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
  31# if ENABLE_FEATURE_SH_STANDALONE || ENABLE_FEATURE_PREFER_APPLETS || !BB_MMU
  32int FAST_FUNC re_execed_comm(void)
  33{
  34        const char *e, *expected_comm;
  35        char comm[16];
  36
  37        BUILD_BUG_ON(CONFIG_BUSYBOX_EXEC_PATH[0] != '/');
  38        e = CONFIG_BUSYBOX_EXEC_PATH;
  39        /* Hopefully (strrchr(e) - e) evaluates to constant at compile time: */
  40        expected_comm = bb_busybox_exec_path + (strrchr(e, '/') - e) + 1;
  41
  42        prctl(PR_GET_NAME, (long)comm, 0, 0, 0);
  43        //bb_error_msg("comm:'%.*s' expected:'%s'", 16, comm, expected_comm);
  44        return strcmp(comm, expected_comm) == 0;
  45}
  46# endif
  47void FAST_FUNC set_task_comm(const char *comm)
  48{
  49        /* okay if too long (truncates) */
  50        prctl(PR_SET_NAME, (long)comm, 0, 0, 0);
  51}
  52#endif
  53
  54/*
  55 * NOFORK/NOEXEC support
  56 */
  57#if NOFORK_SUPPORT
  58static jmp_buf die_jmp;
  59static void jump(void)
  60{
  61        /* Special case. We arrive here if NOFORK applet
  62         * calls xfunc, which then decides to die.
  63         * We don't die, but instead jump back to caller.
  64         * NOFORK applets still cannot carelessly call xfuncs:
  65         * p = xmalloc(10);
  66         * q = xmalloc(10); // BUG! if this dies, we leak p!
  67         */
  68        /* | 0x100 allows to pass zero exitcode (longjmp can't pass 0).
  69         * This works because exitcodes are bytes,
  70         * run_nofork_applet() ensures that by "& 0xff"
  71         */
  72        longjmp(die_jmp, xfunc_error_retval | 0x100);
  73}
  74
  75struct nofork_save_area {
  76        jmp_buf die_jmp;
  77        void (*die_func)(void);
  78        const char *applet_name;
  79        uint32_t option_mask32;
  80        smallint logmode;
  81        uint8_t xfunc_error_retval;
  82};
  83static void save_nofork_data(struct nofork_save_area *save)
  84{
  85        memcpy(&save->die_jmp, &die_jmp, sizeof(die_jmp));
  86        save->die_func = die_func;
  87        save->applet_name = applet_name;
  88        save->option_mask32 = option_mask32;
  89        save->logmode = logmode;
  90        save->xfunc_error_retval = xfunc_error_retval;
  91}
  92static void restore_nofork_data(struct nofork_save_area *save)
  93{
  94        memcpy(&die_jmp, &save->die_jmp, sizeof(die_jmp));
  95        die_func = save->die_func;
  96        applet_name = save->applet_name;
  97        option_mask32 = save->option_mask32;
  98        logmode = save->logmode;
  99        xfunc_error_retval = save->xfunc_error_retval;
 100}
 101
 102int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
 103{
 104        int rc, argc;
 105        struct nofork_save_area old;
 106
 107        save_nofork_data(&old);
 108
 109        logmode = LOGMODE_STDIO;
 110        xfunc_error_retval = EXIT_FAILURE;
 111        /* In case getopt() was already called:
 112         * reset the libc getopt() function, which keeps internal state.
 113         * (getopt32() does it itself, but getopt() doesn't (and can't))
 114         */
 115        GETOPT_RESET();
 116
 117        argc = string_array_len(argv);
 118
 119        /* If xfunc "dies" in NOFORK applet, die_func longjmp's here instead */
 120        die_func = jump;
 121        rc = setjmp(die_jmp);
 122        if (!rc) {
 123                /* Some callers (xargs)
 124                 * need argv untouched because they free argv[i]! */
 125                char *tmp_argv[argc+1];
 126                memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
 127                applet_name = tmp_argv[0];
 128
 129                /* longjmp's (instead of returning) if --help is seen */
 130                show_usage_if_dash_dash_help(applet_no, argv);
 131
 132                /* Finally we can call NOFORK applet's main() */
 133                rc = applet_main[applet_no](argc, tmp_argv);
 134
 135                /* Important for shells: `which CMD` was failing */
 136                fflush_all();
 137        } else {
 138                /* xfunc died in NOFORK applet */
 139        }
 140
 141        /* Restoring some globals */
 142        restore_nofork_data(&old);
 143        /* Other globals can be simply reset to defaults */
 144        GETOPT_RESET();
 145
 146        return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
 147}
 148#endif
 149
 150#if NOEXEC_SUPPORT
 151void FAST_FUNC run_noexec_applet_and_exit(int a, const char *name, char **argv)
 152{
 153        /* reset some state and run without execing */
 154        /* msg_eol = "\n"; - no caller needs this reinited yet */
 155        logmode = LOGMODE_STDIO;
 156        xfunc_error_retval = EXIT_FAILURE;
 157        die_func = NULL;
 158        GETOPT_RESET();
 159
 160//TODO: think pidof, pgrep, pkill!
 161//set_task_comm() makes our pidof find NOEXECs (e.g. "yes >/dev/null"),
 162//but one from procps-ng-3.3.10 needs more!
 163//Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
 164        set_task_comm(name);
 165        /* applet_name is set by this function: */
 166        run_applet_no_and_exit(a, name, argv);
 167}
 168#endif
 169
 170/*
 171 * Higher-level code, hiding optional NOFORK/NOEXEC trickery.
