// gcc -Wall -lcrypt -o p p.c
// su && chown root p && chmod u+s p

#define _XOPEN_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>

#include <sys/types.h>
#include <pwd.h>
#include <shadow.h>

#define BUFFSIZE 1024

void strip(char *inptstri)
{
	int tempsize;

	tempsize = strlen(inptstri);

	if (tempsize > 0)
	{
		inptstri[tempsize - 1] = '\0';
	}
}

int main(int argc, char **argv)
{
	char username[BUFFSIZE], password[BUFFSIZE];
	char datepref[BUFFSIZE], datetime[BUFFSIZE];
	char *cryppass;
	struct spwd *passdata;

	printf("Username: ");
	bzero(username, BUFFSIZE * sizeof(char));
	fgets(username, BUFFSIZE - 1, stdin);
	strip(username);

	printf("Password: ");
	bzero(password, BUFFSIZE * sizeof(char));
	fgets(password, BUFFSIZE - 1, stdin);
	strip(password);

	if ((passdata = getspnam(username)) == NULL)
	{
		printf("Invalid login!\n");
		return 1;
	}

	cryppass = crypt(password, passdata->sp_pwdp);

	if (strcmp(cryppass, passdata->sp_pwdp) != 0)
	{
		printf("Invalid login!\n");
		return 2;
	}

	printf("Set time [hh:mm]: ");
	bzero(datetime, BUFFSIZE * sizeof(char));
	fgets(datetime, BUFFSIZE - 1, stdin);
	strip(datetime);

	bzero(datepref, BUFFSIZE * sizeof(char));
	strncpy(datepref, "date '+%H:%M' --set='", BUFFSIZE - 1);
	strncat(datepref, datetime, BUFFSIZE - 1);
	strncat(datepref, "'", BUFFSIZE - 1);

	system(datepref);
	system("date");

	return 0;
}