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 <linux/ptrace.h>
  41 #include <linux/async.h>
  42 #include <asm/uaccess.h>
  43
  44 #include <trace/events/module.h>
  45
  46 extern int max_threads;
  47
  48 static struct workqueue_struct *khelper_wq;
  49
  50 /*
  51  * kmod_thread_locker is used for deadlock avoidance.  There is no explicit
  52  * locking to protect this global - it is private to the singleton khelper
  53  * thread and should only ever be modified by that thread.
  54  */
  55 static const struct task_struct *kmod_thread_locker;
  56
  57 #define CAP_BSET        (void *)1
  58 #define CAP_PI          (void *)2
  59
  60 static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
  61 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
  62 static DEFINE_SPINLOCK(umh_sysctl_lock);
  63 static DECLARE_RWSEM(umhelper_sem);
  64
  65 #ifdef CONFIG_MODULES
  66
  67 /*
  68         modprobe_path is set via /proc/sys.
  69 */
  70 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
  71
  72 static void free_modprobe_argv(struct subprocess_info *info)
  73 {
  74         kfree(info->argv[3]); /* check call_modprobe() */
  75         kfree(info->argv);
  76 }
  77
  78 static int call_modprobe(char *module_name, int wait)
  79 {
  80         static char *envp[] = {
  81                 "HOME=/",
  82                 "TERM=linux",
  83                 "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
  84                 NULL
  85         };
  86
  87         char **argv = kmalloc(sizeof(char *[5]), GFP_KERNEL);
  88         if (!argv)
  89                 goto out;
  90
  91         module_name = kstrdup(module_name, GFP_KERNEL);
  92         if (!module_name)
  93                 goto free_argv;
  94
  95         argv[0] = modprobe_path;
  96         argv[1] = "-q";
  97         argv[2] = "--";
  98         argv[3] = module_name;  /* check free_modprobe_argv() */
  99         argv[4] = NULL;
 100
 101         return call_usermodehelper_fns(modprobe_path, argv, envp,
 102                 wait | UMH_KILLABLE, NULL, free_modprobe_argv, NULL);
 103 free_argv:
 104         kfree(argv);
 105 out:
 106         return -ENOMEM;
 107 }
 108
 109 /**
 110  * __request_module - try to load a kernel module
 111  * @wait: wait (or not) for the operation to complete
 112  * @fmt: printf style format string for the name of the module
 113  * @...: arguments as specified in the format string
 114  *
 115  * Load a module using the user mode module loader. The function returns
 116  * zero on success or a negative errno code on failure. Note that a
 117  * successful module load does not mean the module did not then unload
 118  * and exit on an error of its own. Callers must check that the service
 119  * they requested is now available not blindly invoke it.
 120  *
 121  * If module auto-loading support is disabled then this function
 122  * becomes a no-operation.
 123  */
 124 int __request_module(bool wait, const char *fmt, ...)
 125 {
 126         va_list args;
 127         char module_name[MODULE_NAME_LEN];
 128         unsigned int max_modprobes;
 129         int ret;
 130         static atomic_t kmod_concurrent = ATOMIC_INIT(0);
 131 #define MAX_KMOD_CONCURRENT 50  /* Completely arbitrary value - KAO */
 132         static int kmod_loop_msg;
 133
 134         /*
 135          * We don't allow synchronous module loading from async.  Module
 136          * init may invoke async_synchronize_full() which will end up
 137          * waiting for this task which already is waiting for the module
 138          * loading to complete, leading to a deadlock.
 139          */
 140         WARN_ON_ONCE(wait && current_is_async());
 141
 142         va_start(args, fmt);
 143         ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args);
 144         va_end(args);
 145         if (ret >= MODULE_NAME_LEN)
 146                 return -ENAMETOOLONG;
 147
 148         ret = security_kernel_module_request(module_name);
 149         if (ret)
 150                 return ret;
 151
 152         /* If modprobe needs a service that is in a module, we get a recursive
 153          * loop.  Limit the number of running kmod threads to max_threads/2 or
 154          * MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
 155          * would be to run the parents of this process, counting how many times
 156          * kmod was invoked.  That would mean accessing the internals of the
 157          * process tables to get the command line, proc_pid_cmdline is static
 158          * and it is not worth changing the proc code just to handle this case.
 159          * KAO.
