busybox/loginutils/login.c

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/* vi: set sw=4 ts=4: */
/*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
//config:config LOGIN
//config: bool "login"
//config: default y
//config: select FEATURE_SYSLOG
//config: help
//config: login is used when signing onto a system.
//config:
//config: Note that Busybox binary must be setuid root for this applet to
//config: work properly.
//config:
//config:config LOGIN_SESSION_AS_CHILD
//config: bool "Run logged in session in a child process"
//config: default y if PAM
//config: depends on LOGIN
//config: help
//config: Run the logged in session in a child process. This allows
//config: login to clean up things such as utmp entries or PAM sessions
//config: when the login session is complete. If you use PAM, you
//config: almost always would want this to be set to Y, else PAM session
//config: will not be cleaned up.
//config:
//config:config LOGIN_SCRIPTS
//config: bool "Support for login scripts"
//config: depends on LOGIN
//config: default y
//config: help
//config: Enable this if you want login to execute $LOGIN_PRE_SUID_SCRIPT
//config: just prior to switching from root to logged-in user.
//config:
//config:config FEATURE_NOLOGIN
//config: bool "Support for /etc/nologin"
//config: default y
//config: depends on LOGIN
//config: help
//config: The file /etc/nologin is used by (some versions of) login(1).
//config: If it exists, non-root logins are prohibited.
//config:
//config:config FEATURE_SECURETTY
//config: bool "Support for /etc/securetty"
//config: default y
//config: depends on LOGIN
//config: help
//config: The file /etc/securetty is used by (some versions of) login(1).
//config: The file contains the device names of tty lines (one per line,
//config: without leading /dev/) on which root is allowed to login.
//applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
//applet:IF_LOGIN(APPLET(login, BB_DIR_BIN, BB_SUID_REQUIRE))
//kbuild:lib-$(CONFIG_LOGIN) += login.o
//usage:#define login_trivial_usage
//usage: "[-p] [-h HOST] [[-f] USER]"
//usage:#define login_full_usage "\n\n"
//usage: "Begin a new session on the system\n"
//usage: "\n -f Don't authenticate (user already authenticated)"
//usage: "\n -h HOST Host user came from (for network logins)"
//usage: "\n -p Preserve environment"
#include "libbb.h"
#include <syslog.h>
#include <sys/resource.h>
#if ENABLE_SELINUX
# include <selinux/selinux.h> /* for is_selinux_enabled() */
# include <selinux/get_context_list.h> /* for get_default_context() */
# include <selinux/flask.h> /* for security class definitions */
#endif
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#if ENABLE_PAM
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/* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
# undef setlocale
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/* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
* Apparently they like to confuse people. */
# include <security/pam_appl.h>
# include <security/pam_misc.h>
# if 0
/* This supposedly can be used to avoid double password prompt,
* if used instead of standard misc_conv():
*
* "When we want to authenticate first with local method and then with tacacs for example,
* the password is asked for local method and if not good is asked a second time for tacacs.
* So if we want to authenticate a user with tacacs, and the user exists localy, the password is
* asked two times before authentication is accepted."
*
* However, code looks shaky. For example, why misc_conv() return value is ignored?
* Are msg[i] and resp[i] indexes handled correctly?
