root/kernel/umh.c

DEFINITIONS

1. call_usermodehelper_freeinfo
2. umh_complete
3. call_usermodehelper_exec_async
4. call_usermodehelper_exec_sync
5. call_usermodehelper_exec_work
6. usermodehelper_read_trylock
7. usermodehelper_read_lock_wait
8. usermodehelper_read_unlock
9. __usermodehelper_set_disable_depth
10. __usermodehelper_disable
11. helper_lock
12. helper_unlock
13. call_usermodehelper_setup
14. call_usermodehelper_setup_file
15. umh_pipe_setup
16. umh_clean_and_save_pid
17. fork_usermode_blob
18. call_usermodehelper_exec
19. call_usermodehelper
20. proc_cap_handler
21. __exit_umh

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * umh - the kernel usermode helper
   4  */
   5 #include <linux/module.h>
   6 #include <linux/sched.h>
   7 #include <linux/sched/task.h>
   8 #include <linux/binfmts.h>
   9 #include <linux/syscalls.h>
  10 #include <linux/unistd.h>
  11 #include <linux/kmod.h>
  12 #include <linux/slab.h>
  13 #include <linux/completion.h>
  14 #include <linux/cred.h>
  15 #include <linux/file.h>
  16 #include <linux/fdtable.h>
  17 #include <linux/workqueue.h>
  18 #include <linux/security.h>
  19 #include <linux/mount.h>
  20 #include <linux/kernel.h>
  21 #include <linux/init.h>
  22 #include <linux/resource.h>
  23 #include <linux/notifier.h>
  24 #include <linux/suspend.h>
  25 #include <linux/rwsem.h>
  26 #include <linux/ptrace.h>
  27 #include <linux/async.h>
  28 #include <linux/uaccess.h>
  29 #include <linux/shmem_fs.h>
  30 #include <linux/pipe_fs_i.h>
  31 
  32 #include <trace/events/module.h>
  33 
  34 #define CAP_BSET        (void *)1
  35 #define CAP_PI          (void *)2
  36 
  37 static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
  38 static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
  39 static DEFINE_SPINLOCK(umh_sysctl_lock);
  40 static DECLARE_RWSEM(umhelper_sem);
  41 static LIST_HEAD(umh_list);
  42 static DEFINE_MUTEX(umh_list_lock);
  43 
  44 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
  45 {
  46         if (info->cleanup)
  47                 (*info->cleanup)(info);
  48         kfree(info);
  49 }
  50 
  51 static void umh_complete(struct subprocess_info *sub_info)
  52 {
  53         struct completion *comp = xchg(&sub_info->complete, NULL);
  54         /*
  55          * See call_usermodehelper_exec(). If xchg() returns NULL
  56          * we own sub_info, the UMH_KILLABLE caller has gone away
  57          * or the caller used UMH_NO_WAIT.
  58          */
  59         if (comp)
  60                 complete(comp);
  61         else
  62                 call_usermodehelper_freeinfo(sub_info);
  63 }
  64 
  65 /*
  66  * This is the task which runs the usermode application
  67  */
  68 static int call_usermodehelper_exec_async(void *data)
  69 {
  70         struct subprocess_info *sub_info = data;
  71         struct cred *new;
  72         int retval;
  73 
  74         spin_lock_irq(&current->sighand->siglock);
  75         flush_signal_handlers(current, 1);
  76         spin_unlock_irq(&current->sighand->siglock);
  77 
  78         /*
  79          * Our parent (unbound workqueue) runs with elevated scheduling
  80          * priority. Avoid propagating that into the userspace child.
  81          */
  82         set_user_nice(current, 0);
  83 
  84         retval = -ENOMEM;
  85         new = prepare_kernel_cred(current);
  86         if (!new)
  87                 goto out;
  88 
  89         spin_lock(&umh_sysctl_lock);
  90         new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
  91         new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
  92                                              new->cap_inheritable);
  93         spin_unlock(&umh_sysctl_lock);
  94 
  95         if (sub_info->init) {
  96                 retval = sub_info->init(sub_info, new);
  97                 if (retval) {
  98                         abort_creds(new);
  99                         goto out;
 100                 }
 101         }
 102 
 103         commit_creds(new);
 104 
 105         sub_info->pid = task_pid_nr(current);
 106         if (sub_info->file) {
 107                 retval = do_execve_file(sub_info->file,
 108                                         sub_info->argv, sub_info->envp);
 109                 if (!retval)
 110                         current->flags |= PF_UMH;
 111         } else
 112                 retval = do_execve(getname_kernel(sub_info->path),
 113                                    (const char __user *const __user *)sub_info->argv,
 114                                    (const char __user *const __user *)sub_info->envp);
 115 out:
 116         sub_info->retval = retval;
 117         /*
 118          * call_usermodehelper_exec_sync() will call umh_complete
 119          * if UHM_WAIT_PROC.
