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[become] / src / daemon.c

/* -*-c-*-
 *
 * $Id: daemon.c,v 1.17 2004/04/08 01:36:20 mdw Exp $
 *
 * Running a `become' daemon
 *
 * (c) 1998 EBI
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of `become'
 *
 * `Become' 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.
 *
 * `Become' 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with `become'; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

/* --- ANSI headers --- */

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* --- Unix headers --- */

#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <netdb.h>
#include <syslog.h>
#include <unistd.h>

/* --- mLib headers --- */

#include <mLib/fwatch.h>
#include <mLib/quis.h>
#include <mLib/report.h>
#include <mLib/sel.h>
#include <mLib/sig.h>
#include <mLib/sym.h>
#include <mLib/trace.h>

/* --- Catacomb headers --- */

#include <catacomb/buf.h>
#include <catacomb/dsa.h>
#include <catacomb/key.h>
#include <catacomb/mp.h>
#include <catacomb/noise.h>
#include <catacomb/paranoia.h>
#include <catacomb/rand.h>
#include <catacomb/sha.h>

/* --- Local headers --- */

#include "become.h"
#include "config.h"
#include "daemon.h"
#include "lexer.h"
#include "name.h"
#include "netg.h"
#include "parse.h"
#include "rule.h"
#include "userdb.h"

/*----- Arbitrary constants -----------------------------------------------*/

#define daemon__awakeEvery (10)		/* Awaken this often to rescan */

/*----- Static variables --------------------------------------------------*/

static int daemon__port = -1;		/* No particular port yet */
static fwatch daemon__cwatch, daemon__kwatch; /* Watching key/config files */
static sel_timer daemon__timer;		/* Timer for reading */
static sel_state daemon__sel;		/* Select context */
static sel_file daemon__listen;		/* Listening socket selector */
static const char *daemon__config;	/* Configuration file for daemon */
static const char *daemon__keyfile;	/* Keyring file for daemon */
static dsa_priv daemon__key;		/* The key data */

/*----- Main code ---------------------------------------------------------*/

/* --- @daemon_usePort@ --- *
 *
 * Arguments:	@int port@ = port to use, please
 *
 * Returns:	---
 *
 * Use:		Instructs the daemon to listen to the given port.
 */

void daemon_usePort(int port)
{
  daemon__port = port;
}

/* --- @daemon__moan@ --- *
 *
 * Arguments:	@const char *f@ = offending file name
 *		@int line@ = offending line of the file
 *		@const char *msg@ = message
 *		@void *p@ = ignored
 *
 * Returns:	---
 *
 * Use:		Reports an error message about a key file.
 */

static void daemon__moan(const char *f, int line, const char *msg, void *p)
{
  syslog(LOG_ERR, "key file error: %s: %d: %s", f, line, msg);
  T( trace(TRACE_DAEMON, "daemon: key file error: %s: %d: %s",
	   f, line, msg); )
}
 
/* --- @daemon_readKey@ --- *
 *
 * Arguments:	@const char *kf@ = pointer to key file name to use
 *
 * Returns:	---
 *
 * Use:		Loads the private key from the key file.
 */

void daemon_readKey(const char *kf)
{
  key_packstruct kps[DSA_PRIVFETCHSZ];
  key_packdef *kp;
  key_file f;
  key *k;
  int err;

  if (daemon__keyfile)
    return;
  T( trace(TRACE_DAEMON, "daemon: reading key from `%s'", kf); )
  if (key_open(&f, kf, KOPEN_READ, daemon__moan, 0))
    return;
  kp = key_fetchinit(dsa_privfetch, kps, &daemon__key);
  if ((k = key_bytype(&f, "become-dsa")) == 0)
    err = KERR_NOTFOUND;
  else
    err = key_fetch(kp, k);
  if (err)
    syslog(LOG_ERR, "couldn't load key: %s", key_strerror(err));
  else {
    mp_copy(daemon__key.dp.p);
    mp_copy(daemon__key.dp.q);
    mp_copy(daemon__key.dp.g);
    mp_copy(daemon__key.x);
    mp_copy(daemon__key.y);
    daemon__keyfile = kf;
  }
  key_fetchdone(kp);
  key_close(&f);
}

