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 source tree.
  16 */
  17#include "busybox.h" /* uses applet tables */
  18#include "NUM_APPLETS.h"
  19
  20#define NOFORK_SUPPORT ((NUM_APPLETS > 1) && (ENABLE_FEATURE_PREFER_APPLETS || ENABLE_FEATURE_SH_NOFORK))
  21#define NOEXEC_SUPPORT ((NUM_APPLETS > 1) && (ENABLE_FEATURE_PREFER_APPLETS || ENABLE_FEATURE_SH_STANDALONE))
  22
  23#if defined(__linux__) && (NUM_APPLETS > 1)
  24# include <sys/prctl.h>
  25# ifndef PR_SET_NAME
  26# define PR_SET_NAME 15
  27# endif
  28# ifndef PR_GET_NAME
  29# define PR_GET_NAME 16
  30# endif
  31void FAST_FUNC set_task_comm(const char *comm)
  32{
  33        /* okay if too long (truncates) */
  34        prctl(PR_SET_NAME, (long)comm, 0, 0, 0);
  35}
  36#endif
  37
  38/*
  39 * NOFORK/NOEXEC support
  40 */
  41#if NOFORK_SUPPORT
  42static jmp_buf die_jmp;
  43static void jump(void)
  44{
  45        /* Special case. We arrive here if NOFORK applet
  46         * calls xfunc, which then decides to die.
  47         * We don't die, but instead jump back to caller.
  48         * NOFORK applets still cannot carelessly call xfuncs:
  49         * p = xmalloc(10);
  50         * q = xmalloc(10); // BUG! if this dies, we leak p!
  51         */
  52        /* | 0x100 allows to pass zero exitcode (longjmp can't pass 0).
  53         * This works because exitcodes are bytes,
  54         * run_nofork_applet() ensures that by "& 0xff"
  55         */
  56        longjmp(die_jmp, xfunc_error_retval | 0x100);
  57}
  58
  59struct nofork_save_area {
  60        jmp_buf die_jmp;
  61        void (*die_func)(void);
  62        const char *applet_name;
  63        uint32_t option_mask32;
  64        smallint logmode;
  65        uint8_t xfunc_error_retval;
  66};
  67static void save_nofork_data(struct nofork_save_area *save)
  68{
  69        memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
  70        save->die_func = die_func;
  71        save->applet_name = applet_name;
  72        save->option_mask32 = option_mask32;
  73        save->logmode = logmode;
  74        save->xfunc_error_retval = xfunc_error_retval;
  75}
  76static void restore_nofork_data(struct nofork_save_area *save)
  77{
  78        memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
  79        die_func = save->die_func;
  80        applet_name = save->applet_name;
  81        option_mask32 = save->option_mask32;
  82        logmode = save->logmode;
  83        xfunc_error_retval = save->xfunc_error_retval;
  84}
  85
  86int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
  87{
  88        int rc, argc;
  89        struct nofork_save_area old;
  90
  91        save_nofork_data(&old);
  92
  93        logmode = LOGMODE_STDIO;
  94        xfunc_error_retval = EXIT_FAILURE;
  95        /* In case getopt() was already called:
  96         * reset the libc getopt() function, which keeps internal state.
  97         * (getopt32() does it itself, but getopt() doesn't (and can't))
  98         */
  99        GETOPT_RESET();
 100
 101        argc = string_array_len(argv);
 102
 103        /* If xfunc "dies" in NOFORK applet, die_func longjmp's here instead */
 104        die_func = jump;
 105        rc = setjmp(die_jmp);
 106        if (!rc) {
 107                /* Some callers (xargs)
 108                 * need argv untouched because they free argv[i]! */
 109                char *tmp_argv[argc+1];
 110                memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
 111                applet_name = tmp_argv[0];
 112
 113                /* longjmp's (instead of returning) if --help is seen */
 114                show_usage_if_dash_dash_help(applet_no, argv);
 115
 116                /* Finally we can call NOFORK applet's main() */
 117                rc = applet_main[applet_no](argc, tmp_argv);
 118
 119                /* Important for shells: `which CMD` was failing */
 120                fflush_all();
 121        } else {
 122                /* xfunc died in NOFORK applet */
 123        }
 124
 125        /* Restoring some globals */
 126        restore_nofork_data(&old);
 127        /* Other globals can be simply reset to defaults */
 128        GETOPT_RESET();
 129
 130        return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
 131}
 132#endif
 133
 134#if NOEXEC_SUPPORT
 135void FAST_FUNC run_noexec_applet_and_exit(int a, const char *name, char **argv)
 136{
 137        /* reset some state and run without execing */
 138        /* msg_eol = "\n"; - no caller needs this reinited yet */
 139        logmode = LOGMODE_STDIO;
 140        xfunc_error_retval = EXIT_FAILURE;
 141        die_func = NULL;
 142        GETOPT_RESET();
 143
 144//TODO: think pidof, pgrep, pkill!
 145//set_task_comm() makes our pidof find NOEXECs (e.g. "yes >/dev/null"),
 146//but one from procps-ng-3.3.10 needs more!
 147//Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
 148        set_task_comm(name);
 149        /* applet_name is set by this function: */
 150        run_applet_no_and_exit(a, name, argv);
 151}
 152#endif
 153
 154/*
 155 * Higher-level code, hiding optional NOFORK/NOEXEC trickery.
