add support for identityagent ssh_config option

This commit adds an `agent_socket` field to the session options
and connects the config parser to that option.

`SSH_OPTIONS_IDENTITY_AGENT` is added to allow applications to
set this option for themselves.

agent.c is updated to take the `agent_socket` value in preference
to the `SSH_AUTH_SOCK` environment variable.

Signed-off-by: Wez Furlong <wez@fb.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/config.h

@@ -61,6 +61,7 @@ enum ssh_config_opcode_e {
     SOC_PUBKEYAUTHENTICATION,
     SOC_PUBKEYACCEPTEDKEYTYPES,
     SOC_REKEYLIMIT,
+    SOC_IDENTITYAGENT,
 
     SOC_MAX /* Keep this one last in the list */
 };

include/libssh/libssh.h

@@ -407,6 +407,7 @@ enum ssh_options_e {
   SSH_OPTIONS_REKEY_DATA,
   SSH_OPTIONS_REKEY_TIME,
   SSH_OPTIONS_RSA_MIN_SIZE,
+  SSH_OPTIONS_IDENTITY_AGENT,
 };
 
 enum {

include/libssh/session.h

@@ -219,6 +219,7 @@ struct ssh_session_struct {
         char *ProxyCommand;
         char *custombanner;
         char *moduli_file;
+        char *agent_socket;
         unsigned long timeout; /* seconds */
         unsigned long timeout_usec;
         unsigned int port;

src/agent.c

@@ -220,7 +220,8 @@ static int agent_connect(ssh_session session) {
   if (session->agent->channel != NULL)
     return 0;
 
-  auth_sock = getenv("SSH_AUTH_SOCK");
+  auth_sock = session->opts.agent_socket ?
+    session->opts.agent_socket : getenv("SSH_AUTH_SOCK");
 
   if (auth_sock && *auth_sock) {
     if (ssh_socket_unix(session->agent->sock, auth_sock) < 0) {

src/config.c

@@ -104,7 +104,7 @@ static struct ssh_config_keyword_table_s ssh_config_keyword_table[] = {
   { "hostbasedacceptedalgorithms", SOC_UNSUPPORTED},
   { "hostkeyalias", SOC_UNSUPPORTED},
   { "identitiesonly", SOC_UNSUPPORTED},
-  { "identityagent", SOC_UNSUPPORTED},
+  { "identityagent", SOC_IDENTITYAGENT},
   { "ipqos", SOC_UNSUPPORTED},
   { "kbdinteractivedevices", SOC_UNSUPPORTED},
   { "nohostauthenticationforlocalhost", SOC_UNSUPPORTED},
@@ -1161,6 +1161,12 @@ ssh_config_parse_line(ssh_session session,
       SSH_LOG(SSH_LOG_INFO, "Unknown option: %s, line: %d",
               keyword, count);
       break;
+    case SOC_IDENTITYAGENT:
+      p = ssh_config_get_str_tok(&s, NULL);
+      if (p && *parsing) {
+          ssh_options_set(session, SSH_OPTIONS_IDENTITY_AGENT, p);
+      }
+      break;
     default:
       ssh_set_error(session, SSH_FATAL, "ERROR - unimplemented opcode: %d",
               opcode);

src/options.c

@@ -476,6 +476,11 @@ int ssh_options_set_algo(ssh_session session,
  *                Setting 0 will revert the value to defaults.
  *                Default is 1024 bits or 2048 bits in FIPS mode.
  *                (int *)
+
+ *              - SSH_OPTIONS_IDENTITY_AGENT
+ *                Set the path to the SSH agent socket. If unset, the
+ *                SSH_AUTH_SOCK environment is consulted.
+ *                (const char *)
  *
  * @param  value The value to set. This is a generic pointer and the
  *               datatype which is used should be set according to the
@@ -1056,6 +1061,22 @@ int ssh_options_set(ssh_session session, enum ssh_options_e type,
                 session->opts.rsa_min_size = *x;
             }
             break;
+        case SSH_OPTIONS_IDENTITY_AGENT:
+            v = value;
+            SAFE_FREE(session->opts.agent_socket);
+            if (v == NULL) {
+                /* The default value will be set by the ssh_options_apply() */
+            } else if (v[0] == '\0') {
+                ssh_set_error_invalid(session);
+                return -1;
+            } else {
+                session->opts.agent_socket = ssh_path_expand_tilde(v);
+                if (session->opts.agent_socket == NULL) {
+                    ssh_set_error_oom(session);
+                    return -1;
+                }
+            }
+            break;
         default:
             ssh_set_error(session, SSH_REQUEST_DENIED, "Unknown ssh option %d", type);
             return -1;

src/socket.c

@@ -445,7 +445,8 @@ int ssh_socket_unix(ssh_socket s, const char *path)
 #endif
 
     if (connect(fd, (struct sockaddr *) &sunaddr, sizeof(sunaddr)) < 0) {
-        ssh_set_error(s->session, SSH_FATAL, "Error from connect(): %s",
+        ssh_set_error(s->session, SSH_FATAL, "Error from connect(%s): %s",
+                      path,
                       strerror(errno));
         CLOSE_SOCKET(fd);
         return -1;