 160          *
 161          * "trace the ppid" is simple, but will fail if someone's
 162          * parent exits.  I think this is as good as it gets. --RR
 163          */
 164         max_modprobes = min(max_threads/2, MAX_KMOD_CONCURRENT);
 165         atomic_inc(&kmod_concurrent);
 166         if (atomic_read(&kmod_concurrent) > max_modprobes) {
 167                 /* We may be blaming an innocent here, but unlikely */
 168                 if (kmod_loop_msg < 5) {
 169                         printk(KERN_ERR
 170                                "request_module: runaway loop modprobe %s\n",
 171                                module_name);
 172                         kmod_loop_msg++;
 173                 }
 174                 atomic_dec(&kmod_concurrent);
 175                 return -ENOMEM;
 176         }
 177
 178         trace_module_request(module_name, wait, _RET_IP_);
 179
 180         ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
 181
 182         atomic_dec(&kmod_concurrent);
 183         return ret;
 184 }
 185 EXPORT_SYMBOL(__request_module);
 186 #endif /* CONFIG_MODULES */
 187
 188 /*
 189  * This is the task which runs the usermode application
 190  */
 191 static int ____call_usermodehelper(void *data)
 192 {
 193         struct subprocess_info *sub_info = data;
 194         struct cred *new;
 195         int retval;
 196
 197         spin_lock_irq(&current->sighand->siglock);
 198         flush_signal_handlers(current, 1);
 199         spin_unlock_irq(&current->sighand->siglock);
 200
 201         /* We can run anywhere, unlike our parent keventd(). */
 202         set_cpus_allowed_ptr(current, cpu_all_mask);
 203
 204         /*
 205          * Our parent is keventd, which runs with elevated scheduling priority.
 206          * Avoid propagating that into the userspace child.
 207          */
 208         set_user_nice(current, 0);
 209
 210         retval = -ENOMEM;
 211         new = prepare_kernel_cred(current);
 212         if (!new)
 213                 goto fail;
 214
 215         spin_lock(&umh_sysctl_lock);
 216         new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
 217         new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
 218                                              new->cap_inheritable);
 219         spin_unlock(&umh_sysctl_lock);
 220
 221         if (sub_info->init) {
 222                 retval = sub_info->init(sub_info, new);
 223                 if (retval) {
 224                         abort_creds(new);
 225                         goto fail;
 226                 }
 227         }
 228
 229         commit_creds(new);
 230
 231         retval = do_execve(sub_info->path,
 232                            (const char __user *const __user *)sub_info->argv,
 233                            (const char __user *const __user *)sub_info->envp);
 234         if (!retval)
 235                 return 0;
 236
 237         /* Exec failed? */
 238 fail:
 239         sub_info->retval = retval;
 240         do_exit(0);
 241 }
 242
 243 static int call_helper(void *data)
 244 {
 245         /* Worker thread started blocking khelper thread. */
 246         kmod_thread_locker = current;
 247         return ____call_usermodehelper(data);
 248 }
 249
 250 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
 251 {
 252         if (info->cleanup)
 253                 (*info->cleanup)(info);
 254         kfree(info);
 255 }
 256
 257 static void umh_complete(struct subprocess_info *sub_info)
 258 {
 259         struct completion *comp = xchg(&sub_info->complete, NULL);
 260         /*
 261          * See call_usermodehelper_exec(). If xchg() returns NULL
 262          * we own sub_info, the UMH_KILLABLE caller has gone away.
 263          */
 264         if (comp)
 265                 complete(comp);
 266         else
 267                 call_usermodehelper_freeinfo(sub_info);
 268 }
 269
 270 /* Keventd can't block, but this (a child) can. */
 271 static int wait_for_helper(void *data)
 272 {
 273         struct subprocess_info *sub_info = data;
 274         pid_t pid;
 275
 276         /* If SIGCLD is ignored sys_wait4 won't populate the status. */
 277         spin_lock_irq(&current->sighand->siglock);
 278         current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL;
 279         spin_unlock_irq(&current->sighand->siglock);
 280
 281         pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD);
 282         if (pid < 0) {
 283                 sub_info->retval = pid;
 284         } else {
 285                 int ret = -ECHILD;
 286                 /*
 287                  * Normally it is bogus to call wait4() from in-kernel because
 288                  * wait4() wants to write the exit code to a userspace address.
 289                  * But wait_for_helper() always runs as keventd, and put_user()
 290                  * to a kernel address works OK for kernel threads, due to their
 291                  * having an mm_segment_t which spans the entire address space.
 292                  *
 293                  * Thus the __user pointer cast is valid here.
 294                  */
 295                 sys_wait4(pid, (int __user *)&ret, 0, NULL);
 296
 297                 /*
 298                  * If ret is 0, either ____call_usermodehelper failed and the
 299                  * real error code is already in sub_info->retval or
 300                  * sub_info->retval is 0 anyway, so don't mess with it then.
