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) 1993-1998 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>
68 #define countof(x) (sizeof((x))/sizeof(*(x)))
70 static int pam_conversation (int nmsgs,
71 const struct pam_message **msg,
72 struct pam_response **resp,
77 const char *typed_passwd;
82 #ifdef HAVE_PAM_FAIL_DELAY
83 /* We handle delays ourself.*/
84 /* Don't set this to 0 (Linux bug workaround.) */
85 # define PAM_NO_DELAY(pamh) pam_fail_delay ((pamh), 1)
86 #else /* !HAVE_PAM_FAIL_DELAY */
87 # define PAM_NO_DELAY(pamh) /* */
88 #endif /* !HAVE_PAM_FAIL_DELAY */
91 /* On SunOS 5.6, and on Linux with PAM 0.64, pam_strerror() takes two args.
92 On some other Linux systems with some other version of PAM (e.g.,
93 whichever Debian release comes with a 2.2.5 kernel) it takes one arg.
94 I can't tell which is more "recent" or "correct" behavior, so configure
95 figures out which is in use for us. Shoot me!
97 #ifdef PAM_STRERROR_TWO_ARGS
98 # define PAM_STRERROR(pamh, status) pam_strerror((pamh), (status))
99 #else /* !PAM_STRERROR_TWO_ARGS */
100 # define PAM_STRERROR(pamh, status) pam_strerror((status))
101 #endif /* !PAM_STRERROR_TWO_ARGS */
104 /* PAM sucks in that there is no way to tell whether a particular service
105 is configured at all. That is, there is no way to tell the difference
106 between "authentication of the FOO service is not allowed" and "the
107 user typed the wrong password."
109 On RedHat 5.1 systems, if a service name is not known, it defaults to
110 being not allowed (because the fallback service, /etc/pam.d/other, is
113 On Solaris 2.6 systems, unknown services default to authenticating normally.
115 So, we could simply require that the person who installs xscreensaver
116 set up an "xscreensaver" PAM service. However, if we went that route,
117 it would have a really awful failure mode: the failure mode would be that
118 xscreensaver was willing to *lock* the screen, but would be unwilling to
119 *unlock* the screen. (With the non-PAM password code, the analagous
120 situation -- security not being configured properly, for example do to the
121 executable not being installed as setuid root -- the failure mode is much
122 more palettable, in that xscreensaver will refuse to *lock* the screen,
123 because it can know up front that there is no password that will work.)
125 Another route would be to have the service name to consult be computed at
126 compile-time (perhaps with a configure option.) However, that doesn't
127 really solve the problem, because it means that the same executable might
128 work fine on one machine, but refuse to unlock when run on another
131 Another alternative would be to look in /etc/pam.conf or /etc/pam.d/ at
132 runtime to see what services actually exist. But I think that's no good,
133 because who is to say that the PAM info is actually specified in those
134 files? Opening and reading those files is not a part of the PAM client
135 API, so it's not guarenteed to work on any given system.
137 An alternative I tried was to specify a list of services to try, and to
138 try them all in turn ("xscreensaver", "xlock", "xdm", and "login").
139 This worked, but it was slow (and I also had to do some contortions to
140 work around bugs in Linux PAM 0.64-3.)
142 So what we do today is, try PAM once, and if that fails, try the usual
143 getpwent() method. So if PAM doesn't work, it will at least make an
144 attempt at looking up passwords in /etc/passwd or /etc/shadow instead.
146 This all kind of blows. I'm not sure what else to do.
150 /* On SunOS 5.6, the `pam_conv.appdata_ptr' slot seems to be ignored, and
151 the `closure' argument to pc.conv always comes in as random garbage.
152 So we get around this by using a global variable instead. Shoot me!
154 (I've been told this is bug 4092227, and is fixed in Solaris 7.)
156 static void *suns_pam_implementation_blows = 0;
159 /* This can be called at any time, and says whether the typed password
160 belongs to either the logged in user (real uid, not effective); or
164 pam_passwd_valid_p (const char *typed_passwd, Bool verbose_p)
166 const char *service = PAM_SERVICE_NAME;
167 pam_handle_t *pamh = 0;
170 struct pam_closure c;
173 struct passwd *p = getpwuid (getuid ());
174 if (!p) return False;
176 user = strdup (p->pw_name);
179 c.typed_passwd = typed_passwd;
180 c.verbose_p = verbose_p;
182 pc.conv = &pam_conversation;
183 pc.appdata_ptr = (void *) &c;
185 /* On SunOS 5.6, the `appdata_ptr' slot seems to be ignored, and the
186 `closure' argument to pc.conv always comes in as random garbage. */
187 suns_pam_implementation_blows = (void *) &c;
192 status = pam_start (service, c.user, &pc, &pamh);
194 fprintf (stderr, "%s: pam_start (\"%s\", \"%s\", ...) ==> %d (%s)\n",
195 blurb(), service, c.user,
196 status, PAM_STRERROR (pamh, status));
197 if (status != PAM_SUCCESS) goto DONE;
199 /* #### We should set PAM_TTY to the display we're using, but we
200 don't have that handy from here. So set it to :0.0, which is a
201 good guess (and has the bonus of counting as a "secure tty" as
202 far as PAM is concerned...)
205 const char *tty = ":0.0";
206 status = pam_set_item (pamh, PAM_TTY, strdup(tty));
208 fprintf (stderr, "%s: pam_set_item (p, PAM_TTY, \"%s\") ==> %d (%s)\n",
209 blurb(), tty, status, PAM_STRERROR(pamh, status));
212 /* Try to authenticate as the current user.
