Loading...
Note: File does not exist in v3.5.6.
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/fs_struct.h>
18#include <linux/workqueue.h>
19#include <linux/security.h>
20#include <linux/mount.h>
21#include <linux/kernel.h>
22#include <linux/init.h>
23#include <linux/resource.h>
24#include <linux/notifier.h>
25#include <linux/suspend.h>
26#include <linux/rwsem.h>
27#include <linux/ptrace.h>
28#include <linux/async.h>
29#include <linux/uaccess.h>
30#include <linux/initrd.h>
31#include <linux/freezer.h>
32
33#include <trace/events/module.h>
34
35#define CAP_BSET (void *)1
36#define CAP_PI (void *)2
37
38static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
39static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
40static DEFINE_SPINLOCK(umh_sysctl_lock);
41static DECLARE_RWSEM(umhelper_sem);
42
43static void call_usermodehelper_freeinfo(struct subprocess_info *info)
44{
45 if (info->cleanup)
46 (*info->cleanup)(info);
47 kfree(info);
48}
49
50static void umh_complete(struct subprocess_info *sub_info)
51{
52 struct completion *comp = xchg(&sub_info->complete, NULL);
53 /*
54 * See call_usermodehelper_exec(). If xchg() returns NULL
55 * we own sub_info, the UMH_KILLABLE caller has gone away
56 * or the caller used UMH_NO_WAIT.
57 */
58 if (comp)
59 complete(comp);
60 else
61 call_usermodehelper_freeinfo(sub_info);
62}
63
64/*
65 * This is the task which runs the usermode application
66 */
67static int call_usermodehelper_exec_async(void *data)
68{
69 struct subprocess_info *sub_info = data;
70 struct cred *new;
71 int retval;
72
73 spin_lock_irq(¤t->sighand->siglock);
74 flush_signal_handlers(current, 1);
75 spin_unlock_irq(¤t->sighand->siglock);
76
77 /*
78 * Initial kernel threads share ther FS with init, in order to
79 * get the init root directory. But we've now created a new
80 * thread that is going to execve a user process and has its own
81 * 'struct fs_struct'. Reset umask to the default.
82 */
83 current->fs->umask = 0022;
84
85 /*
86 * Our parent (unbound workqueue) runs with elevated scheduling
87 * priority. Avoid propagating that into the userspace child.
88 */
89 set_user_nice(current, 0);
90
91 retval = -ENOMEM;
92 new = prepare_kernel_cred(current);
93 if (!new)
94 goto out;
95
96 spin_lock(&umh_sysctl_lock);
97 new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
98 new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
99 new->cap_inheritable);
100 spin_unlock(&umh_sysctl_lock);
101
102 if (sub_info->init) {
103 retval = sub_info->init(sub_info, new);
104 if (retval) {
105 abort_creds(new);
106 goto out;
107 }
108 }
109
110 commit_creds(new);
111
112 wait_for_initramfs();
113 retval = kernel_execve(sub_info->path,
114 (const char *const *)sub_info->argv,
115 (const char *const *)sub_info->envp);
116out:
117 sub_info->retval = retval;
118 /*
119 * call_usermodehelper_exec_sync() will call umh_complete
120 * if UHM_WAIT_PROC.
121 */
122 if (!(sub_info->wait & UMH_WAIT_PROC))
123 umh_complete(sub_info);
124 if (!retval)
125 return 0;
126 do_exit(0);
127}
128
129/* Handles UMH_WAIT_PROC. */
130static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
131{
132 pid_t pid;
133
134 /* If SIGCLD is ignored do_wait won't populate the status. */
135 kernel_sigaction(SIGCHLD, SIG_DFL);
136 pid = user_mode_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
137 if (pid < 0)
138 sub_info->retval = pid;
139 else
140 kernel_wait(pid, &sub_info->retval);
141
142 /* Restore default kernel sig handler */
143 kernel_sigaction(SIGCHLD, SIG_IGN);
144 umh_complete(sub_info);
145}
146
147/*
148 * We need to create the usermodehelper kernel thread from a task that is affine
149 * to an optimized set of CPUs (or nohz housekeeping ones) such that they
150 * inherit a widest affinity irrespective of call_usermodehelper() callers with
151 * possibly reduced affinity (eg: per-cpu workqueues). We don't want
152 * usermodehelper targets to contend a busy CPU.
