path: root/loginutils/login.c (plain)
blob: 03ddadb6bcfa165e4d16b7088d70f54fdfcd5f0c

1	/* vi: set sw=4 ts=4: */
2	/*
3	* Licensed under GPLv2 or later, see file LICENSE in this source tree.
4	*/
5	//config:config LOGIN
6	//config: bool "login"
7	//config: default y
8	//config: select FEATURE_SYSLOG
9	//config: help
10	//config: login is used when signing onto a system.
11	//config:
12	//config: Note that Busybox binary must be setuid root for this applet to
13	//config: work properly.
14	//config:
15	//config:config LOGIN_SESSION_AS_CHILD
16	//config: bool "Run logged in session in a child process"
17	//config: default y if PAM
18	//config: depends on LOGIN
19	//config: help
20	//config: Run the logged in session in a child process. This allows
21	//config: login to clean up things such as utmp entries or PAM sessions
22	//config: when the login session is complete. If you use PAM, you
23	//config: almost always would want this to be set to Y, else PAM session
24	//config: will not be cleaned up.
25	//config:
26	//config:config LOGIN_SCRIPTS
27	//config: bool "Support for login scripts"
28	//config: depends on LOGIN
29	//config: default y
30	//config: help
31	//config: Enable this if you want login to execute $LOGIN_PRE_SUID_SCRIPT
32	//config: just prior to switching from root to logged-in user.
33	//config:
34	//config:config FEATURE_NOLOGIN
35	//config: bool "Support for /etc/nologin"
36	//config: default y
37	//config: depends on LOGIN
38	//config: help
39	//config: The file /etc/nologin is used by (some versions of) login(1).
40	//config: If it exists, non-root logins are prohibited.
41	//config:
42	//config:config FEATURE_SECURETTY
43	//config: bool "Support for /etc/securetty"
44	//config: default y
45	//config: depends on LOGIN
46	//config: help
47	//config: The file /etc/securetty is used by (some versions of) login(1).
48	//config: The file contains the device names of tty lines (one per line,
49	//config: without leading /dev/) on which root is allowed to login.
50
51	//applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
52	//applet:IF_LOGIN(APPLET(login, BB_DIR_BIN, BB_SUID_REQUIRE))
53
54	//kbuild:lib-$(CONFIG_LOGIN) += login.o
55
56	//usage:#define login_trivial_usage
57	//usage: "[-p] [-h HOST] [[-f] USER]"
58	//usage:#define login_full_usage "\n\n"
59	//usage: "Begin a new session on the system\n"
60	//usage: "\n -f Don't authenticate (user already authenticated)"
61	//usage: "\n -h HOST Host user came from (for network logins)"
62	//usage: "\n -p Preserve environment"
63
64	#include "libbb.h"
65	#include "common_bufsiz.h"
66	#include <syslog.h>
67	#include <sys/resource.h>
68
69	#if ENABLE_SELINUX
70	# include <selinux/selinux.h> /* for is_selinux_enabled() */
71	#ifndef __BIONIC__
72	# include <selinux/get_context_list.h> /* for get_default_context() */
73	# /* from deprecated <selinux/flask.h>: */
74	# undef SECCLASS_CHR_FILE
75	# define SECCLASS_CHR_FILE 10
76	#endif
77	#endif
78
79	#if ENABLE_PAM
80	/* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
81	# undef setlocale
82	/* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
83	* Apparently they like to confuse people. */
84	# include <security/pam_appl.h>
85	# include <security/pam_misc.h>
86
87	# if 0
88	/* This supposedly can be used to avoid double password prompt,
89	* if used instead of standard misc_conv():
90	*
91	* "When we want to authenticate first with local method and then with tacacs for example,
92	* the password is asked for local method and if not good is asked a second time for tacacs.
93	* So if we want to authenticate a user with tacacs, and the user exists localy, the password is
94	* asked two times before authentication is accepted."
95	*
96	* However, code looks shaky. For example, why misc_conv() return value is ignored?
97	* Are msg[i] and resp[i] indexes handled correctly?