 120          */
 121         if (!(sub_info->wait & UMH_WAIT_PROC))
 122                 umh_complete(sub_info);
 123         if (!retval)
 124                 return 0;
 125         do_exit(0);
 126 }
 127 
 128 /* Handles UMH_WAIT_PROC.  */
 129 static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
 130 {
 131         pid_t pid;
 132 
 133         /* If SIGCLD is ignored kernel_wait4 won't populate the status. */
 134         kernel_sigaction(SIGCHLD, SIG_DFL);
 135         pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
 136         if (pid < 0) {
 137                 sub_info->retval = pid;
 138         } else {
 139                 int ret = -ECHILD;
 140                 /*
 141                  * Normally it is bogus to call wait4() from in-kernel because
 142                  * wait4() wants to write the exit code to a userspace address.
 143                  * But call_usermodehelper_exec_sync() always runs as kernel
 144                  * thread (workqueue) and put_user() to a kernel address works
 145                  * OK for kernel threads, due to their having an mm_segment_t
 146                  * which spans the entire address space.
 147                  *
 148                  * Thus the __user pointer cast is valid here.
 149                  */
 150                 kernel_wait4(pid, (int __user *)&ret, 0, NULL);
 151 
 152                 /*
 153                  * If ret is 0, either call_usermodehelper_exec_async failed and
 154                  * the real error code is already in sub_info->retval or
 155                  * sub_info->retval is 0 anyway, so don't mess with it then.
 156                  */
 157                 if (ret)
 158                         sub_info->retval = ret;
 159         }
 160 
 161         /* Restore default kernel sig handler */
 162         kernel_sigaction(SIGCHLD, SIG_IGN);
 163 
 164         umh_complete(sub_info);
 165 }
 166 
 167 /*
 168  * We need to create the usermodehelper kernel thread from a task that is affine
 169  * to an optimized set of CPUs (or nohz housekeeping ones) such that they
 170  * inherit a widest affinity irrespective of call_usermodehelper() callers with
 171  * possibly reduced affinity (eg: per-cpu workqueues). We don't want
 172  * usermodehelper targets to contend a busy CPU.
 173  *
 174  * Unbound workqueues provide such wide affinity and allow to block on
 175  * UMH_WAIT_PROC requests without blocking pending request (up to some limit).
 176  *
 177  * Besides, workqueues provide the privilege level that caller might not have
 178  * to perform the usermodehelper request.
 179  *
 180  */
 181 static void call_usermodehelper_exec_work(struct work_struct *work)
 182 {
 183         struct subprocess_info *sub_info =
 184                 container_of(work, struct subprocess_info, work);
 185 
 186         if (sub_info->wait & UMH_WAIT_PROC) {
 187                 call_usermodehelper_exec_sync(sub_info);
 188         } else {
 189                 pid_t pid;
 190                 /*
 191                  * Use CLONE_PARENT to reparent it to kthreadd; we do not
 192                  * want to pollute current->children, and we need a parent
 193                  * that always ignores SIGCHLD to ensure auto-reaping.
 194                  */
 195                 pid = kernel_thread(call_usermodehelper_exec_async, sub_info,
 196                                     CLONE_PARENT | SIGCHLD);
 197                 if (pid < 0) {
 198                         sub_info->retval = pid;
 199                         umh_complete(sub_info);
 200                 }
 201         }
 202 }
 203 
 204 /*
 205  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
 206  * (used for preventing user land processes from being created after the user
 207  * land has been frozen during a system-wide hibernation or suspend operation).
 208  * Should always be manipulated under umhelper_sem acquired for write.
 209  */
 210 static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
 211 
 212 /* Number of helpers running */
 213 static atomic_t running_helpers = ATOMIC_INIT(0);
 214 
 215 /*
 216  * Wait queue head used by usermodehelper_disable() to wait for all running
 217  * helpers to finish.
