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