 301                  */
 302                 if (ret)
 303                         sub_info->retval = ret;
 304         }
 305
 306         umh_complete(sub_info);
 307         do_exit(0);
 308 }
 309
 310 /* This is run by khelper thread  */
 311 static void __call_usermodehelper(struct work_struct *work)
 312 {
 313         struct subprocess_info *sub_info =
 314                 container_of(work, struct subprocess_info, work);
 315         int wait = sub_info->wait & ~UMH_KILLABLE;
 316         pid_t pid;
 317
 318         /* CLONE_VFORK: wait until the usermode helper has execve'd
 319          * successfully We need the data structures to stay around
 320          * until that is done.  */
 321         if (wait == UMH_WAIT_PROC)
 322                 pid = kernel_thread(wait_for_helper, sub_info,
 323                                     CLONE_FS | CLONE_FILES | SIGCHLD);
 324         else {
 325                 pid = kernel_thread(call_helper, sub_info,
 326                                     CLONE_VFORK | SIGCHLD);
 327                 /* Worker thread stopped blocking khelper thread. */
 328                 kmod_thread_locker = NULL;
 329         }
 330
 331         switch (wait) {
 332         case UMH_NO_WAIT:
 333                 call_usermodehelper_freeinfo(sub_info);
 334                 break;
 335
 336         case UMH_WAIT_PROC:
 337                 if (pid > 0)
 338                         break;
 339                 /* FALLTHROUGH */
 340         case UMH_WAIT_EXEC:
 341                 if (pid < 0)
 342                         sub_info->retval = pid;
 343                 umh_complete(sub_info);
 344         }
 345 }
 346
 347 /*
 348  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 349  * (used for preventing user land processes from being created after the user
 350  * land has been frozen during a system-wide hibernation or suspend operation).
 351  * Should always be manipulated under umhelper_sem acquired for write.
 352  */
 353 static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
 354
 355 /* Number of helpers running */
 356 static atomic_t running_helpers = ATOMIC_INIT(0);
 357
 358 /*
 359  * Wait queue head used by usermodehelper_disable() to wait for all running
 360  * helpers to finish.
 361  */
 362 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 363
 364 /*
 365  * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
 366  * to become 'false'.
 367  */
 368 static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
 369
 370 /*
 371  * Time to wait for running_helpers to become zero before the setting of
 372  * usermodehelper_disabled in usermodehelper_disable() fails
 373  */
 374 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 375
 376 int usermodehelper_read_trylock(void)
 377 {
 378         DEFINE_WAIT(wait);
 379         int ret = 0;
 380
 381         down_read(&umhelper_sem);
 382         for (;;) {
 383                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 384                                 TASK_INTERRUPTIBLE);
 385                 if (!usermodehelper_disabled)
 386                         break;
 387
 388                 if (usermodehelper_disabled == UMH_DISABLED)
 389                         ret = -EAGAIN;
 390
 391                 up_read(&umhelper_sem);
 392
 393                 if (ret)
 394                         break;
 395
 396                 schedule();
 397                 try_to_freeze();
 398
 399                 down_read(&umhelper_sem);
 400         }
 401         finish_wait(&usermodehelper_disabled_waitq, &wait);
 402         return ret;
 403 }
 404 EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
 405
 406 long usermodehelper_read_lock_wait(long timeout)
 407 {
 408         DEFINE_WAIT(wait);
 409
 410         if (timeout < 0)
 411                 return -EINVAL;
 412
 413         down_read(&umhelper_sem);
 414         for (;;) {
 415                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 416                                 TASK_UNINTERRUPTIBLE);
 417                 if (!usermodehelper_disabled)
 418                         break;
 419
 420                 up_read(&umhelper_sem);
 421
 422                 timeout = schedule_timeout(timeout);
 423                 if (!timeout)
 424                         break;
 425
 426                 down_read(&umhelper_sem);
 427         }
 428         finish_wait(&usermodehelper_disabled_waitq, &wait);
 429         return timeout;
 430 }
 431 EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
 432
 433 void usermodehelper_read_unlock(void)
 434 {
 435         up_read(&umhelper_sem);
 436 }
 437 EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
 438
 439 /**
 440  * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
 441  * @depth: New value to assign to usermodehelper_disabled.
 442  *
 443  * Change the value of usermodehelper_disabled (under umhelper_sem locked for
 444  * writing) and wakeup tasks waiting for it to change.
 445  */
 446 void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
 447 {
 448         down_write(&umhelper_sem);
 449         usermodehelper_disabled = depth;
 450         wake_up(&usermodehelper_disabled_waitq);
 451         up_write(&umhelper_sem);
 452 }
 453
 454 /**
 455  * __usermodehelper_disable - Prevent new helpers from being started.
