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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
37static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
38static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
39static DEFINE_SPINLOCK(umh_sysctl_lock);
40static DECLARE_RWSEM(umhelper_sem);
41static LIST_HEAD(umh_list);
42static DEFINE_MUTEX(umh_list_lock);
43
44static void call_usermodehelper_freeinfo(struct subprocess_info *info)
45{
46 if (info->cleanup)
47 (*info->cleanup)(info);
48 kfree(info);
49}
50
51static 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 */
68static 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(¤t->sighand->siglock);
75 flush_signal_handlers(current, 1);
76 spin_unlock_irq(¤t->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);
115out:
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. */
129static 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 */
181static 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 */
210static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
211
212/* Number of helpers running */
213static 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 */
219static 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 */
225static 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
233int 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}
261EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
262
263long 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}
288EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
289
290void usermodehelper_read_unlock(void)
291{
292 up_read(&umhelper_sem);
293}
294EXPORT_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 */
303void __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 */
317int __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
344static void helper_lock(void)
345{
346 atomic_inc(&running_helpers);
347 smp_mb__after_atomic();
348}
349
350static 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 */
379struct 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}
406EXPORT_SYMBOL(call_usermodehelper_setup);
407
408struct 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
435static 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
474static void umh_clean_and_save_pid(struct subprocess_info *info)
475{
476 struct umh_info *umh_info = info->data;
477
478 argv_free(info->argv);
479 umh_info->pid = info->pid;
480}
481
482/**
483 * fork_usermode_blob - fork a blob of bytes as a usermode process
484 * @data: a blob of bytes that can be do_execv-ed as a file
485 * @len: length of the blob
486 * @info: information about usermode process (shouldn't be NULL)
487 *
488 * If info->cmdline is set it will be used as command line for the
489 * user process, else "usermodehelper" is used.
490 *
491 * Returns either negative error or zero which indicates success
492 * in executing a blob of bytes as a usermode process. In such
493 * case 'struct umh_info *info' is populated with two pipes
494 * and a pid of the process. The caller is responsible for health
495 * check of the user process, killing it via pid, and closing the
496 * pipes when user process is no longer needed.
497 */
498int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
499{
500 struct subprocess_info *sub_info;
501 struct file *file;
502 ssize_t written;
503 loff_t pos = 0;
504 int err;
505
506 file = shmem_kernel_file_setup("", len, 0);
507 if (IS_ERR(file))
508 return PTR_ERR(file);
509
510 written = kernel_write(file, data, len, &pos);
511 if (written != len) {
512 err = written;
513 if (err >= 0)
514 err = -ENOMEM;
515 goto out;
516 }
517
518 err = -ENOMEM;
519 sub_info = call_usermodehelper_setup_file(file, umh_pipe_setup,
520 umh_clean_and_save_pid, info);
521 if (!sub_info)
522 goto out;
523
524 err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
525 if (!err) {
526 mutex_lock(&umh_list_lock);
527 list_add(&info->list, &umh_list);
528 mutex_unlock(&umh_list_lock);
529 }
530out:
531 fput(file);
532 return err;
533}
534EXPORT_SYMBOL_GPL(fork_usermode_blob);
535
536/**
537 * call_usermodehelper_exec - start a usermode application
538 * @sub_info: information about the subprocessa
539 * @wait: wait for the application to finish and return status.
540 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
541 * when the program couldn't be exec'ed. This makes it safe to call
542 * from interrupt context.
543 *
544 * Runs a user-space application. The application is started
545 * asynchronously if wait is not set, and runs as a child of system workqueues.
546 * (ie. it runs with full root capabilities and optimized affinity).
547 */
548int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
549{
550 DECLARE_COMPLETION_ONSTACK(done);
551 int retval = 0;
552
553 if (!sub_info->path) {
554 call_usermodehelper_freeinfo(sub_info);
555 return -EINVAL;
556 }
557 helper_lock();
558 if (usermodehelper_disabled) {
559 retval = -EBUSY;
560 goto out;
561 }
562
563 /*
564 * If there is no binary for us to call, then just return and get out of
565 * here. This allows us to set STATIC_USERMODEHELPER_PATH to "" and
566 * disable all call_usermodehelper() calls.
567 */
568 if (strlen(sub_info->path) == 0)
569 goto out;
570
571 /*
572 * Set the completion pointer only if there is a waiter.
