pptpmanager.c

/*
 * pptpmanager.c
 *
 * Manages the PoPToP sessions.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#ifdef __linux__
#define _GNU_SOURCE 1           /* broken arpa/inet.h */
#endif

#include "our_syslog.h"

#include <errno.h>
#include <netdb.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>
#include <fcntl.h>
#ifdef VRF
#include <vrf.h>
#endif

#if HAVE_LIBWRAP
/* re-include, just in case HAVE_SYSLOG_H wasn't defined */
#include <syslog.h>
#include <tcpd.h>

int allow_severity = LOG_WARNING;
int deny_severity = LOG_WARNING;
#endif

#ifdef __UCLIBC__
#define socklen_t int
#endif

#include "configfile.h"
#include "defaults.h"
#include "pptpctrl.h"
#include "pptpdefs.h"
#include "pptpmanager.h"
#include "compat.h"

/* command line arg variables */
extern char *ppp_binary;
extern char *pppdoptstr;
extern char *speedstr;
extern char *bindaddr;
extern int pptp_debug;
extern int pptp_noipparam;
extern int pptp_logwtmp;
extern int pptp_delegate;

/* option for timeout on starting ctrl connection */
extern int pptp_stimeout;

extern int pptp_connections;

/* local function prototypes */
static void connectCall(int clientSocket, int clientNumber);
static int createHostSocket(int *hostSocket);

/* this end's call identifier */
uint16_t unique_call_id = 0;

/* slots - begin */

/* data about connection slots */
struct slot {
  pid_t pid;
  char *local;
  char *remote;
} *slots;

/* number of connection slots allocated */
int slot_count;

static void slot_iterate(struct slot *slots, int count, void (*callback) (struct slot *slot))
{
  int i;
  for(i=0; i<count; i++)
    (*callback)(&slots[i]);
}

static void slot_slot_init(struct slot *slot)
{
  slot->pid = 0;
  slot->local = NULL;
  slot->remote = NULL;
}

void slot_init(int count)
{
  slot_count = count;
  slots = (struct slot *) calloc(slot_count, sizeof(struct slot));
  slot_iterate(slots, slot_count, slot_slot_init);
}

static void slot_slot_free(struct slot *slot)
{
  slot->pid = 0;
  if (slot->local) free(slot->local);
  slot->local = NULL;
  if (slot->remote) free(slot->remote);
  slot->remote = NULL;
}

void slot_free()
{
  slot_iterate(slots, slot_count, slot_slot_free);
  free(slots);
  slots = NULL;
  slot_count = 0;
}

void slot_set_local(int i, char *ip)
{
  struct slot *slot = &slots[i];
  if (slot->local) free(slot->local);
  slot->local = strdup(ip);
}

void slot_set_remote(int i, char *ip)
{
  struct slot *slot = &slots[i];
  int j;
  for (j = 0; j < slot_count; j++) {
    if (!slots[j].remote || strcmp(slots[j].remote, ip))
      continue;
    syslog(LOG_ERR, "MGR: Remote IP address %s in config is a duplicate!", ip);
    exit(1);
  }
  if (slot->remote) free(slot->remote);
  slot->remote = strdup(ip);
}

void slot_set_pid(int i, pid_t pid)
{
  struct slot *slot = &slots[i];
  slot->pid = pid; 
}

int slot_find_by_pid(pid_t pid)
{
  int i;
  for(i=0; i<slot_count; i++) {
    struct slot *slot = &slots[i];
    if (slot->pid == pid) return i;
  }
  return -1;
}

int slot_find_empty()
{
  return slot_find_by_pid(0);
}

char *slot_get_local(int i)
{
  struct slot *slot = &slots[i];
  return slot->local; 
}

char *slot_get_remote(int i)
{
  struct slot *slot = &slots[i];
  return slot->remote; 
}

