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/pam_appl.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>
60 extern sigset_t block_sigchld (void);
61 extern void unblock_sigchld (void);
72 #define countof(x) (sizeof((x))/sizeof(*(x)))
74 /* Some time between Red Hat 4.2 and 7.0, the words were transposed
75 in the various PAM_x_CRED macro names. Yay!
77 #ifndef PAM_REFRESH_CRED
78 # define PAM_REFRESH_CRED PAM_CRED_REFRESH
81 static int pam_conversation (int nmsgs,
82 const struct pam_message **msg,
83 struct pam_response **resp,
88 const char *typed_passwd;
93 #ifdef HAVE_PAM_FAIL_DELAY
94 /* We handle delays ourself.*/
95 /* Don't set this to 0 (Linux bug workaround.) */
96 # define PAM_NO_DELAY(pamh) pam_fail_delay ((pamh), 1)
97 #else /* !HAVE_PAM_FAIL_DELAY */
98 # define PAM_NO_DELAY(pamh) /* */
99 #endif /* !HAVE_PAM_FAIL_DELAY */
102 /* On SunOS 5.6, and on Linux with PAM 0.64, pam_strerror() takes two args.
103 On some other Linux systems with some other version of PAM (e.g.,
104 whichever Debian release comes with a 2.2.5 kernel) it takes one arg.
105 I can't tell which is more "recent" or "correct" behavior, so configure
106 figures out which is in use for us. Shoot me!
108 #ifdef PAM_STRERROR_TWO_ARGS
109 # define PAM_STRERROR(pamh, status) pam_strerror((pamh), (status))
110 #else /* !PAM_STRERROR_TWO_ARGS */
111 # define PAM_STRERROR(pamh, status) pam_strerror((status))
112 #endif /* !PAM_STRERROR_TWO_ARGS */
115 /* PAM sucks in that there is no way to tell whether a particular service
116 is configured at all. That is, there is no way to tell the difference
117 between "authentication of the FOO service is not allowed" and "the
118 user typed the wrong password."
120 On RedHat 5.1 systems, if a service name is not known, it defaults to
121 being not allowed (because the fallback service, /etc/pam.d/other, is
124 On Solaris 2.6 systems, unknown services default to authenticating normally.
126 So, we could simply require that the person who installs xscreensaver
127 set up an "xscreensaver" PAM service. However, if we went that route,
128 it would have a really awful failure mode: the failure mode would be that
129 xscreensaver was willing to *lock* the screen, but would be unwilling to
130 *unlock* the screen. (With the non-PAM password code, the analagous
131 situation -- security not being configured properly, for example do to the
132 executable not being installed as setuid root -- the failure mode is much
133 more palettable, in that xscreensaver will refuse to *lock* the screen,
134 because it can know up front that there is no password that will work.)
136 Another route would be to have the service name to consult be computed at
137 compile-time (perhaps with a configure option.) However, that doesn't
138 really solve the problem, because it means that the same executable might
139 work fine on one machine, but refuse to unlock when run on another
142 Another alternative would be to look in /etc/pam.conf or /etc/pam.d/ at
143 runtime to see what services actually exist. But I think that's no good,
144 because who is to say that the PAM info is actually specified in those
145 files? Opening and reading those files is not a part of the PAM client
146 API, so it's not guarenteed to work on any given system.
148 An alternative I tried was to specify a list of services to try, and to
149 try them all in turn ("xscreensaver", "xlock", "xdm", and "login").
150 This worked, but it was slow (and I also had to do some contortions to
151 work around bugs in Linux PAM 0.64-3.)
153 So what we do today is, try PAM once, and if that fails, try the usual
154 getpwent() method. So if PAM doesn't work, it will at least make an
155 attempt at looking up passwords in /etc/passwd or /etc/shadow instead.
157 This all kind of blows. I'm not sure what else to do.
161 /* On SunOS 5.6, the `pam_conv.appdata_ptr' slot seems to be ignored, and
162 the `closure' argument to pc.conv always comes in as random garbage.
163 So we get around this by using a global variable instead. Shoot me!
165 (I've been told this is bug 4092227, and is fixed in Solaris 7.)
166 (I've also been told that it's fixed in Solaris 2.6 by patch 106257-05.)
