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/* Dropping uid/gid privileges of the current process temporarily.
Copyright (C) 2009-2024 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
#include "idpriv.h"
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
/* The privileged uid and gid that the process had earlier. */
#if HAVE_GETUID
static uid_t saved_uid = -1;
#endif
#if HAVE_GETGID
static gid_t saved_gid = -1;
#endif
int
idpriv_temp_drop (void)
{
#if HAVE_GETEUID && HAVE_GETEGID && (HAVE_SETRESUID || HAVE_SETREUID) && (HAVE_SETRESGID || HAVE_SETREGID)
uid_t uid = getuid ();
gid_t gid = getgid ();
/* Find out about the privileged uid and gid at the first call. */
if (saved_uid == -1)
saved_uid = geteuid ();
if (saved_gid == -1)
saved_gid = getegid ();
/* Drop the gid privilege first, because in some cases the gid privilege
cannot be dropped after the uid privilege has been dropped. */
/* This is for executables that have the setgid bit set. */
# if HAVE_SETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
if (setresgid (-1, gid, saved_gid) < 0)
return -1;
# else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
if (setregid (-1, gid) < 0)
return -1;
# endif
/* This is for executables that have the setuid bit set. */
# if HAVE_SETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
/* See
Hao Chen, David Wagner, Drew Dean: Setuid Demystified
<https://www.usenix.org/legacy/publications/library/proceedings/sec02/full_papers/chen/chen.pdf>
figure 14. */
if (setresuid (-1, uid, saved_uid) < 0)
return -1;
# else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
if (setreuid (-1, uid) < 0)
return -1;
# endif
/* Verify that the privileges have really been dropped.
This verification is here for security reasons. Doesn't matter if it
takes a couple of system calls.
When the verification fails, it indicates that we need to use different
API in the code above. Therefore 'abort ()', not 'return -1'. */
# if HAVE_GETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
{
uid_t real;
uid_t effective;
uid_t saved;
if (getresuid (&real, &effective, &saved) < 0
|| real != uid
|| effective != uid
|| saved != saved_uid)
abort ();
}
# else
# if HAVE_GETEUID
if (geteuid () != uid)
abort ();
# endif
if (getuid () != uid)
abort ();
# endif
# if HAVE_GETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
{
uid_t real;
uid_t effective;
uid_t saved;
if (getresgid (&real, &effective, &saved) < 0
|| real != gid
|| effective != gid
|| saved != saved_gid)
abort ();
}
# else
# if HAVE_GETEGID
if (getegid () != gid)
abort ();
# endif
if (getgid () != gid)
abort ();
# endif
return 0;
#else
errno = ENOSYS;
return -1;
#endif
}
int
idpriv_temp_restore (void)
{
#if HAVE_GETEUID && HAVE_GETEGID && (HAVE_SETRESUID || HAVE_SETREUID) && (HAVE_SETRESGID || HAVE_SETREGID)
uid_t uid = getuid ();
gid_t gid = getgid ();
if (saved_uid == -1 || saved_gid == -1)
/* Caller error: idpriv_temp_drop was never invoked. */
abort ();
/* Acquire the gid privilege last, because in some cases the gid privilege
cannot be acquired before the uid privilege has been acquired. */
/* This is for executables that have the setuid bit set. */
# if HAVE_SETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
/* See
Hao Chen, David Wagner, Drew Dean: Setuid Demystified
<https://www.usenix.org/legacy/publications/library/proceedings/sec02/full_papers/chen/chen.pdf>
figure 14. */
if (setresuid (-1, saved_uid, -1) < 0)
return -1;
# else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
if (setreuid (-1, saved_uid) < 0)
return -1;
# endif
/* This is for executables that have the setgid bit set. */
# if HAVE_SETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
if (setresgid (-1, saved_gid, -1) < 0)
return -1;
# else /* Mac OS X, NetBSD, AIX, IRIX, Solaris >= 2.5, OSF/1, Cygwin */
if (setregid (-1, saved_gid) < 0)
return -1;
# endif
/* Verify that the privileges have really been acquired.
This verification is here for security reasons. Doesn't matter if it
takes a couple of system calls.
When the verification fails, it indicates that we need to use different
API in the code above. Therefore 'abort ()', not 'return -1'. */
# if HAVE_GETRESUID /* glibc, FreeBSD, OpenBSD, HP-UX */
{
uid_t real;
uid_t effective;
uid_t saved;
if (getresuid (&real, &effective, &saved) < 0
|| real != uid
|| effective != saved_uid
|| saved != saved_uid)
abort ();
}
# else
# if HAVE_GETEUID
if (geteuid () != saved_uid)
abort ();
# endif
if (getuid () != uid)
abort ();
# endif
# if HAVE_GETRESGID /* glibc, FreeBSD, OpenBSD, HP-UX */
{
uid_t real;
uid_t effective;
uid_t saved;
if (getresgid (&real, &effective, &saved) < 0
|| real != gid
|| effective != saved_gid
|| saved != saved_gid)
abort ();
}
# else
# if HAVE_GETEGID
if (getegid () != saved_gid)
abort ();
# endif
if (getgid () != gid)
abort ();
# endif
return 0;
#else
errno = ENOSYS;
return -1;
#endif
}
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