kernel/kmod.c

   1 /*
   2         kmod, the new module loader (replaces kerneld)
   3         Kirk Petersen
   4
   5         Reorganized not to be a daemon by Adam Richter, with guidance
   6         from Greg Zornetzer.
   7
   8         Modified to avoid chroot and file sharing problems.
   9         Mikael Pettersson
  10
  11         Limit the concurrent number of kmod modprobes to catch loops from
  12         "modprobe needs a service that is in a module".
  13         Keith Owens <kaos@ocs.com.au> December 1999
  14
  15         Unblock all signals when we exec a usermode process.
  16         Shuu Yamaguchi <shuu@wondernetworkresources.com> December 2000
  17
  18         call_usermodehelper wait flag, and remove exec_usermodehelper.
  19         Rusty Russell <rusty@rustcorp.com.au>  Jan 2003
  20 */
  21 #include <linux/module.h>
  22 #include <linux/sched.h>
  23 #include <linux/syscalls.h>
  24 #include <linux/unistd.h>
  25 #include <linux/kmod.h>
  26 #include <linux/slab.h>
  27 #include <linux/completion.h>
  28 #include <linux/cred.h>
  29 #include <linux/file.h>
  30 #include <linux/fdtable.h>
  31 #include <linux/workqueue.h>
  32 #include <linux/security.h>
  33 #include <linux/mount.h>
  34 #include <linux/kernel.h>
  35 #include <linux/init.h>
  36 #include <linux/resource.h>
  37 #include <linux/notifier.h>
  38 #include <linux/suspend.h>
  39 #include <linux/rwsem.h>
  40 #include <asm/uaccess.h>
  41
  42 #include <trace/events/module.h>
  43
  44 extern int max_threads;
  45
  46 static struct workqueue_struct *khelper_wq;
  47
  48 #define CAP_BSET        (void *)1
  49 #define CAP_PI          (void *)2
  50
  51 static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
  52 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
  53 static DEFINE_SPINLOCK(umh_sysctl_lock);
  54 static DECLARE_RWSEM(umhelper_sem);
  55
  56 #ifdef CONFIG_MODULES
  57
  58 /*
  59         modprobe_path is set via /proc/sys.
  60 */
  61 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  62
  63 static void free_modprobe_argv(struct subprocess_info *info)
  64 {
  65         kfree(info->argv[3]); /* check call_modprobe() */
  66         kfree(info->argv);
  67 }
  68
  69 static int call_modprobe(char *module_name, int wait)
  70 {
  71         static char *envp[] = {
  72                 "HOME=/",
  73                 "TERM=linux",
  74                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  75                 NULL
  76         };
  77
  78         char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
  79         if (!argv)
  80                 goto out;
  81
  82         module_name = kstrdup(module_name, GFP_KERNEL);
  83         if (!module_name)
  84                 goto free_argv;
  85
  86         argv[0] = modprobe_path;
  87         argv[1] = "-q";
  88         argv[2] = "--";
  89         argv[3] = module_name;  /* check free_modprobe_argv() */
  90         argv[4] = NULL;
  91
  92         return call_usermodehelper_fns(modprobe_path, argv, envp,
  93                 wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
  94 free_argv:
  95         kfree(argv);
  96 out:
  97         return -ENOMEM;
  98 }
  99
 100 /**
 101  * __request_module - try to load a kernel module
 102  * @wait: wait (or not) for the operation to complete
 103  * @fmt: printf style format string for the name of the module
 104  * @...: arguments as specified in the format string
 105  *
 106  * Load a module using the user mode module loader. The function returns
 107  * zero on success or a negative errno code on failure. Note that a
 108  * successful module load does not mean the module did not then unload
 109  * and exit on an error of its own. Callers must check that the service
 110  * they requested is now available not blindly invoke it.
 111  *
 112  * If module auto-loading support is disabled then this function
 113  * becomes a no-operation.
 114  */
 115 int __request_module(bool wait, const char *fmt, ...)
 116 {
 117         va_list args;
 118         char module_name[MODULE_NAME_LEN];
 119         unsigned int max_modprobes;
 120         int ret;
 121         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
 122 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
 123         static int kmod_loop_msg;
 124
 125         va_start(args, fmt);
 126         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
 127         va_end(args);
 128         if (ret >= MODULE_NAME_LEN)
 129                 return -ENAMETOOLONG;
 130
 131         ret = security_kernel_module_request(module_name);
 132         if (ret)
 133                 return ret;
 134
 135         /* If modprobe needs a service that is in a module, we get a recursive
 136          * loop.  Limit the number of running kmod threads to max_threads/2 or
 137          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
 138          * would be to run the parents of this process, counting how many times
 139          * kmod was invoked.  That would mean accessing the internals of the
 140          * process tables to get the command line, proc_pid_cmdline is static
 141          * and it is not worth changing the proc code just to handle this case.
