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 tarball for details.
  */

 #include <paths.h>
 #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;

 // Ain't it a good place to fflush(NULL)?

 	/* 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;
 		_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) {
 		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;
 }

 pid_t FAST_FUNC safe_waitpid(pid_t pid, int *wstat, int options)
 {
 	pid_t r;

 	do
 		r = waitpid(pid, wstat, options);
 	while ((r == -1) && (errno == EINTR));
 	return r;
 }

 pid_t FAST_FUNC wait_any_nohang(int *wstat)
 {
 	return safe_waitpid(-1, wstat, WNOHANG);
 }

 // Wait for the specified child PID to exit, returning child's error return.
 int FAST_FUNC wait4pid(pid_t pid)
 {
 	int status;

 	if (pid <= 0) {
 		/*errno = ECHILD; -- wrong. */
 		/* we expect errno to be already set from failed [v]fork/exec */
 		return -1;
 	}
 	if (safe_waitpid(pid, &status, 0) == -1)
 		return -1;
 	if (WIFEXITED(status))
 		return WEXITSTATUS(status);
 	if (WIFSIGNALED(status))
 		return WTERMSIG(status) + 1000;
 	return 0;
 }

 #if ENABLE_FEATURE_PREFER_APPLETS
 void FAST_FUNC save_nofork_data(struct nofork_save_area *save)
 {
 	memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
 	save->applet_name = applet_name;
 	save->xfunc_error_retval = xfunc_error_retval;
 	save->option_mask32 = option_mask32;
 	save->die_sleep = die_sleep;
 	save->saved = 1;
 }

 void FAST_FUNC restore_nofork_data(struct nofork_save_area *save)
 {
 	memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
 	applet_name = save->applet_name;
 	xfunc_error_retval = save->xfunc_error_retval;
 	option_mask32 = save->option_mask32;
 	die_sleep = save->die_sleep;
 }

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

 	applet_name = APPLET_NAME(applet_no);

 	xfunc_error_retval = EXIT_FAILURE;

 	/* Special flag for xfunc_die(). If xfunc will "die"
 	 * in NOFORK applet, xfunc_die() sees negative
 	 * die_sleep and longjmp here instead. */
 	die_sleep = -1;

 	/* In case getopt() or getopt32() was already called:
 	 * reset the libc getopt() function, which keeps internal state.
 	 *
 	 * BSD-derived getopt() functions require that optind be set to 1 in
 	 * order to reset getopt() state.  This used to be generally accepted
 	 * way of resetting getopt().  However, glibc's getopt()
 	 * has additional getopt() state beyond optind, and requires that
 	 * optind be set to zero to reset its state.  So the unfortunate state of
 	 * affairs is that BSD-derived versions of getopt() misbehave if
 	 * optind is set to 0 in order to reset getopt(), and glibc's getopt()
 	 * will core dump if optind is set 1 in order to reset getopt().
 	 *
 	 * More modern versions of BSD require that optreset be set to 1 in
 	 * order to reset getopt().  Sigh.  Standards, anyone?
 	 */
 #ifdef __GLIBC__
 	optind = 0;
 #else /* BSD style */
 	optind = 1;
 	/* optreset = 1; */
 #endif
 	/* optarg = NULL; opterr = 1; optopt = 63; - do we need this too? */
 	/* (values above are what they initialized to in glibc and uclibc) */
 	/* option_mask32 = 0; - not needed, no applet depends on it being 0 */

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

 	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]));
 		/* Finally we can call NOFORK applet's main() */
 		rc = applet_main[applet_no](argc, tmp_argv);

 	/* The whole reason behind nofork_save_area is that <applet>_main
 	 * may exit non-locally! For example, in hush Ctrl-Z tries
 	 * (modulo bugs) to dynamically create a child (backgrounded task)
 	 * if it detects that Ctrl-Z was pressed when a NOFORK was running.
 	 * Testcase: interactive "rm -i".
 	 * Don't fool yourself into thinking "and <applet>_main() returns
 	 * quickly here" and removing "useless" nofork_save_area code. */

 	} else { /* xfunc died in NOFORK applet */
 		/* in case they meant to return 0... */
 		if (rc == -2222)
 			rc = 0;
 	}

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

 	/* Other globals can be simply reset to defaults */
 #ifdef __GLIBC__
 	optind = 0;
 #else /* BSD style */
 	optind = 1;
 #endif

 	return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
 }

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

 	/* Saving globals */
 	save_nofork_data(&old);
 	return run_nofork_applet_prime(&old, applet_no, argv);
 }
 #endif /* FEATURE_PREFER_APPLETS */

 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 && (APPLET_IS_NOFORK(a)
 #if BB_MMU
 			|| APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
 #endif
 	)) {
 #if BB_MMU
 		if (APPLET_IS_NOFORK(a))
 #endif
 		{
 			return run_nofork_applet(a, argv);
 		}
 #if BB_MMU
 		/* MMU only */
 		/* a->noexec is true */
 		rc = fork();
 		if (rc) /* parent or error */
 			return wait4pid(rc);
 		/* child */
 		xfunc_error_retval = EXIT_FAILURE;
 		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("exec %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 = vfork();
 	if (pid < 0) /* wtf? */
 		bb_perror_msg_and_die("vfork");
 	if (pid) /* parent */
 		return pid;
 	/* child - re-exec ourself */
 	re_exec(argv);
 }
 #else
 /* Dance around (void)...*/
 #undef fork_or_rexec
 pid_t FAST_FUNC fork_or_rexec(void)
 {
 	pid_t pid;
 	pid = fork();
 	if (pid < 0) /* wtf? */
 		bb_perror_msg_and_die("fork");
 	return pid;
 }
 #define fork_or_rexec(argv) fork_or_rexec()
 #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, make sure we detach from stdio & ctty */
 		setsid();
 		dup2(fd, 0);
 		dup2(fd, 1);
 		dup2(fd, 2);
 	}
 	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 tarball for details.
	*/

	#include <paths.h>
	#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;

	// Ain't it a good place to fflush(NULL)?