 218  */
 219 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
 220 
 221 /*
 222  * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
 223  * to become 'false'.
 224  */
 225 static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
 226 
 227 /*
 228  * Time to wait for running_helpers to become zero before the setting of
 229  * usermodehelper_disabled in usermodehelper_disable() fails
 230  */
 231 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
 232 
 233 int usermodehelper_read_trylock(void)
 234 {
 235         DEFINE_WAIT(wait);
 236         int ret = 0;
 237 
 238         down_read(&umhelper_sem);
 239         for (;;) {
 240                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 241                                 TASK_INTERRUPTIBLE);
 242                 if (!usermodehelper_disabled)
 243                         break;
 244 
 245                 if (usermodehelper_disabled == UMH_DISABLED)
 246                         ret = -EAGAIN;
 247 
 248                 up_read(&umhelper_sem);
 249 
 250                 if (ret)
 251                         break;
 252 
 253                 schedule();
 254                 try_to_freeze();
 255 
 256                 down_read(&umhelper_sem);
 257         }
 258         finish_wait(&usermodehelper_disabled_waitq, &wait);
 259         return ret;
 260 }
 261 EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
 262 
 263 long usermodehelper_read_lock_wait(long timeout)
 264 {
 265         DEFINE_WAIT(wait);
 266 
 267         if (timeout < 0)
 268                 return -EINVAL;
 269 
 270         down_read(&umhelper_sem);
 271         for (;;) {
 272                 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
 273                                 TASK_UNINTERRUPTIBLE);
 274                 if (!usermodehelper_disabled)
 275                         break;
 276 
 277                 up_read(&umhelper_sem);
 278 
 279                 timeout = schedule_timeout(timeout);
 280                 if (!timeout)
 281                         break;
 282 
 283                 down_read(&umhelper_sem);
 284         }
 285         finish_wait(&usermodehelper_disabled_waitq, &wait);
 286         return timeout;
 287 }
 288 EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
 289 
 290 void usermodehelper_read_unlock(void)
 291 {
 292         up_read(&umhelper_sem);
 293 }
 294 EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
 295 
 296 /**
 297  * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
 298  * @depth: New value to assign to usermodehelper_disabled.
 299  *
 300  * Change the value of usermodehelper_disabled (under umhelper_sem locked for
 301  * writing) and wakeup tasks waiting for it to change.
 302  */
 303 void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
 304 {
 305         down_write(&umhelper_sem);
 306         usermodehelper_disabled = depth;
 307         wake_up(&usermodehelper_disabled_waitq);
 308         up_write(&umhelper_sem);
 309 }
 310 
 311 /**
 312  * __usermodehelper_disable - Prevent new helpers from being started.
 313  * @depth: New value to assign to usermodehelper_disabled.
 314  *
 315  * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
 316  */
 317 int __usermodehelper_disable(enum umh_disable_depth depth)
 318 {
 319         long retval;
 320 
 321         if (!depth)
 322                 return -EINVAL;
 323 
 324         down_write(&umhelper_sem);
 325         usermodehelper_disabled = depth;
 326         up_write(&umhelper_sem);
 327 
 328         /*
 329          * From now on call_usermodehelper_exec() won't start any new
 330          * helpers, so it is sufficient if running_helpers turns out to
 331          * be zero at one point (it may be increased later, but that
 332          * doesn't matter).
 333          */
 334         retval = wait_event_timeout(running_helpers_waitq,
 335                                         atomic_read(&running_helpers) == 0,
 336                                         RUNNING_HELPERS_TIMEOUT);
 337         if (retval)
 338                 return 0;
 339 
 340         __usermodehelper_set_disable_depth(UMH_ENABLED);
 341         return -EAGAIN;
 342 }
 343 
 344 static void helper_lock(void)
 345 {
 346         atomic_inc(&running_helpers);
 347         smp_mb__after_atomic();
 348 }
 349 
 350 static void helper_unlock(void)
 351 {
 352         if (atomic_dec_and_test(&running_helpers))
 353                 wake_up(&running_helpers_waitq);
 354 }
 355 
 356 /**
 357  * call_usermodehelper_setup - prepare to call a usermode helper
 358  * @path: path to usermode executable
 359  * @argv: arg vector for process
 360  * @envp: environment for process
 361  * @gfp_mask: gfp mask for memory allocation
 362  * @cleanup: a cleanup function
 363  * @init: an init function
 364  * @data: arbitrary context sensitive data
 365  *
 366  * Returns either %NULL on allocation failure, or a subprocess_info
 367  * structure.  This should be passed to call_usermodehelper_exec to
 368  * exec the process and free the structure.