98	*/
99	static char *passwd = NULL;
100	static int my_conv(int num_msg, const struct pam_message **msg,
101	struct pam_response **resp, void *data)
102	{
103	int i;
104	for (i = 0; i < num_msg; i++) {
105	switch (msg[i]->msg_style) {
106	case PAM_PROMPT_ECHO_OFF:
107	if (passwd == NULL) {
108	misc_conv(num_msg, msg, resp, data);
109	passwd = xstrdup(resp[i]->resp);
110	return PAM_SUCCESS;
111	}
112
113	resp[0] = xzalloc(sizeof(struct pam_response));
114	resp[0]->resp = passwd;
115	passwd = NULL;
116	resp[0]->resp_retcode = PAM_SUCCESS;
117	resp[1] = NULL;
118	return PAM_SUCCESS;
119
120	default:
121	break;
122	}
123	}
124
125	return PAM_SUCCESS;
126	}
127	# endif
128
129	static const struct pam_conv conv = {
130	misc_conv,
131	NULL
132	};
133	#endif
134
135	enum {
136	TIMEOUT = 60,
137	EMPTY_USERNAME_COUNT = 10,
138	/* Some users found 32 chars limit to be too low: */
139	USERNAME_SIZE = 64,
140	TTYNAME_SIZE = 32,
141	};
142
143	struct globals {
144	struct termios tty_attrs;
145	} FIX_ALIASING;
146	#define G (*(struct globals*)bb_common_bufsiz1)
147	#define INIT_G() do { setup_common_bufsiz(); } while (0)
148
149
150	#if ENABLE_FEATURE_NOLOGIN
151	static void die_if_nologin(void)
152	{
153	FILE *fp;
154	int c;
155	int empty = 1;
156
157	fp = fopen_for_read("/etc/nologin");
158	if (!fp) /* assuming it does not exist */
159	return;
160
161	while ((c = getc(fp)) != EOF) {
162	if (c == '\n')
163	bb_putchar('\r');
164	bb_putchar(c);
165	empty = 0;
166	}
167	if (empty)
168	puts("\r\nSystem closed for routine maintenance\r");
169
170	fclose(fp);
171	fflush_all();
172	/* Users say that they do need this prior to exit: */
173	tcdrain(STDOUT_FILENO);
174	exit(EXIT_FAILURE);
175	}
176	#else
177	# define die_if_nologin() ((void)0)
178	#endif
179
180	#if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
181	static int check_securetty(const char *short_tty)
182	{
183	char *buf = (char*)"/etc/securetty"; /* any non-NULL is ok */
184	parser_t *parser = config_open2("/etc/securetty", fopen_for_read);
185	while (config_read(parser, &buf, 1, 1, "# \t", PARSE_NORMAL)) {
186	if (strcmp(buf, short_tty) == 0)
187	break;
188	buf = NULL;
189	}
190	config_close(parser);
191	/* buf != NULL here if config file was not found, empty
192	* or line was found which equals short_tty */
193	return buf != NULL;
194	}
195	#else
196	static ALWAYS_INLINE int check_securetty(const char *short_tty UNUSED_PARAM) { return 1; }
197	#endif
198
199	#if ENABLE_SELINUX
200	static void initselinux(char *username, char *full_tty,
201	security_context_t *user_sid)
202	{
203	security_context_t old_tty_sid, new_tty_sid;
204
205	if (!is_selinux_enabled())
206	return;
207
208	if (get_default_context(username, NULL, user_sid)) {
209	bb_error_msg_and_die("can't get SID for %s", username);
210	}
211	if (getfilecon(full_tty, &old_tty_sid) < 0) {
212	bb_perror_msg_and_die("getfilecon(%s) failed", full_tty);
213	}
214	if (security_compute_relabel(*user_sid, old_tty_sid,
215	SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
216	bb_perror_msg_and_die("security_change_sid(%s) failed", full_tty);
217	}
218	if (setfilecon(full_tty, new_tty_sid) != 0) {
219	if (strcmp(old_tty_sid, new_tty_sid))
220	bb_perror_msg_and_die("chsid(%s, %s) failed", full_tty, new_tty_sid);
221	}
222	}
223	#endif
224
225	#if ENABLE_LOGIN_SCRIPTS
226	static void run_login_script(struct passwd *pw, char *full_tty)
227	{
228	char *t_argv[2];
229
230	t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
231	if (t_argv[0]) {
232	t_argv[1] = NULL;
233	xsetenv("LOGIN_TTY", full_tty);
234	xsetenv("LOGIN_USER", pw->pw_name);
235	xsetenv("LOGIN_UID", utoa(pw->pw_uid));
236	xsetenv("LOGIN_GID", utoa(pw->pw_gid));
237	xsetenv("LOGIN_SHELL", pw->pw_shell);
