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) 1993-2001 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>
58 extern void block_sigchld (void);
59 extern void unblock_sigchld (void);
70 #define countof(x) (sizeof((x))/sizeof(*(x)))
72 static int pam_conversation (int nmsgs,
73 const struct pam_message **msg,
74 struct pam_response **resp,
79 const char *typed_passwd;
84 #ifdef HAVE_PAM_FAIL_DELAY
85 /* We handle delays ourself.*/
86 /* Don't set this to 0 (Linux bug workaround.) */
87 # define PAM_NO_DELAY(pamh) pam_fail_delay ((pamh), 1)
88 #else /* !HAVE_PAM_FAIL_DELAY */
89 # define PAM_NO_DELAY(pamh) /* */
90 #endif /* !HAVE_PAM_FAIL_DELAY */
93 /* On SunOS 5.6, and on Linux with PAM 0.64, pam_strerror() takes two args.
94 On some other Linux systems with some other version of PAM (e.g.,
95 whichever Debian release comes with a 2.2.5 kernel) it takes one arg.
96 I can't tell which is more "recent" or "correct" behavior, so configure
97 figures out which is in use for us. Shoot me!
99 #ifdef PAM_STRERROR_TWO_ARGS
100 # define PAM_STRERROR(pamh, status) pam_strerror((pamh), (status))
101 #else /* !PAM_STRERROR_TWO_ARGS */
102 # define PAM_STRERROR(pamh, status) pam_strerror((status))
103 #endif /* !PAM_STRERROR_TWO_ARGS */
106 /* PAM sucks in that there is no way to tell whether a particular service
107 is configured at all. That is, there is no way to tell the difference
108 between "authentication of the FOO service is not allowed" and "the
109 user typed the wrong password."
111 On RedHat 5.1 systems, if a service name is not known, it defaults to
112 being not allowed (because the fallback service, /etc/pam.d/other, is
115 On Solaris 2.6 systems, unknown services default to authenticating normally.
117 So, we could simply require that the person who installs xscreensaver
118 set up an "xscreensaver" PAM service. However, if we went that route,
119 it would have a really awful failure mode: the failure mode would be that
120 xscreensaver was willing to *lock* the screen, but would be unwilling to
121 *unlock* the screen. (With the non-PAM password code, the analagous
122 situation -- security not being configured properly, for example do to the
123 executable not being installed as setuid root -- the failure mode is much
124 more palettable, in that xscreensaver will refuse to *lock* the screen,
125 because it can know up front that there is no password that will work.)
127 Another route would be to have the service name to consult be computed at
128 compile-time (perhaps with a configure option.) However, that doesn't
129 really solve the problem, because it means that the same executable might
130 work fine on one machine, but refuse to unlock when run on another
133 Another alternative would be to look in /etc/pam.conf or /etc/pam.d/ at
134 runtime to see what services actually exist. But I think that's no good,
135 because who is to say that the PAM info is actually specified in those
136 files? Opening and reading those files is not a part of the PAM client
137 API, so it's not guarenteed to work on any given system.
139 An alternative I tried was to specify a list of services to try, and to
140 try them all in turn ("xscreensaver", "xlock", "xdm", and "login").
141 This worked, but it was slow (and I also had to do some contortions to
142 work around bugs in Linux PAM 0.64-3.)
144 So what we do today is, try PAM once, and if that fails, try the usual
145 getpwent() method. So if PAM doesn't work, it will at least make an
146 attempt at looking up passwords in /etc/passwd or /etc/shadow instead.
148 This all kind of blows. I'm not sure what else to do.
152 /* On SunOS 5.6, the `pam_conv.appdata_ptr' slot seems to be ignored, and
153 the `closure' argument to pc.conv always comes in as random garbage.
154 So we get around this by using a global variable instead. Shoot me!
156 (I've been told this is bug 4092227, and is fixed in Solaris 7.)
157 (I've also been told that it's fixed in Solaris 2.6 by patch 106257-05.)
