usr/klibc/system.c

/*
 * system.c
 *
 * The system() function.  If this turns out to actually be *used*,
 * we may want to try to detect the very simple cases (no shell magic)
 * and handle them internally, instead of requiring that /bin/sh be
 * present.
 */

#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>

int system(const char *string)
{
	pid_t pid;
	struct sigaction ignore, old_int, old_quit;
	sigset_t masked, oldmask;
	static const char *argv[] = { "/bin/sh", "-c", NULL, NULL };
	int status;

	/* Block SIGCHLD and ignore SIGINT and SIGQUIT */
	/* Do this before the fork() to avoid races */

	ignore.sa_handler = SIG_IGN;
	sigemptyset(&ignore.sa_mask);
	ignore.sa_flags = 0;
	sigaction(SIGINT, &ignore, &old_int);
	sigaction(SIGQUIT, &ignore, &old_quit);

	sigemptyset(&masked);
	sigaddset(&masked, SIGCHLD);
	sigprocmask(SIG_BLOCK, &masked, &oldmask);

	pid = fork();

	if (pid < 0)
		return -1;
	else if (pid == 0) {
		sigaction(SIGINT, &old_int, NULL);
		sigaction(SIGQUIT, &old_quit, NULL);
		sigprocmask(SIG_SETMASK, &oldmask, NULL);

		argv[2] = string;

		execve(argv[0], (char *const *)argv, (char *const *)environ);
		_exit(127);
	}

	/* else... */

	waitpid(pid, &status, 0);

	sigaction(SIGINT, &old_int, NULL);
	sigaction(SIGQUIT, &old_quit, NULL);
	sigprocmask(SIG_SETMASK, &oldmask, NULL);

	return status;
}