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/param.h>
31#include <sys/sysctl.h>
32#include <errno.h>
33#include <link.h>
34#include <signal.h>
35#include <string.h>
36#include <syslog.h>
37#include <unistd.h>
38#include "libc_private.h"
39
40/*
41 * We give __guard_setup a defined priority early on so that statically linked
42 * applications have a defined priority at which __stack_chk_guard will be
43 * getting initialized.  This will not matter to most applications, because
44 * they're either not usually statically linked or they simply don't do things
45 * in constructors that would be adversely affected by their positioning with
46 * respect to this initialization.
47 */
48static void __guard_setup(void)
49    __attribute__((__constructor__ (200), __used__));
50
51extern long __stack_chk_guard[8];
52extern int __sysctl(const int *name, u_int namelen, void *oldp,
53    size_t *oldlenp, void *newp, size_t newlen);
54
55long __stack_chk_guard[8] = {0, 0, 0, 0, 0, 0, 0, 0};
56static void __fail(const char *) __dead2;
57void __stack_chk_fail(void) __dead2;
58void __chk_fail(void) __dead2;
59
60/*LINTED used*/
61static void
62__guard_setup(void)
63{
64	static const int mib[2] = { CTL_KERN, KERN_ARND };
65	volatile long tmp_stack_chk_guard[nitems(__stack_chk_guard)];
66	size_t idx, len;
67	int error;
68
69	if (__stack_chk_guard[0] != 0)
70		return;
71	/*
72	 * Avoid using functions which might have stack protection
73	 * enabled, to update the __stack_chk_guard.  First fetch the
74	 * data into a temporal array, then do manual volatile copy to
75	 * not allow optimizer to call memcpy() behind us.
76	 */
77	error = _elf_aux_info(AT_CANARY,
78	    __DEQUALIFY(void *, tmp_stack_chk_guard),
79	    sizeof(tmp_stack_chk_guard));
80	if (error == 0 && tmp_stack_chk_guard[0] != 0) {
81		for (idx = 0; idx < nitems(__stack_chk_guard); idx++) {
82			__stack_chk_guard[idx] = tmp_stack_chk_guard[idx];
83			tmp_stack_chk_guard[idx] = 0;
84		}
85		return;
86	}
87
88	len = sizeof(__stack_chk_guard);
89	if (__sysctl(mib, nitems(mib), __stack_chk_guard, &len, NULL, 0) ==
90	    -1 || len != sizeof(__stack_chk_guard)) {
91		/* If sysctl was unsuccessful, use the "terminator canary". */
92		((unsigned char *)(void *)__stack_chk_guard)[0] = 0;
93		((unsigned char *)(void *)__stack_chk_guard)[1] = 0;
94		((unsigned char *)(void *)__stack_chk_guard)[2] = '\n';
95		((unsigned char *)(void *)__stack_chk_guard)[3] = 255;
96	}
97}
98
99/*ARGSUSED*/
100static void
101__fail(const char *msg)
102{
103	struct sigaction sa;
104	sigset_t mask;
105
106	/* Immediately block all signal handlers from running code */
107	(void)sigfillset(&mask);
108	(void)sigdelset(&mask, SIGABRT);
109	(void)sigprocmask(SIG_BLOCK, &mask, NULL);
110
111	/* This may fail on a chroot jail... */
112	syslog(LOG_CRIT, "%s", msg);
113
114	(void)memset(&sa, 0, sizeof(sa));
115	(void)sigemptyset(&sa.sa_mask);
116	sa.sa_flags = 0;
117	sa.sa_handler = SIG_DFL;
118	(void)sigaction(SIGABRT, &sa, NULL);
119	(void)kill(getpid(), SIGABRT);
120	_exit(127);
121}
122
123void
124__stack_chk_fail(void)
125{
126	__fail("stack overflow detected; terminated");
127}
128
129void
130__chk_fail(void)
131{
132	__fail("buffer overflow detected; terminated");
133}
134
135#ifndef PIC
136__weak_reference(__stack_chk_fail, __stack_chk_fail_local);
137#endif
138