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 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 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 133 __stack_chk_fail(void) 134 { 135 __fail("stack overflow detected; terminated"); 136 } 137 138 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