#define _GNU_SOURCE
#include <crypt.h>
#include <fcntl.h>
#include <grp.h>
#include <pwd.h>
#include <shadow.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <termios.h>
#include <unistd.h>

#define MAX_IDS 100
long long ids[MAX_IDS] = { 0 };
char nopass[MAX_IDS] = { 0 };
size_t ids_len = 0;

read_ids()
{
	FILE *f = fopen("/etc/sus", "r");
	if (!f) return 0;
	while (!feof(f) && ids_len < 99) {
		char ch;
		fscanf(f, "%lld", &ids[ids_len++]);
		if (!feof(f)) {
			if ((ch = fgetc(f)) == 'n')
				nopass[ids_len] = 1;
			else
				ungetc(ch, f);
		}
	}
	if (ids_len == 0) return 0;
	return 1;
}

uid_nopass(uid)
{
	int i;
	for (i = 0; i < ids_len; i++) {
		if (ids[i] == uid && nopass[i])
			return 1;
	}
	return 0;
}

check_password(pass_buf)
char *pass_buf;
{
	struct spwd* shadow_entry;
	struct passwd* pa;
	char *p, *correct, *supplied, *salt;
	pa = getpwuid(getuid());
	
	shadow_entry = getspnam(pa->pw_name);
	if (shadow_entry == NULL)
		return 2;
	
	supplied = crypt(pass_buf, shadow_entry->sp_pwdp);
	if (supplied == NULL)
		return 6;
	return !!strcmp(supplied, shadow_entry->sp_pwdp);
}

int getting_pass = 0;
ask_password()
{
	getting_pass = 1;
	int i = 3;
	while (i--) {
		char *pass_buf = getpass("Password: ");
		if (!pass_buf || *pass_buf == '\0') {
			i++;
			continue;
		}
		int res = check_password(pass_buf);
		memset(pass_buf, 0, strlen(pass_buf)-1);
		if (res == 0) {
			getting_pass = 0;
			return 1;
		} else
		  fputs("Wrong password!\n", stderr);
		sleep(1);
	}
	getting_pass = 0;
	return 0;
}

int_handler()
{
	if (getting_pass)
		return;
	fputs("Cancelled.\n", stderr);
	exit(0);
}

is_valid()
{
	int i, j, groups = getgroups(0, NULL);
	gid_t list[groups];
	int ngroups = getgroups(groups, list);

	if (ngroups < 0)
		return -1;

	for (i = 0; i < groups; i++) {
		struct group* grp;
		grp = getgrgid(list[i]);
		if (grp == NULL)
			return 0;

		for (j = 0; j < ids_len; j++)
			if (grp->gr_gid == ids[j])
				return 1;
	}
	return 0;
}

main(argc, argv, envp, cstart, uid)
char **argv; char **envp;
uid_t uid;
{
	cstart = 1;
	uid = 0;
	struct sigaction savealrm, saveint, savehup, savequit, saveterm;
	struct sigaction savetstp, savettin, savettou, savepipe;
	
	struct sigaction sa;
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	sa.sa_handler = int_handler;
	
	sigaction(SIGALRM, &sa, &savealrm);
	sigaction(SIGHUP,  &sa, &savehup);
	sigaction(SIGINT,  &sa, &saveint);
	sigaction(SIGPIPE, &sa, &savepipe);
	sigaction(SIGQUIT, &sa, &savequit);
	sigaction(SIGTERM, &sa, &saveterm);
	sigaction(SIGTSTP, &sa, &savetstp);
	sigaction(SIGTTIN, &sa, &savettin);
	sigaction(SIGTTOU, &sa, &savettou);

	if (argc < 2) {
		fprintf(stderr, "Usage: %s [- user] -- command\n", argv[0]);
		return 0;
	}

	if (strcmp(*(argv + cstart), "-") == 0) {
		if (argc < 4) {
			fprintf(stderr, "No command or user specified.\n");
			return -1;
		}

		struct passwd *p = getpwnam(argv[2]);
		if (!p) {
			fprintf(stderr, "Invalid user specified.\n");
			return -1;
		}

		uid = p->pw_uid;
		char **envp2 = envp;
		while (*envp2 != NULL) {
			if (strncmp(*envp2, "USER=", 5) == 0) {
				char *new_user_string = malloc(strlen(p->pw_name) + 6);
				sprintf(new_user_string, "USER=%s", p->pw_name);
				strcpy(*envp2, new_user_string);
				free(new_user_string);
				break;
			}
			envp2++;
		}
		cstart += 2;
	}

	if (strcmp(*(argv + cstart), "--") == 0) {
		struct passwd *p = getpwuid(uid);
		if (!p) {
			fprintf(stderr, "UID not found, this should not happen.\n");
			return -1;
		}

		chdir(p->pw_dir);
		cstart++;
		if (argc - cstart < 1) {
			fprintf(stderr, "Command not found.\n");
			return -1;
		}
	}

	if (!read_ids()) {
		fputs("Failed to read ids file /etc/sus.\n", stderr);
		return -1;
	}

	if (!is_valid()) {
		fputs("Not in the susers file, this incident won't be reported.\n", stderr);
		return -1;
	}

	if (!uid_nopass(uid))
		if (ask_password() != 1) {
			fputs("Too many attempts.\n", stderr);
			return -1;
		}

	sigaction(SIGALRM, &sa, NULL);
	sigaction(SIGHUP,  &sa, NULL);
	sigaction(SIGINT,  &sa, NULL);
	sigaction(SIGPIPE, &sa, NULL);
	sigaction(SIGQUIT, &sa, NULL);
	sigaction(SIGTERM, &sa, NULL);
	sigaction(SIGTSTP, &sa, NULL);
	sigaction(SIGTTIN, &sa, NULL);
	sigaction(SIGTTOU, &sa, NULL);
	
	argv += cstart;
	setuid(uid);
	execvpe(argv[0], argv, envp);

	return 0;
}