1/* vi: set sw=4 ts=4: */
2/*
3 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
4 */
5#include "libbb.h"
6#include <syslog.h>
7#if ENABLE_FEATURE_UTMP
8# include <utmp.h> /* USER_PROCESS */
9#endif
10#include <sys/resource.h>
11
12#if ENABLE_SELINUX
13# include <selinux/selinux.h>  /* for is_selinux_enabled()  */
14# include <selinux/get_context_list.h> /* for get_default_context() */
15# include <selinux/flask.h> /* for security class definitions  */
16#endif
17
18#if ENABLE_PAM
19/* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
20# undef setlocale
21/* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
22 * Apparently they like to confuse people. */
23# include <security/pam_appl.h>
24# include <security/pam_misc.h>
25static const struct pam_conv conv = {
26	misc_conv,
27	NULL
28};
29#endif
30
31enum {
32	TIMEOUT = 60,
33	EMPTY_USERNAME_COUNT = 10,
34	USERNAME_SIZE = 32,
35	TTYNAME_SIZE = 32,
36};
37
38static char* short_tty;
39
40#if ENABLE_FEATURE_NOLOGIN
41static void die_if_nologin(void)
42{
43	FILE *fp;
44	int c;
45	int empty = 1;
46
47	fp = fopen_for_read("/etc/nologin");
48	if (!fp) /* assuming it does not exist */
49		return;
50
51	while ((c = getc(fp)) != EOF) {
52		if (c == '\n')
53			bb_putchar('\r');
54		bb_putchar(c);
55		empty = 0;
56	}
57	if (empty)
58		puts("\r\nSystem closed for routine maintenance\r");
59
60	fclose(fp);
61	fflush_all();
62	/* Users say that they do need this prior to exit: */
63	tcdrain(STDOUT_FILENO);
64	exit(EXIT_FAILURE);
65}
66#else
67# define die_if_nologin() ((void)0)
68#endif
69
70#if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
71static int check_securetty(void)
72{
73	char *buf = (char*)"/etc/securetty"; /* any non-NULL is ok */
74	parser_t *parser = config_open2("/etc/securetty", fopen_for_read);
75	while (config_read(parser, &buf, 1, 1, "# \t", PARSE_NORMAL)) {
76		if (strcmp(buf, short_tty) == 0)
77			break;
78		buf = NULL;
79	}
80	config_close(parser);
81	/* buf != NULL here if config file was not found, empty
82	 * or line was found which equals short_tty */
83	return buf != NULL;
84}
85#else
86static ALWAYS_INLINE int check_securetty(void) { return 1; }
87#endif
88
89#if ENABLE_SELINUX
90static void initselinux(char *username, char *full_tty,
91						security_context_t *user_sid)
92{
93	security_context_t old_tty_sid, new_tty_sid;
94
95	if (!is_selinux_enabled())
96		return;
97
98	if (get_default_context(username, NULL, user_sid)) {
99		bb_error_msg_and_die("can't get SID for %s", username);
100	}
101	if (getfilecon(full_tty, &old_tty_sid) < 0) {
102		bb_perror_msg_and_die("getfilecon(%s) failed", full_tty);
103	}
104	if (security_compute_relabel(*user_sid, old_tty_sid,
105				SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
106		bb_perror_msg_and_die("security_change_sid(%s) failed", full_tty);
107	}
108	if (setfilecon(full_tty, new_tty_sid) != 0) {
109		bb_perror_msg_and_die("chsid(%s, %s) failed", full_tty, new_tty_sid);
110	}
111}
112#endif
113
114#if ENABLE_LOGIN_SCRIPTS
115static void run_login_script(struct passwd *pw, char *full_tty)
116{
117	char *t_argv[2];
118
119	t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
120	if (t_argv[0]) {
121		t_argv[1] = NULL;
122		xsetenv("LOGIN_TTY", full_tty);
123		xsetenv("LOGIN_USER", pw->pw_name);
124		xsetenv("LOGIN_UID", utoa(pw->pw_uid));
125		xsetenv("LOGIN_GID", utoa(pw->pw_gid));
126		xsetenv("LOGIN_SHELL", pw->pw_shell);
127		spawn_and_wait(t_argv);	/* NOMMU-friendly */
128		unsetenv("LOGIN_TTY");
129		unsetenv("LOGIN_USER");
130		unsetenv("LOGIN_UID");
131		unsetenv("LOGIN_GID");
132		unsetenv("LOGIN_SHELL");
133	}
134}
135#else
136void run_login_script(struct passwd *pw, char *full_tty);
137#endif
138
139static void get_username_or_die(char *buf, int size_buf)
140{
141	int c, cntdown;
142
143	cntdown = EMPTY_USERNAME_COUNT;
144 prompt:
145	print_login_prompt();
146	/* skip whitespace */
147	do {
148		c = getchar();
149		if (c == EOF)
150			exit(EXIT_FAILURE);
151		if (c == '\n') {
152			if (!--cntdown)
153				exit(EXIT_FAILURE);
154			goto prompt;
155		}
156	} while (isspace(c)); /* maybe isblank? */
157
158	*buf++ = c;
159	if (!fgets(buf, size_buf-2, stdin))
160		exit(EXIT_FAILURE);
161	if (!strchr(buf, '\n'))
162		exit(EXIT_FAILURE);
163	while ((unsigned char)*buf > ' ')
164		buf++;
165	*buf = '\0';
166}
167
168static void motd(void)
169{
170	int fd;
171
172	fd = open(bb_path_motd_file, O_RDONLY);
173	if (fd >= 0) {
174		fflush_all();
175		bb_copyfd_eof(fd, STDOUT_FILENO);
176		close(fd);
177	}
178}
179
180static void alarm_handler(int sig UNUSED_PARAM)
181{
182	/* This is the escape hatch!  Poor serial line users and the like
183	 * arrive here when their connection is broken.
