upstream commit

Add a ProxyJump ssh_config(5) option and corresponding -J
ssh(1) command-line flag to allow simplified indirection through a SSH
bastion or "jump host".

These options construct a proxy command that connects to the
specified jump host(s) (more than one may be specified) and uses
port-forwarding to establish a connection to the next destination.

This codifies the safest way of indirecting connections through SSH
servers and makes it easy to use.

ok markus@

Upstream-ID: fa899cb8b26d889da8f142eb9774c1ea36b04397

1 files changed, 63 insertions, 14 deletions

diff --git a/ssh.c b/ssh.c
index e7d4fd915..a9b685349 100644
--- a/ssh.c
+++ b/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.442 2016/06/03 04:09:39 dtucker Exp $ */
+/* $OpenBSD: ssh.c,v 1.443 2016/07/15 00:24:30 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -330,7 +330,7 @@ resolve_addr(const char *name, int port, char *caddr, size_t clen)
  * NB. this function must operate with a options having undefined members.
  */
 static int
-check_follow_cname(char **namep, const char *cname)
+check_follow_cname(int direct, char **namep, const char *cname)
 {
         int i;
         struct allowed_cname *rule;
@@ -342,9 +342,9 @@ check_follow_cname(char **namep, const char *cname)
                 return 0;
         /*
          * Don't attempt to canonicalize names that will be interpreted by
-         * a proxy unless the user specifically requests so.
+         * a proxy or jump host unless the user specifically requests so.
          */
-        if (!option_clear_or_none(options.proxy_command) &&
+        if (!direct &&
             options.canonicalize_hostname != SSH_CANONICALISE_ALWAYS)
                 return 0;
         debug3("%s: check \"%s\" CNAME \"%s\"", __func__, *namep, cname);
@@ -371,7 +371,7 @@ check_follow_cname(char **namep, const char *cname)
 static struct addrinfo *
 resolve_canonicalize(char **hostp, int port)
 {
-        int i, ndots;
+        int i, direct, ndots;
         char *cp, *fullhost, newname[NI_MAXHOST];
         struct addrinfo *addrs;
 
@@ -382,7 +382,9 @@ resolve_canonicalize(char **hostp, int port)
          * Don't attempt to canonicalize names that will be interpreted by
          * a proxy unless the user specifically requests so.
          */
-        if (!option_clear_or_none(options.proxy_command) &&
+        direct = option_clear_or_none(options.proxy_command) &&
+            options.jump_host == NULL;
+        if (!direct &&
             options.canonicalize_hostname != SSH_CANONICALISE_ALWAYS)
                 return NULL;
 
@@ -437,7 +439,7 @@ resolve_canonicalize(char **hostp, int port)
                 /* Remove trailing '.' */
                 fullhost[strlen(fullhost) - 1] = '\0';
                 /* Follow CNAME if requested */
-                if (!check_follow_cname(&fullhost, newname)) {
+                if (!check_follow_cname(direct, &fullhost, newname)) {
                         debug("Canonicalized hostname \"%s\" => \"%s\"",
                             *hostp, fullhost);
                 }
@@ -510,7 +512,7 @@ int
 main(int ac, char **av)
 {
         struct ssh *ssh = NULL;
-        int i, r, opt, exit_status, use_syslog, config_test = 0;
+        int i, r, opt, exit_status, use_syslog, direct, config_test = 0;
         char *p, *cp, *line, *argv0, buf[PATH_MAX], *host_arg, *logfile;
         char thishost[NI_MAXHOST], shorthost[NI_MAXHOST], portstr[NI_MAXSERV];
         char cname[NI_MAXHOST], uidstr[32], *conn_hash_hex;
@@ -603,7 +605,7 @@ main(int ac, char **av)
 