 369  *
 370  * The init function is used to customize the helper process prior to
 371  * exec.  A non-zero return code causes the process to error out, exit,
 372  * and return the failure to the calling process
 373  *
 374  * The cleanup function is just before ethe subprocess_info is about to
 375  * be freed.  This can be used for freeing the argv and envp.  The
 376  * Function must be runnable in either a process context or the
 377  * context in which call_usermodehelper_exec is called.
 378  */
 379 struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
 380                 char **envp, gfp_t gfp_mask,
 381                 int (*init)(struct subprocess_info *info, struct cred *new),
 382                 void (*cleanup)(struct subprocess_info *info),
 383                 void *data)
 384 {
 385         struct subprocess_info *sub_info;
 386         sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
 387         if (!sub_info)
 388                 goto out;
 389 
 390         INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
 391 
 392 #ifdef CONFIG_STATIC_USERMODEHELPER
 393         sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
 394 #else
 395         sub_info->path = path;
 396 #endif
 397         sub_info->argv = argv;
 398         sub_info->envp = envp;
 399 
 400         sub_info->cleanup = cleanup;
 401         sub_info->init = init;
 402         sub_info->data = data;
 403   out:
 404         return sub_info;
 405 }
 406 EXPORT_SYMBOL(call_usermodehelper_setup);
 407 
 408 struct subprocess_info *call_usermodehelper_setup_file(struct file *file,
 409                 int (*init)(struct subprocess_info *info, struct cred *new),
 410                 void (*cleanup)(struct subprocess_info *info), void *data)
 411 {
 412         struct subprocess_info *sub_info;
 413         struct umh_info *info = data;
 414         const char *cmdline = (info->cmdline) ? info->cmdline : "usermodehelper";
 415 
 416         sub_info = kzalloc(sizeof(struct subprocess_info), GFP_KERNEL);
 417         if (!sub_info)
 418                 return NULL;
 419 
 420         sub_info->argv = argv_split(GFP_KERNEL, cmdline, NULL);
 421         if (!sub_info->argv) {
 422                 kfree(sub_info);
 423                 return NULL;
 424         }
 425 
 426         INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
 427         sub_info->path = "none";
 428         sub_info->file = file;
 429         sub_info->init = init;
 430         sub_info->cleanup = cleanup;
 431         sub_info->data = data;
 432         return sub_info;
 433 }
 434 
 435 static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 436 {
 437         struct umh_info *umh_info = info->data;
 438         struct file *from_umh[2];
 439         struct file *to_umh[2];
 440         int err;
 441 
 442         /* create pipe to send data to umh */
 443         err = create_pipe_files(to_umh, 0);
 444         if (err)
 445                 return err;
 446         err = replace_fd(0, to_umh[0], 0);
 447         fput(to_umh[0]);
 448         if (err < 0) {
 449                 fput(to_umh[1]);
 450                 return err;
 451         }
 452 
 453         /* create pipe to receive data from umh */
 454         err = create_pipe_files(from_umh, 0);
 455         if (err) {
 456                 fput(to_umh[1]);
 457                 replace_fd(0, NULL, 0);
 458                 return err;
 459         }
 460         err = replace_fd(1, from_umh[1], 0);
 461         fput(from_umh[1]);
 462         if (err < 0) {
 463                 fput(to_umh[1]);
 464                 replace_fd(0, NULL, 0);
 465                 fput(from_umh[0]);
 466                 return err;
 467         }
 468 
 469         umh_info->pipe_to_umh = to_umh[1];
 470         umh_info->pipe_from_umh = from_umh[0];
 471         return 0;
 472 }
 473 
 474 static void umh_clean_and_save_pid(struct subprocess_info *info)
 475 {
 476         struct umh_info *umh_info = info->data;
 477 
 478         /* cleanup if umh_pipe_setup() was successful but exec failed */
 479         if (info->pid && info->retval) {
 480                 fput(umh_info->pipe_to_umh);
 481                 fput(umh_info->pipe_from_umh);
 482         }
 483 
 484         argv_free(info->argv);
 485         umh_info->pid = info->pid;
 486 }
 487 
 488 /**
 489  * fork_usermode_blob - fork a blob of bytes as a usermode process
 490  * @data: a blob of bytes that can be do_execv-ed as a file
 491  * @len: length of the blob
 492  * @info: information about usermode process (shouldn't be NULL)
 493  *
 494  * If info->cmdline is set it will be used as command line for the
 495  * user process, else "usermodehelper" is used.