215 status = pam_authenticate (pamh, 0);
217 fprintf (stderr, "%s: pam_authenticate (...) ==> %d (%s)\n",
218 blurb(), status, PAM_STRERROR(pamh, status));
219 if (status == PAM_SUCCESS) /* Win! */
222 /* If that didn't work, set the user to root, and try to authenticate again.
225 status = pam_set_item (pamh, PAM_USER, strdup(c.user));
227 fprintf (stderr, "%s: pam_set_item(p, PAM_USER, \"%s\") ==> %d (%s)\n",
228 blurb(), c.user, status, PAM_STRERROR(pamh, status));
229 if (status != PAM_SUCCESS) goto DONE;
232 status = pam_authenticate (pamh, 0);
234 fprintf (stderr, "%s: pam_authenticate (...) ==> %d (%s)\n",
235 blurb(), status, PAM_STRERROR(pamh, status));
238 if (user) free (user);
241 int status2 = pam_end (pamh, status);
244 fprintf (stderr, "%s: pam_end (...) ==> %d (%s)\n",
246 (status2 == PAM_SUCCESS ? "Success" : "Failure"));
248 return (status == PAM_SUCCESS ? True : False);
253 pam_priv_init (int argc, char **argv, Bool verbose_p)
255 /* We have nothing to do at init-time.
256 However, we might as well do some error checking.
257 If "/etc/pam.d" exists and is a directory, but "/etc/pam.d/xlock"
258 does not exist, warn that PAM probably isn't going to work.
260 This is a priv-init instead of a non-priv init in case the directory
261 is unreadable or something (don't know if that actually happens.)
263 const char dir[] = "/etc/pam.d";
264 const char file[] = "/etc/pam.d/" PAM_SERVICE_NAME;
265 const char file2[] = "/etc/pam.conf";
268 if (stat (dir, &st) == 0 && st.st_mode & S_IFDIR)
270 if (stat (file, &st) != 0)
272 "%s: warning: %s does not exist.\n"
273 "%s: password authentication via PAM is unlikely to work.\n",
274 blurb(), file, blurb());
276 else if (stat (file2, &st) == 0)
278 FILE *f = fopen (file2, "r");
283 while (fgets (buf, sizeof(buf), f))
284 if (strstr (buf, PAM_SERVICE_NAME))
293 "%s: warning: %s does not list the `%s' service.\n"
294 "%s: password authentication via PAM is unlikely to work.\n",
295 blurb(), file2, PAM_SERVICE_NAME, blurb());
298 /* else warn about file2 existing but being unreadable? */
303 "%s: warning: neither %s nor %s exist.\n"
304 "%s: password authentication via PAM is unlikely to work.\n",
305 blurb(), file2, file, blurb());
308 /* Return true anyway, just in case. */
313 /* This is the function PAM calls to have a conversation with the user.
314 Really, this function should be the thing that pops up dialog boxes
315 as needed, and prompts for various strings.
317 But, for now, xscreensaver uses its normal password-prompting dialog
318 first, and then this function simply returns the result that has been
321 This means that if PAM was using a retina scanner for auth, xscreensaver
322 would prompt for a password; then pam_conversation() would be called
323 with a string like "Please look into the retina scanner". The user
324 would never see this string, and the prompted-for password would be
328 pam_conversation (int nmsgs,
329 const struct pam_message **msg,
330 struct pam_response **resp,
334 struct pam_response *reply = 0;
335 struct pam_closure *c = (struct pam_closure *) closure;
337 /* On SunOS 5.6, the `closure' argument always comes in as random garbage. */
338 c = (struct pam_closure *) suns_pam_implementation_blows;
341 reply = (struct pam_response *) calloc (nmsgs, sizeof (*reply));
342 if (!reply) return PAM_CONV_ERR;
344 for (replies = 0; replies < nmsgs; replies++)
346 switch (msg[replies]->msg_style)
348 case PAM_PROMPT_ECHO_ON:
349 reply[replies].resp_retcode = PAM_SUCCESS;
350 reply[replies].resp = strdup (c->user); /* freed by PAM */
352 fprintf (stderr, "%s: PAM ECHO_ON(\"%s\") ==> \"%s\"\n",
353 blurb(), msg[replies]->msg,
354 reply[replies].resp);
356 case PAM_PROMPT_ECHO_OFF:
357 reply[replies].resp_retcode = PAM_SUCCESS;
358 reply[replies].resp = strdup (c->typed_passwd); /* freed by PAM */
360 fprintf (stderr, "%s: PAM ECHO_OFF(\"%s\") ==> password\n",
361 blurb(), msg[replies]->msg);
365 reply[replies].resp_retcode = PAM_SUCCESS;
366 reply[replies].resp = 0;
368 fprintf (stderr, "%s: PAM TEXT_INFO(\"%s\") ==> ignored\n",
369 blurb(), msg[replies]->msg);
373 reply[replies].resp_retcode = PAM_SUCCESS;
374 reply[replies].resp = 0;
376 fprintf (stderr, "%s: PAM ERROR_MSG(\"%s\") ==> ignored\n",
377 blurb(), msg[replies]->msg);
380 /* Must be an error of some sort... */
383 fprintf (stderr, "%s: PAM unknown %d(\"%s\") ==> ignored\n",
384 blurb(), msg[replies]->msg_style, msg[replies]->msg);
392 #endif /* NO_LOCKING -- whole file */