 142          * KAO.
 143          *
 144          * "trace the ppid" is simple, but will fail if someone's
 145          * parent exits.  I think this is as good as it gets. --RR
 146          */
 147         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 148         atomic_inc(&kmod_concurrent);
 149         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 150                 /* We may be blaming an innocent here, but unlikely */
 151                 if (kmod_loop_msg < 5) {
 152                         printk(KERN_ERR
 153                                "request_module: runaway loop modprobe %s\n",
 154                                module_name);
 155                         kmod_loop_msg++;
 156                 }
 157                 atomic_dec(&kmod_concurrent);
 158                 return -ENOMEM;
 159         }
 160
 161         trace_module_request(module_name, wait, _RET_IP_);
 162
 163         ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
 164
 165         atomic_dec(&kmod_concurrent);
 166         return ret;
 167 }
 168 EXPORT_SYMBOL(__request_module);
 169 #endif /* CONFIG_MODULES */
 170
 171 /*
 172  * This is the task which runs the usermode application
 173  */
 174 static int ____call_usermodehelper(void *data)
 175 {
 176         struct subprocess_info *sub_info = data;
 177         struct cred *new;
 178         int retval;
 179
 180         spin_lock_irq(&current->sighand->siglock);
 181         flush_signal_handlers(current, 1);
 182         spin_unlock_irq(&current->sighand->siglock);
 183
 184         /* We can run anywhere, unlike our parent keventd(). */
 185         set_cpus_allowed_ptr(current, cpu_all_mask);
 186
 187         /*
 188          * Our parent is keventd, which runs with elevated scheduling priority.
 189          * Avoid propagating that into the userspace child.
 190          */
 191         set_user_nice(current, 0);
 192
 193         retval = -ENOMEM;
 194         new = prepare_kernel_cred(current);
 195         if (!new)
 196                 goto fail;
 197
 198         spin_lock(&umh_sysctl_lock);
 199         new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
 200         new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
 201                                              new->cap_inheritable);
 202         spin_unlock(&umh_sysctl_lock);
 203
 204         if (sub_info->init) {
 205                 retval = sub_info->init(sub_info, new);
 206                 if (retval) {
 207                         abort_creds(new);
 208                         goto fail;
 209                 }
 210         }
 211
 212         commit_creds(new);
 213
 214         retval = kernel_execve(sub_info->path,
 215                                (const char *const *)sub_info->argv,
 216                                (const char *const *)sub_info->envp);
 217
 218         /* Exec failed? */
 219 fail:
 220         sub_info->retval = retval;
 221         return 0;
 222 }
 223
 224 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
 225 {
 226         if (info->cleanup)
 227                 (*info->cleanup)(info);
 228         kfree(info);
 229 }
 230
 231 static void umh_complete(struct subprocess_info *sub_info)
 232 {
 233         struct completion *comp = xchg(&sub_info->complete, NULL);
 234         /*
 235          * See call_usermodehelper_exec(). If xchg() returns NULL
 236          * we own sub_info, the UMH_KILLABLE caller has gone away.
 237          */
 238         if (comp)
 239                 complete(comp);
 240         else
 241                 call_usermodehelper_freeinfo(sub_info);
 242 }
 243
 244 /* Keventd can't block, but this (a child) can. */
 245 static int wait_for_helper(void *data)
 246 {
 247         struct subprocess_info *sub_info = data;
 248         pid_t pid;
 249
 250         /* If SIGCLD is ignored sys_wait4 won't populate the status. */
 251         spin_lock_irq(&current->sighand->siglock);
 252         current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
 253         spin_unlock_irq(&current->sighand->siglock);
 254
 255         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 256         if (pid < 0) {
 257                 sub_info->retval = pid;
 258         } else {
 259                 int ret = -ECHILD;
 260                 /*
 261                  * Normally it is bogus to call wait4() from in-kernel because
 262                  * wait4() wants to write the exit code to a userspace address.
 263                  * But wait_for_helper() always runs as keventd, and put_user()
 264                  * to a kernel address works OK for kernel threads, due to their
 265                  * having an mm_segment_t which spans the entire address space.