 456  * @depth: New value to assign to usermodehelper_disabled.
 457  *
 458  * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
 459  */
 460 int __usermodehelper_disable(enum umh_disable_depth depth)
 461 {
 462         long retval;
 463
 464         if (!depth)
 465                 return -EINVAL;
 466
 467         down_write(&umhelper_sem);
 468         usermodehelper_disabled = depth;
 469         up_write(&umhelper_sem);
 470
 471         /*
 472          * From now on call_usermodehelper_exec() won't start any new
 473          * helpers, so it is sufficient if running_helpers turns out to
 474          * be zero at one point (it may be increased later, but that
 475          * doesn't matter).
 476          */
 477         retval = wait_event_timeout(running_helpers_waitq,
 478                                         atomic_read(&running_helpers) == 0,
 479                                         RUNNING_HELPERS_TIMEOUT);
 480         if (retval)
 481                 return 0;
 482
 483         __usermodehelper_set_disable_depth(UMH_ENABLED);
 484         return -EAGAIN;
 485 }
 486
 487 static void helper_lock(void)
 488 {
 489         atomic_inc(&running_helpers);
 490         smp_mb__after_atomic_inc();
 491 }
 492
 493 static void helper_unlock(void)
 494 {
 495         if (atomic_dec_and_test(&running_helpers))
 496                 wake_up(&running_helpers_waitq);
 497 }
 498
 499 /**
 500  * call_usermodehelper_setup - prepare to call a usermode helper
 501  * @path: path to usermode executable
 502  * @argv: arg vector for process
 503  * @envp: environment for process
 504  * @gfp_mask: gfp mask for memory allocation
 505  *
 506  * Returns either %NULL on allocation failure, or a subprocess_info
 507  * structure.  This should be passed to call_usermodehelper_exec to
 508  * exec the process and free the structure.
 509  */
 510 static
 511 struct subprocess_info *call_usermodehelper_setup(char *path, char **argv,
 512                                                   char **envp, gfp_t gfp_mask)
 513 {
 514         struct subprocess_info *sub_info;
 515         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 516         if (!sub_info)
 517                 goto out;
 518
 519         INIT_WORK(&sub_info->work, __call_usermodehelper);
 520         sub_info->path = path;
 521         sub_info->argv = argv;
 522         sub_info->envp = envp;
 523   out:
 524         return sub_info;
 525 }
 526
 527 /**
 528  * call_usermodehelper_setfns - set a cleanup/init function
 529  * @info: a subprocess_info returned by call_usermodehelper_setup
 530  * @cleanup: a cleanup function
 531  * @init: an init function
 532  * @data: arbitrary context sensitive data
 533  *
 534  * The init function is used to customize the helper process prior to
 535  * exec.  A non-zero return code causes the process to error out, exit,
 536  * and return the failure to the calling process
 537  *
 538  * The cleanup function is just before ethe subprocess_info is about to
 539  * be freed.  This can be used for freeing the argv and envp.  The
 540  * Function must be runnable in either a process context or the
 541  * context in which call_usermodehelper_exec is called.
 542  */
 543 static
 544 void call_usermodehelper_setfns(struct subprocess_info *info,
 545                     int (*init)(struct subprocess_info *info, struct cred *new),
 546                     void (*cleanup)(struct subprocess_info *info),
 547                     void *data)
 548 {
 549         info->cleanup = cleanup;
 550         info->init = init;
 551         info->data = data;
 552 }
 553
 554 /**
 555  * call_usermodehelper_exec - start a usermode application
 556  * @sub_info: information about the subprocessa
 557  * @wait: wait for the application to finish and return status.
 558  *        when -1 don't wait at all, but you get no useful error back when
 559  *        the program couldn't be exec'ed. This makes it safe to call
 560  *        from interrupt context.
 561  *
 562  * Runs a user-space application.  The application is started
 563  * asynchronously if wait is not set, and runs as a child of keventd.
 564  * (ie. it runs with full root capabilities).
 565  */
 566 static
 567 int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
 568 {
 569         DECLARE_COMPLETION_ONSTACK(done);
 570         int retval = 0;
 571
 572         helper_lock();
 573         if (sub_info->path[0] == '\0')
 574                 goto out;
 575
 576         if (!khelper_wq || usermodehelper_disabled) {
 577                 retval = -EBUSY;
 578                 goto out;
 579         }
 580         /*
 581          * Worker thread must not wait for khelper thread at below
 582          * wait_for_completion() if the thread was created with CLONE_VFORK
 583          * flag, for khelper thread is already waiting for the thread at
 584          * wait_for_completion() in do_fork().
