File: kcheckpass.c

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/*****************************************************************
 *
 *	kcheckpass - Simple password checker
 *
 * 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.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 *
 *	kcheckpass is a simple password checker. Just invoke and
 *      send it the password on stdin.
 *
 *	If the password was accepted, the program exits with 0;
 *	if it was rejected, it exits with 1. Any other exit
 *	code signals an error.
 *
 *	It's hopefully simple enough to allow it to be setuid
 *	root.
 *
 *	Compile with -DHAVE_VSYSLOG if you have vsyslog().
 *	Compile with -DHAVE_PAM if you have a PAM system,
 *	and link with -lpam -ldl.
 *	Compile with -DHAVE_SHADOW if you have a shadow
 *	password system.
 *
 *	Copyright (C) 1998, Caldera, Inc.
 *	Released under the GNU General Public License
 *
 *	Olaf Kirch <okir@caldera.de>         General Framework and PAM support
 *	Christian Esken <esken@kde.org>      Shadow and /etc/passwd support
 *	Roberto Teixeira <maragato@kde.org>  other user (-U) support
 *	Oswald Buddenhagen <ossi@kde.org>    Binary server mode
 *
 *      Other parts were taken from kscreensaver's passwd.cpp.
 *
 *****************************************************************/

#include "kcheckpass.h"

#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <syslog.h>
#include <stdlib.h>
#include <errno.h>
#include <time.h>
#include <signal.h>

#include <config-kscreenlocker.h>
#if HAVE_SYS_PRCTL_H
#include <sys/prctl.h>
#endif
#if HAVE_SYS_PROCCTL_H
#include <unistd.h>
#include <sys/procctl.h>
#endif
#if HAVE_SIGNALFD_H
#include <sys/signalfd.h>
#endif
#if HAVE_EVENT_H
#include <sys/types.h>
#include <sys/event.h>
#include <sys/time.h>
#endif

#define THROTTLE 3

static int havetty, sfd = -1, nullpass;

static int
Reader (void *buf, int count)
{
    int ret, rlen;

    for (rlen = 0; rlen < count; ) {
      dord:
	ret = read (sfd, (void *)((char *)buf + rlen), count - rlen);
	if (ret < 0) {
	    if (errno == EINTR)
		goto dord;
	    if (errno == EAGAIN)
		break;
	    return -1;
	}
	if (!ret)
	    break;
	rlen += ret;
    }
    return rlen;
}

static void
GRead (void *buf, int count)
{
    if (Reader (buf, count) != count) {
	message ("Communication breakdown on read\n");
	exit(15);
    }
}

static void
GWrite (const void *buf, int count)
{
    if (write (sfd, buf, count) != count) {
	message ("Communication breakdown on write\n");
	exit(15);
    }
}

static void
GSendInt (int val)
{
    GWrite (&val, sizeof(val));
}

static void
GSendStr (const char *buf)
{
    unsigned len = buf ? strlen (buf) + 1 : 0;
    GWrite (&len, sizeof(len));
    GWrite (buf, len);
}

static void
GSendArr (int len, const char *buf)
{
    GWrite (&len, sizeof(len));
    GWrite (buf, len);
}

static int
GRecvInt (void)
{
    int val;

    GRead (&val, sizeof(val));
    return val;
}

static char *
GRecvStr (void)
{
    unsigned len;
    char *buf;

    if (!(len = GRecvInt()))
	return (char *)0;
    if (len > 0x1000 || !(buf = malloc (len))) {
	message ("No memory for read buffer\n");
	exit(15);
    }
    GRead (buf, len);
    buf[len - 1] = 0; /* we're setuid ... don't trust "them" */
    return buf;
}

static char *
GRecvArr (void)
{
    unsigned len;
    char *arr;
    unsigned const char *up;

    if (!(len = (unsigned) GRecvInt()))
	return (char *)0;
    if (len < 4) {
	message ("Too short binary authentication data block\n");
	exit(15);
    }
    if (len > 0x10000 || !(arr = malloc (len))) {
	message ("No memory for read buffer\n");
	exit(15);
    }
    GRead (arr, len);
    up = (unsigned const char *)arr;
    if (len != (unsigned)(up[3] | (up[2] << 8) | (up[1] << 16) | (up[0] << 24))) {
	message ("Mismatched binary authentication data block size\n");
	exit(15);
    }
    return arr;
}


static char *
conv_server (ConvRequest what, const char *prompt)
{
    GSendInt (what);
    switch (what) {
    case ConvGetBinary:
      {
	unsigned const char *up = (unsigned const char *)prompt;
	int len = up[3] | (up[2] << 8) | (up[1] << 16) | (up[0] << 24);
	GSendArr (len, prompt);
	return GRecvArr ();
      }
    case ConvGetNormal:
    case ConvGetHidden:
      {
	char *msg;
	GSendStr (prompt);
	msg = GRecvStr ();
	if (msg && (GRecvInt() & IsPassword) && !*msg)
	  nullpass = 1;
	return msg;
      }
    case ConvPutAuthSucceeded:
    case ConvPutAuthFailed:
    case ConvPutAuthError:
    case ConvPutAuthAbort:
    case ConvPutReadyForAuthentication:
        return 0;
    case ConvPutInfo:
    case ConvPutError:
    default:
	GSendStr (prompt);
	return 0;
    }
}

void
message(const char *fmt, ...)
{
  va_list		ap;

