libc_stack_protector.c

/* $NetBSD: stack_protector.c,v 1.4 2006/11/22 17:23:25 christos Exp $	*/
/* $OpenBSD: stack_protector.c,v 1.10 2006/03/31 05:34:44 deraadt Exp $	*/
/*
 * Copyright (c) 2002 Hiroaki Etoh, Federico G. Schwindt, and Miodrag Vallat.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include <sys/param.h>
#include <sys/sysctl.h>
#include <errno.h>
#include <link.h>
#include <signal.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include "libc_private.h"

/*
 * We give __guard_setup a defined priority early on so that statically linked
 * applications have a defined priority at which __stack_chk_guard will be
 * getting initialized.  This will not matter to most applications, because
 * they're either not usually statically linked or they simply don't do things
 * in constructors that would be adversely affected by their positioning with
 * respect to this initialization.
 */
static void __guard_setup(void)
    __attribute__((__constructor__ (200), __used__));

extern long __stack_chk_guard[8];
extern int __sysctl(const int *name, u_int namelen, void *oldp,
    size_t *oldlenp, void *newp, size_t newlen);

long __stack_chk_guard[8] = {0, 0, 0, 0, 0, 0, 0, 0};
static void __fail(const char *) __dead2;
void __stack_chk_fail(void) __dead2;
void __chk_fail(void) __dead2;

/*LINTED used*/
static void
__guard_setup(void)
{
	static const int mib[2] = { CTL_KERN, KERN_ARND };
	volatile long tmp_stack_chk_guard[nitems(__stack_chk_guard)];
	size_t idx, len;
	int error;

	if (__stack_chk_guard[0] != 0)
		return;
	/*
	 * Avoid using functions which might have stack protection
	 * enabled, to update the __stack_chk_guard.  First fetch the
	 * data into a temporal array, then do manual volatile copy to
	 * not allow optimizer to call memcpy() behind us.
	 */
	error = _elf_aux_info(AT_CANARY,
	    __DEQUALIFY(void *, tmp_stack_chk_guard),
	    sizeof(tmp_stack_chk_guard));
	if (error == 0 && tmp_stack_chk_guard[0] != 0) {
		for (idx = 0; idx < nitems(__stack_chk_guard); idx++) {
			__stack_chk_guard[idx] = tmp_stack_chk_guard[idx];
			tmp_stack_chk_guard[idx] = 0;
		}
		return;
	}

	len = sizeof(__stack_chk_guard);
	if (__sysctl(mib, nitems(mib), __stack_chk_guard, &len, NULL, 0) ==
	    -1 || len != sizeof(__stack_chk_guard)) {
		/* If sysctl was unsuccessful, use the "terminator canary". */
		((unsigned char *)(void *)__stack_chk_guard)[0] = 0;
		((unsigned char *)(void *)__stack_chk_guard)[1] = 0;
		((unsigned char *)(void *)__stack_chk_guard)[2] = '\n';
		((unsigned char *)(void *)__stack_chk_guard)[3] = 255;
	}
}

/*ARGSUSED*/
static void
__fail(const char *msg)
{
	struct sigaction sa;
	sigset_t mask;

	/* Immediately block all signal handlers from running code */
	(void)sigfillset(&mask);
	(void)sigdelset(&mask, SIGABRT);
	(void)sigprocmask(SIG_BLOCK, &mask, NULL);

	/* This may fail on a chroot jail... */
	syslog(LOG_CRIT, "%s", msg);

	(void)memset(&sa, 0, sizeof(sa));
	(void)sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	sa.sa_handler = SIG_DFL;
	(void)sigaction(SIGABRT, &sa, NULL);
	(void)kill(getpid(), SIGABRT);
	_exit(127);
}

void
__stack_chk_fail(void)
{
	__fail("stack overflow detected; terminated");
}

void
__chk_fail(void)
{
	__fail("buffer overflow detected; terminated");
}

#ifndef PIC
__weak_reference(__stack_chk_fail, __stack_chk_fail_local);
#endif