/**
 * cerberus – Minimal login program
 * 
 * Copyright © 2013, 2014, 2015, 2016, 2020  Mattias Andrée (m@maandree.se)
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include <pwd.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>

#include "config.h"

#include "login.h"


/**
 * The environment variables
 */
extern char **environ;


/**
 * Set the user gid and uid
 * 
 * @param  entry  The user entry in the password file
 */
void
set_user(struct passwd *entry)
{
	if (setgid(entry->pw_gid) && entry->pw_gid) {
		perror("setgid");
		_exit(1);
	}

	if (setuid(entry->pw_uid) && entry->pw_uid) {
		perror("setuid");
		_exit(1);
	}
}


/**
 * Change directory to the user's home directory
 * 
 * @param  entry  The user entry in the password file
 */
void
chdir_home(struct passwd *entry)
{
	if (chdir(entry->pw_dir)) {
		perror("chdir");
		if (chdir(DEFAULT_HOME)) {
			perror("chdir");
			sleep(ERROR_SLEEP);
			_exit(1);
		}
		entry->pw_dir = strdup(DEFAULT_HOME);
	}
}


/**
 * Make sure the shell to use is definied
 * 
 * @param  entry  The user entry in the password file
 */
void
ensure_shell(struct passwd *entry)
{
	if (!entry->pw_shell || !*entry->pw_shell)
		entry->pw_shell = strdup(DEFAULT_SHELL);
}


/**
 * Set environment variables
 * 
 * @param  entry         The user entry in the password file
 * @param  preserve_env  Whether to preserve the environment
 */
void
set_environ(struct passwd *entry, char preserve_env)
{
	char *_term = getenv("TERM");
	char *term = NULL;
	if (_term) {
		size_t n = 0, i;
		while (_term[n++]) ;
		term = malloc(n * sizeof(char));
		if (!term) {
			perror("malloc");
			sleep(ERROR_SLEEP);
			_exit(1);
		}
		for (i = 0; i < n; i++)
			*(term + i) = *(_term + i);
	}

	if (!preserve_env) {
		environ = malloc(sizeof(char*));
		if (!environ) {
			perror("malloc");
			sleep(ERROR_SLEEP);
			_exit(1);
		}
		*environ = NULL;
	}

	setenv("HOME", entry->pw_dir, 1);
	setenv("USER", entry->pw_name, 1);
	setenv("LOGUSER", entry->pw_name, 1);
	setenv("SHELL", entry->pw_shell, 1);
	setenv("TERM", term ?: DEFAULT_TERM, 1);
	setenv("PATH", entry->pw_uid ? PATH : PATH_ROOT, 1);

	if (term)
		free(term);
}


/**
 * Replace the current image with the user's login shell
 * 
 * @param  entry  The user entry in the password file
 */
void
exec_shell(struct passwd *entry)
{
	int child_argc = 0;
	char **child_argv = malloc(5 * sizeof(char *));
	size_t n = 0;
	char *sh = entry->pw_shell;
	char *login_sh;

	while (sh[n++]) ;

	login_sh = malloc((n + (strchr(sh, ' ') ? 5 : 1)) * sizeof(char));
	if (!login_sh) {
		perror("malloc");
		sleep(ERROR_SLEEP);
		_exit(1);
	}

	if (strchr(sh, ' ')) {
		login_sh += 5;
		strcpy(login_sh, "exec ");
		login_sh[n] = 0;

		child_argv[child_argc++] = strdup(DEFAULT_SHELL);
		child_argv[child_argc++] = strdup("-" DEFAULT_SH);
		child_argv[child_argc++] = strdup("-c");
		child_argv[child_argc++] = login_sh - 5;
	} else {
		ssize_t i;
		for (i = (ssize_t)n - 1; i >= 0; i--)
			if (sh[i] == '/') {
				i++;
				break;
			}

		login_sh = malloc((n + 1U) * sizeof(char));
		*login_sh++ = '-';
		strcpy(login_sh, &sh[i]);
		login_sh[n] = 0;

		child_argv[child_argc++] = sh;
		child_argv[child_argc++] = &login_sh[-1];
	}

	child_argv[child_argc] = NULL;
	execvp(child_argv[0], &child_argv[1]);
	perror("execvp");
	sleep(ERROR_SLEEP);
	_exit(1);
}