/* slots - end */

static void sigchld_responder(int sig)
{
  int child, status;

  while ((child = waitpid(-1, &status, WNOHANG)) > 0) {
    if (pptp_delegate) {
      if (pptp_debug) syslog(LOG_DEBUG, "MGR: Reaped child %d", child);
    } else {
      int i;
      i = slot_find_by_pid(child);
      if (i != -1) {
        slot_set_pid(i, 0);
        if (pptp_debug) syslog(LOG_DEBUG, "MGR: Reaped child %d", child);
      } else {
        syslog(LOG_INFO, "MGR: Reaped unknown child %d", child);
      }
    }
  }
}

int pptp_manager(int argc, char **argv)
{
        int firstOpen = -1;
        int ctrl_pid;
        socklen_t addrsize;

        int hostSocket;
        fd_set connSet;

        int rc, sig_fd;

        rc = sigpipe_create();
        if (rc < 0) {
                syslog(LOG_ERR, "MGR: unable to setup sigchld pipe!");
                syslog_perror("sigpipe_create");
                exit(-1);
        }
        
        sigpipe_assign(SIGCHLD);
        sigpipe_assign(SIGTERM);
        sig_fd = sigpipe_fd();

        /* openlog() not required, done in pptpd.c */

        syslog(LOG_INFO, "MGR: Manager process started");

        if (!pptp_delegate) {
                syslog(LOG_INFO, "MGR: Maximum of %d connections available", 
                       pptp_connections);
        }

        /* Connect the host socket and activate it for listening */
        if (createHostSocket(&hostSocket) < 0) {
                syslog(LOG_ERR, "MGR: Couldn't create host socket");
                syslog_perror("createHostSocket");
                exit(-1);
        }

        while (1) {
                int max_fd;
                FD_ZERO(&connSet);
                if (pptp_delegate) {
                        FD_SET(hostSocket, &connSet);
                } else {
                        firstOpen = slot_find_empty();
                        if (firstOpen == -1) {
                                syslog(LOG_ERR, "MGR: No free connection slots or IPs - no more clients can connect!");
                        } else {
                                FD_SET(hostSocket, &connSet);
                        }
                }
                max_fd = hostSocket;

                FD_SET(sig_fd, &connSet);
                if (max_fd < sig_fd) max_fd = sig_fd;

                while (1) {
                        if (select(max_fd + 1, &connSet, NULL, NULL, NULL) != -1) break;
                        if (errno == EINTR) continue;
                        syslog(LOG_ERR, "MGR: Error with manager select()!");
                        syslog_perror("select");
                        exit(-1);
                }

                if (FD_ISSET(sig_fd, &connSet)) {       /* SIGCHLD */
                        int signum = sigpipe_read();
                        if (signum == SIGCHLD)
                                sigchld_responder(signum);
                        else if (signum == SIGTERM)
                                return signum;
                }

                if (FD_ISSET(hostSocket, &connSet)) {   /* A call came! */
                        int clientSocket;
                        struct sockaddr_in client_addr;

                        /* Accept call and launch PPTPCTRL */
                        addrsize = sizeof(client_addr);
                        clientSocket = accept(hostSocket, (struct sockaddr *) &client_addr, &addrsize);

#if HAVE_LIBWRAP
                        if (clientSocket != -1) {
                                struct request_info r;
                                request_init(&r, RQ_DAEMON, "pptpd", RQ_FILE, clientSocket, NULL);
                                fromhost(&r);
                                if (!hosts_access(&r)) {
                                        /* send a permission denied message? this is a tcp wrapper
                                         * type deny so probably best to just drop it immediately like
                                         * this, as tcp wrappers usually do.
                                         */
                                        close(clientSocket);
                                        /* this would never be file descriptor 0, so use it as a error
                                         * value
                                         */
                                        clientSocket = 0;
                                }
                        }
#endif
                        if (clientSocket == -1) {
                                /* accept failed, but life goes on... */
                                syslog(LOG_ERR, "MGR: accept() failed");
                                syslog_perror("accept");
                        } else if (clientSocket != 0) {
                                fd_set rfds;
                                struct timeval tv;
                                struct pptp_header ph;

                                /* TODO: this select below prevents
                                   other connections from being
                                   processed during the wait for the
                                   first data packet from the
                                   client. */

                                /*
                                 * DOS protection: get a peek at the first packet
                                 * and do some checks on it before we continue.
                                 * A 10 second timeout on the first packet seems reasonable
                                 * to me,  if anything looks sus,  throw it away.
                                 */

                                FD_ZERO(&rfds);
                                FD_SET(clientSocket, &rfds);
                                tv.tv_sec = pptp_stimeout;
                                tv.tv_usec = 0;
                                if (select(clientSocket + 1, &rfds, NULL, NULL, &tv) <= 0) {
                                        syslog(LOG_ERR, "MGR: dropped slow initial connection");
                                        close(clientSocket);
                                        continue;
                                }

