LXR busybox/libbb/vfork_daemon

   1/* vi: set sw=4 ts=4: */
   2/*
   3 * Rexec program for system have fork() as vfork() with foreground option
   4 *
   5 * Copyright (C) Vladimir N. Oleynik <dzo@simtreas.ru>
   6 * Copyright (C) 2003 Russ Dill <Russ.Dill@asu.edu>
   7 *
   8 * daemon() portion taken from uClibc:
   9 *
  10 * Copyright (c) 1991, 1993
  11 *      The Regents of the University of California.  All rights reserved.
  12 *
  13 * Modified for uClibc by Erik Andersen <andersee@debian.org>
  14 *
  15 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  16 */
  17
  18#include <paths.h>
  19#include "busybox.h" /* uses applet tables */
  20
  21/* This does a fork/exec in one call, using vfork().  Returns PID of new child,
  22 * -1 for failure.  Runs argv[0], searching path if that has no / in it. */
  23pid_t FAST_FUNC spawn(char **argv)
  24{
  25        /* Compiler should not optimize stores here */
  26        volatile int failed;
  27        pid_t pid;
  28
  29// Ain't it a good place to fflush(NULL)?
  30
  31        /* Be nice to nommu machines. */
  32        failed = 0;
  33        pid = vfork();
  34        if (pid < 0) /* error */
  35                return pid;
  36        if (!pid) { /* child */
  37                /* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
  38                BB_EXECVP(argv[0], argv);
  39
  40                /* We are (maybe) sharing a stack with blocked parent,
  41                 * let parent know we failed and then exit to unblock parent
  42                 * (but don't run atexit() stuff, which would screw up parent.)
  43                 */
  44                failed = errno;
  45                _exit(111);
  46        }
  47        /* parent */
  48        /* Unfortunately, this is not reliable: according to standards
  49         * vfork() can be equivalent to fork() and we won't see value
  50         * of 'failed'.
  51         * Interested party can wait on pid and learn exit code.
  52         * If 111 - then it (most probably) failed to exec */
  53        if (failed) {
  54                errno = failed;
  55                return -1;
  56        }
  57        return pid;
  58}
  59
  60/* Die with an error message if we can't spawn a child process. */
  61pid_t FAST_FUNC xspawn(char **argv)
  62{
  63        pid_t pid = spawn(argv);
  64        if (pid < 0)
  65                bb_simple_perror_msg_and_die(*argv);
  66        return pid;
  67}
  68
  69pid_t FAST_FUNC safe_waitpid(pid_t pid, int *wstat, int options)
  70{
  71        pid_t r;
  72
  73        do
  74                r = waitpid(pid, wstat, options);
  75        while ((r == -1) && (errno == EINTR));
  76        return r;
  77}
  78
  79pid_t FAST_FUNC wait_any_nohang(int *wstat)
  80{
  81        return safe_waitpid(-1, wstat, WNOHANG);
  82}
  83
  84// Wait for the specified child PID to exit, returning child's error return.
