libbb/vfork_daemon_rexec.c - busybox - Git at Google

 /* vi: set sw=4 ts=4: */
 /*
  * Rexec program for system have fork() as vfork() with foreground option
  *
  * Copyright (C) Vladimir N. Oleynik <dzo@simtreas.ru>
  * Copyright (C) 2003 Russ Dill <Russ.Dill@asu.edu>
  *
  * daemon() portion taken from uClibc:
  *
  * Copyright (c) 1991, 1993
  *      The Regents of the University of California.  All rights reserved.
  *
  * Modified for uClibc by Erik Andersen <andersee@debian.org>
  *
  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */

 #include "busybox.h" /* uses applet tables */

 /* This does a fork/exec in one call, using vfork().  Returns PID of new child,
  * -1 for failure.  Runs argv[0], searching path if that has no / in it. */
 pid_t FAST_FUNC spawn(char **argv)
 {
 	/* Compiler should not optimize stores here */
 	volatile int failed;
 	pid_t pid;

 	fflush_all();

 	/* Be nice to nommu machines. */
 	failed = 0;
 	pid = vfork();
 	if (pid < 0) /* error */
 		return pid;
 	if (!pid) { /* child */
 		/* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
 		BB_EXECVP(argv[0], argv);

 		/* We are (maybe) sharing a stack with blocked parent,
 		 * let parent know we failed and then exit to unblock parent
 		 * (but don't run atexit() stuff, which would screw up parent.)
 		 */
 		failed = errno;
 		/* mount, for example, does not want the message */
 		/*bb_perror_msg("can't execute '%s'", argv[0]);*/
 		_exit(111);
 	}
 	/* parent */
 	/* Unfortunately, this is not reliable: according to standards
 	 * vfork() can be equivalent to fork() and we won't see value
 	 * of 'failed'.
 	 * Interested party can wait on pid and learn exit code.
 	 * If 111 - then it (most probably) failed to exec */
 	if (failed) {
 		safe_waitpid(pid, NULL, 0); /* prevent zombie */
 		errno = failed;
 		return -1;
 	}
 	return pid;
 }

 /* Die with an error message if we can't spawn a child process. */
 pid_t FAST_FUNC xspawn(char **argv)
 {
 	pid_t pid = spawn(argv);
 	if (pid < 0)
 		bb_simple_perror_msg_and_die(*argv);
 	return pid;
 }

 #if ENABLE_FEATURE_PREFER_APPLETS \
  || ENABLE_FEATURE_SH_NOFORK
 static jmp_buf die_jmp;
 static void jump(void)
 {
 	/* Special case. We arrive here if NOFORK applet
 	 * calls xfunc, which then decides to die.
 	 * We don't die, but jump instead back to caller.
 	 * NOFORK applets still cannot carelessly call xfuncs:
 	 * p = xmalloc(10);
 	 * q = xmalloc(10); // BUG! if this dies, we leak p!
 	 */
 	/* | 0x100 allows to pass zero exitcode (longjmp can't pass 0).
 	 * This works because exitcodes are bytes,
 	 * run_nofork_applet() ensures that by "& 0xff" */
 	longjmp(die_jmp, xfunc_error_retval | 0x100);
 }

 struct nofork_save_area {
 	jmp_buf die_jmp;
 	void (*die_func)(void);
 	const char *applet_name;
 	uint32_t option_mask32;
 	uint8_t xfunc_error_retval;
 };
 static void save_nofork_data(struct nofork_save_area *save)
 {
 	memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
 	save->die_func = die_func;
 	save->applet_name = applet_name;
 	save->option_mask32 = option_mask32;
 	save->xfunc_error_retval = xfunc_error_retval;
 }
 static void restore_nofork_data(struct nofork_save_area *save)
 {
 	memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
 	die_func = save->die_func;
 	applet_name = save->applet_name;
 	option_mask32 = save->option_mask32;
 	xfunc_error_retval = save->xfunc_error_retval;
 }

 int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
 {
 	int rc, argc;
 	struct nofork_save_area old;

 	save_nofork_data(&old);

 	xfunc_error_retval = EXIT_FAILURE;

 	/* In case getopt() or getopt32() was already called:
 	 * reset the libc getopt() function, which keeps internal state.
 	 */
 	GETOPT_RESET();

 	argc = 1;
 	while (argv[argc])
 		argc++;