 266                  *
 267                  * Thus the __user pointer cast is valid here.
 268                  */
 269                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 270
 271                 /*
 272                  * If ret is 0, either ____call_usermodehelper failed and the
 273                  * real error code is already in sub_info->retval or
 274                  * sub_info->retval is 0 anyway, so don't mess with it then.
 275                  */
 276                 if (ret)
 277                         sub_info->retval = ret;
 278         }
 279
 280         umh_complete(sub_info);
 281         return 0;
 282 }
 283
 284 /* This is run by khelper thread  */
 285 static void __call_usermodehelper(struct work_struct *work)
 286 {
 287         struct subprocess_info *sub_info =
 288                 container_of(work, struct subprocess_info, work);
 289         int wait = sub_info->wait & ~UMH_KILLABLE;
 290         pid_t pid;
 291
 292         /* CLONE_VFORK: wait until the usermode helper has execve'd
 293          * successfully We need the data structures to stay around
 294          * until that is done.  */
 295         if (wait == UMH_WAIT_PROC)
 296                 pid = kernel_thread(wait_for_helper, sub_info,
 297                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 298         else
 299                 pid = kernel_thread(____call_usermodehelper, sub_info,
 300                                     CLONE_VFORK | SIGCHLD);
 301
 302         switch (wait) {
 303         case UMH_NO_WAIT:
 304                 call_usermodehelper_freeinfo(sub_info);
 305                 break;
 306
 307         case UMH_WAIT_PROC:
 308                 if (pid > 0)
 309                         break;
 310                 /* FALLTHROUGH */
 311         case UMH_WAIT_EXEC:
 312                 if (pid < 0)
 313                         sub_info->retval = pid;
 314                 umh_complete(sub_info);
 315         }
 316 }
 317
 318 /*
 319  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 320  * (used for preventing user land processes from being created after the user
 321  * land has been frozen during a system-wide hibernation or suspend operation).
 322  * Should always be manipulated under umhelper_sem acquired for write.
 323  */
 324 static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
 325
 326 /* Number of helpers running */
 327 static atomic_t running_helpers = ATOMIC_INIT(0);
 328
 329 /*
 330  * Wait queue head used by usermodehelper_disable() to wait for all running
 331  * helpers to finish.
 332  */
 333 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 334
 335 /*
 336  * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
 337  * to become 'false'.
 338  */
 339 static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
 340
 341 /*
 342  * Time to wait for running_helpers to become zero before the setting of
 343  * usermodehelper_disabled in usermodehelper_disable() fails
 344  */
 345 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 346
 347 int usermodehelper_read_trylock(void)
 348 {
 349         DEFINE_WAIT(wait);
 350         int ret = 0;
 351
 352         down_read(&umhelper_sem);
 353         for (;;) {
 354                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 355                                 TASK_INTERRUPTIBLE);
 356                 if (!usermodehelper_disabled)
 357                         break;
 358
 359                 if (usermodehelper_disabled == UMH_DISABLED)
 360                         ret = -EAGAIN;
 361
 362                 up_read(&umhelper_sem);
 363
 364                 if (ret)
 365                         break;
 366
 367                 schedule();
 368                 try_to_freeze();
 369
 370                 down_read(&umhelper_sem);
 371         }
 372         finish_wait(&usermodehelper_disabled_waitq, &wait);
 373         return ret;
 374 }
 375 EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
 376
 377 long usermodehelper_read_lock_wait(long timeout)
 378 {
 379         DEFINE_WAIT(wait);
 380
 381         if (timeout < 0)
 382                 return -EINVAL;
 383
 384         down_read(&umhelper_sem);
 385         for (;;) {
 386                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 387                                 TASK_UNINTERRUPTIBLE);
 388                 if (!usermodehelper_disabled)
 389                         break;
 390
 391                 up_read(&umhelper_sem);
 392
 393                 timeout = schedule_timeout(timeout);
 394                 if (!timeout)
 395                         break;
 396
 397                 down_read(&umhelper_sem);
 398         }
 399         finish_wait(&usermodehelper_disabled_waitq, &wait);
 400         return timeout;
 401 }
 402 EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
 403
 404 void usermodehelper_read_unlock(void)
 405 {
 406         up_read(&umhelper_sem);
 407 }
 408 EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
 409
 410 /**
 411  * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
 412  * @depth: New value to assign to usermodehelper_disabled.