  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  va_end(ap);
}

#ifndef O_NOFOLLOW
# define O_NOFOLLOW 0
#endif

static void ATTR_NORETURN
usage(int exitval)
{
  message(
	  "usage: kcheckpass {-h|[-c caller] [-m method] -S handle}\n"
	  "  options:\n"
	  "    -h           this help message\n"
	  "    -S handle    operate in binary server mode on file descriptor handle\n"
	  "    -m method    use the specified authentication method (default: \"classic\")\n"
	  "  exit codes:\n"
	  "    0 success\n"
	  "    1 invalid password\n"
	  "    2 cannot read password database\n"
	  "    Anything else tells you something's badly hosed.\n"
	);
  exit(exitval);
}

int
main(int argc, char **argv)
{
  const char	*method = "classic";
  const char	*username = 0;
  char		*p;
  struct passwd	*pw;
  int		c, nfd;
  uid_t		uid;
  AuthReturn	ret;
  sigset_t signalMask;
#if HAVE_SIGNALFD_H
  int signalFd;
  struct signalfd_siginfo fdsi;
  ssize_t sigReadSize;
#endif
#if HAVE_EVENT_H
  /* Event Queue */
  int           keventQueue;
  /* Listen for two events: SIGUSR1 and SIGUSR2 */
  struct kevent keventEvent[2];
  int           keventData;
#endif
  pid_t parentPid;

  parentPid = getppid();

  // disable ptrace on kcheckpass
#if HAVE_PR_SET_DUMPABLE
  prctl(PR_SET_DUMPABLE, 0);
#endif
#if HAVE_PROC_TRACE_CTL
  int mode = PROC_TRACE_CTL_DISABLE;
  procctl(P_PID, getpid(), PROC_TRACE_CTL, &mode);
#endif

  // prevent becoming an orphan while waiting for SIGUSR2
#if HAVE_PR_SET_DUMPABLE
  prctl(PR_SET_PDEATHSIG, SIGUSR2);
#endif

  /* Make sure stdout/stderr are open */
  for (c = 1; c <= 2; c++) {
    if (fcntl(c, F_GETFL) == -1) {
      if ((nfd = open("/dev/null", O_WRONLY)) < 0) {
        message("cannot open /dev/null: %s\n", strerror(errno));
        exit(10);
      }
      if (c != nfd) {
        dup2(nfd, c);
        close(nfd);
      }
    }
  }

  havetty = isatty(0);

  while ((c = getopt(argc, argv, "hm:S:")) != -1) {
    switch (c) {
    case 'h':
      usage(0);
      break;
    case 'm':
      method = optarg;
      break;
    case 'S':
      sfd = atoi(optarg);
      break;
    default:
      message("Command line option parsing error\n");
      usage(10);
    }
  }

  if (sfd == -1) {
      message("Only binary protocol supported\n");
      return AuthError;
  }

  uid = getuid();
  if (!(p = getenv("LOGNAME")) || !(pw = getpwnam(p)) || pw->pw_uid != uid)
    if (!(p = getenv("USER")) || !(pw = getpwnam(p)) || pw->pw_uid != uid)
      if (!(pw = getpwuid(uid))) {
        message("Cannot determinate current user\n");
        return AuthError;
      }
  if (!(username = strdup(pw->pw_name))) {
    message("Out of memory\n");
    return AuthError;
  }

