lib/libc/sys/stack_protector.c

   1 /*
   2  * Copyright (c) 2002 Hiroaki Etoh, Federico G. Schwindt, and Miodrag Vallat.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  16  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  17  * DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT,
  18  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  19  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  20  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  22  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  23  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  24  * POSSIBILITY OF SUCH DAMAGE.
  25  *
  26  * $OpenBSD: stack_protector.c,v 1.3 2002/12/10 08:53:42 etoh Exp $
  27  */
  28
  29 #include "namespace.h"
  30 #include <sys/param.h>
  31 #include <sys/sysctl.h>
  32 #include <fcntl.h>
  33 #include <signal.h>
  34 #include <stdio.h>
  35 #include <string.h>
  36 #include <syslog.h>
  37 #include <unistd.h>
  38 #include "un-namespace.h"
  39
  40 extern int __sys_sigaction(int, const struct sigaction *, struct sigaction *);
  41
  42 static void __guard_setup(void) __attribute__ ((constructor));
  43 static void __fail(const char *);
  44 void __stack_chk_fail(void);
  45 void __chk_fail(void);
  46 void __stack_chk_fail_local(void);
  47
  48 long __stack_chk_guard[8] = {0, 0, 0, 0, 0, 0, 0, 0};
  49
  50 /* For compatibility with propolice used by gcc34. */
  51 void __stack_smash_handler(char func[], int damaged);
  52 extern __typeof(__stack_chk_guard) __guard __attribute__ ((alias ("__stack_chk_guard")));
  53
  54 static void
  55 __guard_setup(void)
  56 {
  57     int fd;
  58     ssize_t size;
  59
  60     if (__stack_chk_guard[0] != 0)
  61         return;
  62     if ((fd = _open ("/dev/urandom", 0)) >= 0) {
  63         size = _read (fd, (char*)&__stack_chk_guard, sizeof(__stack_chk_guard));
  64         _close (fd);
  65         if (size == sizeof(__stack_chk_guard))
  66             return;
  67     }
  68
  69     /*
  70      * If a random generator can't be used, the protector switches the
  71      * guard to the "terminator canary"
  72      */
  73     ((char*)__stack_chk_guard)[0] = 0;
  74     ((char*)__stack_chk_guard)[1] = 0;
  75     ((char*)__stack_chk_guard)[2] = '\n';
  76     ((char*)__stack_chk_guard)[3] = 255;
  77 }
  78
  79 static void
  80 __fail(const char *msg)
  81 {
  82     struct sigaction sa;
  83     sigset_t mask;
  84
  85     /* Immediately block all signal handlers from running code */
  86     sigfillset(&mask);
  87     sigdelset(&mask, SIGABRT);
  88     _sigprocmask(SIG_BLOCK, &mask, NULL);
  89
  90     /* This may fail on a chroot jail... */
  91     syslog(LOG_CRIT, msg);
  92
  93     bzero(&sa, sizeof(struct sigaction));
  94     sigemptyset(&sa.sa_mask);
  95     sa.sa_flags = 0;
  96     sa.sa_handler = SIG_DFL;
  97     __sys_sigaction(SIGABRT, &sa, NULL);
  98
  99     kill(getpid(), SIGABRT);
 100
 101     _exit(127);
 102 }
 103
 104 void
 105 __stack_smash_handler(char func[], int damaged  __unused)
 106 {
 107     static char buf[128];
 108
 109     vsnprintf(buf, sizeof(buf), "stack overflow in function %s", func);
 110     __fail(buf);
 111 }
 112
 113 void
 114 __stack_chk_fail(void)
 115 {
 116     __fail("stack overflow detected; terminated");
 117 }
 118
 119 void
 120 __chk_fail(void)
 121 {
 122     __fail("buffer overflow detected; terminated");
 123 }
 124
 125 void
 126 __stack_chk_fail_local(void)
 127 {
 128     __stack_chk_fail();
 129 }