 413  *
 414  * Change the value of usermodehelper_disabled (under umhelper_sem locked for
 415  * writing) and wakeup tasks waiting for it to change.
 416  */
 417 void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
 418 {
 419         down_write(&umhelper_sem);
 420         usermodehelper_disabled = depth;
 421         wake_up(&usermodehelper_disabled_waitq);
 422         up_write(&umhelper_sem);
 423 }
 424
 425 /**
 426  * __usermodehelper_disable - Prevent new helpers from being started.
 427  * @depth: New value to assign to usermodehelper_disabled.
 428  *
 429  * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
 430  */
 431 int __usermodehelper_disable(enum umh_disable_depth depth)
 432 {
 433         long retval;
 434
 435         if (!depth)
 436                 return -EINVAL;
 437
 438         down_write(&umhelper_sem);
 439         usermodehelper_disabled = depth;
 440         up_write(&umhelper_sem);
 441
 442         /*
 443          * From now on call_usermodehelper_exec() won't start any new
 444          * helpers, so it is sufficient if running_helpers turns out to
 445          * be zero at one point (it may be increased later, but that
 446          * doesn't matter).
 447          */
 448         retval = wait_event_timeout(running_helpers_waitq,
 449                                         atomic_read(&running_helpers) == 0,
 450                                         RUNNING_HELPERS_TIMEOUT);
 451         if (retval)
 452                 return 0;
 453
 454         __usermodehelper_set_disable_depth(UMH_ENABLED);
 455         return -EAGAIN;
 456 }
 457
 458 static void helper_lock(void)
 459 {
 460         atomic_inc(&running_helpers);
 461         smp_mb__after_atomic_inc();
 462 }
 463
 464 static void helper_unlock(void)
 465 {
 466         if (atomic_dec_and_test(&running_helpers))
 467                 wake_up(&running_helpers_waitq);
 468 }
 469
 470 /**
 471  * call_usermodehelper_setup - prepare to call a usermode helper
 472  * @path: path to usermode executable
 473  * @argv: arg vector for process
 474  * @envp: environment for process
 475  * @gfp_mask: gfp mask for memory allocation
 476  *
 477  * Returns either %NULL on allocation failure, or a subprocess_info
 478  * structure.  This should be passed to call_usermodehelper_exec to
 479  * exec the process and free the structure.
 480  */
 481 static
 482 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 483                                                   char **envp, gfp_t gfp_mask)
 484 {
 485         struct subprocess_info *sub_info;
 486         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 487         if (!sub_info)
 488                 goto out;
 489
 490         INIT_WORK(&sub_info->work, __call_usermodehelper);
 491         sub_info->path = path;
 492         sub_info->argv = argv;
 493         sub_info->envp = envp;
 494   out:
 495         return sub_info;
 496 }
 497
 498 /**
 499  * call_usermodehelper_setfns - set a cleanup/init function
 500  * @info: a subprocess_info returned by call_usermodehelper_setup
 501  * @cleanup: a cleanup function
 502  * @init: an init function
 503  * @data: arbitrary context sensitive data
 504  *
 505  * The init function is used to customize the helper process prior to
 506  * exec.  A non-zero return code causes the process to error out, exit,
 507  * and return the failure to the calling process
 508  *
 509  * The cleanup function is just before ethe subprocess_info is about to
 510  * be freed.  This can be used for freeing the argv and envp.  The
 511  * Function must be runnable in either a process context or the
 512  * context in which call_usermodehelper_exec is called.
 513  */
 514 static
 515 void call_usermodehelper_setfns(struct subprocess_info *info,
 516                     int (*init)(struct subprocess_info *info, struct cred *new),
 517                     void (*cleanup)(struct subprocess_info *info),
 518                     void *data)
 519 {
 520         info->cleanup = cleanup;
 521         info->init = init;
 522         info->data = data;
 523 }
 524
 525 /**
 526  * call_usermodehelper_exec - start a usermode application
 527  * @sub_info: information about the subprocessa
 528  * @wait: wait for the application to finish and return status.
 529  *        when -1 don't wait at all, but you get no useful error back when
 530  *        the program couldn't be exec'ed. This makes it safe to call
 531  *        from interrupt context.
 532  *
 533  * Runs a user-space application.  The application is started
 534  * asynchronously if wait is not set, and runs as a child of keventd.
 535  * (ie. it runs with full root capabilities).
