busybox/libbb/vfork_daemon_rexec.c
Ron Yorston 610c4c385b applet_tables: save space by removing applet name offsets
The array applet_nameofs consumes two bytes per applet.  It encodes

   nofork/noexec flags
   suid flags
   the offset of the applet name in the applet_name string

Change the applet_table build tool to store the flags in two separate
arrays (applet_flags and applet_suid).  Replace applet_nameofs[] with a
smaller version that only stores a limited number of offsets.

This requires changes to the macros APPLET_IS_NOFORK, APPLET_IS_NOEXEC
and APPLET_SUID.

   According to Valgrind the original find_applet_by_name required
   353 cycles per call, averaged over all names.  Adjusting the number
   of known offsets allows space to be traded off against execution time:

      KNOWN_OFFSETS     cycles     bytes (wrt KNOWN_OFFSETS = 0)

           0             9057        -
           2             4604       32
           4             2407       75
           8             1342       98
          16              908      130
          32              884      194

   This patch uses KNOWN_OFFSETS = 8.

v2:
   Remove some dead code from the applet_table tool;
   Treat the applet in the middle of the table as a special case.

v3:
   Use the middle applet to adjust the start of the linear search as
   well as the last applet found.

v4:
   Use an augmented linear search in find_applet_by_name.
   Drop the special treatment of the middle name from get_applet_name:
   most of the advantage now derives from the last stored value.

v5:
   Don't store index in applet_nameofs, it can be calculated.

v6:
   Tweaks by Denys

function                                             old     new   delta
find_applet_by_name                                   25     125    +100
applet_suid                                            -      92     +92
run_applet_no_and_exit                               452     460      +8
run_applet_and_exit                                  695     697      +2
applet_name_compare                                   31       -     -31
applet_nameofs                                       734      14    -720
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 3/1 up/down: 202/-751)         Total: -549 bytes
   text       data        bss        dec        hex    filename
 925464        906      17160     943530      e65aa    busybox_old
 924915        906      17160     942981      e6385    busybox_unstripped

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2016-03-30 00:44:11 +02:00

292 lines
7.7 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
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.
*
* 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++;
/* 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 */
#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);
}