238	spawn_and_wait(t_argv); /* NOMMU-friendly */
239	unsetenv("LOGIN_TTY");
240	unsetenv("LOGIN_USER");
241	unsetenv("LOGIN_UID");
242	unsetenv("LOGIN_GID");
243	unsetenv("LOGIN_SHELL");
244	}
245	}
246	#else
247	void run_login_script(struct passwd *pw, char *full_tty);
248	#endif
249
250	#if ENABLE_LOGIN_SESSION_AS_CHILD && ENABLE_PAM
251	static void login_pam_end(pam_handle_t *pamh)
252	{
253	int pamret;
254
255	pamret = pam_setcred(pamh, PAM_DELETE_CRED);
256	if (pamret != PAM_SUCCESS) {
257	bb_error_msg("pam_%s failed: %s (%d)", "setcred",
258	pam_strerror(pamh, pamret), pamret);
259	}
260	pamret = pam_close_session(pamh, 0);
261	if (pamret != PAM_SUCCESS) {
262	bb_error_msg("pam_%s failed: %s (%d)", "close_session",
263	pam_strerror(pamh, pamret), pamret);
264	}
265	pamret = pam_end(pamh, pamret);
266	if (pamret != PAM_SUCCESS) {
267	bb_error_msg("pam_%s failed: %s (%d)", "end",
268	pam_strerror(pamh, pamret), pamret);
269	}
270	}
271	#endif /* ENABLE_PAM */
272
273	static void get_username_or_die(char *buf, int size_buf)
274	{
275	int c, cntdown;
276
277	cntdown = EMPTY_USERNAME_COUNT;
278	prompt:
279	print_login_prompt();
280	/* skip whitespace */
281	do {
282	c = getchar();
283	if (c == EOF)
284	exit(EXIT_FAILURE);
285	if (c == '\n') {
286	if (!--cntdown)
287	exit(EXIT_FAILURE);
288	goto prompt;
289	}
290	} while (isspace(c)); /* maybe isblank? */
291
292	*buf++ = c;
293	if (!fgets(buf, size_buf-2, stdin))
294	exit(EXIT_FAILURE);
295	if (!strchr(buf, '\n'))
296	exit(EXIT_FAILURE);
297	while ((unsigned char)*buf > ' ')
298	buf++;
299	*buf = '\0';
300	}
301
302	static void motd(void)
303	{
304	int fd;
305
306	fd = open(bb_path_motd_file, O_RDONLY);
307	if (fd >= 0) {
308	fflush_all();
309	bb_copyfd_eof(fd, STDOUT_FILENO);
310	close(fd);
311	}
312	}
313
314	static void alarm_handler(int sig UNUSED_PARAM)
315	{
316	/* This is the escape hatch! Poor serial line users and the like
317	* arrive here when their connection is broken.
318	* We don't want to block here */
319	ndelay_on(STDOUT_FILENO);
320	/* Test for correct attr restoring:
321	* run "getty 0 -" from a shell, enter bogus username, stop at
322	* password prompt, let it time out. Without the tcsetattr below,
323	* when you are back at shell prompt, echo will be still off.
324	*/
325	tcsetattr_stdin_TCSANOW(&G.tty_attrs);
326	printf("\r\nLogin timed out after %u seconds\r\n", TIMEOUT);
327	fflush_all();
328	/* unix API is brain damaged regarding O_NONBLOCK,
329	* we should undo it, or else we can affect other processes */
330	ndelay_off(STDOUT_FILENO);
331	_exit(EXIT_SUCCESS);
332	}
333
334	int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
335	int login_main(int argc UNUSED_PARAM, char **argv)
336	{
337	enum {
338	LOGIN_OPT_f = (1<<0),
339	LOGIN_OPT_h = (1<<1),
340	LOGIN_OPT_p = (1<<2),
341	};
342	char *fromhost;
343	char username[USERNAME_SIZE];
344	int run_by_root;
345	unsigned opt;
346	int count = 0;
347	struct passwd *pw;
348	char *opt_host = NULL;
349	char *opt_user = opt_user; /* for compiler */
350	char *full_tty;
351	char *short_tty;
352	IF_SELINUX(security_context_t user_sid = NULL;)
353	#if ENABLE_PAM
354	int pamret;
355	pam_handle_t *pamh;
356	const char *pamuser;
357	const char *failed_msg;
358	struct passwd pwdstruct;
359	char pwdbuf[256];
360	char **pamenv;
361	#endif
362	#if ENABLE_LOGIN_SESSION_AS_CHILD
363	pid_t child_pid;
364	#endif
365
366	INIT_G();
367
368	/* More of suid paranoia if called by non-root: */
369	/* Clear dangerous stuff, set PATH */
370	run_by_root = !sanitize_env_if_suid();
371
372	/* Mandatory paranoia for suid applet:
373	* ensure that fd# 0,1,2 are opened (at least to /dev/null)
374	* and any extra open fd's are closed.