  85int FAST_FUNC wait4pid(pid_t pid)
  86{
  87        int status;
  88
  89        if (pid <= 0) {
  90                /*errno = ECHILD; -- wrong. */
  91                /* we expect errno to be already set from failed [v]fork/exec */
  92                return -1;
  93        }
  94        if (safe_waitpid(pid, &status, 0) == -1)
  95                return -1;
  96        if (WIFEXITED(status))
  97                return WEXITSTATUS(status);
  98        if (WIFSIGNALED(status))
  99                return WTERMSIG(status) + 1000;
 100        return 0;
 101}
 102
 103#if ENABLE_FEATURE_PREFER_APPLETS
 104void FAST_FUNC save_nofork_data(struct nofork_save_area *save)
 105{
 106        memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
 107        save->applet_name = applet_name;
 108        save->xfunc_error_retval = xfunc_error_retval;
 109        save->option_mask32 = option_mask32;
 110        save->die_sleep = die_sleep;
 111        save->saved = 1;
 112}
 113
 114void FAST_FUNC restore_nofork_data(struct nofork_save_area *save)
 115{
 116        memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
 117        applet_name = save->applet_name;
 118        xfunc_error_retval = save->xfunc_error_retval;
 119        option_mask32 = save->option_mask32;
 120        die_sleep = save->die_sleep;
 121}
 122
 123int FAST_FUNC run_nofork_applet_prime(struct nofork_save_area *old, int applet_no, char **argv)
 124{
 125        int rc, argc;
 126
 127        applet_name = APPLET_NAME(applet_no);
 128
 129        xfunc_error_retval = EXIT_FAILURE;
 130
 131        /* Special flag for xfunc_die(). If xfunc will "die"
 132         * in NOFORK applet, xfunc_die() sees negative
 133         * die_sleep and longjmp here instead. */
 134        die_sleep = -1;
 135
 136        /* In case getopt() or getopt32() was already called:
 137         * reset the libc getopt() function, which keeps internal state.
 138         *
 139         * BSD-derived getopt() functions require that optind be set to 1 in
 140         * order to reset getopt() state.  This used to be generally accepted
 141         * way of resetting getopt().  However, glibc's getopt()
 142         * has additional getopt() state beyond optind, and requires that
 143         * optind be set to zero to reset its state.  So the unfortunate state of
 144         * affairs is that BSD-derived versions of getopt() misbehave if
 145         * optind is set to 0 in order to reset getopt(), and glibc's getopt()
 146         * will core dump if optind is set 1 in order to reset getopt().
 147         *
 148         * More modern versions of BSD require that optreset be set to 1 in
 149         * order to reset getopt().  Sigh.  Standards, anyone?
 150         */
 151#ifdef __GLIBC__
 152        optind = 0;
 153#else /* BSD style */
 154        optind = 1;
 155        /* optreset = 1; */
 156#endif
 157        /* optarg = NULL; opterr = 1; optopt = 63; - do we need this too? */
 158        /* (values above are what they initialized to in glibc and uclibc) */
 159        /* option_mask32 = 0; - not needed, no applet depends on it being 0 */
 160
 161        argc = 1;
 162        while (argv[argc])
 163                argc++;
 164
 165        rc = setjmp(die_jmp);
 166        if (!rc) {
 167                /* Some callers (xargs)
 168                 * need argv untouched because they free argv[i]! */
 169                char *tmp_argv[argc+1];
 170                memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
 171                /* Finally we can call NOFORK applet's main() */
 172                rc = applet_main[applet_no](argc, tmp_argv);
 173
 174        /* The whole reason behind nofork_save_area is that <applet>_main
 175         * may exit non-locally! For example, in hush Ctrl-Z tries
 176         * (modulo bugs) to dynamically create a child (backgrounded task)
 177         * if it detects that Ctrl-Z was pressed when a NOFORK was running.
 178         * Testcase: interactive "rm -i".
