/* mlogin: minimalistic login                */

/* Copyright (c) 2019  Ørjan Malde           */

/* Released under LGPL, see COPYRIGHT.MLOGIN */

#define _GNU_SOURCE

#include <sys/types.h>

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <stdbool.h>

#include <string.h>

#include <grp.h>

#include <pwd.h>

#include <errno.h>

#include <signal.h>

#ifdef __midipix__

#define IFLAG 1

#else

#define IFLAG 0

#endif

#include "login.h"

#ifndef HAVE_EXPLICIT_BZERO

void explicit_bzero(void*, size_t);

#endif

static bool switch_user_context(struct passwd* pw, const char* username)

{

	#ifndef __midipix__

	if(!getuid()) {

		if(initgroups(username, pw->pw_gid) == -1) {

			printf("initgroups failed: %s", strerror(errno));

			exit(1);

		}

	}

	#else

	(void)username;

	#endif

	/* this works for linux and midipix */

	if(setgid(pw->pw_gid))

		return false;

	if(setuid(pw->pw_uid))

		return false;

	return true;

}

static bool do_login(struct passwd* pwd, int pflag)

{

	if(*pwd->pw_shell == '\0')

		pwd->pw_shell = "/bin/sh"; /* if /bin/sh doesn't exist, I do not care. blow up. */

	if(chdir(pwd->pw_dir) < 0) {

		printf("no home directory %s!\n", pwd->pw_dir); /* handle -EPERM, -ENOMEM, -ESYMLNK */

		if(chdir("/") == -1) {

			printf("chdir failed with %s", strerror(errno));

			return false;

			}

				pwd->pw_dir = "/";

			}

                if(!pflag)

			(void)clearenv();

                (void)setenv("HOME", pwd->pw_dir, 1);

                (void)setenv("SHELL", pwd->pw_shell, 1);

                (void)setenv("TERM", "xterm", 0); /* rrrr. needs researching */

                (void)setenv("LOGNAME", pwd->pw_name, 1);

                (void)setenv("USER", pwd->pw_name, 1);

#if 0

                (void)setenv("PS1", "$ ", 0);

#endif

                (void)setenv("PATH", "/local/sbin:/local/bin:/sbin:/bin", 0);

                (void)signal(SIGTSTP, SIG_DFL);

                (void)signal(SIGQUIT, SIG_DFL);

                (void)signal(SIGINT, SIG_DFL);

                execlp(pwd->pw_shell, "-l", (const char*)NULL);

		return false;

}

int main(int argc, char **argv)

{

	/* we don't want ^D etc to mess up the logic */

	(void)signal(SIGTSTP, SIG_IGN);

	(void)signal(SIGQUIT, SIG_IGN);

	(void)signal(SIGINT, SIG_IGN);

	struct passwd *pwd;

	char* username = NULL;

	int c;

	int pflag, iflag = 0;

	while((c = getopt(argc, argv, "pfh:iw")) != -1)

		switch(c) {

			case 'p':

				pflag = 1; break;

			case 'f':

				(void)0; break; /* unused, pointless currently */

			case 'h':

				if(getuid()) {

					exit(1);

				}

				break;

			case 'i':

				iflag = IFLAG; break;

			default:

			case '?':

				usage();

				break;

		}

	argv += optind;

	if(*argv)

		username = *argv;

	else {

		printf("login: ");

		fflush(0);

		(void)scanf("%ms", &username);

	}

	pwd = getpwnam(username);

	if(pwd) {

		if(!iflag) {

			char* pw = getpass("Password: ");

			if(!(*pwd->pw_passwd == '\0' && !strlen(pw))) {

				char* pw_encrypted = crypt(pw, pwd->pw_passwd);

				if(!timingsafe_memcmp(pw_encrypted, pwd->pw_passwd, strlen(pw_encrypted))) {

					puts("Login incorrect.");

					explicit_bzero(pw, strlen(pw));

					exit(1);

				}

				explicit_bzero(pw, strlen(pw));

			}

		}

	}

	else {

		/* asking for password even if the user is not found, no /etc/passwd is found, etc. */

		/* this stops easy probing for accounts */

		char* pw = getpass("Password: ");

		puts("Login incorrect.");

		explicit_bzero(pw, strlen(pw));

		exit(1);

	}

	endpwent();

	/* authenticated, attempt to set user context and spawn user shell */

	if(switch_user_context(pwd, username)) {

		if(!do_login(pwd, pflag)) {

			puts("failed to spawn shell.");

		}

	}

	puts("could not switch to specified user.");

}

void usage(void) {

	puts("login -p (preserve environment)");

	puts("login -f (no secondary authentication, unused)");

	puts("login -h (pass remote server name to login, unused)");

	exit(0);

}