1 /* passwd-pam.c --- verifying typed passwords with PAM
2 * (Pluggable Authentication Modules.)
3 * written by Bill Nottingham <notting@redhat.com> (and jwz) for
4 * xscreensaver, Copyright (c) 1993-2003 Jamie Zawinski <jwz@jwz.org>
6 * Permission to use, copy, modify, distribute, and sell this software and its
7 * documentation for any purpose is hereby granted without fee, provided that
8 * the above copyright notice appear in all copies and that both that
9 * copyright notice and this permission notice appear in supporting
10 * documentation. No representations are made about the suitability of this
11 * software for any purpose. It is provided "as is" without express or
17 * http://www.us.kernel.org/pub/linux/libs/pam/
20 * http://www.us.kernel.org/pub/linux/libs/pam/FAQ
22 * PAM Application Developers' Guide:
23 * http://www.us.kernel.org/pub/linux/libs/pam/Linux-PAM-html/Linux-PAM_ADG.html
25 * PAM Mailing list archives:
26 * http://www.linuxhq.com/lnxlists/linux-pam/
28 * Compatibility notes, especially between Linux and Solaris:
29 * http://www.contrib.andrew.cmu.edu/u/shadow/pam.html
31 * The Open Group's PAM API documentation:
32 * http://www.opengroup.org/onlinepubs/8329799/pam_start.htm
39 #ifndef NO_LOCKING /* whole file */
46 extern char *blurb(void);
51 #include <sys/types.h>
54 #include <security/pam_appl.h>
57 #include <X11/Intrinsic.h>
63 extern sigset_t block_sigchld (void);
64 extern void unblock_sigchld (void);
75 #define countof(x) (sizeof((x))/sizeof(*(x)))
77 /* Some time between Red Hat 4.2 and 7.0, the words were transposed
78 in the various PAM_x_CRED macro names. Yay!
80 #ifndef PAM_REFRESH_CRED
81 # define PAM_REFRESH_CRED PAM_CRED_REFRESH
84 static int pam_conversation (int nmsgs,
85 const struct pam_message **msg,
86 struct pam_response **resp,
89 void pam_try_unlock(saver_info *si, Bool verbose_p,
90 Bool (*valid_p)(const char *typed_passwd, Bool verbose_p));
92 Bool pam_priv_init (int argc, char **argv, Bool verbose_p);
94 #ifdef HAVE_PAM_FAIL_DELAY
95 /* We handle delays ourself.*/
96 /* Don't set this to 0 (Linux bug workaround.) */
97 # define PAM_NO_DELAY(pamh) pam_fail_delay ((pamh), 1)
98 #else /* !HAVE_PAM_FAIL_DELAY */
99 # define PAM_NO_DELAY(pamh) /* */
100 #endif /* !HAVE_PAM_FAIL_DELAY */
103 /* On SunOS 5.6, and on Linux with PAM 0.64, pam_strerror() takes two args.
104 On some other Linux systems with some other version of PAM (e.g.,
105 whichever Debian release comes with a 2.2.5 kernel) it takes one arg.
106 I can't tell which is more "recent" or "correct" behavior, so configure
107 figures out which is in use for us. Shoot me!
109 #ifdef PAM_STRERROR_TWO_ARGS
110 # define PAM_STRERROR(pamh, status) pam_strerror((pamh), (status))
111 #else /* !PAM_STRERROR_TWO_ARGS */
112 # define PAM_STRERROR(pamh, status) pam_strerror((status))
113 #endif /* !PAM_STRERROR_TWO_ARGS */
116 /* PAM sucks in that there is no way to tell whether a particular service
117 is configured at all. That is, there is no way to tell the difference
118 between "authentication of the FOO service is not allowed" and "the
119 user typed the wrong password."
121 On RedHat 5.1 systems, if a service name is not known, it defaults to
122 being not allowed (because the fallback service, /etc/pam.d/other, is
125 On Solaris 2.6 systems, unknown services default to authenticating normally.
127 So, we could simply require that the person who installs xscreensaver
128 set up an "xscreensaver" PAM service. However, if we went that route,
129 it would have a really awful failure mode: the failure mode would be that
130 xscreensaver was willing to *lock* the screen, but would be unwilling to
131 *unlock* the screen. (With the non-PAM password code, the analagous
132 situation -- security not being configured properly, for example do to the
133 executable not being installed as setuid root -- the failure mode is much
134 more palettable, in that xscreensaver will refuse to *lock* the screen,
135 because it can know up front that there is no password that will work.)