 179         * Don't fool yourself into thinking "and <applet>_main() returns
 180         * quickly here" and removing "useless" nofork_save_area code. */
 181
 182        } else { /* xfunc died in NOFORK applet */
 183                /* in case they meant to return 0... */
 184                if (rc == -2222)
 185                        rc = 0;
 186        }
 187
 188        /* Restoring some globals */
 189        restore_nofork_data(old);
 190
 191        /* Other globals can be simply reset to defaults */
 192#ifdef __GLIBC__
 193        optind = 0;
 194#else /* BSD style */
 195        optind = 1;
 196#endif
 197
 198        return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
 199}
 200
 201int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
 202{
 203        struct nofork_save_area old;
 204
 205        /* Saving globals */
 206        save_nofork_data(&old);
 207        return run_nofork_applet_prime(&old, applet_no, argv);
 208}
 209#endif /* FEATURE_PREFER_APPLETS */
 210
 211int FAST_FUNC spawn_and_wait(char **argv)
 212{
 213        int rc;
 214#if ENABLE_FEATURE_PREFER_APPLETS
 215        int a = find_applet_by_name(argv[0]);
 216
 217        if (a >= 0 && (APPLET_IS_NOFORK(a)
 218#if BB_MMU
 219                        || APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
 220#endif
 221        )) {
 222#if BB_MMU
 223                if (APPLET_IS_NOFORK(a))
 224#endif
 225                {
 226                        return run_nofork_applet(a, argv);
 227                }
 228#if BB_MMU
 229                /* MMU only */
 230                /* a->noexec is true */
 231                rc = fork();
 232                if (rc) /* parent or error */
 233                        return wait4pid(rc);
 234                /* child */
 235                xfunc_error_retval = EXIT_FAILURE;
 236                run_applet_no_and_exit(a, argv);
 237#endif
 238        }
 239#endif /* FEATURE_PREFER_APPLETS */
 240        rc = spawn(argv);
 241        return wait4pid(rc);
 242}
 243
 244#if !BB_MMU
 245void FAST_FUNC re_exec(char **argv)
 246{
 247        /* high-order bit of first char in argv[0] is a hidden
 248         * "we have (already) re-execed, don't do it again" flag */
 249        argv[0][0] |= 0x80;
 250        execv(bb_busybox_exec_path, argv);
 251        bb_perror_msg_and_die("exec %s", bb_busybox_exec_path);
 252}
 253
 254void FAST_FUNC forkexit_or_rexec(char **argv)
 255{
 256        pid_t pid;
 257        /* Maybe we are already re-execed and come here again? */
 258        if (re_execed)
 259                return;
 260
 261        pid = vfork();
 262        if (pid < 0) /* wtf? */
 263                bb_perror_msg_and_die("vfork");
 264        if (pid) /* parent */
 265                exit(EXIT_SUCCESS);
 266        /* child - re-exec ourself */
 267        re_exec(argv);
 268}
 269#else
 270/* Dance around (void)...*/
 271#undef forkexit_or_rexec
 272void FAST_FUNC forkexit_or_rexec(void)
 273{
 274        pid_t pid;
 275        pid = fork();
 276        if (pid < 0) /* wtf? */
 277                bb_perror_msg_and_die("fork");
 278        if (pid) /* parent */
 279                exit(EXIT_SUCCESS);
 280        /* child */
 281}
 282#define forkexit_or_rexec(argv) forkexit_or_rexec()
 283#endif
 284
 285/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 286 * char **argv "vanishes" */
 287void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
 288{
 289        int fd;
 290
 291        if (flags & DAEMON_CHDIR_ROOT)
 292                xchdir("/");
 293
 294        if (flags & DAEMON_DEVNULL_STDIO) {
 295                close(0);
 296                close(1);
 297                close(2);
 298        }
 299
 300        fd = open(bb_dev_null, O_RDWR);
 301        if (fd < 0) {
 302                /* NB: we can be called as bb_sanitize_stdio() from init
 303                 * or mdev, and there /dev/null may legitimately not (yet) exist!
 304                 * Do not use xopen above, but obtain _ANY_ open descriptor,
 305                 * even bogus one as below. */
 306                fd = xopen("/", O_RDONLY); /* don't believe this can fail */
 307        }
 308
 309        while ((unsigned)fd < 2)
 310                fd = dup(fd); /* have 0,1,2 open at least to /dev/null */
 311
 312        if (!(flags & DAEMON_ONLY_SANITIZE)) {
 313                forkexit_or_rexec(argv);
 314                /* if daemonizing, make sure we detach from stdio & ctty */
 315                setsid();
 316                dup2(fd, 0);
 317                dup2(fd, 1);
 318                dup2(fd, 2);
 319        }
 320        while (fd > 2) {
 321                close(fd--);
 322                if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
 323                        return;
 324                /* else close everything after fd#2 */
 325        }
 326}
 327
 328void FAST_FUNC bb_sanitize_stdio(void)
 329{
 330        bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
 331}
 332