 536  */
 537 static
 538 int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
 539 {
 540         DECLARE_COMPLETION_ONSTACK(done);
 541         int retval = 0;
 542
 543         helper_lock();
 544         if (sub_info->path[0] == '\0')
 545                 goto out;
 546
 547         if (!khelper_wq || usermodehelper_disabled) {
 548                 retval = -EBUSY;
 549                 goto out;
 550         }
 551
 552         sub_info->complete = &done;
 553         sub_info->wait = wait;
 554
 555         queue_work(khelper_wq, &sub_info->work);
 556         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 557                 goto unlock;
 558
 559         if (wait & UMH_KILLABLE) {
 560                 retval = wait_for_completion_killable(&done);
 561                 if (!retval)
 562                         goto wait_done;
 563
 564                 /* umh_complete() will see NULL and free sub_info */
 565                 if (xchg(&sub_info->complete, NULL))
 566                         goto unlock;
 567                 /* fallthrough, umh_complete() was already called */
 568         }
 569
 570         wait_for_completion(&done);
 571 wait_done:
 572         retval = sub_info->retval;
 573 out:
 574         call_usermodehelper_freeinfo(sub_info);
 575 unlock:
 576         helper_unlock();
 577         return retval;
 578 }
 579
 580 int call_usermodehelper_fns(
 581         char *path, char **argv, char **envp, int wait,
 582         int (*init)(struct subprocess_info *info, struct cred *new),
 583         void (*cleanup)(struct subprocess_info *), void *data)
 584 {
 585         struct subprocess_info *info;
 586         gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
 587
 588         info = call_usermodehelper_setup(path, argv, envp, gfp_mask);
 589
 590         if (info == NULL)
 591                 return -ENOMEM;
 592
 593         call_usermodehelper_setfns(info, init, cleanup, data);
 594
 595         return call_usermodehelper_exec(info, wait);
 596 }
 597 EXPORT_SYMBOL(call_usermodehelper_fns);
 598
 599 static int proc_cap_handler(struct ctl_table *table, int write,
 600                          void __user *buffer, size_t *lenp, loff_t *ppos)
 601 {
 602         struct ctl_table t;
 603         unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
 604         kernel_cap_t new_cap;
 605         int err, i;
 606
 607         if (write && (!capable(CAP_SETPCAP) ||
 608                       !capable(CAP_SYS_MODULE)))
 609                 return -EPERM;
 610
 611         /*
 612          * convert from the global kernel_cap_t to the ulong array to print to
 613          * userspace if this is a read.
 614          */
 615         spin_lock(&umh_sysctl_lock);
 616         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
 617                 if (table->data == CAP_BSET)
 618                         cap_array[i] = usermodehelper_bset.cap[i];
 619                 else if (table->data == CAP_PI)
 620                         cap_array[i] = usermodehelper_inheritable.cap[i];
 621                 else
 622                         BUG();
 623         }
 624         spin_unlock(&umh_sysctl_lock);
 625
 626         t = *table;
 627         t.data = &cap_array;
 628
 629         /*
 630          * actually read or write and array of ulongs from userspace.  Remember
 631          * these are least significant 32 bits first
 632          */
 633         err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
 634         if (err < 0)
 635                 return err;
 636
 637         /*
 638          * convert from the sysctl array of ulongs to the kernel_cap_t
 639          * internal representation
 640          */
 641         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
 642                 new_cap.cap[i] = cap_array[i];
 643
 644         /*
 645          * Drop everything not in the new_cap (but don't add things)
 646          */
 647         spin_lock(&umh_sysctl_lock);
 648         if (write) {
 649                 if (table->data == CAP_BSET)
 650                         usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
 651                 if (table->data == CAP_PI)
 652                         usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
 653         }
 654         spin_unlock(&umh_sysctl_lock);
 655
 656         return 0;
 657 }
 658
 659 struct ctl_table usermodehelper_table[] = {
 660         {
 661                 .procname       = "bset",
 662                 .data           = CAP_BSET,
 663                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 664                 .mode           = 0600,
 665                 .proc_handler   = proc_cap_handler,
 666         },
 667         {
 668                 .procname       = "inheritable",
 669                 .data           = CAP_PI,
 670                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 671                 .mode           = 0600,
 672                 .proc_handler   = proc_cap_handler,
 673         },
 674         { }
 675 };
 676
 677 void __init usermodehelper_init(void)
 678 {
 679         khelper_wq = create_singlethread_workqueue("khelper");
 680         BUG_ON(!khelper_wq);
 681 }