Line data Source code
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 :
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 :
42 : static void call_usermodehelper_freeinfo(struct subprocess_info *info)
43 : {
44 0 : if (info->cleanup)
45 0 : (*info->cleanup)(info);
46 0 : kfree(info);
47 : }
48 :
49 0 : static void umh_complete(struct subprocess_info *sub_info)
50 : {
51 0 : 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 0 : if (comp)
58 0 : complete(comp);
59 : else
60 : call_usermodehelper_freeinfo(sub_info);
61 0 : }
62 :
63 : /*
64 : * This is the task which runs the usermode application
65 : */
66 0 : static int call_usermodehelper_exec_async(void *data)
67 : {
68 0 : struct subprocess_info *sub_info = data;
69 : struct cred *new;
70 : int retval;
71 :
72 0 : spin_lock_irq(¤t->sighand->siglock);
73 0 : flush_signal_handlers(current, 1);
74 0 : 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 0 : 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 0 : set_user_nice(current, 0);
89 :
90 0 : retval = -ENOMEM;
91 0 : new = prepare_kernel_cred(current);
92 0 : if (!new)
93 : goto out;
94 :
95 0 : spin_lock(&umh_sysctl_lock);
96 0 : new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
97 0 : new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
98 : new->cap_inheritable);
99 0 : spin_unlock(&umh_sysctl_lock);
100 :
101 0 : if (sub_info->init) {
102 0 : retval = sub_info->init(sub_info, new);
103 0 : if (retval) {
104 0 : abort_creds(new);
105 0 : goto out;
106 : }
107 : }
108 :
109 0 : commit_creds(new);
110 :
111 : wait_for_initramfs();
112 0 : retval = kernel_execve(sub_info->path,
113 0 : (const char *const *)sub_info->argv,
114 0 : (const char *const *)sub_info->envp);
115 : out:
116 0 : sub_info->retval = retval;
117 : /*
118 : * call_usermodehelper_exec_sync() will call umh_complete
119 : * if UHM_WAIT_PROC.
120 : */
121 0 : if (!(sub_info->wait & UMH_WAIT_PROC))
122 0 : umh_complete(sub_info);
123 0 : if (!retval)
124 0 : return 0;
125 0 : do_exit(0);
126 : }
127 :
128 : /* Handles UMH_WAIT_PROC. */
129 0 : static 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 0 : kernel_sigaction(SIGCHLD, SIG_DFL);
135 0 : pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
136 0 : if (pid < 0)
137 0 : sub_info->retval = pid;
138 : else
139 0 : kernel_wait(pid, &sub_info->retval);
140 :
141 : /* Restore default kernel sig handler */
142 0 : kernel_sigaction(SIGCHLD, SIG_IGN);
143 0 : umh_complete(sub_info);
144 0 : }
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 : */
160 0 : static void call_usermodehelper_exec_work(struct work_struct *work)
161 : {
162 0 : struct subprocess_info *sub_info =
163 0 : container_of(work, struct subprocess_info, work);
164 :
165 0 : if (sub_info->wait & UMH_WAIT_PROC) {
166 0 : 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 0 : pid = kernel_thread(call_usermodehelper_exec_async, sub_info,
175 : CLONE_PARENT | SIGCHLD);
176 0 : if (pid < 0) {
177 0 : sub_info->retval = pid;
178 0 : umh_complete(sub_info);
179 : }
180 : }
181 0 : }
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 : */
189 : static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
190 :
191 : /* Number of helpers running */
192 : static 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 : */
198 : static 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 : */
204 : static 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 :
212 0 : int usermodehelper_read_trylock(void)
213 : {
214 0 : DEFINE_WAIT(wait);
215 0 : int ret = 0;
216 :
217 0 : down_read(&umhelper_sem);
218 : for (;;) {
219 0 : prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
220 : TASK_INTERRUPTIBLE);
221 0 : if (!usermodehelper_disabled)
222 : break;
223 :
224 0 : if (usermodehelper_disabled == UMH_DISABLED)
225 0 : ret = -EAGAIN;
226 :
227 0 : up_read(&umhelper_sem);
228 :
229 0 : if (ret)
230 : break;
231 :
232 0 : schedule();
233 0 : try_to_freeze();
234 :
235 0 : down_read(&umhelper_sem);
236 : }
237 0 : finish_wait(&usermodehelper_disabled_waitq, &wait);
238 0 : return ret;
239 : }
240 : EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
241 :
242 0 : long usermodehelper_read_lock_wait(long timeout)
243 : {
244 0 : DEFINE_WAIT(wait);
245 :
246 0 : if (timeout < 0)
247 : return -EINVAL;
248 :
249 0 : down_read(&umhelper_sem);
250 : for (;;) {
251 0 : prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
252 : TASK_UNINTERRUPTIBLE);
253 0 : if (!usermodehelper_disabled)
254 : break;
255 :
256 0 : up_read(&umhelper_sem);
257 :
258 0 : timeout = schedule_timeout(timeout);
259 0 : if (!timeout)
260 : break;
261 :
262 0 : down_read(&umhelper_sem);
263 : }
264 0 : finish_wait(&usermodehelper_disabled_waitq, &wait);
265 0 : return timeout;
266 : }
267 : EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
268 :
269 0 : void usermodehelper_read_unlock(void)
270 : {
271 0 : up_read(&umhelper_sem);