168 static void *suns_pam_implementation_blows = 0;
171 /* This can be called at any time, and says whether the typed password
172 belongs to either the logged in user (real uid, not effective); or
176 pam_passwd_valid_p (const char *typed_passwd, Bool verbose_p)
178 const char *service = PAM_SERVICE_NAME;
179 pam_handle_t *pamh = 0;
182 struct pam_closure c;
185 struct timespec timeout;
187 struct passwd *p = getpwuid (getuid ());
188 if (!p) return False;
190 user = strdup (p->pw_name);
193 c.typed_passwd = typed_passwd;
194 c.verbose_p = verbose_p;
196 pc.conv = &pam_conversation;
197 pc.appdata_ptr = (void *) &c;
199 /* On SunOS 5.6, the `appdata_ptr' slot seems to be ignored, and the
200 `closure' argument to pc.conv always comes in as random garbage. */
201 suns_pam_implementation_blows = (void *) &c;
206 status = pam_start (service, c.user, &pc, &pamh);
208 fprintf (stderr, "%s: pam_start (\"%s\", \"%s\", ...) ==> %d (%s)\n",
209 blurb(), service, c.user,
210 status, PAM_STRERROR (pamh, status));
211 if (status != PAM_SUCCESS) goto DONE;
213 /* #### We should set PAM_TTY to the display we're using, but we
214 don't have that handy from here. So set it to :0.0, which is a
215 good guess (and has the bonus of counting as a "secure tty" as
216 far as PAM is concerned...)
219 char *tty = strdup (":0.0");
220 status = pam_set_item (pamh, PAM_TTY, tty);
222 fprintf (stderr, "%s: pam_set_item (p, PAM_TTY, \"%s\") ==> %d (%s)\n",
223 blurb(), tty, status, PAM_STRERROR(pamh, status));
227 /* Try to authenticate as the current user.
228 We must turn off our SIGCHLD handler for the duration of the call to
229 pam_authenticate(), because in some cases, the underlying PAM code
232 1: fork a setuid subprocess to do some dirty work;
233 2: read a response from that subprocess;
234 3: waitpid(pid, ...) on that subprocess.
236 If we (the ignorant parent process) have a SIGCHLD handler, then there's
237 a race condition between steps 2 and 3: if the subprocess exits before
238 waitpid() was called, then our SIGCHLD handler fires, and gets notified
239 of the subprocess death; then PAM's call to waitpid() fails, because the
240 process has already been reaped.
242 I consider this a bug in PAM, since the caller should be able to have
243 whatever signal handlers it wants -- the PAM documentation doesn't say
244 "oh by the way, if you use PAM, you can't use SIGCHLD."
251 set = block_sigchld();
252 status = pam_authenticate (pamh, 0);
253 sigtimedwait (&set, NULL, &timeout);
257 fprintf (stderr, "%s: pam_authenticate (...) ==> %d (%s)\n",
258 blurb(), status, PAM_STRERROR(pamh, status));
259 if (status == PAM_SUCCESS) /* Win! */
261 /* Each time we successfully authenticate, refresh credentials,
262 for Kerberos/AFS/DCE/etc. If this fails, just ignore that
263 failure and blunder along; it shouldn't matter.
265 Note: this used to be PAM_REFRESH_CRED instead of
266 PAM_REINITIALIZE_CRED, but Jason Heiss <jheiss@ee.washington.edu>
267 says that the Linux PAM library ignores that one, and only refreshes
268 credentials when using PAM_REINITIALIZE_CRED.
270 int status2 = pam_setcred (pamh, PAM_REINITIALIZE_CRED);
272 fprintf (stderr, "%s: pam_setcred (...) ==> %d (%s)\n",
273 blurb(), status2, PAM_STRERROR(pamh, status2));
277 /* If that didn't work, set the user to root, and try to authenticate again.
279 if (user) free (user);
280 user = strdup ("root");
282 status = pam_set_item (pamh, PAM_USER, c.user);
284 fprintf (stderr, "%s: pam_set_item(p, PAM_USER, \"%s\") ==> %d (%s)\n",
285 blurb(), c.user, status, PAM_STRERROR(pamh, status));
286 if (status != PAM_SUCCESS) goto DONE;
290 set = block_sigchld();
291 status = pam_authenticate (pamh, 0);
292 sigtimedwait(&set, NULL, &timeout);
296 fprintf (stderr, "%s: pam_authenticate (...) ==> %d (%s)\n",
297 blurb(), status, PAM_STRERROR(pamh, status));
300 if (user) free (user);
303 int status2 = pam_end (pamh, status);
306 fprintf (stderr, "%s: pam_end (...) ==> %d (%s)\n",
308 (status2 == PAM_SUCCESS ? "Success" : "Failure"));
310 return (status == PAM_SUCCESS ? True : False);
315 pam_priv_init (int argc, char **argv, Bool verbose_p)
317 /* We have nothing to do at init-time.