 496  *
 497  * Returns either negative error or zero which indicates success
 498  * in executing a blob of bytes as a usermode process. In such
 499  * case 'struct umh_info *info' is populated with two pipes
 500  * and a pid of the process. The caller is responsible for health
 501  * check of the user process, killing it via pid, and closing the
 502  * pipes when user process is no longer needed.
 503  */
 504 int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
 505 {
 506         struct subprocess_info *sub_info;
 507         struct file *file;
 508         ssize_t written;
 509         loff_t pos = 0;
 510         int err;
 511 
 512         file = shmem_kernel_file_setup("", len, 0);
 513         if (IS_ERR(file))
 514                 return PTR_ERR(file);
 515 
 516         written = kernel_write(file, data, len, &pos);
 517         if (written != len) {
 518                 err = written;
 519                 if (err >= 0)
 520                         err = -ENOMEM;
 521                 goto out;
 522         }
 523 
 524         err = -ENOMEM;
 525         sub_info = call_usermodehelper_setup_file(file, umh_pipe_setup,
 526                                                   umh_clean_and_save_pid, info);
 527         if (!sub_info)
 528                 goto out;
 529 
 530         err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
 531         if (!err) {
 532                 mutex_lock(&umh_list_lock);
 533                 list_add(&info->list, &umh_list);
 534                 mutex_unlock(&umh_list_lock);
 535         }
 536 out:
 537         fput(file);
 538         return err;
 539 }
 540 EXPORT_SYMBOL_GPL(fork_usermode_blob);
 541 
 542 /**
 543  * call_usermodehelper_exec - start a usermode application
 544  * @sub_info: information about the subprocessa
 545  * @wait: wait for the application to finish and return status.
 546  *        when UMH_NO_WAIT don't wait at all, but you get no useful error back
 547  *        when the program couldn't be exec'ed. This makes it safe to call
 548  *        from interrupt context.
 549  *
 550  * Runs a user-space application.  The application is started
 551  * asynchronously if wait is not set, and runs as a child of system workqueues.
 552  * (ie. it runs with full root capabilities and optimized affinity).
 553  *
 554  * Note: successful return value does not guarantee the helper was called at
 555  * all. You can't rely on sub_info->{init,cleanup} being called even for
 556  * UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers
 557  * into a successful no-op.
 558  */
 559 int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
 560 {
 561         DECLARE_COMPLETION_ONSTACK(done);
 562         int retval = 0;
 563 
 564         if (!sub_info->path) {
 565                 call_usermodehelper_freeinfo(sub_info);
 566                 return -EINVAL;
 567         }
 568         helper_lock();
 569         if (usermodehelper_disabled) {
 570                 retval = -EBUSY;
 571                 goto out;
 572         }
 573 
 574         /*
 575          * If there is no binary for us to call, then just return and get out of
 576          * here.  This allows us to set STATIC_USERMODEHELPER_PATH to "" and
 577          * disable all call_usermodehelper() calls.
 578          */
 579         if (strlen(sub_info->path) == 0)
 580                 goto out;
 581 
 582         /*
 583          * Set the completion pointer only if there is a waiter.
 584          * This makes it possible to use umh_complete to free
 585          * the data structure in case of UMH_NO_WAIT.
 586          */
 587         sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
 588         sub_info->wait = wait;
 589 
 590         queue_work(system_unbound_wq, &sub_info->work);
 591         if (wait == UMH_NO_WAIT)        /* task has freed sub_info */
 592                 goto unlock;
 593 
 594         if (wait & UMH_KILLABLE) {
 595                 retval = wait_for_completion_killable(&done);
 596                 if (!retval)
 597                         goto wait_done;
 598 
 599                 /* umh_complete() will see NULL and free sub_info */
 600                 if (xchg(&sub_info->complete, NULL))
 601                         goto unlock;
 602                 /* fallthrough, umh_complete() was already called */
 603         }
 604 
 605         wait_for_completion(&done);
 606 wait_done:
 607         retval = sub_info->retval;
 608 out:
 609         call_usermodehelper_freeinfo(sub_info);
 610 unlock:
 611         helper_unlock();
 612         return retval;
 613 }
 614 EXPORT_SYMBOL(call_usermodehelper_exec);
 615 
 616 /**
 617  * call_usermodehelper() - prepare and start a usermode application
 618  * @path: path to usermode executable
 619  * @argv: arg vector for process
 620  * @envp: environment for process
 621  * @wait: wait for the application to finish and return status.
