1/* $NetBSD: stack_protector.c,v 1.4 2006/11/22 17:23:25 christos Exp $	*/
2/* $OpenBSD: stack_protector.c,v 1.10 2006/03/31 05:34:44 deraadt Exp $	*/
3/*
4 * Copyright (c) 2002 Hiroaki Etoh, Federico G. Schwindt, and Miodrag Vallat.
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 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
19 * DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT,
20 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
21 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
22 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
24 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
25 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 *
28 */
29
30#include <sys/cdefs.h>
31__FBSDID("$FreeBSD$");
32
33#include <sys/param.h>
34#include <sys/sysctl.h>
35#include <errno.h>
36#include <link.h>
37#include <signal.h>
38#include <string.h>
39#include <syslog.h>
40#include <unistd.h>
41#include "libc_private.h"
42
43/*
44 * We give __guard_setup a defined priority early on so that statically linked
45 * applications have a defined priority at which __stack_chk_guard will be
46 * getting initialized.  This will not matter to most applications, because
47 * they're either not usually statically linked or they simply don't do things
48 * in constructors that would be adversely affected by their positioning with
49 * respect to this initialization.
50 *
51 * This conditional should be removed when GCC 4.2 is removed.
52 */
53#if __has_attribute(__constructor__) || __GNUC_PREREQ__(4, 3)
54#define	_GUARD_SETUP_CTOR_ATTR	 \
55    __attribute__((__constructor__ (200), __used__));
56#else
57#define	_GUARD_SETUP_CTOR_ATTR	\
58    __attribute__((__constructor__, __used__));
59#endif
60
61extern long __stack_chk_guard[8];
62extern int __sysctl(const int *name, u_int namelen, void *oldp,
63    size_t *oldlenp, void *newp, size_t newlen);
64
65long __stack_chk_guard[8] = {0, 0, 0, 0, 0, 0, 0, 0};
66static void __guard_setup(void) _GUARD_SETUP_CTOR_ATTR;
67static void __fail(const char *);
68void __stack_chk_fail(void);
69void __chk_fail(void);
70
71/*LINTED used*/
72static void
73__guard_setup(void)
74{
75	static const int mib[2] = { CTL_KERN, KERN_ARND };
76	volatile long tmp_stack_chk_guard[nitems(__stack_chk_guard)];
77	size_t idx, len;
78	int error;
79
80	if (__stack_chk_guard[0] != 0)
81		return;
82	/*
83	 * Avoid using functions which might have stack protection
84	 * enabled, to update the __stack_chk_guard.  First fetch the
85	 * data into a temporal array, then do manual volatile copy to
86	 * not allow optimizer to call memcpy() behind us.
87	 */
88	error = _elf_aux_info(AT_CANARY,
89	    __DEQUALIFY(void *, tmp_stack_chk_guard),
90	    sizeof(tmp_stack_chk_guard));
91	if (error == 0 && tmp_stack_chk_guard[0] != 0) {
92		for (idx = 0; idx < nitems(__stack_chk_guard); idx++) {
93			__stack_chk_guard[idx] = tmp_stack_chk_guard[idx];
94			tmp_stack_chk_guard[idx] = 0;
95		}
96		return;
97	}
98
99	len = sizeof(__stack_chk_guard);
100	if (__sysctl(mib, nitems(mib), __stack_chk_guard, &len, NULL, 0) ==
101	    -1 || len != sizeof(__stack_chk_guard)) {
102		/* If sysctl was unsuccessful, use the "terminator canary". */
103		((unsigned char *)(void *)__stack_chk_guard)[0] = 0;
104		((unsigned char *)(void *)__stack_chk_guard)[1] = 0;
105		((unsigned char *)(void *)__stack_chk_guard)[2] = '\n';
106		((unsigned char *)(void *)__stack_chk_guard)[3] = 255;
107	}
108}
109
110/*ARGSUSED*/
111static void
112__fail(const char *msg)
113{
114	struct sigaction sa;
115	sigset_t mask;
116
117	/* Immediately block all signal handlers from running code */
118	(void)sigfillset(&mask);
119	(void)sigdelset(&mask, SIGABRT);
120	(void)sigprocmask(SIG_BLOCK, &mask, NULL);
121
122	/* This may fail on a chroot jail... */
123	syslog(LOG_CRIT, "%s", msg);
124
125	(void)memset(&sa, 0, sizeof(sa));
126	(void)sigemptyset(&sa.sa_mask);
127	sa.sa_flags = 0;
128	sa.sa_handler = SIG_DFL;
129	(void)sigaction(SIGABRT, &sa, NULL);
130	(void)kill(getpid(), SIGABRT);
131	_exit(127);
132}
133
134void
135__stack_chk_fail(void)
136{
137	__fail("stack overflow detected; terminated");
138}
139
140void
141__chk_fail(void)
142{
143	__fail("buffer overflow detected; terminated");
144}
145
146#ifndef PIC
147__weak_reference(__stack_chk_fail, __stack_chk_fail_local);
148#endif
149