*/
static char *passwd = NULL;
static int my_conv(int num_msg, const struct pam_message **msg,
struct pam_response **resp, void *data)
{
int i;
for (i = 0; i < num_msg; i++) {
switch (msg[i]->msg_style) {
case PAM_PROMPT_ECHO_OFF:
if (passwd == NULL) {
misc_conv(num_msg, msg, resp, data);
passwd = xstrdup(resp[i]->resp);
return PAM_SUCCESS;
}
resp[0] = xzalloc(sizeof(struct pam_response));
resp[0]->resp = passwd;
passwd = NULL;
resp[0]->resp_retcode = PAM_SUCCESS;
resp[1] = NULL;
return PAM_SUCCESS;
default:
break;
}
}
return PAM_SUCCESS;
}
# endif
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static const struct pam_conv conv = {
misc_conv,
NULL
};
#endif
enum {
TIMEOUT = 60,
EMPTY_USERNAME_COUNT = 10,
/* Some users found 32 chars limit to be too low: */
USERNAME_SIZE = 64,
TTYNAME_SIZE = 32,
};
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struct globals {
struct termios tty_attrs;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
#define INIT_G() do { } while (0)
#if ENABLE_FEATURE_NOLOGIN
static void die_if_nologin(void)
{
FILE *fp;
int c;
int empty = 1;
fp = fopen_for_read("/etc/nologin");
if (!fp) /* assuming it does not exist */
return;
while ((c = getc(fp)) != EOF) {
if (c == '\n')
bb_putchar('\r');
bb_putchar(c);
empty = 0;
}
if (empty)
puts("\r\nSystem closed for routine maintenance\r");
fclose(fp);
fflush_all();
/* Users say that they do need this prior to exit: */
tcdrain(STDOUT_FILENO);
exit(EXIT_FAILURE);
}
#else
# define die_if_nologin() ((void)0)
#endif
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#if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
static int check_securetty(const char *short_tty)
{
char *buf = (char*)"/etc/securetty"; /* any non-NULL is ok */
parser_t *parser = config_open2("/etc/securetty", fopen_for_read);
while (config_read(parser, &buf, 1, 1, "# \t", PARSE_NORMAL)) {
if (strcmp(buf, short_tty) == 0)
break;
buf = NULL;
}
config_close(parser);
/* buf != NULL here if config file was not found, empty
* or line was found which equals short_tty */
return buf != NULL;
}
#else
static ALWAYS_INLINE int check_securetty(const char *short_tty UNUSED_PARAM) { return 1; }
#endif
#if ENABLE_SELINUX
static void initselinux(char *username, char *full_tty,
security_context_t *user_sid)
{
security_context_t old_tty_sid, new_tty_sid;
if (!is_selinux_enabled())
return;
if (get_default_context(username, NULL, user_sid)) {
bb_error_msg_and_die("can't get SID for %s", username);
}
if (getfilecon(full_tty, &old_tty_sid) < 0) {
bb_perror_msg_and_die("getfilecon(%s) failed", full_tty);
}
if (security_compute_relabel(*user_sid, old_tty_sid,
SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
bb_perror_msg_and_die("security_change_sid(%s) failed", full_tty);
}
if (setfilecon(full_tty, new_tty_sid) != 0) {
bb_perror_msg_and_die("chsid(%s, %s) failed", full_tty, new_tty_sid);
}
}
#endif
#if ENABLE_LOGIN_SCRIPTS
static void run_login_script(struct passwd *pw, char *full_tty)
{
char *t_argv[2];
t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
if (t_argv[0]) {
t_argv[1] = NULL;
xsetenv("LOGIN_TTY", full_tty);
xsetenv("LOGIN_USER", pw->pw_name);
xsetenv("LOGIN_UID", utoa(pw->pw_uid));
xsetenv("LOGIN_GID", utoa(pw->pw_gid));
xsetenv("LOGIN_SHELL", pw->pw_shell);
