pam_pwdfile.c

/* pam_pwdfile.c copyright 1999-2003 by Charl P. Botha <cpbotha@ieee.org>
 *
 * $Id: pam_pwdfile.c,v 1.18 2003-12-20 19:21:19 cpbotha Exp $
 * 
 * pam authentication module that can be pointed at any username/crypted
 * text file so that pam using application can use an alternate set of
 * passwords than specified in system password database
 * 
 * version 0.99
 *
 * Copyright (c) Charl P. Botha, 1999-2003. All rights reserved
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, and the entire permission notice in its entirety,
 *    including the disclaimer of warranties.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 * 
 * ALTERNATIVELY, this product may be distributed under the terms of
 * the GNU Public License, in which case the provisions of the GPL are
 * required INSTEAD OF the above restrictions.  (This clause is
 * necessary due to a potential bad interaction between the GPL and
 * the restrictions contained in a BSD-style copyright.)
 * 
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <features.h>
#include <syslog.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/file.h>
#include <unistd.h>

#include <security/pam_appl.h>

#define PAM_SM_AUTH
#include <security/pam_modules.h>

#include "md5.h"
extern char *crypt(const char *key, const char *salt);
extern char *bigcrypt(const char *key, const char *salt);

#define PWDF_PARAM "pwdfile"
#define FLOCK_PARAM "flock"
#define NODELAY_PARAM "nodelay"
#define PWDFN_LEN 256
#define CRYPTED_DESPWD_LEN 13
#define CRYPTED_MD5PWD_LEN 34
#define CRYPTED_BCPWD_LEN 178

#ifdef DEBUG
# define D(a) a;
#else
# define D(a) {}
#endif

/* prototypes */
int converse(pam_handle_t *, int, struct pam_message **, struct pam_response **);
int _set_auth_tok(pam_handle_t *, int, int, const char **);

/* logging function ripped from pam_listfile.c */
static void _pam_log(int err, const char *format, ...) {
    va_list args;
    
    va_start(args, format);
    openlog("pam_pwdfile", LOG_CONS|LOG_PID, LOG_AUTH);
    vsyslog(err, format, args);
    va_end(args);
    closelog();
}

static int lock_fd(int fd) {
    int delay;
    
    for (delay = 5; delay <= 40; delay *= 2) {
	if (flock(fd, LOCK_SH | LOCK_NB) == -1) {
	    /* failed */
	    if (errno != EWOULDBLOCK) goto failed;
	    sleep(delay);
	}else{
	    return 0;
	}
    }
    if (flock(fd, LOCK_SH | LOCK_NB) != -1) return 0;
    failed:
    return -1;
}

/* this function ripped from pam_unix/support.c */
int converse(	pam_handle_t *pamh,
		int nargs, 
		struct pam_message **message,
		struct pam_response **response	) {
    int retval;
    struct pam_conv *conv;
    
    retval = pam_get_item(	pamh, PAM_CONV,  (const void **) &conv ) ; 
    if ( retval == PAM_SUCCESS ) {
	retval = conv->conv( 	nargs,  
				( const struct pam_message ** ) message, 
				response, 
				conv->appdata_ptr );
    }
    return retval;
}

/* this function ripped from pam_unix/support.c */
int _set_auth_tok(	pam_handle_t *pamh, 
			int flags, int argc, 
			const char **argv	) {
    int	retval;
    char	*p;
    
    struct pam_message msg[1],*pmsg[1];
    struct pam_response *resp;
    
    /* set up conversation call */
    
    pmsg[0] = &msg[0];
    msg[0].msg_style = PAM_PROMPT_ECHO_OFF;
    msg[0].msg = "Password: ";
    resp = NULL;
    
    if ( ( retval = converse( pamh, 1 , pmsg, &resp ) ) != PAM_SUCCESS ) 
	return retval;
    
    if ( resp ) 
    {
	if ( ( flags & PAM_DISALLOW_NULL_AUTHTOK ) && 
	     resp[0].resp == NULL ) 
	{
	    free( resp );
	    return PAM_AUTH_ERR;
	}
	
	p = resp[ 0 ].resp;
	
	/* This could be a memory leak. If resp[0].resp 
	 is malloc()ed, then it has to be free()ed! 
	 -- alex 
	 */
	
	resp[ 0 ].resp = NULL; 		  				  
	
    } 
    else 
	return PAM_CONV_ERR;
    
    free( resp );
    pam_set_item( pamh, PAM_AUTHTOK, p );
    return PAM_SUCCESS;
}


