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/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* util/support/secure_getenv.c - secure_getenv() portability support */
/*
* Copyright (C) 2019 by the Massachusetts Institute of Technology.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * 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.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
* COPYRIGHT HOLDER 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.
*/
/*
* This file contains the fallback implementation for secure_getenv(), which is
* currently only provided by glibc 2.17 and later. The goal is to ignore the
* environment if this process is (or previously was) running at elevated
* privilege compared to the calling process.
*
* In this fallback version we compare the real and effective uid/gid, and also
* compare the saved uid/gid if possible. These comparisons detect a setuid or
* setgid process which is still running with elevated privilege; if we can
* fetch the saved uid/gid, we also detect a process which has temporarily
* dropped privilege with seteuid() or setegid(). These comparisons do not
* detect the case where a setuid or setgid process has permanently dropped
* privilege before the library initializer ran; this is not ideal because such
* a process may possess a privileged resource or have privileged information
* in its address space.
*
* Heimdal also looks at the ELF aux vector in /proc/self/auxv to determine the
* starting uid/euid/gid/euid on Solaris/Illumos and NetBSD. On FreeBSD this
* approach can determine the executable path to do a stat() check. We do not
* go to this length due to the amount of code required.
*
* The BSDs and Solaris provide issetugid(), but the FreeBSD and NetBSD
* versions are not useful; they return true if a non-setuid/setgid executable
* is run by root and drops privilege, such as Apache httpd. We do not want to
* ignore the process environment in this case.
*
* On some platforms a process may have elevated privilege via mechanisms other
* than setuid/setgid. glibc's secure_getenv() should detect these cases on
* Linux; we do not detect them in this fallback version.
*/
#include "k5-platform.h"
static int elevated_privilege = 0;
MAKE_INIT_FUNCTION(k5_secure_getenv_init);
int
k5_secure_getenv_init(void)
{
int saved_errno = errno;
#ifdef HAVE_GETRESUID
{
uid_t r, e, s;
if (getresuid(&r, &e, &s) == 0) {
if (r != e || r != s)
elevated_privilege = 1;
}
}
#else
if (getuid() != geteuid())
elevated_privilege = 1;
#endif
#ifdef HAVE_GETRESGID
{
gid_t r, e, s;
if (!elevated_privilege && getresgid(&r, &e, &s) == 0) {
if (r != e || r != s)
elevated_privilege = 1;
}
}
#else
if (!elevated_privilege && getgid() != getegid())
elevated_privilege = 1;
#endif
errno = saved_errno;
return 0;
}
char *
k5_secure_getenv(const char *name)
{
if (CALL_INIT_FUNCTION(k5_secure_getenv_init) != 0)
return NULL;
return elevated_privilege ? NULL : getenv(name);
}
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