svr-main.c

/*
 * Dropbear - a SSH2 server
 * 
 * Copyright (c) 2002-2006 Matt Johnston
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE. */

#include "includes.h"
#include "dbutil.h"
#include "session.h"
#include "buffer.h"
#include "signkey.h"
#include "runopts.h"
#include "random.h"

static size_t listensockets(int *sock, size_t sockcount, int *maxfd);
static void sigchld_handler(int dummy);
static void sigsegv_handler(int);
static void sigintterm_handler(int fish);
#ifdef INETD_MODE
static void main_inetd();
#endif
#ifdef NON_INETD_MODE
static void main_noinetd();
#endif
static void commonsetup();

#if defined(DBMULTI_dropbear) || !defined(DROPBEAR_MULTI)
#if defined(DBMULTI_dropbear) && defined(DROPBEAR_MULTI)
int dropbear_main(int argc, char ** argv)
#else
int main(int argc, char ** argv)
#endif
{
      _dropbear_exit = svr_dropbear_exit;
      _dropbear_log = svr_dropbear_log;

      disallow_core();

      /* get commandline options */
      svr_getopts(argc, argv);

#ifdef INETD_MODE
      /* service program mode */
      if (svr_opts.inetdmode) {
            main_inetd();
            /* notreached */
      }
#endif

#ifdef NON_INETD_MODE
      main_noinetd();
      /* notreached */
#endif

      dropbear_exit("Compiled without normal mode, can't run without -i\n");
      return -1;
}
#endif

#ifdef INETD_MODE
static void main_inetd() {

      struct sockaddr_storage remoteaddr;
      socklen_t remoteaddrlen;
      char * addrstring = NULL;

      /* Set up handlers, syslog, seed random */
      commonsetup();

      remoteaddrlen = sizeof(remoteaddr);
      if (getpeername(0, (struct sockaddr*)&remoteaddr, &remoteaddrlen) < 0) {
            dropbear_exit("Unable to getpeername: %s", strerror(errno));
      }

      /* In case our inetd was lax in logging source addresses */
      addrstring = getaddrstring(&remoteaddr, 1);
      dropbear_log(LOG_INFO, "Child connection from %s", addrstring);

      /* Don't check the return value - it may just fail since inetd has
       * already done setsid() after forking (xinetd on Darwin appears to do
       * this */
      setsid();

      /* Start service program 
       * -1 is a dummy childpipe, just something we can close() without 
       * mattering. */
      svr_session(0, -1, getaddrhostname(&remoteaddr), addrstring);

      /* notreached */
}
#endif /* INETD_MODE */

#ifdef NON_INETD_MODE
void main_noinetd() {
      fd_set fds;
      unsigned int i, j;
      int val;
      int maxsock = -1;
      int listensocks[MAX_LISTEN_ADDR];
      size_t listensockcount = 0;
      FILE *pidfile = NULL;

      int childpipes[MAX_UNAUTH_CLIENTS];
      char * preauth_addrs[MAX_UNAUTH_CLIENTS];

      int childsock;
      int childpipe[2];

      /* Note: commonsetup() must happen before we daemon()ise. Otherwise
         daemon() will chdir("/"), and we won't be able to find local-dir
         hostkeys. */
      commonsetup();

      /* sockets to identify pre-authenticated clients */
      for (i = 0; i < MAX_UNAUTH_CLIENTS; i++) {
            childpipes[i] = -1;
      }
      bzero(preauth_addrs, sizeof(preauth_addrs));
      
      /* Set up the listening sockets */
      listensockcount = listensockets(listensocks, MAX_LISTEN_ADDR, &maxsock);
      if (listensockcount == 0)
      {
            dropbear_exit("No listening ports available.");
      }

      /* fork */
      if (svr_opts.forkbg) {
            int closefds = 0;
#ifndef DEBUG_TRACE
            if (!svr_opts.usingsyslog) {
                  closefds = 1;
            }
#endif
            if (daemon(0, closefds) < 0) {
                  dropbear_exit("Failed to daemonize: %s", strerror(errno));
            }
      }

