Posted-From: The MITRE Corporation, Bedford, MA
To: sdorner@qualcomm.com (Steve Dorner)
From: dll@mitre.org (Daniel L. Leavitt)
Subject: Re: Change password server 
Date: Tue, 10 Nov 92 10:56:29 EST
Sender: dll@mbunix.mitre.org


Steve,

        Here it is.  This is the first such program I've ever written so I'd appreciate
any constructive comments if anyone cares to send me any.  

-Dan


--------------
/* 
 * poppassd.c  Update passwords on the UNIX system from the Eudora "Change Password"
 *             client.  Keeps a log of change attempts in /etc/poppassd.log but 
 *             suppresses recording of passwords given by the client.
 *             
 *             Must be owned by root, and executable only by root.  It can be started 
 *             with an entry in /etc/inetd.conf such as the following:
 *
 *                 poppassd stream tcp nowait root  /usr/local/poppassd/poppassd poppassd
 * 
 *             and in /etc/services:
 * 
 *                 ppassd        106/tcp
 *
 */

#include <stdio.h>
#include <string.h>
#include <pwd.h>
#include <signal.h>
#include <unistd.h>
#include <varargs.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/file.h>
#include <time.h>

#define PF_PLATE        "./ptmpXXXXX"   /* original temporary file */
#define PF_TEMP         "./ptmp"        /* lock file */

#define PW_CHANGED      0               /* a OK */
#define PW_CANTLOCK     -1              /* error code -- locking failed */
#define PW_CANTOPEN     -2              /* error code -- open failed */
#define PW_CANTRENAME   -3              /* error code -- rename failed */
#define PW_NOCHANGE     -4              /* error code -- no passwd entry */

#define SUCCESS 1
#define FAILURE 0
#define BUFSIZE 255
#define MAXARGS 32
#define SUPPRESS 1

#define FI_NULL ((FILE *) NULL)                /* NULL file pointer */
#define TI_NULL ((time_t *) NULL)      /* NULL time pointer */


/*
 * library functions
 */
extern char *mktemp();                  /* makes a temp file name */

/*
 * global variables
 */
char *pf_name = "passwd";               /* password file name */
char *pf_tnam;                          /* name of temporary file */
FILE *pf_fp;                            /* pointer to real password file */
FILE *pf_tfp;                           /* pointer to temporary file */
FILE *log;
time_t gNow;
char gDate[BUFSIZE];

main (argc, argv)
int argc;
char *argv[];
{

        char line[BUFSIZE];
        char user[BUFSIZE];
        char pass[BUFSIZE];
        char newpass[BUFSIZE];
        char logFile[BUFSIZE];
        struct passwd *pw;

        chdir( "/etc" );
        sprintf(logFile, "/etc/%s.log", argv[0]);
        strcpy( user, "" );
        strcpy( pass, "" );
        strcpy( newpass, "" );

        /*
         * Open the logfile for append
         */
        if ( !( log = fopen( logFile, "a+" )) ) {
                WriteToClient( "500 Can't open %s.", logFile );
                exit(1);
        }
        
#if 0
        The server's responses should be like an FTP server's responses; 
        1xx for in progress, 2xx for success, 3xx for more information
        needed, 4xx for temporary failure, and 5xx for permanent failure.  
        Putting it all together, here's a sample conversation:

        S: 200 hello\r\n
        E: user yourloginname\r\n
        S: 300 please send your password now\r\n
        E: pass yourcurrentpassword\r\n
        S: 200 My, that was tasty\r\n
        E: newpass yournewpassword\r\n
        S: 200 Happy to oblige\r\n
        E: quit\r\n
        S: 200 Bye-bye\r\n
        S: <closes connection>
        E: <closes connection>
#endif

        WhoAreYou();

        WriteToClient( "200 hello, who are you?" );
        ReadFromClient( line, 0 );
        sscanf(line, "user %s", user) ;
        if ( strlen(user) == 0 ) {
                WriteToClient( "500 username required." );
                exit(1);
        }

        WriteToClient( "200 your password please." );
        ReadFromClient( line, SUPPRESS );
        sscanf( line, "pass %s", pass) ;
        if ( strlen(pass) == 0 ) {
                WriteToClient( "500 password required." );
                exit(1);
        }

        WriteToClient( "200 your new password please." );
        ReadFromClient( line, SUPPRESS );
        sscanf( line, "newpass %s", newpass );

