if (gaierr) {
+		    &hints, &res)) != 0) {
 			error("getaddrinfo: %s: %s", options.bind_address,
-			    ssh_gai_strerror(gaierr));
+			    ssh_gai_strerror(r));
-			close(sock);
+			goto fail;
-			return -1;
 		}
+		if (res == NULL)
+			error("getaddrinfo: no addrs");
+			goto fail;
+		if (res->ai_addrlen > sizeof(bindaddr)) {
+			error("%s: addr doesn't fit", __func__);
+			goto fail;
+		}
+		memcpy(&bindaddr, res->ai_addr, res->ai_addrlen);
+		bindaddrlen = res->ai_addrlen;
+	} else if (options.bind_interface != NULL) {
+		if ((r = getifaddrs(&ifaddrs)) != 0) {
+			error("getifaddrs: %s: %s", options.bind_interface,
+			      strerror(errno));
+			goto fail;
+		}
+		bindaddrlen = sizeof(bindaddr);
+		if (check_ifaddrs(options.bind_interface, ai->ai_family,
+		    ifaddrs, &bindaddr, &bindaddrlen) != 0) {
+			logit("getifaddrs: %s: no suitable addresses",
+			      options.bind_interface);
+			goto fail;
+		}
+	}
+	if ((r = getnameinfo((struct sockaddr *)&bindaddr, bindaddrlen,
+	    ntop, sizeof(ntop), NULL, 0, NI_NUMERICHOST)) != 0) {
+		error("%s: getnameinfo failed: %s", __func__,
+		    ssh_gai_strerror(r));
+		goto fail;
 	}
 	/*
 	 * If we are running as root and want to connect to a privileged
@@ -310,25 +405,30 @@ ssh_create_socket(int privileged, struct addrinfo *ai)
 	 */
 	if (privileged) {
 		PRIV_START;
-		r = bindresvport_sa(sock, res ? res->ai_addr : NULL);
+		r = bindresvport_sa(sock,
+		        bindaddrlen == 0 ? NULL : (struct sockaddr *)&bindaddr);
+		oerrno = errno;
 		PRIV_END;
 		if (r < 0) {
-			error("bindresvport_sa: af=%d %s", ai->ai_family,
+			error("bindresvport_sa %s: %s", ntop,
-			    strerror(errno));
+			    strerror(oerrno));
 			goto fail;
 		}
-	} else {
+	} else if (bind(sock, (struct sockaddr *)&bindaddr, bindaddrlen) != 0) {
-		if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
+		error("bind %s: %s", ntop, strerror(errno));
-			error("bind: %s: %s", options.bind_address,
+		goto fail;
-			    strerror(errno));
+	}
+	debug("%s: bound to %s", __func__, ntop);
+	/* success */
+	goto out;
 fail:
 	close(sock);
-			freeaddrinfo(res);
+	sock = -1;
-			return -1;
+ out:
-		}
-	}
 	if (res != NULL)
 		freeaddrinfo(res);
+	if (ifaddrs != NULL)
+		freeifaddrs(ifaddrs);
 	return sock;
 }