573 * This makes it possible to use umh_complete to free
574 * the data structure in case of UMH_NO_WAIT.
575 */
576 sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
577 sub_info->wait = wait;
578
579 queue_work(system_unbound_wq, &sub_info->work);
580 if (wait == UMH_NO_WAIT) /* task has freed sub_info */
581 goto unlock;
582
583 if (wait & UMH_KILLABLE) {
584 retval = wait_for_completion_killable(&done);
585 if (!retval)
586 goto wait_done;
587
588 /* umh_complete() will see NULL and free sub_info */
589 if (xchg(&sub_info->complete, NULL))
590 goto unlock;
591 /* fallthrough, umh_complete() was already called */
592 }
593
594 wait_for_completion(&done);
595wait_done:
596 retval = sub_info->retval;
597out:
598 call_usermodehelper_freeinfo(sub_info);
599unlock:
600 helper_unlock();
601 return retval;
602}
603EXPORT_SYMBOL(call_usermodehelper_exec);
604
605/**
606 * call_usermodehelper() - prepare and start a usermode application
607 * @path: path to usermode executable
608 * @argv: arg vector for process
609 * @envp: environment for process
610 * @wait: wait for the application to finish and return status.
611 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
612 * when the program couldn't be exec'ed. This makes it safe to call
613 * from interrupt context.
614 *
615 * This function is the equivalent to use call_usermodehelper_setup() and
616 * call_usermodehelper_exec().
617 */
618int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
619{
620 struct subprocess_info *info;
621 gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
622
623 info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
624 NULL, NULL, NULL);
625 if (info == NULL)
626 return -ENOMEM;
627
628 return call_usermodehelper_exec(info, wait);
629}
630EXPORT_SYMBOL(call_usermodehelper);
631
632static int proc_cap_handler(struct ctl_table *table, int write,
633 void __user *buffer, size_t *lenp, loff_t *ppos)
634{
635 struct ctl_table t;
636 unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
637 kernel_cap_t new_cap;
638 int err, i;
639
640 if (write && (!capable(CAP_SETPCAP) ||
641 !capable(CAP_SYS_MODULE)))
642 return -EPERM;
643
644 /*
645 * convert from the global kernel_cap_t to the ulong array to print to
646 * userspace if this is a read.
647 */
648 spin_lock(&umh_sysctl_lock);
649 for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) {
650 if (table->data == CAP_BSET)
651 cap_array[i] = usermodehelper_bset.cap[i];
652 else if (table->data == CAP_PI)
653 cap_array[i] = usermodehelper_inheritable.cap[i];
654 else
655 BUG();
656 }
657 spin_unlock(&umh_sysctl_lock);
658
659 t = *table;
660 t.data = &cap_array;
661
662 /*
663 * actually read or write and array of ulongs from userspace. Remember
664 * these are least significant 32 bits first
665 */
666 err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
667 if (err < 0)
668 return err;
669
670 /*
671 * convert from the sysctl array of ulongs to the kernel_cap_t
672 * internal representation
673 */
674 for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
675 new_cap.cap[i] = cap_array[i];
676
677 /*
678 * Drop everything not in the new_cap (but don't add things)
679 */
680 if (write) {
681 spin_lock(&umh_sysctl_lock);
682 if (table->data == CAP_BSET)
683 usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
684 if (table->data == CAP_PI)
685 usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
686 spin_unlock(&umh_sysctl_lock);
687 }
688
689 return 0;
690}
691
692void __exit_umh(struct task_struct *tsk)
693{
694 struct umh_info *info;
695 pid_t pid = tsk->pid;
696
697 mutex_lock(&umh_list_lock);
698 list_for_each_entry(info, &umh_list, list) {
699 if (info->pid == pid) {
700 list_del(&info->list);
701 mutex_unlock(&umh_list_lock);
702 goto out;
703 }
704 }
705 mutex_unlock(&umh_list_lock);
706 return;
707out:
708 if (info->cleanup)
709 info->cleanup(info);
710}
711
712struct ctl_table usermodehelper_table[] = {
713 {
714 .procname = "bset",
715 .data = CAP_BSET,
716 .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
717 .mode = 0600,
718 .proc_handler = proc_cap_handler,
719 },
720 {
721 .procname = "inheritable",
722 .data = CAP_PI,
723 .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
724 .mode = 0600,
725 .proc_handler = proc_cap_handler,
726 },
727 { }
728};