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                /* Finally we can call NOFORK applet's main() */
 113                rc = applet_main[applet_no](argc, tmp_argv);
 114                /* Important for shells: `which CMD` was failing */
 115                fflush_all();
 116        } else {
 117                /* xfunc died in NOFORK applet */
 118        }
 119
 120        /* Restoring some globals */
 121        restore_nofork_data(&old);
 122        /* Other globals can be simply reset to defaults */
 123        GETOPT_RESET();
 124
 125        return rc & 0xff; /* don't confuse people with "exitcodes" >255 */
 126}
 127#endif
 128
 129#if NOEXEC_SUPPORT
 130void FAST_FUNC run_noexec_applet_and_exit(int a, const char *name, char **argv)
 131{
 132        /* reset some state and run without execing */
 133        /* msg_eol = "\n"; - no caller needs this reinited yet */
 134        logmode = LOGMODE_STDIO;
 135        xfunc_error_retval = EXIT_FAILURE;
 136        die_func = NULL;
 137        GETOPT_RESET();
 138
 139//TODO: think pidof, pgrep, pkill!
 140//set_task_comm() makes our pidof find NOEXECs (e.g. "yes >/dev/null"),
 141//but one from procps-ng-3.3.10 needs more!
 142//Rewrite /proc/PID/cmdline? (need to save argv0 and length at init for this to work!)
 143        set_task_comm(name);
 144        /* applet_name is set by this function: */
 145        run_applet_no_and_exit(a, name, argv);
 146}
 147#endif
 148
 149/*
 150 * Higher-level code, hiding optional NOFORK/NOEXEC trickery.
 151 */
 152
 153/* This does a fork/exec in one call, using vfork().  Returns PID of new child,
 154 * -1 for failure.  Runs argv[0], searching path if that has no / in it. */
 155pid_t FAST_FUNC spawn(char **argv)
 156{
 157        /* Compiler should not optimize stores here */
 158        volatile int failed;
 159        pid_t pid;
 160
 161        fflush_all();
 162
 163        /* Be nice to nommu machines. */
 164        failed = 0;
 165        pid = vfork();
 166        if (pid < 0) /* error */
 167                return pid;
 168        if (!pid) { /* child */
 169                /* This macro is ok - it doesn't do NOEXEC/NOFORK tricks */
 170                BB_EXECVP(argv[0], argv);
 171
 172                /* We are (maybe) sharing a stack with blocked parent,
 173                 * let parent know we failed and then exit to unblock parent
 174                 * (but don't run atexit() stuff, which would screw up parent.)
 175                 */
 176                failed = errno;
 177                /* mount, for example, does not want the message */
 178                /*bb_perror_msg("can't execute '%s'", argv[0]);*/
 179                _exit(111);
 180        }
 181        /* parent */
 182        /* Unfortunately, this is not reliable: according to standards
 183         * vfork() can be equivalent to fork() and we won't see value
 184         * of 'failed'.
 185         * Interested party can wait on pid and learn exit code.
 186         * If 111 - then it (most probably) failed to exec */
 187        if (failed) {
 188                safe_waitpid(pid, NULL, 0); /* prevent zombie */
 189                errno = failed;
 190                return -1;
 191        }
 192        return pid;
 193}
 194
 195/* Die with an error message if we can't spawn a child process. */
 196pid_t FAST_FUNC xspawn(char **argv)
 197{
 198        pid_t pid = spawn(argv);
 199        if (pid < 0)
 200                bb_simple_perror_msg_and_die(*argv);
 201        return pid;
 202}
 203
 204int FAST_FUNC spawn_and_wait(char **argv)
 205{
 206        int rc;
 207#if ENABLE_FEATURE_PREFER_APPLETS && (NUM_APPLETS > 1)
 208        int a = find_applet_by_name(argv[0]);
 209
 210        if (a >= 0) {
 211                if (APPLET_IS_NOFORK(a))
 212                        return run_nofork_applet(a, argv);
 213# if BB_MMU /* NOEXEC needs fork(), thus this is done only on MMU machines: */
 214                if (APPLET_IS_NOEXEC(a)) {
 215                        fflush_all();
 216                        rc = fork();
 217                        if (rc) /* parent or error */
 218                                return wait4pid(rc);
 219
 220                        /* child */
 221                        run_noexec_applet_and_exit(a, argv[0], argv);
 222                }
 223# endif
 224        }
 225#endif
 226        rc = spawn(argv);
 227        return wait4pid(rc);
 228}
 229
 230#if !BB_MMU
 231void FAST_FUNC re_exec(char **argv)
 232{
 233        /* high-order bit of first char in argv[0] is a hidden
 234         * "we have (already) re-execed, don't do it again" flag */
 235        argv[0][0] |= 0x80;
 236        execv(bb_busybox_exec_path, argv);
 237        bb_perror_msg_and_die("can't execute '%s'", bb_busybox_exec_path);
 238}
 239
 240pid_t FAST_FUNC fork_or_rexec(char **argv)
 241{
 242        pid_t pid;
 243        /* Maybe we are already re-execed and come here again? */
 244        if (re_execed)
 245                return 0;
 246
 247        /* fflush_all(); ? - so far all callers had no buffered output to flush */
 248
 249        pid = xvfork();
 250        if (pid) /* parent */
 251                return pid;
 252        /* child - re-exec ourself */
 253        re_exec(argv);
 254}
 255#endif
 256
 257/* Due to a #define in libbb.h on MMU systems we actually have 1 argument -
 258 * char **argv "vanishes" */
 259void FAST_FUNC bb_daemonize_or_rexec(int flags, char **argv)
 260{
 261        int fd;
 262
 263        if (flags & DAEMON_CHDIR_ROOT)
 264                xchdir("/");
 265
 266        if (flags & DAEMON_DEVNULL_STDIO) {
 267                close(0);
 268                close(1);
 269                close(2);
 270        }
 271
 272        fd = open(bb_dev_null, O_RDWR);
 273        if (fd < 0) {
 274                /* NB: we can be called as bb_sanitize_stdio() from init
 275                 * or mdev, and there /dev/null may legitimately not (yet) exist!
 276                 * Do not use xopen above, but obtain _ANY_ open descriptor,
 277                 * even bogus one as below. */
 278                fd = xopen("/", O_RDONLY); /* don't believe this can fail */
 279        }
 280
 281        while ((unsigned)fd < 2)
 282                fd = dup(fd); /* have 0,1,2 open at least to /dev/null */
 283
 284        if (!(flags & DAEMON_ONLY_SANITIZE)) {
 285
 286                /* fflush_all(); - add it in fork_or_rexec() if necessary */
 287
 288                if (fork_or_rexec(argv))
 289                        _exit(EXIT_SUCCESS); /* parent */
 290                /* if daemonizing, detach from stdio & ctty */
 291                setsid();
 292                dup2(fd, 0);
 293                dup2(fd, 1);
 294                dup2(fd, 2);
 295                if (flags & DAEMON_DOUBLE_FORK) {
 296                        /* On Linux, session leader can acquire ctty
 297                         * unknowingly, by opening a tty.
 298                         * Prevent this: stop being a session leader.
 299                         */
 300                        if (fork_or_rexec(argv))
 301                                _exit(EXIT_SUCCESS); /* parent */
 302                }
 303        }
 304        while (fd > 2) {
 305                close(fd--);
 306                if (!(flags & DAEMON_CLOSE_EXTRA_FDS))
 307                        return;
 308                /* else close everything after fd#2 */
 309        }
 310}
 311
 312void FAST_FUNC bb_sanitize_stdio(void)
 313{
 314        bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE, NULL);
 315}
 316