        /* new pass required */
        if ( strlen(newpass) == 0 ) {
                WriteToClient( "500 new password required." );
                exit(1);
        }
        /* new pass must be 6 char or longer */
        else if ( strlen(newpass) < 6 ) {
                WriteToClient( "500 New password too short" );
                exit(1);
        }
        /* new pass must be different from old pass */
        else if ( !strcmp(pass, newpass) ) {
                WriteToClient( "500 New password must be different." );
                exit(1);
        }

        /* test for valid user */
        if ( (pw=getpwnam(user)) == NULL ) {
                WriteToClient( "500 Unknown user, %s.", user);
                exit(1);
        }

        /* authenticate user */
        if ( chkPass( user, pass, pw ) == FAILURE ) {
                WriteToClient( "500 Authentication failure.");
                exit(1);
        }
                
        if ( setPass( user, pass, newpass, pw ) == FAILURE ) { 
                WriteToClient( "500 Unable to change password." );
                exit(1);
        }

        WriteToClient( "200 Password changed, thank-you." );
        return(1);
}

 
WhoAreYou()
{
        struct sockaddr_in bobby;
        int   bobbyLen = sizeof(struct sockaddr);
        struct passwd *pw;
        char   *inet_ntoa();
        char   *ttyname();

        fputs( "\n", log );

        if (isatty(fileno(stdin))) {
                pw = getpwuid(getuid());
                WriteLog( "Connection on %s by %s",
                        ttyname(fileno(stdin)), pw->pw_name);
        }

        else if (lseek(fileno(stdin), 0, L_INCR) >= 0) {
                pw = getpwuid(getuid());
                WriteLog( "Connection on FILE by %s", pw->pw_name);
        }

        else if (getpeername(fileno(stdin), (struct sockaddr *)&bobby, 
                        &bobbyLen) < 0) {
                pw = getpwuid(getuid());
                WriteLog( "Connection on PIPE by %s", pw->pw_name);
        }

        else {
#               if defined(sparc) && __GNUC__ == 1 
                        WriteLog( "NET connection from  %s", 
                                inet_ntoa(&bobby.sin_addr));
#               else
                        WriteLog( "NET connection from %s", 
                                inet_ntoa(bobby.sin_addr));
#               endif
        }
}

WriteToClient( va_alist )
va_dcl
{
        va_list ap;
        char *fmt;      
        char *args[MAXARGS];
        int argno = 0;
        char string[BUFSIZE];
        
        UpdateTime( );

        va_start( ap );
        fmt = va_arg(ap, char *);
        while ((args[argno++] = va_arg(ap, char *)) != (char *)0)
                    ;

        vfprintf(stdout, fmt, args);
        fputs("\r\n", stdout );
        fflush(stdout);

        vsprintf(string, fmt, args);
        WriteLog( "Server> %s", string );

        va_end( ap );
}

ReadFromClient( line , suppress)
char *line;
int suppress;
{
        char *sp;
        int i;

        UpdateTime();
        strcpy(line, "" );
        fgets( line, BUFSIZE, stdin );
        if (( sp = strchr(line, '\n')) != NULL ) *sp = '\0'; 
        if (( sp = strchr(line, '\r')) != NULL ) *sp = '\0'; 
        if ( suppress )
                WriteLog( "Client> ..." );
        else
                WriteLog( "Client> %s", line );
}

UpdateTime( )
{
        struct tm *date;
        
        gNow = time( NULL );            /* get current calendar time */
        date = localtime( &gNow );      /* convert it to a broken-down time */
        strftime( gDate, BUFSIZE, "%b %d %H:%M:%S", date );
}

WriteLog( va_alist )
va_dcl
{
        va_list ap;
        char *fmt;      
        char *args[MAXARGS];
        int argno = 0;
        UpdateTime( );


        va_start( ap );
        fmt = va_arg(ap, char *);
        while ((args[argno++] = va_arg(ap, char *)) != (char *)0)
                    ;
        fprintf( log, "%s: ", gDate );
        vfprintf(log, fmt, args);
        fputs( "\n", log );
        fflush(log);
        va_end( ap );
}

int chkPass( user, pass, pw )
char *user;
char *pass;
struct passwd *pw;
{
        /*  Compare the supplied password with the password file entry */
        if (strcmp (crypt (pass, pw->pw_passwd), pw->pw_passwd) != 0)
                return ( FAILURE );
        else 
                return ( SUCCESS );
}




makesalt( c )
char c[2];                      /* salt characters */
{
        register long salt;             /* used to compute a salt */
        register int i;                 /* counter in a for loop */

