micro-utils/src/loginutils/login/login.c

#include <pwd.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <unistd.h>
#include <signal.h>
#include <termios.h>
#include "pw_check.h"

#define ECHOFLAGS (ECHO | ECHOE | ECHOK | ECHONL)

int hide_input(int fd, int flag) {
	struct termios term;
	if (tcgetattr(fd, &term) < 0)
		return 1;

	if (flag)
		term.c_lflag &= ~ECHOFLAGS;

	else
		term.c_lflag |= ECHOFLAGS;

	if (tcsetattr(fd, TCSAFLUSH, &term) < 0)
		return 1;

	return 0;
}

void login(const struct passwd *pw) {
	char *shell = (pw->pw_shell[0] == '\0') ? "/bin/sh" : pw->pw_shell;

	setenv("HOME", pw->pw_dir, 1);
	setenv("SHELL", shell, 1);
	setenv("USER", pw->pw_name, 1);
	setenv("LOGNAME", pw->pw_name, 1);
	setenv("PATH", "/bin", 1);

	if (chdir(pw->pw_dir) < 0) {
		fprintf(stderr, "login: %s\n", strerror(errno));
		return;
	}

	execlp(shell, shell, "-l", NULL);
}

struct passwd *proccess_input(char *hostname) {
	static char user[512];
	static char psswd[512];

	/* Username */
	printf("Login on %s: ", hostname);
	fflush(stdout);

	off_t ret = 0;
	if ((ret = read(STDIN_FILENO, user, sizeof(user))) <= 0)
		return NULL;

	user[ret - 1] = '\0';

	struct passwd *pw = getpwnam(user);
	if (!pw) {
		fprintf(stderr, "login: Incorrent username\n");
		return NULL;
	}

	/* Password */
	printf("Password: ");
	fflush(stdout);
	if (hide_input(STDIN_FILENO, 1))
		return NULL;

	if ((ret = read(STDIN_FILENO, psswd, sizeof(psswd))) <= 0)
		return NULL;

	psswd[ret - 1] = '\0';
	printf("\n");
	if (pw_check("login", pw, psswd)) {
		memset(psswd, '\0', sizeof(psswd));
		return NULL;
	}

	memset(psswd, '\0', sizeof(psswd));
	return pw;
}

int main(void) {
	if ((!isatty(STDIN_FILENO) || !isatty(STDOUT_FILENO))) {
		fprintf(stderr, "login: no tty\n");
		return 1;
	}

	/* For prompt */
	char hostname[HOST_NAME_MAX + 1];
	if (gethostname(hostname, sizeof(hostname)) < 0) {
		fprintf(stderr, "login: %s\n", strerror(errno));
		return 1;
	}

	signal(SIGQUIT, SIG_IGN);
	signal(SIGINT, SIG_IGN);
	signal(SIGHUP, SIG_IGN);

	struct passwd *pw = proccess_input(hostname);
	hide_input(STDIN_FILENO, 0);
	if (!pw)
		return 1;

	/* Start */
	if (setgid(pw->pw_gid) < 0) {
		fprintf(stderr, "login: %s\n", strerror(errno));
		return 1;
	}

	if (setuid(pw->pw_uid) < 0) {
		fprintf(stderr, "login: %s\n", strerror(errno));
		return 1;
	}

	login(pw);
	return 0;
}