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/* vi: set sw=4 ts=4:
*
* login.c - Start a session on the system.
*
* Copyright 2012 Elie De Brauwer <eliedebrauwer@gmail.com>
*
* Not in SUSv4.
* No support for PAM/securetty/selinux/login script/issue/utmp
* Relies on libcrypt for hash calculation.
USE_LOGIN(NEWTOY(login, ">1fph:", TOYFLAG_BIN))
config LOGIN
bool "login"
default y
help
usage: login [-p] [-h host] [[-f] username]
Establish a new session with the system.
-p Preserve environment
-h The name of the remote host for this login
-f Do not perform authentication
*/
#include "toys.h"
#define LOGIN_TIMEOUT 60
#define LOGIN_FAIL_TIMEOUT 3
#define USER_NAME_MAX_SIZE 32
#define HOSTNAME_SIZE 32
DEFINE_GLOBALS(
char *hostname;
)
#define TT this.login
static void login_timeout_handler(int sig __attribute__((unused)))
{
printf("\nLogin timed out after %d seconds.\n", LOGIN_TIMEOUT);
exit(0);
}
static char *forbid[] = {
"BASH_ENV",
"ENV",
"HOME",
"IFS",
"LD_LIBRARY_PATH",
"LD_PRELOAD",
"LD_TRACE_LOADED_OBJECTS",
"LD_BIND_NOW",
"LD_AOUT_LIBRARY_PATH",
"LD_AOUT_PRELOAD",
"LD_NOWARN",
"LD_KEEPDIR",
"SHELL",
NULL
};
int verify_password(char * pwd)
{
char *pass;
if (read_password(toybuf, sizeof(toybuf), "Password: ")) return 1;
if (!pwd) return 1;
if (pwd[0] == '!' || pwd[0] == '*') return 1;
pass = crypt(toybuf, pwd);
if (pass && !strcmp(pass, pwd)) return 0;
return 1;
}
void read_user(char * buff, int size)
{
char hostname[HOSTNAME_SIZE+1];
int i = 0;
hostname[HOSTNAME_SIZE] = 0;
if(!gethostname(hostname, HOSTNAME_SIZE)) fputs(hostname, stdout);
fputs(" login: ", stdout);
fflush(stdout);
do {
buff[0] = getchar();
if (buff[0] == EOF)
exit(EXIT_FAILURE);
} while (isblank(buff[0]));
if (buff[0] != '\n')
if(!fgets(&buff[1], HOSTNAME_SIZE-1, stdin))
_exit(1);
while(i<HOSTNAME_SIZE-1 && isgraph(buff[i])) i++;
buff[i] = 0;
}
void handle_nologin(void)
{
int fd = open("/etc/nologin", O_RDONLY);
int size;
if (fd == -1) return;
size = readall(fd, toybuf,sizeof(toybuf)-1);
toybuf[size] = 0;
if (!size) puts("System closed for routine maintenance\n");
else puts(toybuf);
close(fd);
fflush(stdout);
exit(EXIT_FAILURE);
}
void handle_motd(void)
{
int fd = open("/etc/motd", O_RDONLY);
int size;
if (fd == -1) return;
size = readall(fd, toybuf,sizeof(toybuf)-1);
toybuf[size] = 0;
puts(toybuf);
close(fd);
fflush(stdout);
}
int change_identity(const struct passwd *pwd)
{
if (initgroups(pwd->pw_name,pwd->pw_gid)) return 1;
if (setgid(pwd->pw_uid)) return 1;
if (setuid(pwd->pw_uid)) return 1;
return 0;
}
void spawn_shell(const char *shell)
{
const char * exec_name = strrchr(shell,'/');
if (exec_name) exec_name++;
else exec_name = shell;
snprintf(toybuf,sizeof(toybuf)-1, "-%s", shell);
execl(shell, toybuf, NULL);
error_exit("Failed to spawn shell");
}
void setup_environment(const struct passwd *pwd, int clear_env)
{
if (chdir(pwd->pw_dir)) printf("bad home dir: %s\n", pwd->pw_dir);
if (clear_env) {
const char * term = getenv("TERM");
clearenv();
if (term) setenv("TERM", term, 1);
}
setenv("USER", pwd->pw_name, 1);
setenv("LOGNAME", pwd->pw_name, 1);
setenv("HOME", pwd->pw_dir, 1);
setenv("SHELL", pwd->pw_shell, 1);
}
void login_main(void)
{
int f_flag = (toys.optflags & 4) >> 2;
int p_flag = (toys.optflags & 2) >> 1;
int h_flag = toys.optflags & 1;
char username[USER_NAME_MAX_SIZE+1], *pass = NULL, **ss;
struct passwd * pwd = NULL;
struct spwd * spwd = NULL;
int auth_fail_cnt = 0;
if (f_flag && toys.optc != 1)
error_exit("-f requires username");
if (geteuid()) error_exit("not root");
if (!isatty(0) || !isatty(1) || !isatty(2)) error_exit("no tty");
openlog("login", LOG_PID | LOG_CONS, LOG_AUTH);
signal(SIGALRM, login_timeout_handler);
alarm(LOGIN_TIMEOUT);
for (ss = forbid; *ss; ss++) unsetenv(*ss);
while (1) {
tcflush(0, TCIFLUSH);
username[USER_NAME_MAX_SIZE] = 0;
if (toys.optargs[0])
strncpy(username, toys.optargs[0], USER_NAME_MAX_SIZE);
else {
read_user(username, USER_NAME_MAX_SIZE+1);
if (username[0] == 0) continue;
}
pwd = getpwnam(username);
if (!pwd) goto query_pass; // Non-existing user
if (pwd->pw_passwd[0] == '!' || pwd->pw_passwd[0] == '*')
goto query_pass; // Locked account
if (f_flag) break; // Pre-authenticated
if (!pwd->pw_passwd[0]) break; // Password-less account
pass = pwd->pw_passwd;
if (pwd->pw_passwd[0] == 'x') {
spwd = getspnam (username);
if (spwd) pass = spwd->sp_pwdp;
}
query_pass:
if (!verify_password(pass)) break;
f_flag = 0;
syslog(LOG_WARNING, "invalid password for '%s' on %s %s %s", username,
ttyname(0), (h_flag)?"from":"", (h_flag)?TT.hostname:"");
sleep(LOGIN_FAIL_TIMEOUT);
puts("Login incorrect");
if (++auth_fail_cnt == 3)
error_exit("Maximum number of tries exceeded (%d)\n", auth_fail_cnt);
username[0] = 0;
pwd = NULL;
spwd = NULL;
}
alarm(0);
if (pwd->pw_uid) handle_nologin();
if (change_identity(pwd)) error_exit("Failed to change identity");
setup_environment(pwd, !p_flag);
handle_motd();
syslog(LOG_INFO, "%s logged in on %s %s %s", pwd->pw_name,
ttyname(0), (h_flag)?"from":"", (h_flag)?TT.hostname:"");
spawn_shell(pwd->pw_shell);
}
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