                                if (recv(clientSocket, &ph, sizeof(ph), MSG_PEEK) !=
                                                sizeof(ph)) {
                                        syslog(LOG_ERR, "MGR: dropped small initial connection");
                                        close(clientSocket);
                                        continue;
                                }

                                ph.length = ntohs(ph.length);
                                ph.pptp_type = ntohs(ph.pptp_type);
                                ph.magic = ntohl(ph.magic);
                                ph.ctrl_type = ntohs(ph.ctrl_type);

                                if (ph.length <= 0 || ph.length > PPTP_MAX_CTRL_PCKT_SIZE) {
                                        syslog(LOG_WARNING, "MGR: initial packet length %d outside "
                                                        "(0 - %d)",  ph.length, PPTP_MAX_CTRL_PCKT_SIZE);
                                        goto dos_exit;
                                }

                                if (ph.magic != PPTP_MAGIC_COOKIE) {
                                        syslog(LOG_WARNING, "MGR: initial packet bad magic");
                                        goto dos_exit;
                                }

                                if (ph.pptp_type != PPTP_CTRL_MESSAGE) {
                                        syslog(LOG_WARNING, "MGR: initial packet has bad type");
                                        goto dos_exit;
                                }

                                if (ph.ctrl_type != START_CTRL_CONN_RQST) {
                                        syslog(LOG_WARNING, "MGR: initial packet has bad ctrl type "
                                                        "0x%x", ph.ctrl_type);
                dos_exit:
                                        close(clientSocket);
                                        continue;
                                }

#ifndef HAVE_FORK
                                switch (ctrl_pid = vfork()) {
#else
                                switch (ctrl_pid = fork()) {
#endif
                                case -1:        /* error */
                                        syslog(LOG_ERR, "MGR: fork() failed launching " PPTP_CTRL_BIN);
                                        close(clientSocket);
                                        break;

                                case 0: /* child */
                                        close(hostSocket);
                                        if (pptp_debug)
                                                syslog(LOG_DEBUG, "MGR: Launching " PPTP_CTRL_BIN " to handle client");
                                        connectCall(clientSocket, !pptp_delegate ? firstOpen : 0);
                                        _exit(1);
                                        /* NORETURN */
                                default:        /* parent */
                                        close(clientSocket);
                                        unique_call_id += MAX_CALLS_PER_TCP_LINK;
                                        if (!pptp_delegate)
                                                slot_set_pid(firstOpen, ctrl_pid);
                                        break;
                                }
                        }
                }               /* FD_ISSET(hostSocket, &connSet) */
        }                       /* while (1) */
}                               /* pptp_manager() */

/*
 * Author: Kevin Thayer
 * 
 * This creates a socket to listen on, sets the max # of pending connections and 
 * various other options.
 * 
 * Returns the fd of the host socket.
 * 
 * The function return values are:
 * 0 for sucessful
 * -1 for bad socket creation
 * -2 for bad socket options
 * -3 for bad bind
 * -4 for bad listen
 */
static int createHostSocket(int *hostSocket)
{
        int opt = 1;
        struct sockaddr_in address;
#ifdef HAVE_GETSERVBYNAME
        struct servent *serv;
#endif

        /* create the master socket and check it worked */
        if ((*hostSocket = vrf_socket(vrf, AF_INET, SOCK_STREAM, 0)) <= 0)
                return -1;

        /* set master socket to allow daemon to be restarted with connections active  */
        if (setsockopt(*hostSocket, SOL_SOCKET, SO_REUSEADDR,
                       (char *) &opt, sizeof(opt)) < 0)
                return -2;

        /* set up socket */
        memset(&address, 0, sizeof(address));
        address.sin_family = AF_INET;
        if(bindaddr)
                address.sin_addr.s_addr = inet_addr(bindaddr);
        else
                address.sin_addr.s_addr = INADDR_ANY;
#ifdef HAVE_GETSERVBYNAME
        if ((serv = getservbyname("pptp", "tcp")) != NULL) {
                address.sin_port = serv->s_port;
        } else
#endif
                address.sin_port = htons(PPTP_PORT);

        /* bind the socket to the pptp port */
        if (bind(*hostSocket, (struct sockaddr *) &address, sizeof(address)) < 0)
                return -3;