318 However, we might as well do some error checking.
319 If "/etc/pam.d" exists and is a directory, but "/etc/pam.d/xlock"
320 does not exist, warn that PAM probably isn't going to work.
322 This is a priv-init instead of a non-priv init in case the directory
323 is unreadable or something (don't know if that actually happens.)
325 const char dir[] = "/etc/pam.d";
326 const char file[] = "/etc/pam.d/" PAM_SERVICE_NAME;
327 const char file2[] = "/etc/pam.conf";
330 if (stat (dir, &st) == 0 && st.st_mode & S_IFDIR)
332 if (stat (file, &st) != 0)
334 "%s: warning: %s does not exist.\n"
335 "%s: password authentication via PAM is unlikely to work.\n",
336 blurb(), file, blurb());
338 else if (stat (file2, &st) == 0)
340 FILE *f = fopen (file2, "r");
345 while (fgets (buf, sizeof(buf), f))
346 if (strstr (buf, PAM_SERVICE_NAME))
355 "%s: warning: %s does not list the `%s' service.\n"
356 "%s: password authentication via PAM is unlikely to work.\n",
357 blurb(), file2, PAM_SERVICE_NAME, blurb());
360 /* else warn about file2 existing but being unreadable? */
365 "%s: warning: neither %s nor %s exist.\n"
366 "%s: password authentication via PAM is unlikely to work.\n",
367 blurb(), file2, file, blurb());
370 /* Return true anyway, just in case. */
375 /* This is the function PAM calls to have a conversation with the user.
376 Really, this function should be the thing that pops up dialog boxes
377 as needed, and prompts for various strings.
379 But, for now, xscreensaver uses its normal password-prompting dialog
380 first, and then this function simply returns the result that has been
383 This means that if PAM was using a retina scanner for auth, xscreensaver
384 would prompt for a password; then pam_conversation() would be called
385 with a string like "Please look into the retina scanner". The user
386 would never see this string, and the prompted-for password would be
390 pam_conversation (int nmsgs,
391 const struct pam_message **msg,
392 struct pam_response **resp,
396 struct pam_response *reply = 0;
397 struct pam_closure *c = (struct pam_closure *) closure;
399 /* On SunOS 5.6, the `closure' argument always comes in as random garbage. */
400 c = (struct pam_closure *) suns_pam_implementation_blows;
403 reply = (struct pam_response *) calloc (nmsgs, sizeof (*reply));
404 if (!reply) return PAM_CONV_ERR;
406 for (replies = 0; replies < nmsgs; replies++)
408 switch (msg[replies]->msg_style)
410 case PAM_PROMPT_ECHO_ON:
411 reply[replies].resp_retcode = PAM_SUCCESS;
412 reply[replies].resp = strdup (c->user); /* freed by PAM */
414 fprintf (stderr, "%s: PAM ECHO_ON(\"%s\") ==> \"%s\"\n",
415 blurb(), msg[replies]->msg,
416 reply[replies].resp);
418 case PAM_PROMPT_ECHO_OFF:
419 reply[replies].resp_retcode = PAM_SUCCESS;
420 reply[replies].resp = strdup (c->typed_passwd); /* freed by PAM */
422 fprintf (stderr, "%s: PAM ECHO_OFF(\"%s\") ==> password\n",
423 blurb(), msg[replies]->msg);
427 reply[replies].resp_retcode = PAM_SUCCESS;
428 reply[replies].resp = 0;
430 fprintf (stderr, "%s: PAM TEXT_INFO(\"%s\") ==> ignored\n",
431 blurb(), msg[replies]->msg);
435 reply[replies].resp_retcode = PAM_SUCCESS;
436 reply[replies].resp = 0;
438 fprintf (stderr, "%s: PAM ERROR_MSG(\"%s\") ==> ignored\n",
439 blurb(), msg[replies]->msg);
442 /* Must be an error of some sort... */
445 fprintf (stderr, "%s: PAM unknown %d(\"%s\") ==> ignored\n",
446 blurb(), msg[replies]->msg_style, msg[replies]->msg);
454 #endif /* NO_LOCKING -- whole file */