 	/* If xfunc "dies" in NOFORK applet, die_func longjmp's here instead */
 	die_func = jump;
 	rc = setjmp(die_jmp);
 	if (!rc) {
 		/* Some callers (xargs)
 		 * need argv untouched because they free argv[i]! */
 		char *tmp_argv[argc+1];
 		memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
 		applet_name = tmp_argv[0];
 		/* Finally we can call NOFORK applet's main() */
 		rc = applet_main[applet_no](argc, tmp_argv);
 	} else {
 		/* xfunc died in NOFORK applet */
 	}

 	/* Restoring some globals */
 	restore_nofork_data(&old);

 	/* Other globals can be simply reset to defaults */
 	GETOPT_RESET();

 	return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
 }
 #endif /* FEATURE_PREFER_APPLETS || FEATURE_SH_NOFORK */

 int FAST_FUNC spawn_and_wait(char **argv)
 {
 	int rc;
 #if ENABLE_FEATURE_PREFER_APPLETS
 	int a = find_applet_by_name(argv[0]);

 	if (a >= 0) {
 		if (APPLET_IS_NOFORK(a))
 			return run_nofork_applet(a, argv);
 # if BB_MMU /* NOEXEC needs fork(), thus this is done only on MMU machines: */
 		if (APPLET_IS_NOEXEC(a)) {
 			fflush_all();
 			rc = fork();
 			if (rc) /* parent or error */
 				return wait4pid(rc);

 			/* child */
 			/* reset some state and run without execing */

 			/* msg_eol = "\n"; - no caller needs this reinited yet */
 			logmode = LOGMODE_STDIO;
 			/* die_func = NULL; - needed if the caller is a shell,
 			 * init, or a NOFORK applet. But none of those call us
 			 * as of yet (and that should probably always stay true).
 			 */
 			/* xfunc_error_retval and applet_name are init by: */
 			run_applet_no_and_exit(a, argv);
 		}
 # endif
 	}
 #endif /* FEATURE_PREFER_APPLETS */
 	rc = spawn(argv);
 	return wait4pid(rc);
 }

 #if !BB_MMU
 void FAST_FUNC re_exec(char **argv)
 {
 	/* high-order bit of first char in argv[0] is a hidden
 	 * "we have (already) re-execed, don't do it again" flag */
 	argv[0][0] |= 0x80;
 	execv(bb_busybox_exec_path, argv);
 	bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
 }

 pid_t FAST_FUNC fork_or_rexec(char **argv)
 {
 	pid_t pid;
 	/* Maybe we are already re-execed and come here again? */
 	if (re_execed)
 		return 0;
 	pid = xvfork();
 	if (pid) /* parent */
 		return pid;
 	/* child - re-exec ourself */
 	re_exec(argv);
 }
 #endif

 /* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
  * char **argv "vanishes" */
 void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
 {
 	int fd;

 	if (flags & DAEMON_CHDIR_ROOT)
 		xchdir("/");

 	if (flags & DAEMON_DEVNULL_STDIO) {
 		close(0);
 		close(1);
 		close(2);
 	}

 	fd = open(bb_dev_null, O_RDWR);
 	if (fd < 0) {
 		/* NB: we can be called as bb_sanitize_stdio() from init
 		 * or mdev, and there /dev/null may legitimately not (yet) exist!
 		 * Do not use xopen above, but obtain _ANY_ open descriptor,
 		 * even bogus one as below. */
 		fd = xopen("/", O_RDONLY); /* don't believe this can fail */
 	}

 	while ((unsigned)fd < 2)
 		fd = dup(fd); /* have 0,1,2 open at least to /dev/null */

 	if (!(flags & DAEMON_ONLY_SANITIZE)) {
 		if (fork_or_rexec(argv))
 			exit(EXIT_SUCCESS); /* parent */
 		/* if daemonizing, detach from stdio & ctty */
 		setsid();
 		dup2(fd, 0);
 		dup2(fd, 1);
 		dup2(fd, 2);
 		if (flags & DAEMON_DOUBLE_FORK) {
 			/* On Linux, session leader can acquire ctty
 			 * unknowingly, by opening a tty.
 			 * Prevent this: stop being a session leader.
 			 */
 			if (fork_or_rexec(argv))
 				exit(EXIT_SUCCESS); /* parent */
 		}
 	}
 	while (fd > 2) {
 		close(fd--);
 		if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
 			return;
 		/* else close everything after fd#2 */
 	}
 }