  again:
         while ((opt = getopt(ac, av, "1246ab:c:e:fgi:kl:m:no:p:qstvx"
-            "ACD:E:F:GI:KL:MNO:PQ:R:S:TVw:W:XYy")) != -1) {
+            "ACD:E:F:GI:J:KL:MNO:PQ:R:S:TVw:W:XYy")) != -1) {
                 switch (opt) {
                 case '1':
                         options.protocol = SSH_PROTO_1;
@@ -728,6 +730,15 @@ main(int ac, char **av)
                         fprintf(stderr, "no support for PKCS#11.\n");
 #endif
                         break;
+                case 'J':
+                        if (options.jump_host != NULL)
+                                fatal("Only a single -J option permitted");
+                        if (options.proxy_command != NULL)
+                                fatal("Cannot specify -J with ProxyCommand");
+                        if (parse_jump(optarg, &options, 1) == -1)
+                                fatal("Invalid -J argument");
+                        options.proxy_command = xstrdup("none");
+                        break;
                 case 't':
                         if (options.request_tty == REQUEST_TTY_YES)
                                 options.request_tty = REQUEST_TTY_FORCE;
@@ -739,8 +750,10 @@ main(int ac, char **av)
                                 debug_flag = 1;
                                 options.log_level = SYSLOG_LEVEL_DEBUG1;
                         } else {
-                                if (options.log_level < SYSLOG_LEVEL_DEBUG3)
+                                if (options.log_level < SYSLOG_LEVEL_DEBUG3) {
+                                        debug_flag++;
                                         options.log_level++;
+                                }
                         }
                         break;
                 case 'V':
@@ -1038,9 +1051,10 @@ main(int ac, char **av)
          * has specifically requested canonicalisation for this case via
          * CanonicalizeHostname=always
          */
-        if (addrs == NULL && options.num_permitted_cnames != 0 &&
-            (option_clear_or_none(options.proxy_command) ||
-            options.canonicalize_hostname == SSH_CANONICALISE_ALWAYS)) {
+        direct = option_clear_or_none(options.proxy_command) &&
+            options.jump_host == NULL;
+        if (addrs == NULL && options.num_permitted_cnames != 0 && (direct ||
+            options.canonicalize_hostname == SSH_CANONICALISE_ALWAYS)) {
                 if ((addrs = resolve_host(host, options.port,
                     option_clear_or_none(options.proxy_command),
                     cname, sizeof(cname))) == NULL) {
@@ -1048,7 +1062,7 @@ main(int ac, char **av)
                         if (option_clear_or_none(options.proxy_command))
                                 cleanup_exit(255); /* logged in resolve_host */
                 } else
-                        check_follow_cname(&host, cname);
+                        check_follow_cname(direct, &host, cname);
         }
 
         /*
@@ -1073,6 +1087,41 @@ main(int ac, char **av)
         /* Fill configuration defaults. */
         fill_default_options(&options);
 
+        /*
+         * If ProxyJump option specified, then construct a ProxyCommand now.
+         */
+        if (options.jump_host != NULL) {
+                char port_s[8];
+
+                /* Consistency check */
+                if (options.proxy_command != NULL)
+                        fatal("inconsistent options: ProxyCommand+ProxyJump");
+                /* Never use FD passing for ProxyJump */
+                options.proxy_use_fdpass = 0;
+                snprintf(port_s, sizeof(port_s), "%d", options.jump_port);
+                xasprintf(&options.proxy_command,
+                    "ssh%s%s%s%s%s%s%s%s%s%.*s -W %%h:%%p %s",
+                    /* Optional "-l user" argument if jump_user set */
+                    options.jump_user == NULL ? "" : " -l ",
+                    options.jump_user == NULL ? "" : options.jump_user,
+                    /* Optional "-p port" argument if jump_port set */
+                    options.jump_port <= 0 ? "" : " -p ",
+                    options.jump_port <= 0 ? "" : port_s,
+                    /* Optional additional jump hosts ",..." */
+                    options.jump_extra == NULL ? "" : " -J ",
+                    options.jump_extra == NULL ? "" : options.jump_extra,
+                    /* Optional "-F" argumment if -F specified */
+                    config == NULL ? "" : " -F ",
+                    config == NULL ? "" : config,
+                    /* Optional "-v" arguments if -v set */
+                    debug_flag ? " -" : "",
+                    debug_flag, "vvv",
+                    /* Mandatory hostname */
+                    options.jump_host);
+                debug("Setting implicit ProxyCommand from ProxyJump: %s",
+                    options.proxy_command);
+        }
+
         if (options.port == 0)
                 options.port = default_ssh_port();
         channel_set_af(options.address_family);