272 0 : }
273 : EXPORT_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 : */
282 1 : void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
283 : {
284 1 : down_write(&umhelper_sem);
285 1 : usermodehelper_disabled = depth;
286 1 : wake_up(&usermodehelper_disabled_waitq);
287 1 : up_write(&umhelper_sem);
288 1 : }
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 : */
296 1 : int __usermodehelper_disable(enum umh_disable_depth depth)
297 : {
298 : long retval;
299 :
300 1 : if (!depth)
301 : return -EINVAL;
302 :
303 1 : down_write(&umhelper_sem);
304 1 : usermodehelper_disabled = depth;
305 1 : 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 2 : retval = wait_event_timeout(running_helpers_waitq,
314 : atomic_read(&running_helpers) == 0,
315 : RUNNING_HELPERS_TIMEOUT);
316 1 : if (retval)
317 : return 0;
318 :
319 0 : __usermodehelper_set_disable_depth(UMH_ENABLED);
320 0 : return -EAGAIN;
321 : }
322 :
323 : static void helper_lock(void)
324 : {
325 0 : atomic_inc(&running_helpers);
326 0 : smp_mb__after_atomic();
327 : }
328 :
329 0 : static void helper_unlock(void)
330 : {
331 0 : if (atomic_dec_and_test(&running_helpers))
332 0 : wake_up(&running_helpers_waitq);
333 0 : }
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 : */
358 0 : struct 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 0 : sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
366 0 : if (!sub_info)
367 : goto out;
368 :
369 0 : 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 0 : sub_info->path = path;
375 : #endif
376 0 : sub_info->argv = argv;
377 0 : sub_info->envp = envp;
378 :
379 0 : sub_info->cleanup = cleanup;
380 0 : sub_info->init = init;
381 0 : sub_info->data = data;
382 : out:
383 0 : return sub_info;
384 : }
385 : EXPORT_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 : */
404 0 : int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
405 : {
406 0 : DECLARE_COMPLETION_ONSTACK(done);
407 0 : int retval = 0;
408 :
409 0 : if (!sub_info->path) {
410 0 : call_usermodehelper_freeinfo(sub_info);
411 0 : return -EINVAL;
412 : }
413 : helper_lock();
414 0 : 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 0 : 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 0 : sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
433 0 : sub_info->wait = wait;
434 :
435 0 : queue_work(system_unbound_wq, &sub_info->work);
436 0 : if (wait == UMH_NO_WAIT) /* task has freed sub_info */
437 : goto unlock;
438 :
439 0 : if (wait & UMH_KILLABLE) {
440 0 : retval = wait_for_completion_killable(&done);
441 0 : if (!retval)
442 : goto wait_done;
443 :
444 : /* umh_complete() will see NULL and free sub_info */
445 0 : if (xchg(&sub_info->complete, NULL))
446 : goto unlock;
447 : /* fallthrough, umh_complete() was already called */
448 : }
449 :
450 0 : wait_for_completion(&done);
451 : wait_done:
452 0 : retval = sub_info->retval;
453 : out:
454 : call_usermodehelper_freeinfo(sub_info);
455 : unlock:
456 0 : helper_unlock();
457 0 : return retval;
458 : }
459 : EXPORT_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 : */
474 0 : int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
475 : {
476 : struct subprocess_info *info;
477 0 : gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
478 :
479 0 : info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
480 : NULL, NULL, NULL);
481 0 : if (info == NULL)
482 : return -ENOMEM;
483 :
484 0 : return call_usermodehelper_exec(info, wait);
485 : }
486 : EXPORT_SYMBOL(call_usermodehelper);
487 :
488 0 : static 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 0 : if (write && (!capable(CAP_SETPCAP) ||
497 0 : !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 0 : spin_lock(&umh_sysctl_lock);
505 0 : for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) {
506 0 : if (table->data == CAP_BSET)
507 0 : cap_array[i] = usermodehelper_bset.cap[i];
508 0 : else if (table->data == CAP_PI)
509 0 : cap_array[i] = usermodehelper_inheritable.cap[i];
510 : else
511 0 : BUG();
512 : }
513 0 : spin_unlock(&umh_sysctl_lock);
514 :
515 0 : t = *table;
516 0 : 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 0 : err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
523 0 : 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 0 : for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
531 0 : new_cap.cap[i] = cap_array[i];
532 :
533 : /*
534 : * Drop everything not in the new_cap (but don't add things)
535 : */
536 0 : if (write) {
537 0 : spin_lock(&umh_sysctl_lock);
538 0 : if (table->data == CAP_BSET)
539 0 : usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
540 0 : if (table->data == CAP_PI)
541 0 : usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
542 : spin_unlock(&umh_sysctl_lock);
543 : }
544 :
545 : return 0;
546 : }
547 :
548 : struct 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 : };
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