 void FAST_FUNC bb_sanitize_stdio(void)
 {
 	bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
 }
	/* vi: set sw=4 ts=4: */
	/*
	* Rexec program for system have fork() as vfork() with foreground option
	*
	* Copyright (C) Vladimir N. Oleynik <dzo@simtreas.ru>
	* Copyright (C) 2003 Russ Dill <Russ.Dill@asu.edu>
	*
	* daemon() portion taken from uClibc:
	*
	* Copyright (c) 1991, 1993
	* The Regents of the University of California. All rights reserved.
	*
	* Modified for uClibc by Erik Andersen <andersee@debian.org>
	*
	* Licensed under GPLv2 or later, see file LICENSE in this source tree.
	*/

	#include "busybox.h" /* uses applet tables */

	/* This does a fork/exec in one call, using vfork(). Returns PID of new child,
	* -1 for failure. Runs argv[0], searching path if that has no / in it. */
	pid_t FAST_FUNC spawn(char **argv)
	{
	/* Compiler should not optimize stores here */
	volatile int failed;
	pid_t pid;

	fflush_all();

	/* Be nice to nommu machines. */
	failed = 0;
	pid = vfork();
	if (pid < 0) /* error */
	return pid;
	if (!pid) { /* child */
	/* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
	BB_EXECVP(argv[0], argv);

	/* We are (maybe) sharing a stack with blocked parent,
	* let parent know we failed and then exit to unblock parent
	* (but don't run atexit() stuff, which would screw up parent.)
	*/
	failed = errno;
	/* mount, for example, does not want the message */
	/bb_perror_msg("can't execute '%s'", argv[0]);/
	_exit(111);
	}
	/* parent */
	/* Unfortunately, this is not reliable: according to standards
	* vfork() can be equivalent to fork() and we won't see value
	* of 'failed'.
	* Interested party can wait on pid and learn exit code.
	* If 111 - then it (most probably) failed to exec */
	if (failed) {
	safe_waitpid(pid, NULL, 0); /* prevent zombie */
	errno = failed;
	return -1;
	}
	return pid;
	}

	/* Die with an error message if we can't spawn a child process. */
	pid_t FAST_FUNC xspawn(char **argv)
	{
	pid_t pid = spawn(argv);
	if (pid < 0)
	bb_simple_perror_msg_and_die(*argv);
	return pid;
	}

	#if ENABLE_FEATURE_PREFER_APPLETS \
	\|\| ENABLE_FEATURE_SH_NOFORK
	static jmp_buf die_jmp;
	static void jump(void)
	{
	/* Special case. We arrive here if NOFORK applet
	* calls xfunc, which then decides to die.
	* We don't die, but jump instead back to caller.
	* NOFORK applets still cannot carelessly call xfuncs:
	* p = xmalloc(10);
	* q = xmalloc(10); // BUG! if this dies, we leak p!
	*/
	/* \| 0x100 allows to pass zero exitcode (longjmp can't pass 0).
	* This works because exitcodes are bytes,
	* run_nofork_applet() ensures that by "& 0xff" */
	longjmp(die_jmp, xfunc_error_retval \| 0x100);
	}

	struct nofork_save_area {
	jmp_buf die_jmp;
	void (*die_func)(void);
	const char *applet_name;
	uint32_t option_mask32;
	uint8_t xfunc_error_retval;
	};
	static void save_nofork_data(struct nofork_save_area *save)
	{
	memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
	save->die_func = die_func;
	save->applet_name = applet_name;
	save->option_mask32 = option_mask32;
	save->xfunc_error_retval = xfunc_error_retval;
	}
	static void restore_nofork_data(struct nofork_save_area *save)
	{
	memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
	die_func = save->die_func;
	applet_name = save->applet_name;
	option_mask32 = save->option_mask32;
	xfunc_error_retval = save->xfunc_error_retval;
	}

	int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
	{
	int rc, argc;
	struct nofork_save_area old;

	save_nofork_data(&old);

	xfunc_error_retval = EXIT_FAILURE;

	/* In case getopt() or getopt32() was already called:
	* reset the libc getopt() function, which keeps internal state.
	*/
	GETOPT_RESET();

	argc = 1;
	while (argv[argc])
	argc++;