      /* should be done after syslog is working */
      if (svr_opts.forkbg) {
            dropbear_log(LOG_INFO, "Running in background");
      } else {
            dropbear_log(LOG_INFO, "Not backgrounding");
      }

      /* create a PID file so that we can be killed easily */
      pidfile = fopen(svr_opts.pidfile, "w");
      if (pidfile) {
            fprintf(pidfile, "%d\n", getpid());
            fclose(pidfile);
      }

      /* incoming connection select loop */
      for(;;) {

            FD_ZERO(&fds);
            
            /* listening sockets */
            for (i = 0; i < listensockcount; i++) {
                  FD_SET(listensocks[i], &fds);
            }

            /* pre-authentication clients */
            for (i = 0; i < MAX_UNAUTH_CLIENTS; i++) {
                  if (childpipes[i] >= 0) {
                        FD_SET(childpipes[i], &fds);
                        maxsock = MAX(maxsock, childpipes[i]);
                  }
            }

            val = select(maxsock+1, &fds, NULL, NULL, NULL);

            if (exitflag) {
                  unlink(svr_opts.pidfile);
                  dropbear_exit("Terminated by signal");
            }
            
            if (val == 0) {
                  /* timeout reached - shouldn't happen. eh */
                  continue;
            }

            if (val < 0) {
                  if (errno == EINTR) {
                        continue;
                  }
                  dropbear_exit("Listening socket error");
            }

            /* close fds which have been authed or closed - svr-auth.c handles
             * closing the auth sockets on success */
            for (i = 0; i < MAX_UNAUTH_CLIENTS; i++) {
                  if (childpipes[i] >= 0 && FD_ISSET(childpipes[i], &fds)) {
                        m_close(childpipes[i]);
                        childpipes[i] = -1;
                        m_free(preauth_addrs[i]);
                  }
            }

            /* handle each socket which has something to say */
            for (i = 0; i < listensockcount; i++) {

                  struct sockaddr_storage remoteaddr;
                  socklen_t remoteaddrlen = 0;
                  size_t num_unauthed_for_addr = 0;
                  size_t num_unauthed_total = 0;
                  char * remote_addr_str = NULL;
                  pid_t fork_ret = 0;
                  size_t conn_idx = 0;

                  if (!FD_ISSET(listensocks[i], &fds)) 
                        continue;

                  remoteaddrlen = sizeof(remoteaddr);
                  childsock = accept(listensocks[i], 
                              (struct sockaddr*)&remoteaddr, &remoteaddrlen);

                  if (childsock < 0) {
                        /* accept failed */
                        continue;
                  }

                  /* Limit the number of unauthenticated connections per IP */
                  remote_addr_str = getaddrstring(&remoteaddr, 0);

                  num_unauthed_for_addr = 0;
                  num_unauthed_total = 0;
                  for (j = 0; j < MAX_UNAUTH_CLIENTS; j++) {
                        if (childpipes[j] >= 0) {
                              num_unauthed_total++;
                              if (strcmp(remote_addr_str, preauth_addrs[j]) == 0) {
                                    num_unauthed_for_addr++;
                              }
                        } else {
                              /* a free slot */
                              conn_idx = j;
                        }
                  }

                  if (num_unauthed_total >= MAX_UNAUTH_CLIENTS
                              || num_unauthed_for_addr >= MAX_UNAUTH_PER_IP) {
                        goto out;
                  }

                  if (pipe(childpipe) < 0) {
                        TRACE(("error creating child pipe"))
                        goto out;
                  }

#ifdef DEBUG_NOFORK
                  fork_ret = 0;
#else
                  fork_ret = fork();
#endif
                  if (fork_ret < 0) {
                        dropbear_log(LOG_WARNING, "error forking: %s", strerror(errno));
                        goto out;

                  } else if (fork_ret > 0) {

                        /* parent */
                        childpipes[conn_idx] = childpipe[0];
                        m_close(childpipe[1]);
                        preauth_addrs[conn_idx] = remote_addr_str;
                        remote_addr_str = NULL;

