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