1 /* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
2 /* util/support/secure_getenv.c - secure_getenv() portability support */
3 /*
4 * Copyright (C) 2019 by the Massachusetts Institute of Technology.
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 *
11 * * Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 *
14 * * Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in
16 * the documentation and/or other materials provided with the
17 * distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
22 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
23 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
24 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
25 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
26 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
28 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
30 * OF THE POSSIBILITY OF SUCH DAMAGE.
31 */
32
33 /*
34 * This file contains the fallback implementation for secure_getenv(), which is
35 * currently only provided by glibc 2.17 and later. The goal is to ignore the
36 * environment if this process is (or previously was) running at elevated
37 * privilege compared to the calling process.
38 *
39 * In this fallback version we compare the real and effective uid/gid, and also
40 * compare the saved uid/gid if possible. These comparisons detect a setuid or
41 * setgid process which is still running with elevated privilege; if we can
42 * fetch the saved uid/gid, we also detect a process which has temporarily
43 * dropped privilege with seteuid() or setegid(). These comparisons do not
44 * detect the case where a setuid or setgid process has permanently dropped
45 * privilege before the library initializer ran; this is not ideal because such
46 * a process may possess a privileged resource or have privileged information
47 * in its address space.
48 *
49 * Heimdal also looks at the ELF aux vector in /proc/self/auxv to determine the
50 * starting uid/euid/gid/euid on Solaris/Illumos and NetBSD. On FreeBSD this
51 * approach can determine the executable path to do a stat() check. We do not
52 * go to this length due to the amount of code required.
53 *
54 * The BSDs and Solaris provide issetugid(), but the FreeBSD and NetBSD
55 * versions are not useful; they return true if a non-setuid/setgid executable
56 * is run by root and drops privilege, such as Apache httpd. We do not want to
57 * ignore the process environment in this case.
58 *
59 * On some platforms a process may have elevated privilege via mechanisms other
60 * than setuid/setgid. glibc's secure_getenv() should detect these cases on
61 * Linux; we do not detect them in this fallback version.
62 */
63
64 #include "k5-platform.h"
65
66 static int elevated_privilege = 0;
67
68 MAKE_INIT_FUNCTION(k5_secure_getenv_init);
69
70 int
k5_secure_getenv_init()71 k5_secure_getenv_init()
72 {
73 int saved_errno = errno;
74
75 #ifdef HAVE_GETRESUID
76 {
77 uid_t r, e, s;
78 if (getresuid(&r, &e, &s) == 0) {
79 if (r != e || r != s)
80 elevated_privilege = 1;
81 }
82 }
83 #else
84 if (getuid() != geteuid())
85 elevated_privilege = 1;
86 #endif
87
88 #ifdef HAVE_GETRESGID
89 {
90 gid_t r, e, s;
91 if (!elevated_privilege && getresgid(&r, &e, &s) == 0) {
92 if (r != e || r != s)
93 elevated_privilege = 1;
94 }
95 }
96 #else
97 if (!elevated_privilege && getgid() != getegid())
98 elevated_privilege = 1;
99 #endif
100
101 errno = saved_errno;
102 return 0;
103 }
104
105 char *
k5_secure_getenv(const char * name)106 k5_secure_getenv(const char *name)
107 {
108 if (CALL_INIT_FUNCTION(k5_secure_getenv_init) != 0)
109 return NULL;
110 return elevated_privilege ? NULL : getenv(name);
111 }
112