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
61 extern int __sysctl(const int *name, u_int namelen, void *oldp,
62 size_t *oldlenp, void *newp, size_t newlen);
63
64 long __stack_chk_guard[8] = {0, 0, 0, 0, 0, 0, 0, 0};
65 static void __guard_setup(void) _GUARD_SETUP_CTOR_ATTR;
66 static void __fail(const char *);
67 void __stack_chk_fail(void);
68 void __chk_fail(void);
69
70 /*LINTED used*/
71 static void
__guard_setup(void)72 __guard_setup(void)
73 {
74 static const int mib[2] = { CTL_KERN, KERN_ARND };
75 volatile long tmp_stack_chk_guard[nitems(__stack_chk_guard)];
76 size_t len;
77 int error, idx;
78
79 if (__stack_chk_guard[0] != 0)
80 return;
81 /*
82 * Avoid using functions which might have stack protection
83 * enabled, to update the __stack_chk_guard. First fetch the
84 * data into a temporal array, then do manual volatile copy to
85 * not allow optimizer to call memcpy() behind us.
86 */
87 error = _elf_aux_info(AT_CANARY, (void *)tmp_stack_chk_guard,
88 sizeof(tmp_stack_chk_guard));
89 if (error == 0 && tmp_stack_chk_guard[0] != 0) {
90 for (idx = 0; idx < nitems(__stack_chk_guard); idx++) {
91 __stack_chk_guard[idx] = tmp_stack_chk_guard[idx];
92 tmp_stack_chk_guard[idx] = 0;
93 }
94 return;
95 }
96
97 len = sizeof(__stack_chk_guard);
98 if (__sysctl(mib, nitems(mib), __stack_chk_guard, &len, NULL, 0) ==
99 -1 || len != sizeof(__stack_chk_guard)) {
100 /* If sysctl was unsuccessful, use the "terminator canary". */
101 ((unsigned char *)(void *)__stack_chk_guard)[0] = 0;
102 ((unsigned char *)(void *)__stack_chk_guard)[1] = 0;
103 ((unsigned char *)(void *)__stack_chk_guard)[2] = '\n';
104 ((unsigned char *)(void *)__stack_chk_guard)[3] = 255;
105 }
106 }
107
108 /*ARGSUSED*/
109 static void
__fail(const char * msg)110 __fail(const char *msg)
111 {
112 struct sigaction sa;
113 sigset_t mask;
114
115 /* Immediately block all signal handlers from running code */
116 (void)sigfillset(&mask);
117 (void)sigdelset(&mask, SIGABRT);
118 (void)sigprocmask(SIG_BLOCK, &mask, NULL);
119
120 /* This may fail on a chroot jail... */
121 syslog(LOG_CRIT, "%s", msg);
122
123 (void)memset(&sa, 0, sizeof(sa));
124 (void)sigemptyset(&sa.sa_mask);
125 sa.sa_flags = 0;
126 sa.sa_handler = SIG_DFL;
127 (void)sigaction(SIGABRT, &sa, NULL);
128 (void)kill(getpid(), SIGABRT);
129 _exit(127);
130 }
131
132 void
__stack_chk_fail(void)133 __stack_chk_fail(void)
134 {
135 __fail("stack overflow detected; terminated");
136 }
137
138 void
__chk_fail(void)139 __chk_fail(void)
140 {
141 __fail("buffer overflow detected; terminated");
142 }
143
144 #ifndef PIC
145 __weak_reference(__stack_chk_fail, __stack_chk_fail_local);
146 #endif
147