184	 * We don't want to block here */
185	ndelay_on(1);
186	printf("\r\nLogin timed out after %d seconds\r\n", TIMEOUT);
187	fflush_all();
188	/* unix API is brain damaged regarding O_NONBLOCK,
189	 * we should undo it, or else we can affect other processes */
190	ndelay_off(1);
191	_exit(EXIT_SUCCESS);
192}
193
194int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
195int login_main(int argc UNUSED_PARAM, char **argv)
196{
197	enum {
198		LOGIN_OPT_f = (1<<0),
199		LOGIN_OPT_h = (1<<1),
200		LOGIN_OPT_p = (1<<2),
201	};
202	char *fromhost;
203	char username[USERNAME_SIZE];
204	const char *shell;
205	int run_by_root;
206	unsigned opt;
207	int count = 0;
208	struct passwd *pw;
209	char *opt_host = NULL;
210	char *opt_user = opt_user; /* for compiler */
211	char *full_tty;
212	IF_SELINUX(security_context_t user_sid = NULL;)
213#if ENABLE_PAM
214	int pamret;
215	pam_handle_t *pamh;
216	const char *pamuser;
217	const char *failed_msg;
218	struct passwd pwdstruct;
219	char pwdbuf[256];
220#endif
221
222	username[0] = '\0';
223	signal(SIGALRM, alarm_handler);
224	alarm(TIMEOUT);
225
226	/* More of suid paranoia if called by non-root: */
227	/* Clear dangerous stuff, set PATH */
228	run_by_root = !sanitize_env_if_suid();
229
230	/* Mandatory paranoia for suid applet:
231	 * ensure that fd# 0,1,2 are opened (at least to /dev/null)
232	 * and any extra open fd's are closed.
233	 * (The name of the function is misleading. Not daemonizing here.) */
234	bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
235
236	opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
237	if (opt & LOGIN_OPT_f) {
238		if (!run_by_root)
239			bb_error_msg_and_die("-f is for root only");
240		safe_strncpy(username, opt_user, sizeof(username));
241	}
242	argv += optind;
243	if (argv[0]) /* user from command line (getty) */
244		safe_strncpy(username, argv[0], sizeof(username));
245
246	/* Let's find out and memorize our tty */
247	if (!isatty(STDIN_FILENO) || !isatty(STDOUT_FILENO) || !isatty(STDERR_FILENO))
248		return EXIT_FAILURE;		/* Must be a terminal */
249	full_tty = xmalloc_ttyname(STDIN_FILENO);
250	if (!full_tty)
251		full_tty = xstrdup("UNKNOWN");
252	short_tty = skip_dev_pfx(full_tty);
253
254	if (opt_host) {
255		fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
256	} else {
257		fromhost = xasprintf(" on '%s'", short_tty);
258	}
259
260	/* Was breaking "login <username>" from shell command line: */
261	/*bb_setpgrp();*/
262
263	openlog(applet_name, LOG_PID | LOG_CONS, LOG_AUTH);
264
265	while (1) {
266		/* flush away any type-ahead (as getty does) */
267		ioctl(0, TCFLSH, TCIFLUSH);
268
269		if (!username[0])
270			get_username_or_die(username, sizeof(username));
271
272#if ENABLE_PAM
273		pamret = pam_start("login", username, &conv, &pamh);
274		if (pamret != PAM_SUCCESS) {
275			failed_msg = "start";
276			goto pam_auth_failed;
277		}
278		/* set TTY (so things like securetty work) */
279		pamret = pam_set_item(pamh, PAM_TTY, short_tty);
280		if (pamret != PAM_SUCCESS) {
281			failed_msg = "set_item(TTY)";
282			goto pam_auth_failed;
283		}
284		pamret = pam_authenticate(pamh, 0);
285		if (pamret != PAM_SUCCESS) {
286			failed_msg = "authenticate";
287			goto pam_auth_failed;
288			/* TODO: or just "goto auth_failed"
289			 * since user seems to enter wrong password
290			 * (in this case pamret == 7)
291			 */
292		}
293		/* check that the account is healthy */
294		pamret = pam_acct_mgmt(pamh, 0);
295		if (pamret != PAM_SUCCESS) {
296			failed_msg = "acct_mgmt";
297			goto pam_auth_failed;
298		}
299		/* read user back */
300		pamuser = NULL;
301		/* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
302		 * thus we cast to (void*) */
303		if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
304			failed_msg = "get_item(USER)";
305			goto pam_auth_failed;
306		}
307		if (!pamuser || !pamuser[0])
308			goto auth_failed;
309		safe_strncpy(username, pamuser, sizeof(username));
310		/* Don't use "pw = getpwnam(username);",