/* puts the crypted password corresponding to user "name" in password,
 * from a file with lines consisting of: name:crypted_password
 * if unsucessful, returns 0
 */
static int fgetpwnam(FILE *stream, const char *name, char *password) {
    char tempLine[256], *tpointer, *curname, *curpass, *fgr;
    int loopdone, pwdfound;
    int len;
    
    /* go to beginning of file */
    rewind(stream);
    /* some control variables */
    loopdone = pwdfound = 0;
    /* fgets should do this, but we make sure */
    tempLine[255] = '\0';
    /* iterate through lines in file, until end of file */
    do {
	/* get the current line */
	fgr = fgets(tempLine,255,stream);
	/* if it's valid, go on */
	if ( fgr != NULL) {
	    /* first get the username out */
	    tpointer = tempLine;
	    curname = strsep(&tpointer,":");
	    /* check to see if it's the right one */
	    if (strcmp(curname,name)==0) {
		/* at least we know our loop is done */
		loopdone = 1;
		/* remove possible trailing newline */
		len = strlen(tpointer);
		if (tpointer[len - 1] == '\n')
		    tpointer[len - 1] = '\0';
		/* get the password and put it in its place */
		curpass = strsep(&tpointer,":");
		if (curpass != NULL) {
		    /* we use bigcrypt pwd len, as this is just a safe maximum */
		    strncpy(password,curpass,CRYPTED_BCPWD_LEN+1);
		    pwdfound = 1;
		} /* if (curpass... */
	    } /* if (strcmp(curname... */
	} /* if (tempLine... */
    } while (fgr != NULL);
    return pwdfound;
}

/* expected hook for auth service */
PAM_EXTERN int pam_sm_authenticate(pam_handle_t *pamh, int flags,
				   int argc, const char **argv) {
    int retval, pcnt, pwdfilename_found;
    const char *name;
    char *password;
    char pwdfilename[PWDFN_LEN];
    char salt[12], stored_crypted_password[CRYPTED_BCPWD_LEN+1];
    char *crypted_password;
    FILE *pwdfile;
    int use_flock = 0;
    int use_delay = 1;
    int temp_result = 0;
    
    /* we require the pwdfile switch and argument to be present, else we don't work */
    /* pcnt is the parameter counter variable for iterating through argv */
    pcnt = pwdfilename_found = 0;
    do {
	/* see if the current parameter looks like "pwdfile" */
	if (strcmp(argv[pcnt],PWDF_PARAM)==0) {
	    /* if argv is long enough, grab the subsequent parameter */
	    if (pcnt+1 < argc) {
		/* make sure we can't overflow */
		strncpy(pwdfilename,argv[++pcnt],PWDFN_LEN);
		/* indicate that we've found it */
		pwdfilename_found = 1;
	    }
	    /* also check for "pwdfile=blah" */
	} else if (strncmp(argv[pcnt],PWDF_PARAM "=",sizeof(PWDF_PARAM "=")-1)==0) {
	    /* make sure we can't overflow */
	    strncpy(pwdfilename,argv[pcnt]+sizeof(PWDF_PARAM),PWDFN_LEN);
	    /* indicate that we've found it */
	    pwdfilename_found = 1;
	} else if (strcmp(argv[pcnt],FLOCK_PARAM)==0) {
	    /* we have a "flock" parameter */
	    use_flock = 1;
	} else if (strcmp(argv[pcnt],"no" FLOCK_PARAM)==0) {
	    /* or a "noflock" parameter */
	    use_flock = 0;
	} else if (strcmp(argv[pcnt],NODELAY_PARAM)==0) {
	    /* no delay on authentication failure */
	    use_delay = 0;
	}
	
    } while (++pcnt < argc);
    
#ifdef HAVE_PAM_FAIL_DELAY
    if (use_delay) {
	D(("setting delay"));
	(void) pam_fail_delay(pamh, 2000000);   /* 2 sec delay for on failure */
    }
#endif
    
    /* for some or other reason, the password file wasn't specified */
    if (!pwdfilename_found) {
	_pam_log(LOG_ERR,"password file name not specified");
	return PAM_AUTHINFO_UNAVAIL;
    }
    
    /* DEBUG */
    D(_pam_log(LOG_ERR, "password filename extracted"));
    
    /* now try to open the password file */
    if ((pwdfile=fopen(pwdfilename,"r"))==NULL) {
	_pam_log(LOG_ERR,"couldn't open password file %s",pwdfilename);
	return PAM_AUTHINFO_UNAVAIL;
    }
    
    /* set a lock on the password file */
    if (use_flock && lock_fd(fileno(pwdfile)) == -1) {
	_pam_log(LOG_ERR,"couldn't lock password file %s",pwdfilename);
	return PAM_AUTHINFO_UNAVAIL;
    }
    