137 Another route would be to have the service name to consult be computed at
138 compile-time (perhaps with a configure option.) However, that doesn't
139 really solve the problem, because it means that the same executable might
140 work fine on one machine, but refuse to unlock when run on another
143 Another alternative would be to look in /etc/pam.conf or /etc/pam.d/ at
144 runtime to see what services actually exist. But I think that's no good,
145 because who is to say that the PAM info is actually specified in those
146 files? Opening and reading those files is not a part of the PAM client
147 API, so it's not guarenteed to work on any given system.
149 An alternative I tried was to specify a list of services to try, and to
150 try them all in turn ("xscreensaver", "xlock", "xdm", and "login").
151 This worked, but it was slow (and I also had to do some contortions to
152 work around bugs in Linux PAM 0.64-3.)
154 So what we do today is, try PAM once, and if that fails, try the usual
155 getpwent() method. So if PAM doesn't work, it will at least make an
156 attempt at looking up passwords in /etc/passwd or /etc/shadow instead.
158 This all kind of blows. I'm not sure what else to do.
162 /* On SunOS 5.6, the `pam_conv.appdata_ptr' slot seems to be ignored, and
163 the `closure' argument to pc.conv always comes in as random garbage.
164 So we get around this by using a global variable instead. Shoot me!
166 (I've been told this is bug 4092227, and is fixed in Solaris 7.)
167 (I've also been told that it's fixed in Solaris 2.6 by patch 106257-05.)
169 static void *suns_pam_implementation_blows = 0;
173 * This function is the PAM conversation driver. It conducts a full
174 * authentication round by invoking the GUI with various prompts.
177 pam_try_unlock(saver_info *si, Bool verbose_p,
178 Bool (*valid_p)(const char *typed_passwd, Bool verbose_p))
180 const char *service = PAM_SERVICE_NAME;
181 pam_handle_t *pamh = 0;
185 struct timespec timeout;
187 pc.conv = &pam_conversation;
188 pc.appdata_ptr = (void *) si;
190 /* On SunOS 5.6, the `appdata_ptr' slot seems to be ignored, and the
191 `closure' argument to pc.conv always comes in as random garbage. */
192 suns_pam_implementation_blows = (void *) si;
197 status = pam_start (service, si->user, &pc, &pamh);
199 fprintf (stderr, "%s: pam_start (\"%s\", \"%s\", ...) ==> %d (%s)\n",
200 blurb(), service, si->user,
201 status, PAM_STRERROR (pamh, status));
202 if (status != PAM_SUCCESS) goto DONE;
204 /* #### We should set PAM_TTY to the display we're using, but we
205 don't have that handy from here. So set it to :0.0, which is a
206 good guess (and has the bonus of counting as a "secure tty" as
207 far as PAM is concerned...)
210 char *tty = strdup (":0.0");
211 status = pam_set_item (pamh, PAM_TTY, tty);
213 fprintf (stderr, "%s: pam_set_item (p, PAM_TTY, \"%s\") ==> %d (%s)\n",
214 blurb(), tty, status, PAM_STRERROR(pamh, status));
218 /* Try to authenticate as the current user.
219 We must turn off our SIGCHLD handler for the duration of the call to
220 pam_authenticate(), because in some cases, the underlying PAM code
223 1: fork a setuid subprocess to do some dirty work;
224 2: read a response from that subprocess;
225 3: waitpid(pid, ...) on that subprocess.
227 If we (the ignorant parent process) have a SIGCHLD handler, then there's
228 a race condition between steps 2 and 3: if the subprocess exits before
229 waitpid() was called, then our SIGCHLD handler fires, and gets notified
230 of the subprocess death; then PAM's call to waitpid() fails, because the
231 process has already been reaped.
233 I consider this a bug in PAM, since the caller should be able to have
234 whatever signal handlers it wants -- the PAM documentation doesn't say
235 "oh by the way, if you use PAM, you can't use SIGCHLD."
242 set = block_sigchld();
243 status = pam_authenticate (pamh, 0);
244 sigtimedwait (&set, NULL, &timeout);
248 fprintf (stderr, "%s: pam_authenticate (...) ==> %d (%s)\n",
249 blurb(), status, PAM_STRERROR(pamh, status));
251 if (status == PAM_SUCCESS) /* Win! */
255 /* We don't actually care if the account modules fail or succeed,
256 * but we need to run them anyway because certain pam modules
257 * depend on side effects of the account modules getting run.
259 status2 = pam_acct_mgmt (pamh, 0);
262 fprintf (stderr, "%s: pam_acct_mgmt (...) ==> %d (%s)\n",
263 blurb(), status2, PAM_STRERROR(pamh, status2));
265 /* HPUX for some reason likes to make PAM defines different from
266 * everyone else's. */
267 #ifdef PAM_AUTHTOKEN_REQD
268 if (status2 == PAM_AUTHTOKEN_REQD)
270 if (status2 == PAM_NEW_AUTHTOK_REQD)
273 status2 = pam_chauthtok (pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
275 fprintf (stderr, "%s: pam_chauthtok (...) ==> %d (%s)\n",
276 blurb(), status2, PAM_STRERROR(pamh, status2));
279 /* Each time we successfully authenticate, refresh credentials,
280 for Kerberos/AFS/DCE/etc. If this fails, just ignore that
281 failure and blunder along; it shouldn't matter.