spawn_and_wait(t_argv); /* NOMMU-friendly */
unsetenv("LOGIN_TTY");
unsetenv("LOGIN_USER");
unsetenv("LOGIN_UID");
unsetenv("LOGIN_GID");
unsetenv("LOGIN_SHELL");
}
}
#else
void run_login_script(struct passwd *pw, char *full_tty);
#endif
#if ENABLE_LOGIN_SESSION_AS_CHILD && ENABLE_PAM
static void login_pam_end(pam_handle_t *pamh)
{
int pamret;
pamret = pam_setcred(pamh, PAM_DELETE_CRED);
if (pamret != PAM_SUCCESS) {
bb_error_msg("pam_%s failed: %s (%d)", "setcred",
pam_strerror(pamh, pamret), pamret);
}
pamret = pam_close_session(pamh, 0);
if (pamret != PAM_SUCCESS) {
bb_error_msg("pam_%s failed: %s (%d)", "close_session",
pam_strerror(pamh, pamret), pamret);
}
pamret = pam_end(pamh, pamret);
if (pamret != PAM_SUCCESS) {
bb_error_msg("pam_%s failed: %s (%d)", "end",
pam_strerror(pamh, pamret), pamret);
}
}
#endif /* ENABLE_PAM */
static void get_username_or_die(char *buf, int size_buf)
{
int c, cntdown;
cntdown = EMPTY_USERNAME_COUNT;
prompt:
print_login_prompt();
/* skip whitespace */
do {
c = getchar();
if (c == EOF)
exit(EXIT_FAILURE);
if (c == '\n') {
if (!--cntdown)
exit(EXIT_FAILURE);
goto prompt;
}
} while (isspace(c)); /* maybe isblank? */
*buf++ = c;
if (!fgets(buf, size_buf-2, stdin))
exit(EXIT_FAILURE);
if (!strchr(buf, '\n'))
exit(EXIT_FAILURE);
while ((unsigned char)*buf > ' ')
buf++;
*buf = '\0';
}
static void motd(void)
{
int fd;
fd = open(bb_path_motd_file, O_RDONLY);
if (fd >= 0) {
fflush_all();
bb_copyfd_eof(fd, STDOUT_FILENO);
close(fd);
}
}
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static void alarm_handler(int sig UNUSED_PARAM)
{
/* This is the escape hatch! Poor serial line users and the like
* arrive here when their connection is broken.
* We don't want to block here */
ndelay_on(STDOUT_FILENO);
/* Test for correct attr restoring:
* run "getty 0 -" from a shell, enter bogus username, stop at
* password prompt, let it time out. Without the tcsetattr below,
* when you are back at shell prompt, echo will be still off.
*/
tcsetattr_stdin_TCSANOW(&G.tty_attrs);
printf("\r\nLogin timed out after %u seconds\r\n", TIMEOUT);
fflush_all();
/* unix API is brain damaged regarding O_NONBLOCK,
* we should undo it, or else we can affect other processes */
ndelay_off(STDOUT_FILENO);
_exit(EXIT_SUCCESS);
}
int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int login_main(int argc UNUSED_PARAM, char **argv)
{
enum {
LOGIN_OPT_f = (1<<0),
LOGIN_OPT_h = (1<<1),
LOGIN_OPT_p = (1<<2),
};
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char *fromhost;
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char username[USERNAME_SIZE];
int run_by_root;
unsigned opt;
int count = 0;
struct passwd *pw;
char *opt_host = NULL;
char *opt_user = opt_user; /* for compiler */
char *full_tty;
char *short_tty;
IF_SELINUX(security_context_t user_sid = NULL;)
#if ENABLE_PAM
int pamret;
pam_handle_t *pamh;
const char *pamuser;
const char *failed_msg;
struct passwd pwdstruct;
char pwdbuf[256];
char **pamenv;
#endif
#if ENABLE_LOGIN_SESSION_AS_CHILD
pid_t child_pid;
#endif
INIT_G();
/* More of suid paranoia if called by non-root: */
/* Clear dangerous stuff, set PATH */
run_by_root = !sanitize_env_if_suid();
/* Mandatory paranoia for suid applet:
* ensure that fd# 0,1,2 are opened (at least to /dev/null)
* and any extra open fd's are closed.