    /* get user name */
    if ((retval = pam_get_user(pamh,&name,"login: ")) != PAM_SUCCESS) {
	_pam_log(LOG_ERR, "username not found");
	fclose(pwdfile);
	return retval;
    }
    
    
    /* DEBUG */
    D(_pam_log(LOG_ERR,"username is %s", name));
    
    /* get password - code from pam_unix_auth.c */
    pam_get_item(pamh, PAM_AUTHTOK, (void *)&password);
    if (!password) {
	retval = _set_auth_tok(pamh, flags, argc, argv);
	if (retval!=PAM_SUCCESS) {
	    fclose(pwdfile);
	    return retval;
	}
    }
    pam_get_item(pamh, PAM_AUTHTOK, (void *)&password);
    
    if ((retval = pam_get_item(pamh, PAM_AUTHTOK, (void *)&password)) != PAM_SUCCESS) {
	_pam_log(LOG_ERR, "auth token not found");
	fclose(pwdfile);
	return retval;
    }
    
    /* DEBUG */
    D(_pam_log(LOG_ERR,"got password from user", password));
    
    /* now crypt password and compare to the user entry in the password file */
    /* first make sure password is long enough -- may I do this? */
    if (strlen(password)<2 || password==NULL) {
	_pam_log(LOG_ERR,"password too short or NULL");
	fclose(pwdfile);
	return PAM_AUTH_ERR;
    }
    
    /* get the crypted password corresponding to this user */
    if (!fgetpwnam(pwdfile, name, stored_crypted_password)) {
	_pam_log(LOG_ERR,"user not found in password database");
	fclose(pwdfile);
	return PAM_AUTHINFO_UNAVAIL;
    }
    
    /* DEBUG */
    D(_pam_log(LOG_ERR,"got crypted password == '%s'", stored_crypted_password));
    
    
    temp_result = 0;
    
    /* Extract the salt and set the passwd length, depending on MD5 or DES */
    if (strncmp(stored_crypted_password, "$1$", 3) == 0) {
	D(_pam_log(LOG_ERR,"password hash type is 'md5'"));
	/* get out the salt into "salt" */
	strncpy(salt, stored_crypted_password, 11);
	salt[11] = '\0';
	stored_crypted_password[CRYPTED_MD5PWD_LEN] = '\0';
	/* try both md5 crypts */
	crypted_password = Goodcrypt_md5(password, salt);
	if (strcmp(crypted_password, stored_crypted_password) == 0)
	{
	    temp_result = 1;
	}
	else
	{
	    crypted_password = Brokencrypt_md5(password, salt);
	    if (strcmp(crypted_password, stored_crypted_password) == 0)
	    {
		temp_result = 1;
	    }
	}
    } else {
	/* get the salt out into "salt" */
	strncpy(salt, stored_crypted_password, 2);
	salt[2] = '\0';
	stored_crypted_password[CRYPTED_BCPWD_LEN] = '\0';

	if (strlen(stored_crypted_password) <= CRYPTED_DESPWD_LEN) {
	    D(_pam_log(LOG_ERR,"password hash type is 'crypt'"));
	    crypted_password = crypt(password, salt);
	} else {
	    D(_pam_log(LOG_ERR,"password hash type is 'bigcrypt'"));
	    crypted_password = bigcrypt(password, salt);
	}

	if (strcmp(crypted_password, stored_crypted_password) == 0)
	{
	    temp_result = 1;
	}
    }
    
    /* DEBUG */
    D(_pam_log(LOG_ERR,"user password crypted is '%s'", crypted_password));
    
    /* if things don't match up, complain */
    if (!temp_result) 
    {
	_pam_log(LOG_ERR,"wrong password for user %s",name);
	fclose(pwdfile);
	return PAM_AUTH_ERR;
    }
    
    /* DEBUG */
    D(_pam_log(LOG_ERR,"passwords match"));
    
    /* we've gotten here, i.e. authentication was sucessful! */
    fclose(pwdfile);
    return PAM_SUCCESS;
}

/* another expected hook */
PAM_EXTERN int pam_sm_setcred(pam_handle_t *pamh, int flags, 
			      int argc, const char **argv)
{
    return PAM_SUCCESS;
}

#ifdef PAM_STATIC
struct pam_module _pam_listfile_modstruct = {
    "pam_pwdfile",
	pam_sm_authenticate,
	pam_sm_setcred,
	NULL,
	NULL,
	NULL,
	NULL,
};
#endif