283 Note: this used to be PAM_REFRESH_CRED instead of
284 PAM_REINITIALIZE_CRED, but Jason Heiss <jheiss@ee.washington.edu>
285 says that the Linux PAM library ignores that one, and only refreshes
286 credentials when using PAM_REINITIALIZE_CRED.
288 status2 = pam_setcred (pamh, PAM_REINITIALIZE_CRED);
290 fprintf (stderr, "%s: pam_setcred (...) ==> %d (%s)\n",
291 blurb(), status2, PAM_STRERROR(pamh, status2));
297 int status2 = pam_end (pamh, status);
300 fprintf (stderr, "%s: pam_end (...) ==> %d (%s)\n",
302 (status2 == PAM_SUCCESS ? "Success" : "Failure"));
305 si->unlock_state = (status == PAM_SUCCESS) ? ul_success : ul_fail;
310 pam_priv_init (int argc, char **argv, Bool verbose_p)
312 /* We have nothing to do at init-time.
313 However, we might as well do some error checking.
314 If "/etc/pam.d" exists and is a directory, but "/etc/pam.d/xlock"
315 does not exist, warn that PAM probably isn't going to work.
317 This is a priv-init instead of a non-priv init in case the directory
318 is unreadable or something (don't know if that actually happens.)
320 const char dir[] = "/etc/pam.d";
321 const char file[] = "/etc/pam.d/" PAM_SERVICE_NAME;
322 const char file2[] = "/etc/pam.conf";
326 # define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
329 if (stat (dir, &st) == 0 && S_ISDIR(st.st_mode))
331 if (stat (file, &st) != 0)
333 "%s: warning: %s does not exist.\n"
334 "%s: password authentication via PAM is unlikely to work.\n",
335 blurb(), file, blurb());
337 else if (stat (file2, &st) == 0)
339 FILE *f = fopen (file2, "r");
344 while (fgets (buf, sizeof(buf), f))
345 if (strstr (buf, PAM_SERVICE_NAME))
354 "%s: warning: %s does not list the `%s' service.\n"
355 "%s: password authentication via PAM is unlikely to work.\n",
356 blurb(), file2, PAM_SERVICE_NAME, blurb());
359 /* else warn about file2 existing but being unreadable? */
364 "%s: warning: neither %s nor %s exist.\n"
365 "%s: password authentication via PAM is unlikely to work.\n",
366 blurb(), file2, file, blurb());
369 /* Return true anyway, just in case. */
375 pam_conversation (int nmsgs,
376 const struct pam_message **msg,
377 struct pam_response **resp,
381 struct auth_message *messages = 0;
382 struct auth_response *authresp = 0;
383 struct pam_response *pam_responses;
384 saver_info *si = (saver_info *) vsaver_info;
386 /* On SunOS 5.6, the `closure' argument always comes in as random garbage. */
387 si = (saver_info *) suns_pam_implementation_blows;
389 /* Converting the PAM prompts into the XScreenSaver native format.
390 * It was a design goal to collapse (INFO,PROMPT) pairs from PAM
391 * into a single call to the unlock_cb function. The unlock_cb function
392 * does that, but only if it is passed several prompts at a time. Most PAM
393 * modules only send a single prompt at a time, but because there is no way
394 * of telling whether there will be more prompts to follow, we can only ever
395 * pass along whatever was passed in here.
398 messages = calloc(nmsgs, sizeof(struct auth_message));
399 pam_responses = calloc(nmsgs, sizeof(*pam_responses));
401 if (!pam_responses || !messages)
404 for (i = 0; i < nmsgs; ++i)
406 messages[i].msg = msg[i]->msg;
408 /* Default fallback of PROMPT_ECHO */
410 msg[i]->msg_style == PAM_PROMPT_ECHO_OFF
411 ? AUTH_MSGTYPE_PROMPT_NOECHO
412 : msg[i]->msg_style == PAM_PROMPT_ECHO_ON
413 ? AUTH_MSGTYPE_PROMPT_ECHO
414 : msg[i]->msg_style == PAM_ERROR_MSG
416 : msg[i]->msg_style == PAM_TEXT_INFO
418 : AUTH_MSGTYPE_PROMPT_ECHO;
421 ret = si->unlock_cb(nmsgs, messages, &authresp, si);
425 for (i = 0; i < nmsgs; ++i)
426 pam_responses[i].resp = authresp[i].response;
438 *resp = pam_responses;
449 #endif /* NO_LOCKING -- whole file */