/* --- @daemon__readConfig@ --- *
 *
 * Arguments:	@const char *cf@ = pointer to configuration file to use
 *
 * Returns:	Zero if it worked, nonzero if it hurt...
 *
 * Use:		Reads the configuration file, and other things.
 */

static int daemon__readConfig(const char *cf)
{
  FILE *fp;

  daemon__keyfile = 0;
  if ((fp = fopen(cf, "r")) == 0)
    return (-1);
  lexer_scan(fp);
  parse();
  fclose(fp);
  if (!daemon__keyfile)
    daemon_readKey(file_KEY);
  T( trace(TRACE_DAEMON, "daemon: read config file"); )
  return (0);
}

/* --- @daemon__read@ --- *
 *
 * Arguments:	@int fd@ = socket handle
 *		@unsigned mode@ = ignored
 *		@void *p@ = ignored
 *
 * Returns:	---
 *
 * Use:		Examines a buffer, and returns a response.
 */

void daemon__read(int fd, unsigned mode, void *p)
{
  unsigned char buff[65536];		/* Buffer for incoming packets */
  struct sockaddr_in sin;		/* Address of packet sender */
  char sender[64];			/* Sender's hostname (resolved) */
  octet h[SHA_HASHSZ];			/* Hash of the transmission buffer */
  sha_ctx hc;				/* Hashing context */
  request rq;				/* Request buffer for verification */
  ssize_t sz;				/* Length of incoming message */
  socklen_t slen;			/* Length of incoming address */
  uint32 u;				/* Scratch integer */
  uint16 ul;				/* And another */
  struct hostent *he;			/* Resolve structure */
  mp *m, *k, *r, *s;			/* Integers for signing */
  int ans;				/* Answer from the check */
  buf b;				/* Buffer for parsing request */

  /* --- Kick some randomness in the pot --- */

  noise_timer(RAND_GLOBAL);

  /* --- Read the message --- */

  slen = sizeof(sin);
  if ((sz = recvfrom(fd, (char *)buff, sizeof(buff), 0,
		     (struct sockaddr *)&sin, &slen)) < 0) {
    T( trace(TRACE_DAEMON, "daemon: error reading packet: %s",
	     strerror(errno)); )
    syslog(LOG_INFO, "duff packet received: %e");
    return;
  }

  /* --- Resolve the host name --- */

  he = gethostbyaddr((char *)&sin.sin_addr, sizeof(sin.sin_addr), AF_INET);
  sender[0] = 0;
  strncat(sender, he ? he->h_name : inet_ntoa(sin.sin_addr),
	  sizeof(sender) - 1);
  syslog(LOG_DEBUG, "packet received from %s", sender);
  T( trace(TRACE_DAEMON, "daemon: received request from %s", sender); )

  /* --- Sanity check --- */

  if (!daemon__keyfile) {
    syslog(LOG_NOTICE, "no key file: ignoring request");
    T( trace(TRACE_DAEMON, "daemon: no key file: ignoring request"); )
    return;
  }

  /* --- Unpack the block --- */

  rq.host = sin.sin_addr;
  buf_init(&b, buff, sz);
  if (buf_ensure(&b, SHA_HASHSZ)) goto fail;  BSTEP(&b, SHA_HASHSZ);
  if (buf_getu32(&b, &u)) goto fail;  rq.from = u;
  if (buf_getu32(&b, &u)) goto fail;  rq.to = u;
  if (buf_getu16(&b, &ul) || buf_ensure(&b, ul) || ul >= sizeof(rq.cmd))
    goto fail;
  memcpy(rq.cmd, BCUR(&b), ul);
  rq.cmd[ul] = 0;
  BSTEP(&b, ul);
  if (BLEFT(&b)) goto fail;

  /* --- Hash the request block --- */

  sha_init(&hc);
  sha_hash(&hc, buff, sz);
  sha_done(&hc, h);

