stack_protector

stack_protector

#include <sys/param.h>
#include <sys/sysctl.h>
#include <signal.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>

extern int __sysctl(int *, u_int, void *, size_t *, void *, size_t);

long __guard[8] = {0, 0, 0, 0, 0, 0, 0, 0};
static void __guard_setup(void) __attribute__ ((constructor));
void __stack_smash_handler(char func[], int damaged __attribute__((unused)));

static void
__guard_setup(void)
{
	int mib[2];
	size_t len;

	if (__guard[0] != 0)
		return;

	mib[0] = CTL_KERN;
	mib[1] = KERN_ARND;

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

/*ARGSUSED*/
void
__stack_smash_handler(char func[], int damaged)
{
	struct syslog_data sdata = SYSLOG_DATA_INIT;
	const char message[] = "stack overflow in function %s";
	struct sigaction sa;
	sigset_t mask;

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

	/* This may fail on a chroot jail... */
	syslog_r(LOG_CRIT, &sdata, message, func);

	bzero(&sa, sizeof(struct sigaction));
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = 0;
	sa.sa_handler = SIG_DFL;
	sigaction(SIGABRT, &sa, NULL);

	kill(getpid(), SIGABRT);

	_exit(127);
}