        /*
         * just mix a few things up for the salt ...
         * no rhyme or reason here
         */
        salt = (((long) time(TI_NULL))&0x3f) | (getpid() << 5);

        /*
         * use the bottom 12 bits and map them into the legal alphabet
         */
        for(i = 0; i < 2; i++){
                c[i] = (salt & 0x3f) + '.';
                if (c[i] > '9')
                        c[i] += 7;
                if (c[i] > 'Z')
                        c[i] += 6;
                salt >>= 6;
        }
}


setPass( user, pass, newpass, pw )
char *user;
char *pass;
char *newpass;
struct passwd *pw;
{

        char saltc[2];          /* the password's salt */

        makesalt(saltc);
        strcpy( pw->pw_passwd, crypt(newpass, saltc));

        if ( UpdatePasswordFile( pw ) == PW_CHANGED )
                return (SUCCESS);
        else
                return (FAILURE);
}



UpdatePasswordFile(p)
struct passwd *p;               /* new password structure */
{
        char nbuf[BUFSIZ];              /* buffer for passwords being read */
        char obuf[BUFSIZ];              /* buffer for new entry */
        register char *q, *s;           /* used for quick name comparison */
        int retval = PW_NOCHANGE;       /* return value */

        /*
         * disable ALL signals at this point
         */
        sigoff();

        /*
         * open the temporary password file
         */
        umask(022);
        pf_tnam = mktemp(PF_PLATE);
        if ((pf_tfp = fopen(pf_tnam, "w")) == FI_NULL){
                retval = PW_CANTOPEN;
                goto cantlock;
        }

        /*
         * lock the password file
         */
        if (link(pf_tnam, PF_TEMP) < 0){
                retval = PW_CANTLOCK;
                goto cantlock;
        }
        
        /*
         * copy the new password structure
         */
        sprintf(obuf, "%s:%s:%d:%d:%s:%s:%s\n",
                        p->pw_name, p->pw_passwd, p->pw_uid, p->pw_gid,
                        p->pw_gecos, p->pw_dir, p->pw_shell);

        /*
         * open the password file
         */
        if ((pf_fp = fopen(pf_name, "r")) == FI_NULL){
                retval = PW_CANTOPEN;
                goto getout;
        }


        /*
         * copy the password file into the temporary one
         */
        while(fgets(nbuf, BUFSIZ, pf_fp) != NULL){
                for(s = nbuf, q = p->pw_name; *s && *s != ':'; s++, q++)
                        if (*s != *q)
                                break;
                if (*s == ':' && *q == '\0') {
                        fputs(obuf, pf_tfp);
                        retval = PW_CHANGED;
                } else 
                        fputs(nbuf, pf_tfp);
        }
        if (retval == PW_NOCHANGE) {
                goto getout;
        }

        /*
         * close the temporary file and the real one
         */
        (void) fclose(pf_tfp);
        pf_tfp = FI_NULL;
        (void) fclose(pf_fp);
        pf_fp = FI_NULL;

        /*
         * now relink; note the lock file is still there
         */
        if ( unlink(pf_name) >= 0
                && link(pf_tnam, pf_name) >= 0
                && unlink(pf_tnam) >= 0){
                retval = PW_CHANGED;
        }
        else
                retval = PW_CANTRENAME;

getout:
        /*
         * Only remove lock file if this program obtained it
         */
         (void) unlink(PF_TEMP); 

cantlock:
        /* some clean up */
        if (pf_tfp != FI_NULL)
                (void) fclose(pf_tfp);
        if (pf_fp != FI_NULL)
                (void) fclose(pf_fp);
        (void) unlink(pf_tnam);

        sigon(); /* re-enable ALL signals at this point */

        return(retval);
}


/*
 * signal handling routines
 */
void (*trap[NSIG])();           /* values returned by signal() */


/*
 * disable ALL signal trapping
 */
sigoff()
{
        register int i;         /* counter in a for loop */

        for(i = 0; i < NSIG; i++)
                (void) signal(i, SIG_IGN);
}

/*
 * restore to the initial setting all signals
 */
sigon()
{
        register int i;         /* counter in a for loop */

        for(i = 0; i < NSIG; i++)
                (void) signal(i, trap[i]);

}






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