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 struct nofork_save_area {
  73         jmp_buf die_jmp;
  74         const char *applet_name;
  75         uint32_t option_mask32;
  76         int die_sleep;
  77         uint8_t xfunc_error_retval;
  78 };
  79 static void save_nofork_data(struct nofork_save_area *save)
  80 {
  81         memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
  82         save->applet_name = applet_name;
  83         save->xfunc_error_retval = xfunc_error_retval;
  84         save->option_mask32 = option_mask32;
  85         save->die_sleep = die_sleep;
  86 }
  87 static void restore_nofork_data(struct nofork_save_area *save)
  88 {
  89         memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
  90         applet_name = save->applet_name;
  91         xfunc_error_retval = save->xfunc_error_retval;
  92         option_mask32 = save->option_mask32;
  93         die_sleep = save->die_sleep;
  94 }
  95
  96 int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
  97 {
  98         int rc, argc;
  99         struct nofork_save_area old;
 100
 101         save_nofork_data(&old);
 102
 103         applet_name = APPLET_NAME(applet_no);
 104
 105         xfunc_error_retval = EXIT_FAILURE;
 106
 107         /* In case getopt() or getopt32() was already called:
 108          * reset the libc getopt() function, which keeps internal state.
 109          *
 110          * BSD-derived getopt() functions require that optind be set to 1 in
 111          * order to reset getopt() state.  This used to be generally accepted
 112          * way of resetting getopt().  However, glibc's getopt()
 113          * has additional getopt() state beyond optind, and requires that
 114          * optind be set to zero to reset its state.  So the unfortunate state of
 115          * affairs is that BSD-derived versions of getopt() misbehave if
 116          * optind is set to 0 in order to reset getopt(), and glibc's getopt()
 117          * will core dump if optind is set 1 in order to reset getopt().
 118          *
 119          * More modern versions of BSD require that optreset be set to 1 in
 120          * order to reset getopt().  Sigh.  Standards, anyone?
 121          */
 122 #ifdef __GLIBC__
 123         optind = 0;
 124 #else /* BSD style */
 125         optind = 1;
 126         /* optreset = 1; */
 127 #endif
 128         /* optarg = NULL; opterr = 1; optopt = 63; - do we need this too? */
 129         /* (values above are what they initialized to in glibc and uclibc) */
 130         /* option_mask32 = 0; - not needed, no applet depends on it being 0 */
 131
 132         argc = 1;
 133         while (argv[argc])
 134                 argc++;
 135
 136         /* Special flag for xfunc_die(). If xfunc will "die"
 137          * in NOFORK applet, xfunc_die() sees negative
 138          * die_sleep and longjmp here instead. */
 139         die_sleep = -1;
 140
 141         rc = setjmp(die_jmp);
 142         if (!rc) {
 143                 /* Some callers (xargs)
 144                  * need argv untouched because they free argv[i]! */
 145                 char *tmp_argv[argc+1];
 146                 memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
 147                 /* Finally we can call NOFORK applet's main() */
 148                 rc = applet_main[applet_no](argc, tmp_argv);
 149         } else { /* xfunc died in NOFORK applet */
 150                 /* in case they meant to return 0... */
 151                 if (rc == -2222)
 152                         rc = 0;
 153         }
 154
 155         /* Restoring some globals */
 156         restore_nofork_data(&old);
 157
 158         /* Other globals can be simply reset to defaults */
 159 #ifdef __GLIBC__
 160         optind = 0;
 161 #else /* BSD style */
 162         optind = 1;
 163 #endif
 164
 165         return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
 166 }
 167 #endif /* FEATURE_PREFER_APPLETS */
 168
 169 int FAST_FUNC spawn_and_wait(char **argv)
 170 {
 171         int rc;
 172 #if ENABLE_FEATURE_PREFER_APPLETS
 173         int a = find_applet_by_name(argv[0]);
 174
 175         if (a >= 0 && (APPLET_IS_NOFORK(a)
 176 # if BB_MMU
 177                         || APPLET_IS_NOEXEC(a) /* NOEXEC trick needs fork() */
 178 # endif
 179         )) {
 180 # if BB_MMU
 181                 if (APPLET_IS_NOFORK(a))
 182 # endif
 183                 {
 184                         return run_nofork_applet(a, argv);
 185                 }
 186 # if BB_MMU
 187                 /* MMU only */
 188                 /* a->noexec is true */
 189                 rc = fork();
 190                 if (rc) /* parent or error */
 191                         return wait4pid(rc);
 192                 /* child */
 193                 xfunc_error_retval = EXIT_FAILURE;
 194                 run_applet_no_and_exit(a, argv);
 195 # endif
 196         }
 197 #endif /* FEATURE_PREFER_APPLETS */
 198         rc = spawn(argv);
 199         return wait4pid(rc);
 200 }
 201
 202 #if !BB_MMU
 203 void FAST_FUNC re_exec(char **argv)
 204 {
 205         /* high-order bit of first char in argv[0] is a hidden
 206          * "we have (already) re-execed, don't do it again" flag */
 207         argv[0][0] |= 0x80;
 208         execv(bb_busybox_exec_path, argv);
 209         bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
 210 }
 211
 212 pid_t FAST_FUNC fork_or_rexec(char **argv)
 213 {
 214         pid_t pid;
 215         /* Maybe we are already re-execed and come here again? */
 216         if (re_execed)
 217                 return 0;
 218         pid = xvfork();
 219         if (pid) /* parent */
 220                 return pid;
 221         /* child - re-exec ourself */
 222         re_exec(argv);
 223 }
 224 #endif
 225
 226 /* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 227  * char **argv "vanishes" */
 228 void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
 229 {
 230         int fd;
 231
 232         if (flags & DAEMON_CHDIR_ROOT)
 233                 xchdir("/");
 234
 235         if (flags & DAEMON_DEVNULL_STDIO) {
 236                 close(0);
 237                 close(1);
 238                 close(2);
 239         }
 240
 241         fd = open(bb_dev_null, O_RDWR);
 242         if (fd < 0) {
 243                 /* NB: we can be called as bb_sanitize_stdio() from init
 244                  * or mdev, and there /dev/null may legitimately not (yet) exist!
 245                  * Do not use xopen above, but obtain _ANY_ open descriptor,
 246                  * even bogus one as below. */
 247                 fd = xopen("/", O_RDONLY); /* don't believe this can fail */
 248         }
 249
 250         while ((unsigned)fd < 2)
 251                 fd = dup(fd); /* have 0,1,2 open at least to /dev/null */
 252
 253         if (!(flags & DAEMON_ONLY_SANITIZE)) {
 254                 if (fork_or_rexec(argv))
 255                         exit(EXIT_SUCCESS); /* parent */
 256                 /* if daemonizing, detach from stdio & ctty */
 257                 setsid();
 258                 dup2(fd, 0);
 259                 dup2(fd, 1);
 260                 dup2(fd, 2);
 261                 if (flags & DAEMON_DOUBLE_FORK) {
 262                         /* On Linux, session leader can acquire ctty
 263                          * unknowingly, by opening a tty.
 264                          * Prevent this: stop being a session leader.
 265                          */
 266                         if (fork_or_rexec(argv))
 267                                 exit(EXIT_SUCCESS); /* parent */
 268                 }
 269         }
 270         while (fd > 2) {
 271                 close(fd--);
 272                 if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
 273                         return;
 274                 /* else close everything after fd#2 */
 275         }
 276 }
 277
 278 void FAST_FUNC bb_sanitize_stdio(void)
 279 {
 280         bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
 281 }