375	* (The name of the function is misleading. Not daemonizing here.) */
376	bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
377
378	username[0] = '\0';
379	opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
380	if (opt & LOGIN_OPT_f) {
381	if (!run_by_root)
382	bb_error_msg_and_die("-f is for root only");
383	safe_strncpy(username, opt_user, sizeof(username));
384	}
385	argv += optind;
386	if (argv[0]) /* user from command line (getty) */
387	safe_strncpy(username, argv[0], sizeof(username));
388
389	/* Save tty attributes - and by doing it, check that it's indeed a tty */
390	if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0
391	|| !isatty(STDOUT_FILENO)
392	/*|| !isatty(STDERR_FILENO) - no, guess some people might want to redirect this */
393	) {
394	return EXIT_FAILURE; /* Must be a terminal */
395	}
396
397	/* We install timeout handler only _after_ we saved G.tty_attrs */
398	signal(SIGALRM, alarm_handler);
399	alarm(TIMEOUT);
400
401	/* Find out and memorize our tty name */
402	full_tty = xmalloc_ttyname(STDIN_FILENO);
403	if (!full_tty)
404	full_tty = xstrdup("UNKNOWN");
405	short_tty = skip_dev_pfx(full_tty);
406
407	if (opt_host) {
408	fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
409	} else {
410	fromhost = xasprintf(" on '%s'", short_tty);
411	}
412
413	/* Was breaking "login <username>" from shell command line: */
414	/*bb_setpgrp();*/
415
416	openlog(applet_name, LOG_PID | LOG_CONS, LOG_AUTH);
417
418	while (1) {
419	/* flush away any type-ahead (as getty does) */
420	tcflush(0, TCIFLUSH);
421
422	if (!username[0])
423	get_username_or_die(username, sizeof(username));
424
425	#if ENABLE_PAM
426	pamret = pam_start("login", username, &conv, &pamh);
427	if (pamret != PAM_SUCCESS) {
428	failed_msg = "start";
429	goto pam_auth_failed;
430	}
431	/* set TTY (so things like securetty work) */
432	pamret = pam_set_item(pamh, PAM_TTY, short_tty);
433	if (pamret != PAM_SUCCESS) {
434	failed_msg = "set_item(TTY)";
435	goto pam_auth_failed;
436	}
437	/* set RHOST */
438	if (opt_host) {
439	pamret = pam_set_item(pamh, PAM_RHOST, opt_host);
440	if (pamret != PAM_SUCCESS) {
441	failed_msg = "set_item(RHOST)";
442	goto pam_auth_failed;
443	}
444	}
445	if (!(opt & LOGIN_OPT_f)) {
446	pamret = pam_authenticate(pamh, 0);
447	if (pamret != PAM_SUCCESS) {
448	failed_msg = "authenticate";
449	goto pam_auth_failed;
450	/* TODO: or just "goto auth_failed"
451	* since user seems to enter wrong password
452	* (in this case pamret == 7)
453	*/
454	}
455	}
456	/* check that the account is healthy */
457	pamret = pam_acct_mgmt(pamh, 0);
458	if (pamret != PAM_SUCCESS) {
459	failed_msg = "acct_mgmt";
460	goto pam_auth_failed;
461	}
462	/* read user back */
463	pamuser = NULL;
464	/* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
465	* thus we cast to (void*) */
466	if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
467	failed_msg = "get_item(USER)";
468	goto pam_auth_failed;
469	}
470	if (!pamuser || !pamuser[0])
471	goto auth_failed;
472	safe_strncpy(username, pamuser, sizeof(username));
473	/* Don't use "pw = getpwnam(username);",
474	* PAM is said to be capable of destroying static storage
475	* used by getpwnam(). We are using safe(r) function */
476	pw = NULL;
477	getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
478	if (!pw)
479	goto auth_failed;
480	pamret = pam_open_session(pamh, 0);
481	if (pamret != PAM_SUCCESS) {
482	failed_msg = "open_session";
483	goto pam_auth_failed;
484	}
485	pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
486	if (pamret != PAM_SUCCESS) {
487	failed_msg = "setcred";
488	goto pam_auth_failed;
489	}
490	break; /* success, continue login process */
491
492	pam_auth_failed:
493	/* syslog, because we don't want potential attacker
494	* to know _why_ login failed */
495	syslog(LOG_WARNING, "pam_%s call failed: %s (%d)", failed_msg,
496	pam_strerror(pamh, pamret), pamret);
497	safe_strncpy(username, "UNKNOWN", sizeof(username));
498	#else /* not PAM */
499	pw = safegetpwnam(username);
500	if (!pw) {
501	strcpy(username, "UNKNOWN");
502	goto fake_it;
503	}
504
505	if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
506	goto auth_failed;
507
508	if (opt & LOGIN_OPT_f)
509	break; /* -f USER: success without asking passwd */
510
511	if (pw->pw_uid == 0 && !check_securetty(short_tty))
512	goto auth_failed;
513
514	/* Don't check the password if password entry is empty (!) */
515	if (!pw->pw_passwd[0])
516	break;
517	fake_it:
518	/* Password reading and authorization takes place here.