 585          */
 586         if (wait != UMH_NO_WAIT && current == kmod_thread_locker) {
 587                 retval = -EBUSY;
 588                 goto out;
 589         }
 590
 591         sub_info->complete = &done;
 592         sub_info->wait = wait;
 593
 594         queue_work(khelper_wq, &sub_info->work);
 595         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 596                 goto unlock;
 597
 598         if (wait & UMH_KILLABLE) {
 599                 retval = wait_for_completion_killable(&done);
 600                 if (!retval)
 601                         goto wait_done;
 602
 603                 /* umh_complete() will see NULL and free sub_info */
 604                 if (xchg(&sub_info->complete, NULL))
 605                         goto unlock;
 606                 /* fallthrough, umh_complete() was already called */
 607         }
 608
 609         wait_for_completion(&done);
 610 wait_done:
 611         retval = sub_info->retval;
 612 out:
 613         call_usermodehelper_freeinfo(sub_info);
 614 unlock:
 615         helper_unlock();
 616         return retval;
 617 }
 618
 619 /*
 620  * call_usermodehelper_fns() will not run the caller-provided cleanup function
 621  * if a memory allocation failure is experienced.  So the caller might need to
 622  * check the call_usermodehelper_fns() return value: if it is -ENOMEM, perform
 623  * the necessaary cleanup within the caller.
 624  */
 625 int call_usermodehelper_fns(
 626         char *path, char **argv, char **envp, int wait,
 627         int (*init)(struct subprocess_info *info, struct cred *new),
 628         void (*cleanup)(struct subprocess_info *), void *data)
 629 {
 630         struct subprocess_info *info;
 631         gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
 632
 633         info = call_usermodehelper_setup(path, argv, envp, gfp_mask);
 634
 635         if (info == NULL)
 636                 return -ENOMEM;
 637
 638         call_usermodehelper_setfns(info, init, cleanup, data);
 639
 640         return call_usermodehelper_exec(info, wait);
 641 }
 642 EXPORT_SYMBOL(call_usermodehelper_fns);
 643
 644 static int proc_cap_handler(struct ctl_table *table, int write,
 645                          void __user *buffer, size_t *lenp, loff_t *ppos)
 646 {
 647         struct ctl_table t;
 648         unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
 649         kernel_cap_t new_cap;
 650         int err, i;
 651
 652         if (write && (!capable(CAP_SETPCAP) ||
 653                       !capable(CAP_SYS_MODULE)))
 654                 return -EPERM;
 655
 656         /*
 657          * convert from the global kernel_cap_t to the ulong array to print to
 658          * userspace if this is a read.
 659          */
 660         spin_lock(&umh_sysctl_lock);
 661         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
 662                 if (table->data == CAP_BSET)
 663                         cap_array[i] = usermodehelper_bset.cap[i];
 664                 else if (table->data == CAP_PI)
 665                         cap_array[i] = usermodehelper_inheritable.cap[i];
 666                 else
 667                         BUG();
 668         }
 669         spin_unlock(&umh_sysctl_lock);
 670
 671         t = *table;
 672         t.data = &cap_array;
 673
 674         /*
 675          * actually read or write and array of ulongs from userspace.  Remember
 676          * these are least significant 32 bits first
 677          */
 678         err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
 679         if (err < 0)
 680                 return err;
 681
 682         /*
 683          * convert from the sysctl array of ulongs to the kernel_cap_t
 684          * internal representation
 685          */
 686         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
 687                 new_cap.cap[i] = cap_array[i];
 688
 689         /*
 690          * Drop everything not in the new_cap (but don't add things)
 691          */
 692         spin_lock(&umh_sysctl_lock);
 693         if (write) {
 694                 if (table->data == CAP_BSET)
 695                         usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
 696                 if (table->data == CAP_PI)
 697                         usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
 698         }
 699         spin_unlock(&umh_sysctl_lock);
 700
 701         return 0;
 702 }
 703
 704 struct ctl_table usermodehelper_table[] = {
 705         {
 706                 .procname       = "bset",
 707                 .data           = CAP_BSET,
 708                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 709                 .mode           = 0600,
 710                 .proc_handler   = proc_cap_handler,
 711         },
 712         {
 713                 .procname       = "inheritable",
 714                 .data           = CAP_PI,
 715                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 716                 .mode           = 0600,
 717                 .proc_handler   = proc_cap_handler,
 718         },
 719         { }
 720 };
 721
 722 void __init usermodehelper_init(void)
 723 {
 724         khelper_wq = create_singlethread_workqueue("khelper");
 725         BUG_ON(!khelper_wq);
 726 }