* (The name of the function is misleading. Not daemonizing here.) */
bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
username[0] = '\0';
opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
if (opt & LOGIN_OPT_f) {
if (!run_by_root)
bb_error_msg_and_die("-f is for root only");
safe_strncpy(username, opt_user, sizeof(username));
}
argv += optind;
if (argv[0]) /* user from command line (getty) */
safe_strncpy(username, argv[0], sizeof(username));
/* Save tty attributes - and by doing it, check that it's indeed a tty */
if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0
|| !isatty(STDOUT_FILENO)
/*|| !isatty(STDERR_FILENO) - no, guess some people might want to redirect this */
) {
return EXIT_FAILURE; /* Must be a terminal */
}
/* We install timeout handler only _after_ we saved G.tty_attrs */
signal(SIGALRM, alarm_handler);
alarm(TIMEOUT);
/* Find out and memorize our tty name */
full_tty = xmalloc_ttyname(STDIN_FILENO);
if (!full_tty)
full_tty = xstrdup("UNKNOWN");
short_tty = skip_dev_pfx(full_tty);
if (opt_host) {
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fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
} else {
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fromhost = xasprintf(" on '%s'", short_tty);
}
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/* Was breaking "login <username>" from shell command line: */
/*bb_setpgrp();*/
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openlog(applet_name, LOG_PID | LOG_CONS, LOG_AUTH);
while (1) {
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/* flush away any type-ahead (as getty does) */
tcflush(0, TCIFLUSH);
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if (!username[0])
get_username_or_die(username, sizeof(username));
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#if ENABLE_PAM
pamret = pam_start("login", username, &conv, &pamh);
if (pamret != PAM_SUCCESS) {
failed_msg = "start";
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goto pam_auth_failed;
}
/* set TTY (so things like securetty work) */
pamret = pam_set_item(pamh, PAM_TTY, short_tty);
if (pamret != PAM_SUCCESS) {
failed_msg = "set_item(TTY)";
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goto pam_auth_failed;
}
/* set RHOST */
if (opt_host) {
pamret = pam_set_item(pamh, PAM_RHOST, opt_host);
if (pamret != PAM_SUCCESS) {
failed_msg = "set_item(RHOST)";
goto pam_auth_failed;
}
}
if (!(opt & LOGIN_OPT_f)) {
pamret = pam_authenticate(pamh, 0);
if (pamret != PAM_SUCCESS) {
failed_msg = "authenticate";
goto pam_auth_failed;
/* TODO: or just "goto auth_failed"
* since user seems to enter wrong password
* (in this case pamret == 7)
*/
}
}
/* check that the account is healthy */
pamret = pam_acct_mgmt(pamh, 0);
if (pamret != PAM_SUCCESS) {
failed_msg = "acct_mgmt";
goto pam_auth_failed;
}
/* read user back */
pamuser = NULL;
/* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
* thus we cast to (void*) */
if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
failed_msg = "get_item(USER)";
goto pam_auth_failed;
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}
if (!pamuser || !pamuser[0])
goto auth_failed;
safe_strncpy(username, pamuser, sizeof(username));
/* Don't use "pw = getpwnam(username);",
* PAM is said to be capable of destroying static storage
* used by getpwnam(). We are using safe(r) function */
pw = NULL;
getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
if (!pw)
goto auth_failed;
pamret = pam_open_session(pamh, 0);
if (pamret != PAM_SUCCESS) {
failed_msg = "open_session";
goto pam_auth_failed;
}
pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
if (pamret != PAM_SUCCESS) {
failed_msg = "setcred";
goto pam_auth_failed;
}
break; /* success, continue login process */
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pam_auth_failed:
/* syslog, because we don't want potential attacker
* to know _why_ login failed */
syslog(LOG_WARNING, "pam_%s call failed: %s (%d)", failed_msg,
pam_strerror(pamh, pamret), pamret);
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safe_strncpy(username, "UNKNOWN", sizeof(username));
#else /* not PAM */
pw = getpwnam(username);
if (!pw) {
strcpy(username, "UNKNOWN");
goto fake_it;
}
if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
goto auth_failed;
if (opt & LOGIN_OPT_f)
break; /* -f USER: success without asking passwd */
if (pw->pw_uid == 0 && !check_securetty(short_tty))
goto auth_failed;
/* Don't check the password if password entry is empty (!) */
if (!pw->pw_passwd[0])
break;
fake_it:
/* Password reading and authorization takes place here.
