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      1 /*	$NetBSD: openpam_check_owner_perms.c,v 1.4 2023/06/30 21:46:20 christos Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2011 Dag-Erling Smrgrav
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  * 3. The name of the author may not be used to endorse or promote
     16  *    products derived from this software without specific prior written
     17  *    permission.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     29  * SUCH DAMAGE.
     30  */
     31 
     32 #ifdef HAVE_CONFIG_H
     33 # include "config.h"
     34 #endif
     35 
     36 #include <sys/cdefs.h>
     37 __RCSID("$NetBSD: openpam_check_owner_perms.c,v 1.4 2023/06/30 21:46:20 christos Exp $");
     38 
     39 #include <sys/types.h>
     40 #include <sys/stat.h>
     41 
     42 #include <errno.h>
     43 #include <limits.h>
     44 #include <stdlib.h>
     45 #include <string.h>
     46 #include <unistd.h>
     47 
     48 #include <security/pam_appl.h>
     49 
     50 #include "openpam_impl.h"
     51 
     52 /*
     53  * OpenPAM internal
     54  *
     55  * Verify that the file or directory referenced by the given descriptor is
     56  * owned by either root or the arbitrator and that it is not writable by
     57  * group or other.
     58  */
     59 
     60 int
     61 openpam_check_desc_owner_perms(const char *name, int fd)
     62 {
     63 	uid_t root, arbitrator;
     64 	struct stat sb;
     65 	int serrno;
     66 
     67 	root = 0;
     68 	arbitrator = geteuid();
     69 	if (fstat(fd, &sb) != 0) {
     70 		serrno = errno;
     71 		openpam_log(PAM_LOG_ERROR, "%s: %s", name, strerror(errno));
     72 		errno = serrno;
     73 		return (-1);
     74 	}
     75 	if (!S_ISREG(sb.st_mode)) {
     76 		openpam_log(PAM_LOG_ERROR,
     77 		    "%s: not a regular file", name);
     78 		errno = EINVAL;
     79 		return (-1);
     80 	}
     81 	if ((sb.st_uid != root && sb.st_uid != arbitrator) ||
     82 	    (sb.st_mode & (S_IWGRP|S_IWOTH)) != 0) {
     83 		openpam_log(PAM_LOG_ERROR,
     84 		    "%s: insecure ownership or permissions", name);
     85 		errno = EPERM;
     86 		return (-1);
     87 	}
     88 	return (0);
     89 }
     90 
     91 /*
     92  * OpenPAM internal
     93  *
     94  * Verify that a file or directory and all components of the path leading
     95  * up to it are owned by either root or the arbitrator and that they are
     96  * not writable by group or other.
     97  *
     98  * Note that openpam_check_desc_owner_perms() should be used instead if
     99  * possible to avoid a race between the ownership / permission check and
    100  * the actual open().
    101  */
    102 
    103 int
    104 openpam_check_path_owner_perms(const char *path)
    105 {
    106 	uid_t root, arbitrator;
    107 	char pathbuf[PATH_MAX];
    108 	struct stat sb;
    109 	size_t len;
    110 	int serrno, tip;
    111 
    112 	tip = 1;
    113 	root = 0;
    114 	arbitrator = geteuid();
    115 	if (realpath(path, pathbuf) == NULL)
    116 		return (-1);
    117 	len = strlen(pathbuf);
    118 	while (len > 0) {
    119 		if (stat(pathbuf, &sb) != 0) {
    120 			if (errno != ENOENT) {
    121 				serrno = errno;
    122 				openpam_log(PAM_LOG_ERROR, "%s: %m", pathbuf);
    123 				errno = serrno;
    124 			}
    125 			return (-1);
    126 		}
    127 		if (tip && !S_ISREG(sb.st_mode)) {
    128 			openpam_log(PAM_LOG_ERROR,
    129 			    "%s: not a regular file", pathbuf);
    130 			errno = EINVAL;
    131 			return (-1);
    132 		}
    133 		if ((sb.st_uid != root && sb.st_uid != arbitrator) ||
    134 		    (sb.st_mode & (S_IWGRP|S_IWOTH)) != 0) {
    135 			openpam_log(PAM_LOG_ERROR,
    136 			    "%s: insecure ownership or permissions", pathbuf);
    137 			errno = EPERM;
    138 			return (-1);
    139 		}
    140 		while (--len > 0 && pathbuf[len] != '/')
    141 			pathbuf[len] = '\0';
    142 		tip = 0;
    143 	}
    144 	return (0);
    145 }
    146 
    147 /*
    148  * NOPARSE
    149  */
    150