  /* --- Build a reply block --- */

  ans = rule_check(&rq);
  syslog(LOG_INFO, "request from %s for %i to become %i to run %s %s",
	 sender, rq.from, rq.to, rq.cmd, ans ? "granted" : "denied");
  buf_init(&b, buff, sizeof(buff));
  if (buf_put(&b, h, sizeof(h)) || buf_putbyte(&b, ans))
    goto fail;

  /* --- Sign the reply block --- */

  sha_init(&hc);
  sha_hash(&hc, BBASE(&b), BLEN(&b));
  sha_done(&hc, h);
  m = mp_loadb(MP_NEW, h, sizeof(h));
  rand_get(RAND_GLOBAL, h, sizeof(h));
  k = mp_loadb(MP_NEWSEC, h, sizeof(h));
  r = s = MP_NEW;
  dsa_mksig(&daemon__key.dp, daemon__key.x, m, k, &r, &s);
  buf_putmp(&b, r);
  buf_putmp(&b, s);
  mp_drop(m);
  mp_drop(k);
  mp_drop(r);
  mp_drop(s);
  if (BBAD(&b))
    goto fail;

  /* --- Send the reply off --- */

  sendto(fd, BBASE(&b), BLEN(&b), 0, (struct sockaddr *)&sin, sizeof(sin));
  T( trace(TRACE_DAEMON, "daemon: reply sent"); )
  return;

fail:
  syslog(LOG_ERR, "couldn't respond to query");
  T( trace(TRACE_DAEMON, "daemon: failed to answer query"); )  
}

/* --- @daemon__die@ --- *
 *
 * Arguments:	@int n@ = signal number
 *		@void *p@ = ignored
 *
 * Returns:	Doesn't.
 *
 * Use:		Exits the daemon.
 */

static void daemon__die(int n, void *p)
{
  T( trace(TRACE_DAEMON, "daemon: killed by signal %i", n); )
  syslog(LOG_NOTICE, "killed by signal type %i", n);
  remove(file_PID);
  exit(0);
}

/* --- @daemon__setTimer@ --- *
 *
 * Arguments:	---
 *
 * Returns:	---
 *
 * Use:		Sets the interval timer up.
 */

static void daemon__wakeUp(struct timeval *tv, void *p);

static void daemon__setTimer(void)
{
  struct timeval tv;

  gettimeofday(&tv, 0);
  tv.tv_sec += daemon__awakeEvery;
  sel_addtimer(&daemon__sel, &daemon__timer, &tv, daemon__wakeUp, 0);
}

/* --- @daemon__rescan@ --- *
 *
 * Arguments:	@int n@ = signal number
 *		@void *p@ = ignored
 *
 * Returns:	---
 *
 * Use:		Forces a rescan of the daemon's configuration.
 */

static void daemon__rescan(int n, void *p)
{
  syslog(LOG_INFO, "rescanning configuration file");
  name_end();
  rule_end();
  netg_end();
  userdb_end();
  dsa_privfree(&daemon__key);
  userdb_init();
  userdb_local();
  userdb_yp();
  netg_init();
  rule_init();
  name_init();
  if (daemon__readConfig(daemon__config))
    syslog(LOG_ERR, "error reading configuration file");
  sel_rmtimer(&daemon__timer);
  daemon__setTimer();
  fwatch_update(&daemon__cwatch, daemon__config);
  fwatch_update(&daemon__kwatch, daemon__keyfile);
}

/* --- @daemon__wakeUp@ --- *
 *
 * Arguments:	@struct timeval *tv@ = ignored
 *		@void *p@ = ignored
 *
 * Returns:	---
 *
 * Use:		Wakes up periodically to check the configuration file.
 */

static void daemon__wakeUp(struct timeval *tv, void *p)
{
  T( trace(TRACE_DAEMON, "daemon: interval timer"); )
  rand_seed(RAND_GLOBAL, 160);
  daemon__setTimer();
  if (fwatch_update(&daemon__cwatch, daemon__config))
    daemon__rescan(0, 0);
  else if (fwatch_update(&daemon__kwatch, daemon__keyfile)) {
    const char *kf = daemon__keyfile;
    daemon__keyfile = 0;
    daemon_readKey(kf);
  }
}