 156 */
 157
 158/* This does a fork/exec in one call, using vfork().  Returns PID of new child,
 159 * -1 for failure.  Runs argv[0], searching path if that has no / in it. */
 160pid_t FAST_FUNC spawn(char **argv)
 161{
 162        /* Compiler should not optimize stores here */
 163        volatile int failed;
 164        pid_t pid;
 165
 166        fflush_all();
 167
 168        /* Be nice to nommu machines. */
 169        failed = 0;
 170        pid = vfork();
 171        if (pid < 0) /* error */
 172                return pid;
 173        if (!pid) { /* child */
 174                /* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
 175                BB_EXECVP(argv[0], argv);
 176
 177                /* We are (maybe) sharing a stack with blocked parent,
 178                 * let parent know we failed and then exit to unblock parent
 179                 * (but don't run atexit() stuff, which would screw up parent.)
 180                 */
 181                failed = errno;
 182                /* mount, for example, does not want the message */
 183                /*bb_perror_msg("can't execute '%s'", argv[0]);*/
 184                _exit(111);
 185        }
 186        /* parent */
 187        /* Unfortunately, this is not reliable: according to standards
 188         * vfork() can be equivalent to fork() and we won't see value
 189         * of 'failed'.
 190         * Interested party can wait on pid and learn exit code.
 191         * If 111 - then it (most probably) failed to exec */
 192        if (failed) {
 193                safe_waitpid(pid, NULL, 0); /* prevent zombie */
 194                errno = failed;
 195                return -1;
 196        }
 197        return pid;
 198}
 199
 200/* Die with an error message if we can't spawn a child process. */
 201pid_t FAST_FUNC xspawn(char **argv)
 202{
 203        pid_t pid = spawn(argv);
 204        if (pid < 0)
 205                bb_simple_perror_msg_and_die(*argv);
 206        return pid;
 207}
 208
 209int FAST_FUNC spawn_and_wait(char **argv)
 210{
 211        int rc;
 212#if ENABLE_FEATURE_PREFER_APPLETS && (NUM_APPLETS > 1)
 213        int a = find_applet_by_name(argv[0]);
 214
 215        if (a >= 0) {
 216                if (APPLET_IS_NOFORK(a))
 217                        return run_nofork_applet(a, argv);
 218# if BB_MMU /* NOEXEC needs fork(), thus this is done only on MMU machines: */
 219                if (APPLET_IS_NOEXEC(a)) {
 220                        fflush_all();
 221                        rc = fork();
 222                        if (rc) /* parent or error */
 223                                return wait4pid(rc);
 224
 225                        /* child */
 226                        run_noexec_applet_and_exit(a, argv[0], argv);
 227                }
 228# endif
 229        }
 230#endif
 231        rc = spawn(argv);
 232        return wait4pid(rc);
 233}
 234
 235#if !BB_MMU
 236void FAST_FUNC re_exec(char **argv)
 237{
 238        /* high-order bit of first char in argv[0] is a hidden
 239         * "we have (already) re-execed, don't do it again" flag */
 240        argv[0][0] |= 0x80;
 241        execv(bb_busybox_exec_path, argv);
 242        bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
 243}
 244
 245pid_t FAST_FUNC fork_or_rexec(char **argv)
 246{
 247        pid_t pid;
 248        /* Maybe we are already re-execed and come here again? */
 249        if (re_execed)
 250                return 0;
 251
 252        /* fflush_all(); ? - so far all callers had no buffered output to flush */
 253
 254        pid = xvfork();
 255        if (pid) /* parent */
 256                return pid;
 257        /* child - re-exec ourself */
 258        re_exec(argv);
 259}
 260#endif
 261
 262/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 263 * char **argv "vanishes" */
 264void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
 265{
 266        int fd;
 267
 268        if (flags & DAEMON_CHDIR_ROOT)
 269                xchdir("/");
 270
 271        fd = open(bb_dev_null, O_RDWR);
 272        if (fd < 0) {
 273                /* NB: we can be called as bb_sanitize_stdio() from init
 274                 * or mdev, and there /dev/null may legitimately not (yet) exist!
 275                 * Do not use xopen above, but obtain _ANY_ open descriptor,
 276                 * even bogus one as below. */
 277                fd = xopen("/", O_RDONLY); /* don't believe this can fail */
 278        }
 279
 280        if (flags & DAEMON_DEVNULL_STDIO) {
 281                xdup2(fd, 0);
 282                xdup2(fd, 1);
 283                xdup2(fd, 2);
 284        } else {
 285                /* have 0,1,2 open at least to /dev/null */
 286                while ((unsigned)fd < 2)
 287                        fd = dup(fd);
 288        }
 289
 290        if (!(flags & DAEMON_ONLY_SANITIZE)) {
 291
 292                /* fflush_all(); - add it in fork_or_rexec() if necessary */
 293
 294                if (fork_or_rexec(argv))
 295                        _exit(EXIT_SUCCESS); /* parent */
 296                /* if daemonizing, detach from stdio & ctty */
 297                setsid();
 298                dup2(fd, 0);
 299                dup2(fd, 1);
 300                dup2(fd, 2);
 301//              if (flags & DAEMON_DOUBLE_FORK) {
 302//                      /* On Linux, session leader can acquire ctty
 303//                       * unknowingly, by opening a tty.
 304//                       * Prevent this: stop being a session leader.
 305//                       */
 306//                      if (fork_or_rexec(argv))
 307//                              _exit(EXIT_SUCCESS); /* parent */
 308//              }
 309        }
 310        while (fd > 2) {
 311                close(fd--);
 312                if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
 313                        return;
 314                /* else close everything after fd#2 */
 315        }
 316}
 317
 318void FAST_FUNC bb_sanitize_stdio(void)
 319{
 320        bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
 321}
 322