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

1 files changed, 121 insertions, 21 deletions

diff --git a/sshconnect.c b/sshconnect.c
index 6eff397d6..d9618bcf7 100644
--- a/sshconnect.c
+++ b/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"
@@ -271,13 +273,78 @@ ssh_kill_proxy_command(void)
 }
 
 /*
+ * 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) {
@@ -287,48 +354,81 @@ 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 (gaierr) {
+                if ((r = getaddrinfo(options.bind_address, NULL,
+                    &hints, &res)) != 0) {
                         error("getaddrinfo: %s: %s", options.bind_address,
-                            ssh_gai_strerror(gaierr));
-                        close(sock);
-                        return -1;
+                            ssh_gai_strerror(r));
+                        goto fail;
+                }
+                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
          * port, bind our own socket to a privileged port.
          */
         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,
-                            strerror(errno));
+                        error("bindresvport_sa %s: %s", ntop,
+                            strerror(oerrno));
                         goto fail;
                 }
-        } else {
-                if (bind(sock, res->ai_addr, res->ai_addrlen) < 0) {
-                        error("bind: %s: %s", options.bind_address,
-                            strerror(errno));
- fail:
-                        close(sock);
-                        freeaddrinfo(res);
-                        return -1;
-                }
+        } else if (bind(sock, (struct sockaddr *)&bindaddr, bindaddrlen) != 0) {
+                error("bind %s: %s", ntop, strerror(errno));
+                goto fail;
         }
+        debug("%s: bound to %s", __func__, ntop);
+        /* success */
+        goto out;
+fail:
+        close(sock);
+        sock = -1;
+ out:
         if (res != NULL)
                 freeaddrinfo(res);
+        if (ifaddrs != NULL)
+                freeifaddrs(ifaddrs);
         return sock;
 }