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EDA263/lab1/login_linux.c
2022-02-03 18:35:28 +01:00

194 lines
6.0 KiB
C
Executable File

/* $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 */
/* Note, makepass.c is first used to create hashed password
then, info is manually saved in file passdb */
#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 "pwent.h" /* Step 2 */
#include <termios.h>
#include <stdbool.h>
#define TRUE 1
#define FALSE 0
#define LENGTH 16
void sighandler() {
//sigset_t mask;
//sigfillset(&mask);
//sigprocmask(SIG_SETMASK, &mask, NULL);
signal(SIGINT, SIG_IGN); /* This will catch ctrl+c and ignore it*/
signal(SIGTSTP, SIG_IGN); /* This will catch ctrl+z and ignore it*/
//signal(SIGTERM,SIG_IGN); //TODO block termios kanske...
}
int main(int argc, char *argv[]) {
//struct passwd *passwddata /* Step 1 */
mypwent *passwddata; /* Step 2 */
char important1[LENGTH] = "**IMPORTANT 1**";
char user[LENGTH];
char important2[LENGTH] = "**IMPORTANT 2**";
//char *c_pass; //you might want to use this variable later... TODO
//char prompt[] = "password: ";
//char *user_pass;
char user_pass[LENGTH]; // TODO la till denna
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 */
bool okusername = true;
/* using fgets instead of gets to avoid buffer overflow attacks*/
if (fgets(user,sizeof(user),stdin) == NULL ) {
// if error or EOF (ctrl+d)
// TODO need for more error handling ?
clearerr(stdin);
okusername = false;
}
if (strlen(user) == sizeof(user)-1 || strlen(user) == 1){
// too long username or no username was entered
okusername = false;
}
else{
// replacing \n with \0
user[strcspn(user,"\n")] = '\0';
}
//////////////////////////////////////////////////////////////////////////////////////////
/* 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);
//////////////////////////////////////////////////////////////////////////////////////////
// using termios instead of the outdated getpass for a more secure program
// user_pass = getpass(prompt);
struct termios old_term_flags, new_term_flags;
/* Turn echoing off so password will not be shown in terminal */
if (tcgetattr(fileno(stdin), &old_term_flags) != 0){
perror("Error");
exit(EXIT_FAILURE);
}
new_term_flags = old_term_flags;
new_term_flags.c_lflag &= ~ECHO;
if (tcsetattr(fileno(stdin), TCSAFLUSH, &new_term_flags) != 0) {
perror("Error");
exit(EXIT_FAILURE);
}
bool okpassword = true;
printf("password: ");
if (fgets(user_pass,sizeof(user_pass),stdin) == NULL ) {
clearerr(stdin);
okpassword = false;
}
if (strlen(user_pass) == sizeof(user_pass)-1 || strlen(user_pass) == 1){
okpassword = false;
}
/* Restore terminal */
if (tcsetattr(fileno(stdin), TCSAFLUSH, &old_term_flags) != 0) {
perror("Error");
exit(EXIT_FAILURE);
}
if (!okpassword || !okusername){
printf("\nLogin Incorrect \n \n");
continue;
}
user_pass[strcspn(user_pass, "\n")] = '\0'; // replacing \n with \0
//////////////////////////////////////////////////////////////////////////////////////////
// get user info from passdb
passwddata = mygetpwnam(user);
if (passwddata != NULL) {
if (passwddata->pwfailed >= 10) {
printf("\nToo many failed login attempts. Your account has been locked.\nContact and Admin to unlock your account.\n");
continue;
}
/* Encryp user_pass with salt included */
char *user_pass_encrypted = crypt(user_pass, passwddata->passwd_salt);
if (user_pass_encrypted == NULL) {
perror("Error");exit(EXIT_FAILURE);
}
if (!strcmp(user_pass_encrypted, passwddata->passwd)) {
// successfull login
printf("\n%d failed attemts to login \n",passwddata->pwfailed);
passwddata->pwfailed = 0;
passwddata->pwage = passwddata->pwage + 1;
if (mysetpwent(user, passwddata) < 0) {
perror("Error");exit(EXIT_FAILURE);
}
if (passwddata->pwage > 10) {
printf("You need to change your password !\n");
}
/* check UID, see setuid(2) */
if (setuid(passwddata->uid) < 0) {
perror("Error");
exit(EXIT_FAILURE);
// TODO kommer alltid bara hit
}
/* start a shell, use execve(2) */
if (execve("/bin/bash",NULL,NULL) < 0) {
perror("Error");
exit(EXIT_FAILURE);
}
printf("\nWelcome to this system !\n");
}
else {
// user name exists but password does not match
passwddata->pwfailed = passwddata->pwfailed + 1;
if (mysetpwent(user, passwddata) < 0) {
perror("Error");
exit(EXIT_FAILURE);
}
}
}
printf("\nLogin Incorrect \n \n");
}
return 0;
}