	/* 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;
	_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) {
	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;
	}

	pid_t FAST_FUNC safe_waitpid(pid_t pid, int *wstat, int options)
	{
	pid_t r;

	do
	r = waitpid(pid, wstat, options);
	while ((r == -1) && (errno == EINTR));
	return r;
	}

	pid_t FAST_FUNC wait_any_nohang(int *wstat)
	{
	return safe_waitpid(-1, wstat, WNOHANG);
	}

	// Wait for the specified child PID to exit, returning child's error return.
	int FAST_FUNC wait4pid(pid_t pid)
	{
	int status;

	if (pid <= 0) {
	/errno = ECHILD; -- wrong. /
	/* we expect errno to be already set from failed [v]fork/exec */
	return -1;
	}
	if (safe_waitpid(pid, &status, 0) == -1)
	return -1;
	if (WIFEXITED(status))
	return WEXITSTATUS(status);
	if (WIFSIGNALED(status))
	return WTERMSIG(status) + 1000;
	return 0;
	}

	#if ENABLE_FEATURE_PREFER_APPLETS
	void FAST_FUNC save_nofork_data(struct nofork_save_area *save)
	{
	memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
	save->applet_name = applet_name;
	save->xfunc_error_retval = xfunc_error_retval;
	save->option_mask32 = option_mask32;
	save->die_sleep = die_sleep;
	save->saved = 1;
	}

	void FAST_FUNC restore_nofork_data(struct nofork_save_area *save)
	{
	memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
	applet_name = save->applet_name;
	xfunc_error_retval = save->xfunc_error_retval;
	option_mask32 = save->option_mask32;
	die_sleep = save->die_sleep;
	}

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

	applet_name = APPLET_NAME(applet_no);

	xfunc_error_retval = EXIT_FAILURE;

	/* Special flag for xfunc_die(). If xfunc will "die"
	* in NOFORK applet, xfunc_die() sees negative
	* die_sleep and longjmp here instead. */
	die_sleep = -1;

	/* In case getopt() or getopt32() was already called:
	* reset the libc getopt() function, which keeps internal state.
	*
	* BSD-derived getopt() functions require that optind be set to 1 in
	* order to reset getopt() state. This used to be generally accepted
	* way of resetting getopt(). However, glibc's getopt()
	* has additional getopt() state beyond optind, and requires that
	* optind be set to zero to reset its state. So the unfortunate state of
	* affairs is that BSD-derived versions of getopt() misbehave if
	* optind is set to 0 in order to reset getopt(), and glibc's getopt()
	* will core dump if optind is set 1 in order to reset getopt().
	*
	* More modern versions of BSD require that optreset be set to 1 in
	* order to reset getopt(). Sigh. Standards, anyone?
	*/
	#ifdef __GLIBC__
	optind = 0;
	#else /* BSD style */
	optind = 1;
	/* optreset = 1; */
	#endif
	/* optarg = NULL; opterr = 1; optopt = 63; - do we need this too? */
	/* (values above are what they initialized to in glibc and uclibc) */
	/* option_mask32 = 0; - not needed, no applet depends on it being 0 */

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

	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]));
	/* Finally we can call NOFORK applet's main() */
	rc = applet_main[applet_no](argc, tmp_argv);

	/* The whole reason behind nofork_save_area is that <applet>_main
	* may exit non-locally! For example, in hush Ctrl-Z tries
	* (modulo bugs) to dynamically create a child (backgrounded task)
	* if it detects that Ctrl-Z was pressed when a NOFORK was running.
	* Testcase: interactive "rm -i".
	* Don't fool yourself into thinking "and <applet>_main() returns
	* quickly here" and removing "useless" nofork_save_area code. */

	} else { /* xfunc died in NOFORK applet */
	/* in case they meant to return 0... */
	if (rc == -2222)
	rc = 0;
	}

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

	/* Other globals can be simply reset to defaults */
	#ifdef __GLIBC__
	optind = 0;
	#else /* BSD style */
	optind = 1;
	#endif

	return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
	}

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

	/* Saving globals */
	save_nofork_data(&old);
	return run_nofork_applet_prime(&old, applet_no, argv);
	}
	#endif /* FEATURE_PREFER_APPLETS */

	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 && (APPLET_IS_NOFORK(a)
	#if BB_MMU
	\|\| APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
	#endif
	)) {
	#if BB_MMU
	if (APPLET_IS_NOFORK(a))
	#endif
	{
	return run_nofork_applet(a, argv);
	}
	#if BB_MMU
	/* MMU only */
	/* a->noexec is true */
	rc = fork();
	if (rc) /* parent or error */
	return wait4pid(rc);
	/* child */
	xfunc_error_retval = EXIT_FAILURE;
	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("exec %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 = vfork();
	if (pid < 0) /* wtf? */
	bb_perror_msg_and_die("vfork");
	if (pid) /* parent */
	return pid;
	/* child - re-exec ourself */
	re_exec(argv);
	}
	#else
	/* Dance around (void)...*/
	#undef fork_or_rexec
	pid_t FAST_FUNC fork_or_rexec(void)
	{
	pid_t pid;
	pid = fork();
	if (pid < 0) /* wtf? */
	bb_perror_msg_and_die("fork");
	return pid;
	}
	#define fork_or_rexec(argv) fork_or_rexec()
	#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, make sure we detach from stdio & ctty */
	setsid();
	dup2(fd, 0);
	dup2(fd, 1);
	dup2(fd, 2);
	}
	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);
	}