519	* Note that reads (in no-echo mode) trash tty attributes.
520	* If we get interrupted by SIGALRM, we need to restore attrs.
521	*/
522	if (ask_and_check_password(pw) > 0)
523	break;
524	#endif /* ENABLE_PAM */
525	auth_failed:
526	opt &= ~LOGIN_OPT_f;
527	bb_do_delay(LOGIN_FAIL_DELAY);
528	/* TODO: doesn't sound like correct English phrase to me */
529	puts("Login incorrect");
530	if (++count == 3) {
531	syslog(LOG_WARNING, "invalid password for '%s'%s",
532	username, fromhost);
533
534	if (ENABLE_FEATURE_CLEAN_UP)
535	free(fromhost);
536
537	return EXIT_FAILURE;
538	}
539	username[0] = '\0';
540	} /* while (1) */
541
542	alarm(0);
543	/* We can ignore /etc/nologin if we are logging in as root,
544	* it doesn't matter whether we are run by root or not */
545	if (pw->pw_uid != 0)
546	die_if_nologin();
547
548	#if ENABLE_LOGIN_SESSION_AS_CHILD
549	child_pid = vfork();
550	if (child_pid != 0) {
551	if (child_pid < 0)
552	bb_perror_msg("vfork");
553	else {
554	if (safe_waitpid(child_pid, NULL, 0) == -1)
555	bb_perror_msg("waitpid");
556	update_utmp_DEAD_PROCESS(child_pid);
557	}
558	IF_PAM(login_pam_end(pamh);)
559	return 0;
560	}
561	#endif
562
563	IF_SELINUX(initselinux(username, full_tty, &user_sid);)
564
565	/* Try these, but don't complain if they fail.
566	* _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
567	fchown(0, pw->pw_uid, pw->pw_gid);
568	fchmod(0, 0600);
569
570	update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
571
572	/* We trust environment only if we run by root */
573	if (ENABLE_LOGIN_SCRIPTS && run_by_root)
574	run_login_script(pw, full_tty);
575
576	change_identity(pw);
577	setup_environment(pw->pw_shell,
578	(!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV) + SETUP_ENV_CHANGEENV,
579	pw);
580
581	#if ENABLE_PAM
582	/* Modules such as pam_env will setup the PAM environment,
583	* which should be copied into the new environment. */
584	pamenv = pam_getenvlist(pamh);
585	if (pamenv) while (*pamenv) {
586	putenv(*pamenv);
587	pamenv++;
588	}
589	#endif
590
591	if (access(".hushlogin", F_OK) != 0)
592	motd();
593
594	if (pw->pw_uid == 0)
595	syslog(LOG_INFO, "root login%s", fromhost);
596
597	if (ENABLE_FEATURE_CLEAN_UP)
598	free(fromhost);
599
600	/* well, a simple setexeccon() here would do the job as well,
601	* but let's play the game for now */
602	IF_SELINUX(set_current_security_context(user_sid);)
603
604	// util-linux login also does:
605	// /* start new session */
606	// setsid();
607	// /* TIOCSCTTY: steal tty from other process group */
608	// if (ioctl(0, TIOCSCTTY, 1)) error_msg...
609	// BBox login used to do this (see above):
610	// bb_setpgrp();
611	// If this stuff is really needed, add it and explain why!
612
613	/* Set signals to defaults */
614	/* Non-ignored signals revert to SIG_DFL on exec anyway */
615	/*signal(SIGALRM, SIG_DFL);*/
616
617	/* Is this correct? This way user can ctrl-c out of /etc/profile,
618	* potentially creating security breach (tested with bash 3.0).
619	* But without this, bash 3.0 will not enable ctrl-c either.
620	* Maybe bash is buggy?
621	* Need to find out what standards say about /bin/login -
622	* should we leave SIGINT etc enabled or disabled? */
623	signal(SIGINT, SIG_DFL);
624
625	/* Exec login shell with no additional parameters */
626	run_shell(pw->pw_shell, 1, NULL);
627
628	/* return EXIT_FAILURE; - not reached */
629	}
630