hush/libbb/vfork_daemon_rexec.c
Peter Korsgaard 743edac6c8 bb_daemonize_or_rexec(): add flag to double-fork; use it in start-stop-daemon
Add a DAEMON_DOUBLE_FORK flag to make bb_daemonize double-fork so it isn't a
session leader, and hence doesn't get a controlling tty on Linux if a tty is
ever opened, similar to how libdaemon's daemon_fork or the big
start-stop-daemon does it - And use it in start-stop-daemon.

For details, see http://www.win.tue.nl/~aeb/linux/lk/lk-10.html#ss10.3

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2011-11-09 19:44:37 +01:00

282 lines
7.4 KiB
C

/* 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
struct nofork_save_area {
jmp_buf die_jmp;
const char *applet_name;
uint32_t option_mask32;
int die_sleep;
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->applet_name = applet_name;
save->xfunc_error_retval = xfunc_error_retval;
save->option_mask32 = option_mask32;
save->die_sleep = die_sleep;
}
static void 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(int applet_no, char **argv)
{
int rc, argc;
struct nofork_save_area old;
save_nofork_data(&old);
applet_name = APPLET_NAME(applet_no);
xfunc_error_retval = EXIT_FAILURE;
/* 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++;
/* 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;
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);
} 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 */
}
#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("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);
}