/* --- @daemon_init@ --- *
 *
 * Arguments:	@const char *cf@ = pointer to name of configuration file
 *		@int port@ = port to listen to, or %$-1$% for default
 *		@unsigned f@ = various flags
 *
 * Returns:	Never.
 *
 * Use:		Starts `become' up in daemon mode.
 */

void daemon_init(const char *cf, int port, unsigned f)
{
  int s;
  int i;

  static struct sigvec {
    int sig;
    void (*proc)(int n, void *p);
    sig s;
  } sigs[] = {
    { SIGHUP, daemon__rescan },
    { SIGINT, daemon__die },
    { SIGTERM, daemon__die },
    { SIGQUIT, daemon__die },
    { 0, 0 }
  };

  /* --- Remove my root privileges --- *
   *
   * Just in case there's anything dodgy in my configuration file, or the
   * user wants me to start on a funny port.
   */

  setuid(getuid());

  /* --- Initialize the random number generator --- */

  rand_noisesrc(RAND_GLOBAL, &noise_source);
  rand_seed(RAND_GLOBAL, 160);

  /* --- Initialise bits of the program --- */

  daemon__config = cf;
  daemon__port = port;
  sel_init(&daemon__sel);
  sig_init(&daemon__sel);
  userdb_init();
  userdb_local();
  userdb_yp();
  netg_init();
  name_init();
  rule_init();
  openlog(quis(), 0, LOG_DAEMON);
  syslog(LOG_NOTICE, "starting up");

  if (daemon__readConfig(daemon__config))
    die(1, "couldn't read configuration file");
  fwatch_init(&daemon__cwatch, daemon__config);
  fwatch_init(&daemon__kwatch, daemon__keyfile);

  /* --- Decide on a port to use --- *
   *
   * If I don't have a port yet (e.g., from the configuration file) then
   * look it up in /etc/services under whatever name I was started as.
   */

  if (daemon__port == 0) {
    struct servent *se = getservbyname(quis(), "udp");
    if (se)
      daemon__port = se->s_port;
    else
      daemon__port = htons(SERVER_PORT);
  }

  /* --- Now set up a socket --- */

  {
    struct sockaddr_in sin;

    if ((s = socket(PF_INET, SOCK_DGRAM, 0)) == -1)
      die(1, "couldn't create socket: %s", strerror(errno));
    sin.sin_family = AF_INET;
    sin.sin_port = daemon__port;
    sin.sin_addr.s_addr = htonl(INADDR_ANY);
    if (bind(s, (struct sockaddr *)&sin, sizeof(sin))) {
      die(1, "couldn't bind socket to port %i: %s",
	  ntohs(daemon__port), strerror(errno));
    }
  }

  /* --- Fork off into the sunset --- */

  if (!(f & df_nofork)) {
    int pid = fork();
    FILE *fp;

    /* --- Make a background process --- */

    if (pid == -1)
      die(1, "couldn't fork daemon: %s", strerror(errno));
    else if (pid != 0)
      return;

    /* --- Disconnect from the terminal --- */

    setsid();

    /* --- Write my process id to a file --- */

    if ((fp = fopen(file_PID, "w")) != 0) {
      fprintf(fp, "%lu\n", (unsigned long)getpid());
      fclose(fp);
    }
    T( trace(TRACE_DAEMON, "daemon: forked to pid %li", (long)getpid()); )
  }

  /* --- Set signal handlers --- */

  for (i = 0; sigs[i].proc; i++)
    sig_add(&sigs[i].s, sigs[i].sig, sigs[i].proc, 0);

  /* --- Set the timer for rescanning the file --- */

  daemon__setTimer();

  /* --- Watch for input --- */

  sel_initfile(&daemon__sel, &daemon__listen, s, SEL_READ,
	       daemon__read, 0);
  sel_addfile(&daemon__listen);

  /* --- Now wait for something exciting to happen --- */

  for (;;) {
    if (sel_select(&daemon__sel)) {
      if (errno == EINTR || errno == EAGAIN)
	continue;
      syslog(LOG_ERR, "error from select: %s", strerror(errno));
      exit(1);
    }
  }
}

/*----- That's all, folks -------------------------------------------------*/