159 static void *suns_pam_implementation_blows = 0;
162 /* This can be called at any time, and says whether the typed password
163 belongs to either the logged in user (real uid, not effective); or
167 pam_passwd_valid_p (const char *typed_passwd, Bool verbose_p)
169 const char *service = PAM_SERVICE_NAME;
170 pam_handle_t *pamh = 0;
173 struct pam_closure c;
176 struct passwd *p = getpwuid (getuid ());
177 if (!p) return False;
179 user = strdup (p->pw_name);
182 c.typed_passwd = typed_passwd;
183 c.verbose_p = verbose_p;
185 pc.conv = &pam_conversation;
186 pc.appdata_ptr = (void *) &c;
188 /* On SunOS 5.6, the `appdata_ptr' slot seems to be ignored, and the
189 `closure' argument to pc.conv always comes in as random garbage. */
190 suns_pam_implementation_blows = (void *) &c;
195 status = pam_start (service, c.user, &pc, &pamh);
197 fprintf (stderr, "%s: pam_start (\"%s\", \"%s\", ...) ==> %d (%s)\n",
198 blurb(), service, c.user,
199 status, PAM_STRERROR (pamh, status));
200 if (status != PAM_SUCCESS) goto DONE;
202 /* #### We should set PAM_TTY to the display we're using, but we
203 don't have that handy from here. So set it to :0.0, which is a
204 good guess (and has the bonus of counting as a "secure tty" as
205 far as PAM is concerned...)
208 const char *tty = ":0.0";
209 status = pam_set_item (pamh, PAM_TTY, strdup(tty));
211 fprintf (stderr, "%s: pam_set_item (p, PAM_TTY, \"%s\") ==> %d (%s)\n",
212 blurb(), tty, status, PAM_STRERROR(pamh, status));
215 /* Try to authenticate as the current user.
216 We must turn off our SIGCHLD handler for the duration of the call to
217 pam_authenticate(), because in some cases, the underlying PAM code
220 1: fork a setuid subprocess to do some dirty work;
221 2: read a response from that subprocess;
222 3: waitpid(pid, ...) on that subprocess.
224 If we (the ignorant parent process) have a SIGCHLD handler, then there's
225 a race condition between steps 2 and 3: if the subprocess exits before
226 waitpid() was called, then our SIGCHLD handler fires, and gets notified
227 of the subprocess death; then PAM's call to waitpid() fails, because the
228 process has already been reaped.
230 I consider this a bug in PAM, since the caller should be able to have
231 whatever signal handlers it wants -- the PAM documentation doesn't say
232 "oh by the way, if you use PAM, you can't use SIGCHLD."
238 status = pam_authenticate (pamh, 0);
242 fprintf (stderr, "%s: pam_authenticate (...) ==> %d (%s)\n",
243 blurb(), status, PAM_STRERROR(pamh, status));
244 if (status == PAM_SUCCESS) /* Win! */
246 /* Each time we successfully authenticate, refresh credentials,
247 for Kerberos/AFS/DCE/etc. If this fails, just ignore that
248 failure and blunder along; it shouldn't matter.
250 int status2 = pam_setcred (pamh, PAM_REFRESH_CRED);
252 fprintf (stderr, "%s: pam_setcred (...) ==> %d (%s)\n",
253 blurb(), status2, PAM_STRERROR(pamh, status2));
257 /* If that didn't work, set the user to root, and try to authenticate again.
260 status = pam_set_item (pamh, PAM_USER, strdup(c.user));
262 fprintf (stderr, "%s: pam_set_item(p, PAM_USER, \"%s\") ==> %d (%s)\n",
263 blurb(), c.user, status, PAM_STRERROR(pamh, status));
264 if (status != PAM_SUCCESS) goto DONE;
267 status = pam_authenticate (pamh, 0);
269 fprintf (stderr, "%s: pam_authenticate (...) ==> %d (%s)\n",
270 blurb(), status, PAM_STRERROR(pamh, status));
273 if (user) free (user);
276 int status2 = pam_end (pamh, status);
279 fprintf (stderr, "%s: pam_end (...) ==> %d (%s)\n",
281 (status2 == PAM_SUCCESS ? "Success" : "Failure"));
283 return (status == PAM_SUCCESS ? True : False);
288 pam_priv_init (int argc, char **argv, Bool verbose_p)
290 /* We have nothing to do at init-time.
