source: branches/2.2.9/mindi-busybox/loginutils/login.c

Last change on this file was 3320, checked in by bruno, 5 years ago
  • Re-add (thanks git BTW) the 2.2.9 branch which had been destroyed in the move to 3.0
  • Property svn:eol-style set to native
File size: 11.4 KB
Line 
1/* vi: set sw=4 ts=4: */
2/*
3 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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        tcflush(0, 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
368            if (ENABLE_FEATURE_CLEAN_UP)
369                free(fromhost);
370
371            return EXIT_FAILURE;
372        }
373        username[0] = '\0';
374    } /* while (1) */
375
376    alarm(0);
377    /* We can ignore /etc/nologin if we are logging in as root,
378     * it doesn't matter whether we are run by root or not */
379    if (pw->pw_uid != 0)
380        die_if_nologin();
381
382    IF_SELINUX(initselinux(username, full_tty, &user_sid));
383
384    /* Try these, but don't complain if they fail.
385     * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
386    fchown(0, pw->pw_uid, pw->pw_gid);
387    fchmod(0, 0600);
388
389    update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
390
391    /* We trust environment only if we run by root */
392    if (ENABLE_LOGIN_SCRIPTS && run_by_root)
393        run_login_script(pw, full_tty);
394
395    change_identity(pw);
396    shell = pw->pw_shell;
397    if (!shell || !shell[0])
398        shell = DEFAULT_SHELL;
399    setup_environment(shell,
400            (!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV) + SETUP_ENV_CHANGEENV,
401            pw);
402
403    motd();
404
405    if (pw->pw_uid == 0)
406        syslog(LOG_INFO, "root login%s", fromhost);
407
408    if (ENABLE_FEATURE_CLEAN_UP)
409        free(fromhost);
410
411    /* well, a simple setexeccon() here would do the job as well,
412     * but let's play the game for now */
413    IF_SELINUX(set_current_security_context(user_sid);)
414
415    // util-linux login also does:
416    // /* start new session */
417    // setsid();
418    // /* TIOCSCTTY: steal tty from other process group */
419    // if (ioctl(0, TIOCSCTTY, 1)) error_msg...
420    // BBox login used to do this (see above):
421    // bb_setpgrp();
422    // If this stuff is really needed, add it and explain why!
423
424    /* Set signals to defaults */
425    /* Non-ignored signals revert to SIG_DFL on exec anyway */
426    /*signal(SIGALRM, SIG_DFL);*/
427
428    /* Is this correct? This way user can ctrl-c out of /etc/profile,
429     * potentially creating security breach (tested with bash 3.0).
430     * But without this, bash 3.0 will not enable ctrl-c either.
431     * Maybe bash is buggy?
432     * Need to find out what standards say about /bin/login -
433     * should we leave SIGINT etc enabled or disabled? */
434    signal(SIGINT, SIG_DFL);
435
436    /* Exec login shell with no additional parameters */
437    run_shell(shell, 1, NULL, NULL);
438
439    /* return EXIT_FAILURE; - not reached */
440}
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