A. Sample PAM Application
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## A. Sample PAM Application

The following is a minimal implementation of su(1) using PAM. Note that it uses the OpenPAM-specific openpam_ttyconv(3) conversation function, which is prototyped in `security/openpam.h`. If you wish build this application on a system with a different PAM library, you will have to provide your own conversation function. A robust conversation function is surprisingly difficult to implement; the one presented in Appendix C, Sample PAM Conversation Function is a good starting point, but should not be used in real-world applications.

/*- * Copyright (c) 2002,2003 Networks Associates Technology, Inc. * All rights reserved. * * This software was developed for the FreeBSD Project by ThinkSec AS and * Network Associates Laboratories, the Security Research Division of * Network Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 * ("CBOSS"), as part of the DARPA CHATS research program. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. The name of the author may not be used to endorse or promote * products derived from this software without specific prior written * permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * $P4: //depot/projects/openpam/bin/su/su.c#10 $ * $FreeBSD: head/en_US.ISO8859-1/articles/pam/su.c 38826 2012-05-17 19:12:14Z hrs $ */ #include <sys/param.h> #include <sys/wait.h> #include <err.h> #include <pwd.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <syslog.h> #include <unistd.h> #include <security/pam_appl.h> #include <security/openpam.h> /* for openpam_ttyconv() */ extern char **environ; static pam_handle_t *pamh; static struct pam_conv pamc; static void usage(void) { fprintf(stderr, "Usage: su [login [args]]\n"); exit(1); } int main(int argc, char *argv[]) { char hostname[MAXHOSTNAMELEN]; const char *user, *tty; char **args, **pam_envlist, **pam_env; struct passwd *pwd; int o, pam_err, status; pid_t pid; while ((o = getopt(argc, argv, "h")) != -1) switch (o) { case 'h': default: usage(); } argc -= optind; argv += optind; if (argc > 0) { user = *argv; --argc; ++argv; } else { user = "root"; } /* initialize PAM */ pamc.conv = &openpam_ttyconv; pam_start("su", user, &pamc, &pamh); /* set some items */ gethostname(hostname, sizeof(hostname)); if ((pam_err = pam_set_item(pamh, PAM_RHOST, hostname)) != PAM_SUCCESS) goto pamerr; user = getlogin(); if ((pam_err = pam_set_item(pamh, PAM_RUSER, user)) != PAM_SUCCESS) goto pamerr; tty = ttyname(STDERR_FILENO); if ((pam_err = pam_set_item(pamh, PAM_TTY, tty)) != PAM_SUCCESS) goto pamerr; /* authenticate the applicant */ if ((pam_err = pam_authenticate(pamh, 0)) != PAM_SUCCESS) goto pamerr; if ((pam_err = pam_acct_mgmt(pamh, 0)) == PAM_NEW_AUTHTOK_REQD) pam_err = pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK); if (pam_err != PAM_SUCCESS) goto pamerr; /* establish the requested credentials */ if ((pam_err = pam_setcred(pamh, PAM_ESTABLISH_CRED)) != PAM_SUCCESS) goto pamerr; /* authentication succeeded; open a session */ if ((pam_err = pam_open_session(pamh, 0)) != PAM_SUCCESS) goto pamerr; /* get mapped user name; PAM may have changed it */ pam_err = pam_get_item(pamh, PAM_USER, (const void **)&user); if (pam_err != PAM_SUCCESS || (pwd = getpwnam(user)) == NULL) goto pamerr; /* export PAM environment */ if ((pam_envlist = pam_getenvlist(pamh)) != NULL) { for (pam_env = pam_envlist; *pam_env != NULL; ++pam_env) { putenv(*pam_env); free(*pam_env); } free(pam_envlist); } /* build argument list */ if ((args = calloc(argc + 2, sizeof *args)) == NULL) { warn("calloc()"); goto err; } *args = pwd->pw_shell; memcpy(args + 1, argv, argc * sizeof *args); /* fork and exec */ switch ((pid = fork())) { case -1: warn("fork()"); goto err; case 0: /* child: give up privs and start a shell */ /* set uid and groups */ if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { warn("initgroups()"); _exit(1); } if (setgid(pwd->pw_gid) == -1) { warn("setgid()"); _exit(1); } if (setuid(pwd->pw_uid) == -1) { warn("setuid()"); _exit(1); } execve(*args, args, environ); warn("execve()"); _exit(1); default: /* parent: wait for child to exit */ waitpid(pid, &status, 0); /* close the session and release PAM resources */ pam_err = pam_close_session(pamh, 0); pam_end(pamh, pam_err); exit(WEXITSTATUS(status)); } pamerr: fprintf(stderr, "Sorry\n"); err: pam_end(pamh, pam_err); exit(1); }

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