release/src/router/busybox/libbb/vfork_daemon_rexec.c

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