sslh-fork.c

/*
   sslh-fork: forking server

# Copyright (C) 2007-2012  Yves Rutschle
# 
# This program is free software; you can redistribute it
# and/or modify it under the terms of the GNU General Public
# License as published by the Free Software Foundation; either
# version 2 of the License, or (at your option) any later
# version.
# 
# This program is distributed in the hope that it will be
# useful, but WITHOUT ANY WARRANTY; without even the implied
# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
# PURPOSE.  See the GNU General Public License for more
# details.
# 
# The full text for the General Public License is here:
# http://www.gnu.org/licenses/gpl.html

*/

#include "common.h"
#include "probe.h"

const char* server_type = "sslh-fork";

#define MAX(a, b)  (((a) > (b)) ? (a) : (b))

/* shovels data from one fd to the other and vice-versa 
   returns after one socket closed
 */
int shovel(struct connection *cnx)
{
   fd_set fds;
   int res, i;
   int max_fd = MAX(cnx->q[0].fd, cnx->q[1].fd) + 1;

   FD_ZERO(&fds);
   while (1) {
      FD_SET(cnx->q[0].fd, &fds);
      FD_SET(cnx->q[1].fd, &fds);

      res = select(
                   max_fd,
                   &fds,
                   NULL,
                   NULL,
                   NULL
                  );
      CHECK_RES_DIE(res, "select");

      for (i = 0; i < 2; i++) {
          if (FD_ISSET(cnx->q[i].fd, &fds)) {
              res = fd2fd(&cnx->q[1-i], &cnx->q[i]);
              if (!res) {
                  if (verbose) 
                      fprintf(stderr, "%s %s", i ? "client" : "server", "socket closed\n");
                  return res;
              }
          }
      }
   }
}

/* Child process that finds out what to connect to and proxies 
 */
void start_shoveler(int in_socket)
{
   fd_set fds;
   struct timeval tv;
   int res = PROBE_AGAIN;
   int out_socket;
   struct connection cnx;

   init_cnx(&cnx);
   cnx.q[0].fd = in_socket;

   FD_ZERO(&fds);
   FD_SET(in_socket, &fds);
   memset(&tv, 0, sizeof(tv));
   tv.tv_sec = probing_timeout;

   while (res == PROBE_AGAIN) {
       /* POSIX does not guarantee that tv will be updated, but the client can
        * only postpone the inevitable for so long */
       res = select(in_socket + 1, &fds, NULL, NULL, &tv);
       if (res == -1)
           perror("select");

       if (FD_ISSET(in_socket, &fds)) {
           /* Received data: figure out what protocol it is */
           res = probe_client_protocol(&cnx);
       } else {
           /* Timed out: it's necessarily SSH */
           cnx.proto = timeout_protocol();
           if (verbose) 
               log_message(LOG_INFO, "timed out, connect to %s\n", cnx.proto->description);
           break;
       }
   }

   if (cnx.proto->service &&
       check_access_rights(in_socket, cnx.proto->service)) {
       exit(0);
   }

   /* Connect the target socket */
   out_socket = connect_addr(&cnx, in_socket);
   CHECK_RES_DIE(out_socket, "connect");

   cnx.q[1].fd = out_socket;

   log_connection(&cnx);

   flush_deferred(&cnx.q[1]);

   shovel(&cnx);

   close(in_socket);
   close(out_socket);
   
   if (verbose)
      fprintf(stderr, "connection closed down\n");

   exit(0);
}

static int *listener_pid;
static int listener_pid_number = 0;

void stop_listeners(int sig)
{
    int i;

    for (i = 0; i < listener_pid_number; i++) {
        kill(listener_pid[i], sig);
    }
}

void main_loop(int listen_sockets[], int num_addr_listen)
{
    int in_socket, i, res;
    struct sigaction action;

    listener_pid_number = num_addr_listen;
    listener_pid = malloc(listener_pid_number * sizeof(listener_pid[0]));
    CHECK_ALLOC(listener_pid, "malloc");

    /* Start one process for each listening address */
    for (i = 0; i < num_addr_listen; i++) {
        listener_pid[i] = fork();
        switch(listener_pid[i]) {
        // Log if fork() fails for some reason
        case -1: log_message(LOG_ERR, "fork failed: err %d: %s\n", errno, strerror(errno));
                 break;
        // We're in the child, we have work to do 
        case 0:
            /* Listening process just accepts a connection, forks, and goes
             * back to listening */
            while (1)
            {
                in_socket = accept(listen_sockets[i], 0, 0);
                if (verbose) fprintf(stderr, "accepted fd %d\n", in_socket);

                switch(fork()) {
                case -1: log_message(LOG_ERR, "fork failed: err %d: %s\n", errno, strerror(errno));
                         break;

                /* In child process */
                case 0:
                    for (i = 0; i < num_addr_listen; ++i)
                        close(listen_sockets[i]);
                    start_shoveler(in_socket);
                    exit(0);

                /* In parent process */
                default: break;
                }
                close(in_socket);
            }
	    break;
	// We're in the parent, we don't need to do anything
	default:
	    break;
        }
    }

    /* Set SIGTERM to "stop_listeners" which further kills all listener
     * processes. Note this won't kill processes that listeners forked, which
     * means active connections remain active. */
    memset(&action, 0, sizeof(action));
    action.sa_handler = stop_listeners;
    res = sigaction(SIGTERM, &action, NULL);
    CHECK_RES_DIE(res, "sigaction");

    wait(NULL);
}

/* The actual main is in common.c: it's the same for both version of
 * the server
 */