* Note that reads (in no-echo mode) trash tty attributes.
* If we get interrupted by SIGALRM, we need to restore attrs.
*/
if (ask_and_check_password(pw) > 0)
break;
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#endif /* ENABLE_PAM */
auth_failed:
opt &= ~LOGIN_OPT_f;
bb_do_delay(LOGIN_FAIL_DELAY);
/* TODO: doesn't sound like correct English phrase to me */
puts("Login incorrect");
if (++count == 3) {
syslog(LOG_WARNING, "invalid password for '%s'%s",
username, fromhost);
if (ENABLE_FEATURE_CLEAN_UP)
free(fromhost);
return EXIT_FAILURE;
}
username[0] = '\0';
} /* while (1) */
alarm(0);
/* We can ignore /etc/nologin if we are logging in as root,
* it doesn't matter whether we are run by root or not */
if (pw->pw_uid != 0)
die_if_nologin();
#if ENABLE_LOGIN_SESSION_AS_CHILD
child_pid = vfork();
if (child_pid != 0) {
if (child_pid < 0)
bb_perror_msg("vfork");
else {
if (safe_waitpid(child_pid, NULL, 0) == -1)
bb_perror_msg("waitpid");
update_utmp_DEAD_PROCESS(child_pid);
}
IF_PAM(login_pam_end(pamh);)
return 0;
}
#endif
IF_SELINUX(initselinux(username, full_tty, &user_sid);)
/* Try these, but don't complain if they fail.
* _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
fchown(0, pw->pw_uid, pw->pw_gid);
fchmod(0, 0600);
update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
/* We trust environment only if we run by root */
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if (ENABLE_LOGIN_SCRIPTS && run_by_root)
run_login_script(pw, full_tty);
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change_identity(pw);
setup_environment(pw->pw_shell,
(!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV) + SETUP_ENV_CHANGEENV,
pw);
#if ENABLE_PAM
/* Modules such as pam_env will setup the PAM environment,
* which should be copied into the new environment. */
pamenv = pam_getenvlist(pamh);
if (pamenv) while (*pamenv) {
putenv(*pamenv);
pamenv++;
}
#endif
if (access(".hushlogin", F_OK) != 0)
motd();
if (pw->pw_uid == 0)
syslog(LOG_INFO, "root login%s", fromhost);
if (ENABLE_FEATURE_CLEAN_UP)
free(fromhost);
/* well, a simple setexeccon() here would do the job as well,
* but let's play the game for now */
IF_SELINUX(set_current_security_context(user_sid);)
// util-linux login also does:
// /* start new session */
// setsid();
// /* TIOCSCTTY: steal tty from other process group */
// if (ioctl(0, TIOCSCTTY, 1)) error_msg...
// BBox login used to do this (see above):
// bb_setpgrp();
// If this stuff is really needed, add it and explain why!
/* Set signals to defaults */
/* Non-ignored signals revert to SIG_DFL on exec anyway */
/*signal(SIGALRM, SIG_DFL);*/
/* Is this correct? This way user can ctrl-c out of /etc/profile,
* potentially creating security breach (tested with bash 3.0).
* But without this, bash 3.0 will not enable ctrl-c either.
* Maybe bash is buggy?
* Need to find out what standards say about /bin/login -
* should we leave SIGINT etc enabled or disabled? */
signal(SIGINT, SIG_DFL);
/* Exec login shell with no additional parameters */
run_shell(pw->pw_shell, 1, NULL, NULL);
/* return EXIT_FAILURE; - not reached */
}