153 *
154 * Unbound workqueues provide such wide affinity and allow to block on
155 * UMH_WAIT_PROC requests without blocking pending request (up to some limit).
156 *
157 * Besides, workqueues provide the privilege level that caller might not have
158 * to perform the usermodehelper request.
159 *
160 */
161static void call_usermodehelper_exec_work(struct work_struct *work)
162{
163 struct subprocess_info *sub_info =
164 container_of(work, struct subprocess_info, work);
165
166 if (sub_info->wait & UMH_WAIT_PROC) {
167 call_usermodehelper_exec_sync(sub_info);
168 } else {
169 pid_t pid;
170 /*
171 * Use CLONE_PARENT to reparent it to kthreadd; we do not
172 * want to pollute current->children, and we need a parent
173 * that always ignores SIGCHLD to ensure auto-reaping.
174 */
175 pid = user_mode_thread(call_usermodehelper_exec_async, sub_info,
176 CLONE_PARENT | SIGCHLD);
177 if (pid < 0) {
178 sub_info->retval = pid;
179 umh_complete(sub_info);
180 }
181 }
182}
183
184/*
185 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
186 * (used for preventing user land processes from being created after the user
187 * land has been frozen during a system-wide hibernation or suspend operation).
188 * Should always be manipulated under umhelper_sem acquired for write.
189 */
190static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
191
192/* Number of helpers running */
193static atomic_t running_helpers = ATOMIC_INIT(0);
194
195/*
196 * Wait queue head used by usermodehelper_disable() to wait for all running
197 * helpers to finish.
198 */
199static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
200
201/*
202 * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
203 * to become 'false'.
204 */
205static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
206
207/*
208 * Time to wait for running_helpers to become zero before the setting of
209 * usermodehelper_disabled in usermodehelper_disable() fails
210 */
211#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
212
213int usermodehelper_read_trylock(void)
214{
215 DEFINE_WAIT(wait);
216 int ret = 0;
217
218 down_read(&umhelper_sem);
219 for (;;) {
220 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
221 TASK_INTERRUPTIBLE);
222 if (!usermodehelper_disabled)
223 break;
224
225 if (usermodehelper_disabled == UMH_DISABLED)
226 ret = -EAGAIN;
227
228 up_read(&umhelper_sem);
229
230 if (ret)
231 break;
232
233 schedule();
234 try_to_freeze();
235
236 down_read(&umhelper_sem);
237 }
238 finish_wait(&usermodehelper_disabled_waitq, &wait);
239 return ret;
240}
241EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
242
243long usermodehelper_read_lock_wait(long timeout)
244{
245 DEFINE_WAIT(wait);
246
247 if (timeout < 0)
248 return -EINVAL;
249
250 down_read(&umhelper_sem);
251 for (;;) {
252 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
253 TASK_UNINTERRUPTIBLE);
254 if (!usermodehelper_disabled)
255 break;
256
257 up_read(&umhelper_sem);
258
259 timeout = schedule_timeout(timeout);
260 if (!timeout)
261 break;
262
263 down_read(&umhelper_sem);
264 }
265 finish_wait(&usermodehelper_disabled_waitq, &wait);
266 return timeout;
267}
268EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
269
270void usermodehelper_read_unlock(void)
271{
272 up_read(&umhelper_sem);
273}
274EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
275
276/**
277 * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
278 * @depth: New value to assign to usermodehelper_disabled.
279 *
280 * Change the value of usermodehelper_disabled (under umhelper_sem locked for
281 * writing) and wakeup tasks waiting for it to change.
282 */
283void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
284{
285 down_write(&umhelper_sem);
286 usermodehelper_disabled = depth;
287 wake_up(&usermodehelper_disabled_waitq);
288 up_write(&umhelper_sem);
289}
290
291/**
292 * __usermodehelper_disable - Prevent new helpers from being started.
293 * @depth: New value to assign to usermodehelper_disabled.
