/* passwd-helper.c --- verifying typed passwords with external helper program
* xscreensaver, Copyright © 1993-2021 Jamie Zawinski <jwz@jwz.org>
* written by Olaf Kirch <okir@suse.de>
*
* Permission to use, copy, modify, distribute, and sell this software and its
* documentation for any purpose is hereby granted without fee, provided that
* the above copyright notice appear in all copies and that both that
* copyright notice and this permission notice appear in supporting
* documentation. No representations are made about the suitability of this
* software for any purpose. It is provided "as is" without express or
* implied warranty.
*/
/*****************************************************************************
I strongly suspect that this code has not been used in decades, and I
am considering removing it. These details should be hidden behind PAM.
If you are using this code, email me and tell me why. -- jwz, Feb 2021
*****************************************************************************/
#error "email jwz@jwz.org about passwd-helper.c"
/* The idea here is to be able to run xscreensaver without any setuid bits.
* Password verification happens through an external program that you feed
* your password to on stdin. The external command is invoked with a user
* name argument.
*
* The external helper does whatever authentication is necessary. Currently,
* SuSE uses "unix2_chkpwd", which is a variation of "unix_chkpwd" from the
* PAM distribution.
*
* Normally, the password helper should just authenticate the calling user
* (i.e. based on the caller's real uid). This is in order to prevent
* brute-forcing passwords in a shadow environment. A less restrictive
* approach would be to allow verifying other passwords as well, but always
* with a 2 second delay or so. (Not sure what SuSE's "unix2_chkpwd"
* currently does.)
* -- Olaf Kirch <okir@suse.de>, 16-Dec-2003
*/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#ifndef NO_LOCKING /* whole file */
#include <stdlib.h>
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>
#include <errno.h>
#include <sys/wait.h>
#include "blurb.h"
#include "auth.h"
static int
ext_run (const char *user, const char *typed_passwd)
{
int pfd[2], status;
pid_t pid;
if (pipe(pfd) < 0)
return 0;
if (verbose_p)
fprintf (stderr, "%s: EXT: %s\n", blurb(), PASSWD_HELPER_PROGRAM);
if ((pid = fork()) < 0) {
close(pfd[0]);
close(pfd[1]);
return 0;
}
if (pid == 0) {
close(pfd[1]);
if (pfd[0] != 0)
dup2(pfd[0], 0);
/* Helper is invoked as helper service-name [user] */
execlp(PASSWD_HELPER_PROGRAM, PASSWD_HELPER_PROGRAM, "xscreensaver", user, NULL);
if (verbose_p)
fprintf(stderr, "%s: EXT: %s\n", PASSWD_HELPER_PROGRAM,
strerror(errno));
exit(1);
}
close(pfd[0]);
/* Write out password to helper process */
if (!typed_passwd)
typed_passwd = "";
write(pfd[1], typed_passwd, strlen(typed_passwd));
close(pfd[1]);
while (waitpid(pid, &status, 0) < 0) {
if (errno == EINTR)
continue;
if (verbose_p)
fprintf(stderr, "%s: EXT: waitpid failed: %s\n",
blurb(), strerror(errno));
return 0;
}
if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
return 0;
return 1;
}
/* This can be called at any time, and says whether the typed password
belongs to either the logged in user (real uid, not effective); or
to root.
*/
int
ext_passwd_valid_p (void *closure, const char *typed_passwd)
{
struct passwd *pw;
int res = 0;
if ((pw = getpwuid(getuid())) != NULL)
res = ext_run (pw->pw_name, typed_passwd);
endpwent();
#ifdef ALLOW_ROOT_PASSWD
if (!res)
res = ext_run ("root", typed_passwd);
#endif /* ALLOW_ROOT_PASSWD */
return res;
}
Bool
ext_priv_init (void)
{
/* Make sure the passwd helper exists */
if (access(PASSWD_HELPER_PROGRAM, X_OK) < 0) {
fprintf(stderr,
"%s: EXT: warning: %s does not exist.\n"
"%s: EXT password authentication will not work.\n",
blurb(), PASSWD_HELPER_PROGRAM, blurb());
return False;
}
return True;
}
#endif /* NO_LOCKING -- whole file */