 172 */
 173
 174/* This does a fork/exec in one call, using vfork().  Returns PID of new child,
 175 * -1 for failure.  Runs argv[0], searching path if that has no / in it. */
 176pid_t FAST_FUNC spawn(char **argv)
 177{
 178        /* Compiler should not optimize stores here */
 179        volatile int failed;
 180        pid_t pid;
 181
 182        fflush_all();
 183
 184        /* Be nice to nommu machines. */
 185        failed = 0;
 186        pid = vfork();
 187        if (pid < 0) /* error */
 188                return pid;
 189        if (!pid) { /* child */
 190                /* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
 191                BB_EXECVP(argv[0], argv);
 192
 193                /* We are (maybe) sharing a stack with blocked parent,
 194                 * let parent know we failed and then exit to unblock parent
 195                 * (but don't run atexit() stuff, which would screw up parent.)
 196                 */
 197                failed = errno;
 198                /* mount, for example, does not want the message */
 199                /*bb_perror_msg("can't execute '%s'", argv[0]);*/
 200                _exit(111);
 201        }
 202        /* parent */
 203        /* Unfortunately, this is not reliable: according to standards
 204         * vfork() can be equivalent to fork() and we won't see value
 205         * of 'failed'.
 206         * Interested party can wait on pid and learn exit code.
 207         * If 111 - then it (most probably) failed to exec */
 208        if (failed) {
 209                safe_waitpid(pid, NULL, 0); /* prevent zombie */
 210                errno = failed;
 211                return -1;
 212        }
 213        return pid;
 214}
 215
 216/* Die with an error message if we can't spawn a child process. */
 217pid_t FAST_FUNC xspawn(char **argv)
 218{
 219        pid_t pid = spawn(argv);
 220        if (pid < 0)
 221                bb_simple_perror_msg_and_die(*argv);
 222        return pid;
 223}
 224
 225int FAST_FUNC spawn_and_wait(char **argv)
 226{
 227        int rc;
 228#if ENABLE_FEATURE_PREFER_APPLETS && (NUM_APPLETS > 1)
 229        int a = find_applet_by_name(argv[0]);
 230
 231        if (a >= 0) {
 232                if (APPLET_IS_NOFORK(a))
 233                        return run_nofork_applet(a, argv);
 234# if BB_MMU /* NOEXEC needs fork(), thus this is done only on MMU machines: */
 235                if (APPLET_IS_NOEXEC(a)) {
 236                        fflush_all();
 237                        rc = fork();
 238                        if (rc) /* parent or error */
 239                                return wait4pid(rc);
 240
 241                        /* child */
 242                        run_noexec_applet_and_exit(a, argv[0], argv);
 243                }
 244# endif
 245        }
 246#endif
 247        rc = spawn(argv);
 248        return wait4pid(rc);
 249}
 250
 251#if !BB_MMU
 252void FAST_FUNC re_exec(char **argv)
 253{
 254        /* high-order bit of first char in argv[0] is a hidden
 255         * "we have (already) re-execed, don't do it again" flag */
 256        argv[0][0] |= 0x80;
 257        execv(bb_busybox_exec_path, argv);
 258        bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
 259}
 260
 261pid_t FAST_FUNC fork_or_rexec(char **argv)
 262{
 263        pid_t pid;
 264        /* Maybe we are already re-execed and come here again? */
 265        if (re_execed)
 266                return 0;
 267
 268        /* fflush_all(); ? - so far all callers had no buffered output to flush */
 269
 270        pid = xvfork();
 271        if (pid) /* parent */
 272                return pid;
 273        /* child - re-exec ourself */
 274        re_exec(argv);
 275}
 276#endif
 277
 278/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 279 * char **argv "vanishes" */
 280void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
 281{
 282        int fd;
 283
 284        if (flags & DAEMON_CHDIR_ROOT)
 285                xchdir("/");
 286
 287        fd = open(bb_dev_null, O_RDWR);
 288        if (fd < 0) {
 289                /* NB: we can be called as bb_sanitize_stdio() from init
 290                 * or mdev, and there /dev/null may legitimately not (yet) exist!
 291                 * Do not use xopen above, but obtain _ANY_ open descriptor,
 292                 * even bogus one as below. */
 293                fd = xopen("/", O_RDONLY); /* don't believe this can fail */
 294        }
 295
 296        if (flags & DAEMON_DEVNULL_STDIO) {
 297                xdup2(fd, 0);
 298                xdup2(fd, 1);
 299                xdup2(fd, 2);
 300        } else {
 301                /* have 0,1,2 open at least to /dev/null */
 302                while ((unsigned)fd < 2)
 303                        fd = dup(fd);
 304        }
 305
 306        if (!(flags & DAEMON_ONLY_SANITIZE)) {
 307
 308                /* fflush_all(); - add it in fork_or_rexec() if necessary */
 309
 310                if (fork_or_rexec(argv))
 311                        _exit_SUCCESS(); /* parent */
 312                /* if daemonizing, detach from stdio & ctty */
 313                setsid();
 314                dup2(fd, 0);
 315                dup2(fd, 1);
 316                dup2(fd, 2);
 317//              if (flags & DAEMON_DOUBLE_FORK) {
 318//                      /* On Linux, session leader can acquire ctty
 319//                       * unknowingly, by opening a tty.
 320//                       * Prevent this: stop being a session leader.
 321//                       */
 322//                      if (fork_or_rexec(argv))
 323//                              _exit_SUCCESS(); /* parent */
 324//              }
 325        }
 326        while (fd > 2) {
 327                close(fd--);
 328                if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
 329                        return;
 330                /* else close everything after fd#2 */
 331        }
 332}
 333
 334void FAST_FUNC bb_sanitize_stdio(void)
 335{
 336        bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
 337}
 338