 622  *        when UMH_NO_WAIT don't wait at all, but you get no useful error back
 623  *        when the program couldn't be exec'ed. This makes it safe to call
 624  *        from interrupt context.
 625  *
 626  * This function is the equivalent to use call_usermodehelper_setup() and
 627  * call_usermodehelper_exec().
 628  */
 629 int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
 630 {
 631         struct subprocess_info *info;
 632         gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
 633 
 634         info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
 635                                          NULL, NULL, NULL);
 636         if (info == NULL)
 637                 return -ENOMEM;
 638 
 639         return call_usermodehelper_exec(info, wait);
 640 }
 641 EXPORT_SYMBOL(call_usermodehelper);
 642 
 643 static int proc_cap_handler(struct ctl_table *table, int write,
 644                          void __user *buffer, size_t *lenp, loff_t *ppos)
 645 {
 646         struct ctl_table t;
 647         unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
 648         kernel_cap_t new_cap;
 649         int err, i;
 650 
 651         if (write && (!capable(CAP_SETPCAP) ||
 652                       !capable(CAP_SYS_MODULE)))
 653                 return -EPERM;
 654 
 655         /*
 656          * convert from the global kernel_cap_t to the ulong array to print to
 657          * userspace if this is a read.
 658          */
 659         spin_lock(&umh_sysctl_lock);
 660         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)  {
 661                 if (table->data == CAP_BSET)
 662                         cap_array[i] = usermodehelper_bset.cap[i];
 663                 else if (table->data == CAP_PI)
 664                         cap_array[i] = usermodehelper_inheritable.cap[i];
 665                 else
 666                         BUG();
 667         }
 668         spin_unlock(&umh_sysctl_lock);
 669 
 670         t = *table;
 671         t.data = &cap_array;
 672 
 673         /*
 674          * actually read or write and array of ulongs from userspace.  Remember
 675          * these are least significant 32 bits first
 676          */
 677         err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
 678         if (err < 0)
 679                 return err;
 680 
 681         /*
 682          * convert from the sysctl array of ulongs to the kernel_cap_t
 683          * internal representation
 684          */
 685         for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
 686                 new_cap.cap[i] = cap_array[i];
 687 
 688         /*
 689          * Drop everything not in the new_cap (but don't add things)
 690          */
 691         if (write) {
 692                 spin_lock(&umh_sysctl_lock);
 693                 if (table->data == CAP_BSET)
 694                         usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
 695                 if (table->data == CAP_PI)
 696                         usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
 697                 spin_unlock(&umh_sysctl_lock);
 698         }
 699 
 700         return 0;
 701 }
 702 
 703 void __exit_umh(struct task_struct *tsk)
 704 {
 705         struct umh_info *info;
 706         pid_t pid = tsk->pid;
 707 
 708         mutex_lock(&umh_list_lock);
 709         list_for_each_entry(info, &umh_list, list) {
 710                 if (info->pid == pid) {
 711                         list_del(&info->list);
 712                         mutex_unlock(&umh_list_lock);
 713                         goto out;
 714                 }
 715         }
 716         mutex_unlock(&umh_list_lock);
 717         return;
 718 out:
 719         if (info->cleanup)
 720                 info->cleanup(info);
 721 }
 722 
 723 struct ctl_table usermodehelper_table[] = {
 724         {
 725                 .procname       = "bset",
 726                 .data           = CAP_BSET,
 727                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 728                 .mode           = 0600,
 729                 .proc_handler   = proc_cap_handler,
 730         },
 731         {
 732                 .procname       = "inheritable",
 733                 .data           = CAP_PI,
 734                 .maxlen         = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
 735                 .mode           = 0600,
 736                 .proc_handler   = proc_cap_handler,
 737         },
 738         { }
 739 };