311		 * PAM is said to be capable of destroying static storage
312		 * used by getpwnam(). We are using safe(r) function */
313		pw = NULL;
314		getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
315		if (!pw)
316			goto auth_failed;
317		pamret = pam_open_session(pamh, 0);
318		if (pamret != PAM_SUCCESS) {
319			failed_msg = "open_session";
320			goto pam_auth_failed;
321		}
322		pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
323		if (pamret != PAM_SUCCESS) {
324			failed_msg = "setcred";
325			goto pam_auth_failed;
326		}
327		break; /* success, continue login process */
328
329 pam_auth_failed:
330		/* syslog, because we don't want potential attacker
331		 * to know _why_ login failed */
332		syslog(LOG_WARNING, "pam_%s call failed: %s (%d)", failed_msg,
333					pam_strerror(pamh, pamret), pamret);
334		safe_strncpy(username, "UNKNOWN", sizeof(username));
335#else /* not PAM */
336		pw = getpwnam(username);
337		if (!pw) {
338			strcpy(username, "UNKNOWN");
339			goto fake_it;
340		}
341
342		if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
343			goto auth_failed;
344
345		if (opt & LOGIN_OPT_f)
346			break; /* -f USER: success without asking passwd */
347
348		if (pw->pw_uid == 0 && !check_securetty())
349			goto auth_failed;
350
351		/* Don't check the password if password entry is empty (!) */
352		if (!pw->pw_passwd[0])
353			break;
354 fake_it:
355		/* authorization takes place here */
356		if (correct_password(pw))
357			break;
358#endif /* ENABLE_PAM */
359 auth_failed:
360		opt &= ~LOGIN_OPT_f;
361		bb_do_delay(FAIL_DELAY);
362		/* TODO: doesn't sound like correct English phrase to me */
363		puts("Login incorrect");
364		if (++count == 3) {
365			syslog(LOG_WARNING, "invalid password for '%s'%s",
366						username, fromhost);
367			return EXIT_FAILURE;
368		}
369		username[0] = '\0';
370	} /* while (1) */
371
372	alarm(0);
373	/* We can ignore /etc/nologin if we are logging in as root,
374	 * it doesn't matter whether we are run by root or not */
375	if (pw->pw_uid != 0)
376		die_if_nologin();
377
378	IF_SELINUX(initselinux(username, full_tty, &user_sid));
379
380	/* Try these, but don't complain if they fail.
381	 * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
382	fchown(0, pw->pw_uid, pw->pw_gid);
383	fchmod(0, 0600);
384
385	update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
386
387	/* We trust environment only if we run by root */
388	if (ENABLE_LOGIN_SCRIPTS && run_by_root)
389		run_login_script(pw, full_tty);
390
391	change_identity(pw);
392	shell = pw->pw_shell;
393	if (!shell || !shell[0])
394		shell = DEFAULT_SHELL;
395	setup_environment(shell,
396			(!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV) + SETUP_ENV_CHANGEENV,
397			pw);
398
399	motd();
400
401	if (pw->pw_uid == 0)
402		syslog(LOG_INFO, "root login%s", fromhost);
403
404	/* well, a simple setexeccon() here would do the job as well,
405	 * but let's play the game for now */
406	IF_SELINUX(set_current_security_context(user_sid);)
407
408	// util-linux login also does:
409	// /* start new session */
410	// setsid();
411	// /* TIOCSCTTY: steal tty from other process group */
412	// if (ioctl(0, TIOCSCTTY, 1)) error_msg...
413	// BBox login used to do this (see above):
414	// bb_setpgrp();
415	// If this stuff is really needed, add it and explain why!
416
417	/* Set signals to defaults */
418	/* Non-ignored signals revert to SIG_DFL on exec anyway */
419	/*signal(SIGALRM, SIG_DFL);*/
420
421	/* Is this correct? This way user can ctrl-c out of /etc/profile,
422	 * potentially creating security breach (tested with bash 3.0).
423	 * But without this, bash 3.0 will not enable ctrl-c either.
424	 * Maybe bash is buggy?
425	 * Need to find out what standards say about /bin/login -
426	 * should we leave SIGINT etc enabled or disabled? */
427	signal(SIGINT, SIG_DFL);
428
429	/* Exec login shell with no additional parameters */
430	run_shell(shell, 1, NULL, NULL);
431
432	/* return EXIT_FAILURE; - not reached */
433}
434