/* $Header: https://svn.ita.chalmers.se/repos/security/edu/course/computer_security/trunk/lab/login_linux/login_linux.c 585 2013-01-19 10:31:04Z pk@CHALMERS.SE $ */

/* gcc -std=gnu99 -Wall -g -o mylogin login_linux.c -lcrypt */

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <stdio_ext.h>
#include <string.h>
#include <signal.h>
#include <pwd.h>
#include <sys/types.h>
#include <crypt.h>
#include <shadow.h>
#include "pwent.h" /* Step 2 */

#define TRUE 1
#define FALSE 0
#define LENGTH 16

void sighandler() {

	/* add signalhandling routines here */
	/* see 'man 2 signal' */
}

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

	struct passwd *passwddata; /* this has to be redefined in step 2 */
	/* see pwent.h */
	struct spwd *shadowpasswddata; /* this has to be redefined in step 2 */
	/* see pwent.h */

	char important1[LENGTH] = "**IMPORTANT 1**";

	char user[LENGTH];

	char important2[LENGTH] = "**IMPORTANT 2**";

	//char   *c_pass; //you might want to use this variable later...
	char prompt[] = "password: ";
	char *user_pass;

	sighandler();

	while (TRUE) {
		/* check what important variable contains - do not remove, part of buffer overflow test */
		printf("Value of variable 'important1' before input of login name: %s\n",
				important1);
		printf("Value of variable 'important2' before input of login name: %s\n",
				important2);

		printf("login: ");
		fflush(NULL); /* Flush all  output buffers */
		__fpurge(stdin); /* Purge any data in stdin buffer */

		if (gets(user) == NULL) /* gets() is vulnerable to buffer */
			exit(0); /*  overflow attacks.  */

		/* check to see if important variable is intact after input of login name - do not remove */
		printf("Value of variable 'important 1' after input of login name: %*.*s\n",
				LENGTH - 1, LENGTH - 1, important1);
		printf("Value of variable 'important 2' after input of login name: %*.*s\n",
		 		LENGTH - 1, LENGTH - 1, important2);

		user_pass = getpass(prompt); //enter password using deprecated function :/
		//passwddata = getpwnam(user); //get user info from /etc/passwd /* Step 1 */

		if (passwddata != NULL) {
			/* You have to encrypt user_pass for this to work */
			/* Don't forget to include the salt */
			shadowpasswddata = getspnam(user); //get encrypted password from /etc/shadow
			//printf("password in shadow file: %s \n", shadowpasswddata->sp_pwdp);

			char *user_pass_encrypted = crypt(user_pass, shadowpasswddata->sp_pwdp);
			//printf("encryption of typed pass: %s \n", user_pass_encrypted);
			// schulze:
			// $6
			// $Dvon03J3/yxkUTWF$
			// JiIGRAV22.iMUOMPW9MJidTt.aPsKOYK4Bx.Av5EMcVmifp1SkhRELWHLKPWCGmv3nhcFk7tgi7/9.YCO/C
			//schulze:$6$Dvon03J3/yxkUTWF$JiIGRAV22.iMUOMPW9MJidTt.aPsKOYK4Bx.Av5EMcVmifp1SkhRELWHLKPWCGmv3nhcFk7tgi7/9.YCO/CnS/:18577:0:99999:7:::

			if (!strcmp(user_pass_encrypted, shadowpasswddata->sp_pwdp)) {

				printf(" You're in !\n");

				/*  check UID, see setuid(2) */
				/*  start a shell, use execve(2) */

			}
		}
		printf("Login Incorrect \n");
	}
	return 0;
}