294 *
295 * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
296 */
297int __usermodehelper_disable(enum umh_disable_depth depth)
298{
299 long retval;
300
301 if (!depth)
302 return -EINVAL;
303
304 down_write(&umhelper_sem);
305 usermodehelper_disabled = depth;
306 up_write(&umhelper_sem);
307
308 /*
309 * From now on call_usermodehelper_exec() won't start any new
310 * helpers, so it is sufficient if running_helpers turns out to
311 * be zero at one point (it may be increased later, but that
312 * doesn't matter).
313 */
314 retval = wait_event_timeout(running_helpers_waitq,
315 atomic_read(&running_helpers) == 0,
316 RUNNING_HELPERS_TIMEOUT);
317 if (retval)
318 return 0;
319
320 __usermodehelper_set_disable_depth(UMH_ENABLED);
321 return -EAGAIN;
322}
323
324static void helper_lock(void)
325{
326 atomic_inc(&running_helpers);
327 smp_mb__after_atomic();
328}
329
330static void helper_unlock(void)
331{
332 if (atomic_dec_and_test(&running_helpers))
333 wake_up(&running_helpers_waitq);
334}
335
336/**
337 * call_usermodehelper_setup - prepare to call a usermode helper
338 * @path: path to usermode executable
339 * @argv: arg vector for process
340 * @envp: environment for process
341 * @gfp_mask: gfp mask for memory allocation
342 * @init: an init function
343 * @cleanup: a cleanup function
344 * @data: arbitrary context sensitive data
345 *
346 * Returns either %NULL on allocation failure, or a subprocess_info
347 * structure. This should be passed to call_usermodehelper_exec to
348 * exec the process and free the structure.
349 *
350 * The init function is used to customize the helper process prior to
351 * exec. A non-zero return code causes the process to error out, exit,
352 * and return the failure to the calling process
353 *
354 * The cleanup function is just before the subprocess_info is about to
355 * be freed. This can be used for freeing the argv and envp. The
356 * Function must be runnable in either a process context or the
357 * context in which call_usermodehelper_exec is called.
358 */
359struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
360 char **envp, gfp_t gfp_mask,
361 int (*init)(struct subprocess_info *info, struct cred *new),
362 void (*cleanup)(struct subprocess_info *info),
363 void *data)
364{
365 struct subprocess_info *sub_info;
366 sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
367 if (!sub_info)
368 goto out;
369
370 INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
371
372#ifdef CONFIG_STATIC_USERMODEHELPER
373 sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
374#else
375 sub_info->path = path;
376#endif
377 sub_info->argv = argv;
378 sub_info->envp = envp;
379
380 sub_info->cleanup = cleanup;
381 sub_info->init = init;
382 sub_info->data = data;
383 out:
384 return sub_info;
385}
386EXPORT_SYMBOL(call_usermodehelper_setup);
387
388/**
389 * call_usermodehelper_exec - start a usermode application
390 * @sub_info: information about the subprocess
391 * @wait: wait for the application to finish and return status.
392 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
393 * when the program couldn't be exec'ed. This makes it safe to call
394 * from interrupt context.
395 *
396 * Runs a user-space application. The application is started
397 * asynchronously if wait is not set, and runs as a child of system workqueues.
398 * (ie. it runs with full root capabilities and optimized affinity).
399 *
400 * Note: successful return value does not guarantee the helper was called at
401 * all. You can't rely on sub_info->{init,cleanup} being called even for
402 * UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers
403 * into a successful no-op.
404 */
405int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
406{
407 unsigned int state = TASK_UNINTERRUPTIBLE;
408 DECLARE_COMPLETION_ONSTACK(done);
409 int retval = 0;
410
411 if (!sub_info->path) {
412 call_usermodehelper_freeinfo(sub_info);
413 return -EINVAL;
414 }
415 helper_lock();
416 if (usermodehelper_disabled) {
417 retval = -EBUSY;
418 goto out;
419 }
420
421 /*
422 * If there is no binary for us to call, then just return and get out of
423 * here. This allows us to set STATIC_USERMODEHELPER_PATH to "" and
424 * disable all call_usermodehelper() calls.
425 */
426 if (strlen(sub_info->path) == 0)
427 goto out;
428
429 /*
430 * Set the completion pointer only if there is a waiter.
431 * This makes it possible to use umh_complete to free
432 * the data structure in case of UMH_NO_WAIT.