	/* If xfunc "dies" in NOFORK applet, die_func longjmp's here instead */
	die_func = jump;
	rc = setjmp(die_jmp);
	if (!rc) {
	/* Some callers (xargs)
	* need argv untouched because they free argv[i]! */
	char *tmp_argv[argc+1];
	memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
	applet_name = tmp_argv[0];
	/* Finally we can call NOFORK applet's main() */
	rc = applet_main[applet_no](argc, tmp_argv);
	} else {
	/* xfunc died in NOFORK applet */
	}

	/* Restoring some globals */
	restore_nofork_data(&old);

	/* Other globals can be simply reset to defaults */
	GETOPT_RESET();

	return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
	}
	#endif /* FEATURE_PREFER_APPLETS \|\| FEATURE_SH_NOFORK */

	int FAST_FUNC spawn_and_wait(char **argv)
	{
	int rc;
	#if ENABLE_FEATURE_PREFER_APPLETS
	int a = find_applet_by_name(argv[0]);

	if (a >= 0) {
	if (APPLET_IS_NOFORK(a))
	return run_nofork_applet(a, argv);
	# if BB_MMU /* NOEXEC needs fork(), thus this is done only on MMU machines: */
	if (APPLET_IS_NOEXEC(a)) {
	fflush_all();
	rc = fork();
	if (rc) /* parent or error */
	return wait4pid(rc);

	/* child */
	/* reset some state and run without execing */

	/* msg_eol = "\n"; - no caller needs this reinited yet */
	logmode = LOGMODE_STDIO;
	/* die_func = NULL; - needed if the caller is a shell,
	* init, or a NOFORK applet. But none of those call us
	* as of yet (and that should probably always stay true).
	*/
	/* xfunc_error_retval and applet_name are init by: */
	run_applet_no_and_exit(a, argv);
	}
	# endif
	}
	#endif /* FEATURE_PREFER_APPLETS */
	rc = spawn(argv);
	return wait4pid(rc);
	}

	#if !BB_MMU
	void FAST_FUNC re_exec(char **argv)
	{
	/* high-order bit of first char in argv[0] is a hidden
	* "we have (already) re-execed, don't do it again" flag */
	argv[0][0] \|= 0x80;
	execv(bb_busybox_exec_path, argv);
	bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
	}

	pid_t FAST_FUNC fork_or_rexec(char **argv)
	{
	pid_t pid;
	/* Maybe we are already re-execed and come here again? */
	if (re_execed)
	return 0;
	pid = xvfork();
	if (pid) /* parent */
	return pid;
	/* child - re-exec ourself */
	re_exec(argv);
	}
	#endif

	/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
	* char *argv "vanishes" /
	void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
	{
	int fd;

	if (flags & DAEMON_CHDIR_ROOT)
	xchdir("/");

	if (flags & DAEMON_DEVNULL_STDIO) {
	close(0);
	close(1);
	close(2);
	}

	fd = open(bb_dev_null, O_RDWR);
	if (fd < 0) {
	/* NB: we can be called as bb_sanitize_stdio() from init
	* or mdev, and there /dev/null may legitimately not (yet) exist!
	* Do not use xopen above, but obtain _ANY_ open descriptor,
	* even bogus one as below. */
	fd = xopen("/", O_RDONLY); /* don't believe this can fail */
	}

	while ((unsigned)fd < 2)
	fd = dup(fd); /* have 0,1,2 open at least to /dev/null */

	if (!(flags & DAEMON_ONLY_SANITIZE)) {
	if (fork_or_rexec(argv))
	exit(EXIT_SUCCESS); /* parent */
	/* if daemonizing, detach from stdio & ctty */
	setsid();
	dup2(fd, 0);
	dup2(fd, 1);
	dup2(fd, 2);
	if (flags & DAEMON_DOUBLE_FORK) {
	/* On Linux, session leader can acquire ctty
	* unknowingly, by opening a tty.
	* Prevent this: stop being a session leader.
	*/
	if (fork_or_rexec(argv))
	exit(EXIT_SUCCESS); /* parent */
	}
	}
	while (fd > 2) {
	close(fd--);
	if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
	return;
	/* else close everything after fd#2 */
	}
	}

	void FAST_FUNC bb_sanitize_stdio(void)
	{
	bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
	}