        /* minimal backlog to avoid DoS */
        if (listen(*hostSocket, 3) < 0)
                return -4;

        return 0;
}

/*
 * Author: Kevin Thayer
 * 
 * this routine sets up the arguments for the call handler and calls it.
 */

static void connectCall(int clientSocket, int clientNumber)
{

#define NUM2ARRAY(array, num) snprintf(array, sizeof(array), "%d", num)
        
        char *ctrl_argv[16];    /* arguments for launching 'pptpctrl' binary */

        int pptpctrl_argc = 0;  /* count the number of arguments sent to pptpctrl */

        /* lame strings to hold passed args. */
        char ctrl_debug[2];
        char ctrl_noipparam[2];
        char pppdoptfile_argv[2];
        char speedgiven_argv[2];
        extern char **environ;

        char callid_argv[16];

        /*
         * Launch the CTRL manager binary; we send it some information such as
         * speed and option file on the command line.
         */

#ifdef HAVE_SETPROCTITLE
        ctrl_argv[pptpctrl_argc++] = PPTP_CTRL_BIN;
#else
        /* Add some padding so the forked process can change the title */
        ctrl_argv[pptpctrl_argc++] = PPTP_CTRL_BIN "                                ";
#endif

        /* Pass socket as stdin */
        if (clientSocket != 0) {
                dup2(clientSocket, 0);
                close(clientSocket);
        }

        /* get argv set up */
        NUM2ARRAY(ctrl_debug, pptp_debug ? 1 : 0);
        ctrl_debug[1] = '\0';
        ctrl_argv[pptpctrl_argc++] = ctrl_debug;

        NUM2ARRAY(ctrl_noipparam, pptp_noipparam ? 1 : 0);
        ctrl_noipparam[1] = '\0';
        ctrl_argv[pptpctrl_argc++] = ctrl_noipparam;

#ifdef VRF
        ctrl_argv[pptpctrl_argc++] = vrf ? vrf : "";
#endif

        /* optionfile = TRUE or FALSE; so the CTRL manager knows whether to load a non-standard options file */
        NUM2ARRAY(pppdoptfile_argv, pppdoptstr ? 1 : 0);
        pppdoptfile_argv[1] = '\0';
        ctrl_argv[pptpctrl_argc++] = pppdoptfile_argv;
        if (pppdoptstr) {
                /* send the option filename so the CTRL manager can launch pppd with this alternate file */
                ctrl_argv[pptpctrl_argc++] = pppdoptstr;
        }
        /* tell the ctrl manager whether we were given a speed */
        NUM2ARRAY(speedgiven_argv, speedstr ? 1 : 0);
        speedgiven_argv[1] = '\0';
        ctrl_argv[pptpctrl_argc++] = speedgiven_argv;
        if (speedstr) {
                /* send the CTRL manager the speed of the connection so it can fire pppd at that speed */
                ctrl_argv[pptpctrl_argc++] = speedstr;
        }
        if (pptp_delegate) {
                /* no local or remote address to specify */
                ctrl_argv[pptpctrl_argc++] = "0";
                ctrl_argv[pptpctrl_argc++] = "0";
        } else {
                /* specify local & remote addresses for this call */
                ctrl_argv[pptpctrl_argc++] = "1";
                ctrl_argv[pptpctrl_argc++] = slot_get_local(clientNumber);
                ctrl_argv[pptpctrl_argc++] = "1";
                ctrl_argv[pptpctrl_argc++] = slot_get_remote(clientNumber);
        }

        /* our call id to be included in GRE packets the client
         * will send to us */
        NUM2ARRAY(callid_argv, unique_call_id);
        ctrl_argv[pptpctrl_argc++] = callid_argv;

        /* pass path to ppp binary */
        ctrl_argv[pptpctrl_argc++] = ppp_binary;

        /* pass logwtmp flag */
        ctrl_argv[pptpctrl_argc++] = pptp_logwtmp ? "1" : "0";

        /* note: update pptpctrl.8 if the argument list format is changed */

        /* terminate argv array with a NULL */
        ctrl_argv[pptpctrl_argc] = NULL;
        pptpctrl_argc++;

        /* ok, args are setup: invoke the call handler */
        execve(PPTP_CTRL_BIN, ctrl_argv, environ);
        syslog(LOG_ERR, "MGR: Failed to exec " PPTP_CTRL_BIN "!");
        _exit(1);
}