291 However, we might as well do some error checking.
292 If "/etc/pam.d" exists and is a directory, but "/etc/pam.d/xlock"
293 does not exist, warn that PAM probably isn't going to work.
295 This is a priv-init instead of a non-priv init in case the directory
296 is unreadable or something (don't know if that actually happens.)
298 const char dir[] = "/etc/pam.d";
299 const char file[] = "/etc/pam.d/" PAM_SERVICE_NAME;
300 const char file2[] = "/etc/pam.conf";
303 if (stat (dir, &st) == 0 && st.st_mode & S_IFDIR)
305 if (stat (file, &st) != 0)
307 "%s: warning: %s does not exist.\n"
308 "%s: password authentication via PAM is unlikely to work.\n",
309 blurb(), file, blurb());
311 else if (stat (file2, &st) == 0)
313 FILE *f = fopen (file2, "r");
318 while (fgets (buf, sizeof(buf), f))
319 if (strstr (buf, PAM_SERVICE_NAME))
328 "%s: warning: %s does not list the `%s' service.\n"
329 "%s: password authentication via PAM is unlikely to work.\n",
330 blurb(), file2, PAM_SERVICE_NAME, blurb());
333 /* else warn about file2 existing but being unreadable? */
338 "%s: warning: neither %s nor %s exist.\n"
339 "%s: password authentication via PAM is unlikely to work.\n",
340 blurb(), file2, file, blurb());
343 /* Return true anyway, just in case. */
348 /* This is the function PAM calls to have a conversation with the user.
349 Really, this function should be the thing that pops up dialog boxes
350 as needed, and prompts for various strings.
352 But, for now, xscreensaver uses its normal password-prompting dialog
353 first, and then this function simply returns the result that has been
356 This means that if PAM was using a retina scanner for auth, xscreensaver
357 would prompt for a password; then pam_conversation() would be called
358 with a string like "Please look into the retina scanner". The user
359 would never see this string, and the prompted-for password would be
363 pam_conversation (int nmsgs,
364 const struct pam_message **msg,
365 struct pam_response **resp,
369 struct pam_response *reply = 0;
370 struct pam_closure *c = (struct pam_closure *) closure;
372 /* On SunOS 5.6, the `closure' argument always comes in as random garbage. */
373 c = (struct pam_closure *) suns_pam_implementation_blows;
376 reply = (struct pam_response *) calloc (nmsgs, sizeof (*reply));
377 if (!reply) return PAM_CONV_ERR;
379 for (replies = 0; replies < nmsgs; replies++)
381 switch (msg[replies]->msg_style)
383 case PAM_PROMPT_ECHO_ON:
384 reply[replies].resp_retcode = PAM_SUCCESS;
385 reply[replies].resp = strdup (c->user); /* freed by PAM */
387 fprintf (stderr, "%s: PAM ECHO_ON(\"%s\") ==> \"%s\"\n",
388 blurb(), msg[replies]->msg,
389 reply[replies].resp);
391 case PAM_PROMPT_ECHO_OFF:
392 reply[replies].resp_retcode = PAM_SUCCESS;
393 reply[replies].resp = strdup (c->typed_passwd); /* freed by PAM */
395 fprintf (stderr, "%s: PAM ECHO_OFF(\"%s\") ==> password\n",
396 blurb(), msg[replies]->msg);
400 reply[replies].resp_retcode = PAM_SUCCESS;
401 reply[replies].resp = 0;
403 fprintf (stderr, "%s: PAM TEXT_INFO(\"%s\") ==> ignored\n",
404 blurb(), msg[replies]->msg);
408 reply[replies].resp_retcode = PAM_SUCCESS;
409 reply[replies].resp = 0;
411 fprintf (stderr, "%s: PAM ERROR_MSG(\"%s\") ==> ignored\n",
412 blurb(), msg[replies]->msg);
415 /* Must be an error of some sort... */
418 fprintf (stderr, "%s: PAM unknown %d(\"%s\") ==> ignored\n",
419 blurb(), msg[replies]->msg_style, msg[replies]->msg);
427 #endif /* NO_LOCKING -- whole file */