/*      $NetBSD: pt_file.c,v 1.20 2019/05/23 11:13:17 kre Exp $ */

/*
 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software donated to Berkeley by
 * Jan-Simon Pendry.
 *
 * 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. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      from: Id: pt_file.c,v 1.1 1992/05/25 21:43:09 jsp Exp
 *      @(#)pt_file.c   8.3 (Berkeley) 7/3/94
 */

#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: pt_file.c,v 1.20 2019/05/23 11:13:17 kre Exp $");
#endif /* not lint */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/syslog.h>

#include "portald.h"

#ifdef DEBUG
#define DEBUG_SYSLOG    syslog
#else
/*
 * The "if (0) ..." will be optimized away by the compiler if
 * DEBUG is not defined.
 */
#define DEBUG_SYSLOG    if (0) syslog
#endif

int
lose_credentials(struct portal_cred *pcr)
{
        /*
         * If we are root, then switch into the caller's credentials.
         * By the way, we _always_ log failures, to make
         * sure questionable activity is noticed.
         */
        if (getuid() == 0) {
                /* Set groups first ... */
                if (setgroups(pcr->pcr_ngroups, pcr->pcr_groups) < 0) {
                        syslog(LOG_WARNING,
                            "lose_credentials: setgroups() failed (%m)");
                        return (errno);
                }
                /* ... then gid ... */
                if (setgid(pcr->pcr_gid) < 0) {
                        syslog(LOG_WARNING,
                                "lose_credentials: setgid(%d) failed (%m)",
                                pcr->pcr_gid);
                }
                /*
                 * ... and now do the seteuid() where we temporarily give
                 * away our root privileges. 
                 */
                if (seteuid(pcr->pcr_uid) < 0) {
                        syslog(LOG_WARNING,
                                "lose_credentials: setuid(%d) failed (%m)",
                                pcr->pcr_uid);
                }
                /* The credential change was successful! */
                DEBUG_SYSLOG(LOG_DEBUG, "Root-owned mount process lowered credentials -- returning successfully!\n");
                return 0;
        }
        DEBUG_SYSLOG(LOG_DEBUG, "Actual/effective/caller's creds are:");
        DEBUG_SYSLOG(LOG_DEBUG, "%d/%d %d/%d %d/%d", getuid(),
            getgid(), geteuid(), getegid(), pcr->pcr_uid, pcr->pcr_gid);
        /*
         * Else, fail if the uid is neither actual or effective
         * uid of mount process...
         */
        if ((getuid() != pcr->pcr_uid) && (geteuid() != pcr->pcr_uid)) {
                syslog(LOG_WARNING,
                    "lose_credentials: uid %d != uid %d, or euid %d != uid %d",
                    getuid(), pcr->pcr_uid, geteuid(), pcr->pcr_uid);
                return EPERM;
        }
        /*
         * ... or the gid is neither the actual or effective
         * gid of the mount process.
         */
        if ((getgid() != pcr->pcr_gid) && (getegid() != pcr->pcr_gid)) {
                syslog(LOG_WARNING,
                    "lose_credentials: gid %d != gid %d, or egid %d != gid %d",
                    getgid(), pcr->pcr_gid, getegid(), pcr->pcr_gid);
                return EPERM;
        }
        /*
         * If we make it here, we have a uid _and_ gid match! Allow the
         * access.
         */
        DEBUG_SYSLOG(LOG_DEBUG, "Returning successfully!\n");
        return 0;
}

int
portal_file(struct portal_cred *pcr, char *key, char **v, int *fdp)
{
        int     fd;
        char    pbuf[MAXPATHLEN];
        int     error;
        int     origuid;

        origuid = getuid();
        pbuf[0] = '/';
        strlcpy(pbuf + 1, key + (v[1] ? strlen(v[1]) : 0), sizeof(pbuf) - 1);
        DEBUG_SYSLOG(LOG_DEBUG, "path = %s, uid = %d, gid = %d",
            pbuf, pcr->pcr_uid, pcr->pcr_gid);

        if ((error = lose_credentials(pcr)) != 0) {
                DEBUG_SYSLOG(LOG_DEBUG, "portal_file: Credential err %d", error);
                return error;
        }
        error = 0;
        /*
         * Be careful -- only set error to errno if there is an error.
         * errno could hold an old, uncaught value, from a routine
         * called long before now.
         */
        fd = open(pbuf, O_RDWR | O_CREAT, 0666);
        if (fd < 0) {
                error = errno;
                if (error == EACCES || error == EISDIR) {
                        DEBUG_SYSLOG(LOG_DEBUG, "Error:  could not open '%s' "
                            "read/write with create flag.  "
                            "Trying read-only open...", pbuf);
                        /* Try opening read-only. */
                        fd = open(pbuf, O_RDONLY, 0);
                        if (fd < 0) {
                                error = errno;
                                DEBUG_SYSLOG(LOG_DEBUG, "That failed too!  %m");
                        } else {
                                /* Clear the error indicator. */
                                error = 0;
                        }
                } else {
                        DEBUG_SYSLOG(LOG_DEBUG, "Error:  could not open '%s': %m", pbuf);
                }

        }
        if (seteuid((uid_t) origuid) < 0) {     /* XXX - should reset gidset
                                                 * too */
                error = errno;
                syslog(LOG_WARNING, "setcred: %m");
                if (fd >= 0) {
                        (void) close(fd);
                        fd = -1;
                }
        }
        if (error == 0)
                *fdp = fd;

        DEBUG_SYSLOG(LOG_DEBUG, "pt_file returns *fdp = %d, error = %d", *fdp,
            error);
        return (error);
}