                  } else {

                        /* child */
                        char * addrstring = NULL;
#ifdef DEBUG_FORKGPROF
                        extern void _start(void), etext(void);
                        monstartup((u_long)&_start, (u_long)&etext);
#endif /* DEBUG_FORKGPROF */

                        m_free(remote_addr_str);
                        addrstring = getaddrstring(&remoteaddr, 1);
                        dropbear_log(LOG_INFO, "Child connection from %s", addrstring);

#ifndef DEBUG_NOFORK
                        if (setsid() < 0) {
                              dropbear_exit("setsid: %s", strerror(errno));
                        }
#endif

                        /* make sure we close sockets */
                        for (i = 0; i < listensockcount; i++) {
                              m_close(listensocks[i]);
                        }

                        m_close(childpipe[0]);

                        /* start the session */
                        svr_session(childsock, childpipe[1], 
                                                getaddrhostname(&remoteaddr),
                                                addrstring);
                        /* don't return */
                        dropbear_assert(0);
                  }

out:
                  /* This section is important for the parent too */
                  m_close(childsock);
                  if (remote_addr_str) {
                        m_free(remote_addr_str);
                  }
            }
      } /* for(;;) loop */

      /* don't reach here */
}
#endif /* NON_INETD_MODE */


/* catch + reap zombie children */
static void sigchld_handler(int UNUSED(unused)) {
      struct sigaction sa_chld;

      while(waitpid(-1, NULL, WNOHANG) > 0); 

      sa_chld.sa_handler = sigchld_handler;
      sa_chld.sa_flags = SA_NOCLDSTOP;
      if (sigaction(SIGCHLD, &sa_chld, NULL) < 0) {
            dropbear_exit("signal() error");
      }
}

/* catch any segvs */
static void sigsegv_handler(int UNUSED(unused)) {
      fprintf(stderr, "Aiee, segfault! You should probably report "
                  "this as a bug to the developer\n");
      exit(EXIT_FAILURE);
}

/* catch ctrl-c or sigterm */
static void sigintterm_handler(int UNUSED(unused)) {

      exitflag = 1;
}

/* Things used by inetd and non-inetd modes */
static void commonsetup() {

      struct sigaction sa_chld;
#ifndef DISABLE_SYSLOG
      if (svr_opts.usingsyslog) {
            startsyslog();
      }
#endif

      /* set up cleanup handler */
      if (signal(SIGINT, sigintterm_handler) == SIG_ERR || 
#ifndef DEBUG_VALGRIND
            signal(SIGTERM, sigintterm_handler) == SIG_ERR ||
#endif
            signal(SIGPIPE, SIG_IGN) == SIG_ERR) {
            dropbear_exit("signal() error");
      }

      /* catch and reap zombie children */
      sa_chld.sa_handler = sigchld_handler;
      sa_chld.sa_flags = SA_NOCLDSTOP;
      if (sigaction(SIGCHLD, &sa_chld, NULL) < 0) {
            dropbear_exit("signal() error");
      }
      if (signal(SIGSEGV, sigsegv_handler) == SIG_ERR) {
            dropbear_exit("signal() error");
      }

      /* Now we can setup the hostkeys - needs to be after logging is on,
       * otherwise we might end up blatting error messages to the socket */
      loadhostkeys();

    seedrandom();
}

/* Set up listening sockets for all the requested ports */
static size_t listensockets(int *sock, size_t sockcount, int *maxfd) {
      
      unsigned int i;
      char* errstring = NULL;
      size_t sockpos = 0;
      int nsock;

      TRACE(("listensockets: %d to try\n", svr_opts.portcount))

      for (i = 0; i < svr_opts.portcount; i++) {

            TRACE(("listening on '%s:%s'", svr_opts.addresses[i], svr_opts.ports[i]))

            nsock = dropbear_listen(svr_opts.addresses[i], svr_opts.ports[i], &sock[sockpos], 
                        sockcount - sockpos,
                        &errstring, maxfd);

            if (nsock < 0) {
                  dropbear_log(LOG_WARNING, "Failed listening on '%s': %s", 
                                          svr_opts.ports[i], errstring);
                  m_free(errstring);
                  continue;
            }

            sockpos += nsock;

      }
      return sockpos;
}