    // setup signals
    sigemptyset(&signalMask);
    sigaddset(&signalMask, SIGUSR1);
    sigaddset(&signalMask, SIGUSR2);
    // block them
    if (sigprocmask(SIG_BLOCK, &signalMask, NULL) == -1) {
        message("Block signal failed\n");
        conv_server(ConvPutAuthError, 0);
        return 1;
    }
#if HAVE_SIGNALFD_H
    signalFd = signalfd(-1, &signalMask, SFD_CLOEXEC);
    if (signalFd == -1) {
        message("Signal fd failed\n");
        conv_server(ConvPutAuthError, 0);
        return 1;
    }
#endif
#if HAVE_EVENT_H
    /* Setup the kequeu */
    keventQueue = kqueue();
    if (keventQueue == -1) {
        message("Failed to create kqueue for SIGUSR1\n");
        conv_server(ConvPutAuthError, 0);
        return 1;
    }
    /* Setup the events */
    EV_SET(&keventEvent[0], SIGUSR1, EVFILT_SIGNAL, EV_ADD, 0, 0, NULL);
    EV_SET(&keventEvent[1], SIGUSR2, EVFILT_SIGNAL, EV_ADD, 0, 0, NULL);
    int setupResult = kevent(keventQueue, &keventEvent, 2, NULL, 0, NULL);
    if (setupResult == -1) {
        message("Failed to attach event to the kqueue\n");
        conv_server(ConvPutAuthError, 0);
        return 1;
    }
    if (keventEvent[0].flags & EV_ERROR) {
        message("Error in kevent for SIGUSR1: %s\n", strerror(keventEvent[0].data));
        conv_server(ConvPutAuthError, 0);
        return 1;
    }
    if (keventEvent[1].flags & EV_ERROR) {
        message("Error in kevent for SIGUSR2: %s\n", strerror(keventEvent[1].data));
        conv_server(ConvPutAuthError, 0);
        return 1;
    }

    /* signal_info for sigwaitinfo() */
    siginfo_t signalInfo;

#endif
    // now lets block on the fd
    for (;;) {
        conv_server(ConvPutReadyForAuthentication, 0);
#if HAVE_SIGNALFD_H
        sigReadSize = read(signalFd, &fdsi, sizeof(struct signalfd_siginfo));
        if (sigReadSize != sizeof(struct signalfd_siginfo)) {
            message("Read wrong size\n");
            return 1;
        }
        if (fdsi.ssi_signo == SIGUSR1) {
            if (fdsi.ssi_pid != parentPid) {
                message("signal from wrong process\n");
                continue;
            }
#endif
#if HAVE_EVENT_H
        keventData = kevent(keventQueue, NULL, 0, keventEvent, 1, NULL);
        if ( keventData == -1 ) {
            /* Let's figure this out in the future, shall we */
            message("kevent() failed with %d\n", errno);
            return 1;
        }
        else if ( keventData == 0 ) {
            /* Do we need to handle timeouts? */
            message("kevent timeout\n");
            continue;
        }
        // We know we got a SIGUSR1 or SIGUSR2, so fetch it via sigwaitinfo()
        // (otherwise, we could have used sigtimedwait() )
        int signalReturn = sigwaitinfo(&signalMask, &signalInfo);
        if (signalReturn < 0) {
            if (errno == EINTR) {
                message("sigawaitinfo() interrupted by unblocked caught signal");
                continue;
            }
            else if (errno == EAGAIN) {
                /* This should not happen, as kevent notified us about such a signal */
                message("no signal of type USR1 or USR2 pending.");
                continue;
            }
            else {
                message("Unhandled error in sigwaitinfo()");
                conv_server(ConvPutAuthError, 0);
                return 1;
            }
        }
        if (signalReturn == SIGUSR1) {
            if (signalInfo.si_pid != parentPid) {
                message("signal from wrong process\n");
                continue;
            }
#endif
            /* Now do the fandango */
            ret = Authenticate(method,
                                username,
                                conv_server);

            if (ret == AuthBad) {
                message("Authentication failure\n");
                if (!nullpass) {
                    openlog("kcheckpass", LOG_PID, LOG_AUTH);
                    syslog(LOG_NOTICE, "Authentication failure for %s (invoked by uid %d)", username, uid);
                }
            }
            switch (ret) {
                case AuthOk:
                    conv_server(ConvPutAuthSucceeded, 0);
                    break;
                case AuthBad:
                    conv_server(ConvPutAuthFailed, 0);
                    break;
                case AuthError:
                    conv_server(ConvPutAuthError, 0);
                    break;
                case AuthAbort:
                    conv_server(ConvPutAuthAbort, 0);
                default:
                    break;
            }
            if (uid != geteuid()) {
                // we don't support multiple auth for setuid kcheckpass
                break;
            }
#if HAVE_SIGNALFD_H
        } else if (fdsi.ssi_signo == SIGUSR2) {
            if (fdsi.ssi_pid != parentPid) {
                message("signal from wrong process\n");
                continue;
            }
            break;
#endif
#if HAVE_EVENT_H
        } else if (signalReturn == SIGUSR2 ) {
            if (signalInfo.si_pid != parentPid) {
                message("signal from wrong process\n");
                continue;
            }
            break;
#endif
        } else {
            message("unexpected signal\n");
        }
    }

  return 0;
}

void
dispose(char *str)
{
    memset(str, 0, strlen(str));
    free(str);
}

/*****************************************************************
  The real authentication methods are in separate source files.
  Look in checkpass_*.c
*****************************************************************/