433 */
434 sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
435 sub_info->wait = wait;
436
437 queue_work(system_unbound_wq, &sub_info->work);
438 if (wait == UMH_NO_WAIT) /* task has freed sub_info */
439 goto unlock;
440
441 if (wait & UMH_FREEZABLE)
442 state |= TASK_FREEZABLE;
443
444 if (wait & UMH_KILLABLE) {
445 retval = wait_for_completion_state(&done, state | TASK_KILLABLE);
446 if (!retval)
447 goto wait_done;
448
449 /* umh_complete() will see NULL and free sub_info */
450 if (xchg(&sub_info->complete, NULL))
451 goto unlock;
452
453 /*
454 * fallthrough; in case of -ERESTARTSYS now do uninterruptible
455 * wait_for_completion_state(). Since umh_complete() shall call
456 * complete() in a moment if xchg() above returned NULL, this
457 * uninterruptible wait_for_completion_state() will not block
458 * SIGKILL'ed processes for long.
459 */
460 }
461 wait_for_completion_state(&done, state);
462
463wait_done:
464 retval = sub_info->retval;
465out:
466 call_usermodehelper_freeinfo(sub_info);
467unlock:
468 helper_unlock();
469 return retval;
470}
471EXPORT_SYMBOL(call_usermodehelper_exec);
472
473/**
474 * call_usermodehelper() - prepare and start a usermode application
475 * @path: path to usermode executable
476 * @argv: arg vector for process
477 * @envp: environment for process
478 * @wait: wait for the application to finish and return status.
479 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
480 * when the program couldn't be exec'ed. This makes it safe to call
481 * from interrupt context.
482 *
483 * This function is the equivalent to use call_usermodehelper_setup() and
484 * call_usermodehelper_exec().
485 */
486int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
487{
488 struct subprocess_info *info;
489 gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
490
491 info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
492 NULL, NULL, NULL);
493 if (info == NULL)
494 return -ENOMEM;
495
496 return call_usermodehelper_exec(info, wait);
497}
498EXPORT_SYMBOL(call_usermodehelper);
499
500static int proc_cap_handler(struct ctl_table *table, int write,
501 void *buffer, size_t *lenp, loff_t *ppos)
502{
503 struct ctl_table t;
504 unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
505 kernel_cap_t new_cap;
506 int err, i;
507
508 if (write && (!capable(CAP_SETPCAP) ||
509 !capable(CAP_SYS_MODULE)))
510 return -EPERM;
511
512 /*
513 * convert from the global kernel_cap_t to the ulong array to print to
514 * userspace if this is a read.
515 */
516 spin_lock(&umh_sysctl_lock);
517 for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) {
518 if (table->data == CAP_BSET)
519 cap_array[i] = usermodehelper_bset.cap[i];
520 else if (table->data == CAP_PI)
521 cap_array[i] = usermodehelper_inheritable.cap[i];
522 else
523 BUG();
524 }
525 spin_unlock(&umh_sysctl_lock);
526
527 t = *table;
528 t.data = &cap_array;
529
530 /*
531 * actually read or write and array of ulongs from userspace. Remember
532 * these are least significant 32 bits first
533 */
534 err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
535 if (err < 0)
536 return err;
537
538 /*
539 * convert from the sysctl array of ulongs to the kernel_cap_t
540 * internal representation
541 */
542 for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
543 new_cap.cap[i] = cap_array[i];
544
545 /*
546 * Drop everything not in the new_cap (but don't add things)
547 */
548 if (write) {
549 spin_lock(&umh_sysctl_lock);
550 if (table->data == CAP_BSET)
551 usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
552 if (table->data == CAP_PI)
553 usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
554 spin_unlock(&umh_sysctl_lock);
555 }
556
557 return 0;
558}
559
560struct ctl_table usermodehelper_table[] = {
561 {
562 .procname = "bset",
563 .data = CAP_BSET,
564 .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
565 .mode = 0600,
566 .proc_handler = proc_cap_handler,
567 },
568 {
569 .procname = "inheritable",
570 .data = CAP_PI,
571 .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
572 .mode = 0600,
573 .proc_handler = proc_cap_handler,
574 },
575 { }
576};