projects/linux·blob uaccess-cleanups · refs

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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/fs_struct.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/initrd.h>
30#include <linux/freezer.h>
31
32#include <trace/events/module.h>
33
34static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
35static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
36static DEFINE_SPINLOCK(umh_sysctl_lock);
37static DECLARE_RWSEM(umhelper_sem);
38
39static void call_usermodehelper_freeinfo(struct subprocess_info *info)
40{
41 if (info->cleanup)
42 (*info->cleanup)(info);
43 kfree(info);
44}
45
46static void umh_complete(struct subprocess_info *sub_info)
47{
48 struct completion *comp = xchg(&sub_info->complete, NULL);
49 /*
50 * See call_usermodehelper_exec(). If xchg() returns NULL
51 * we own sub_info, the UMH_KILLABLE caller has gone away
52 * or the caller used UMH_NO_WAIT.
53 */
54 if (comp)
55 complete(comp);
56 else
57 call_usermodehelper_freeinfo(sub_info);
58}
59
60/*
61 * This is the task which runs the usermode application
62 */
63static int call_usermodehelper_exec_async(void *data)
64{
65 struct subprocess_info *sub_info = data;
66 struct cred *new;
67 int retval;
68
69 spin_lock_irq(&current->sighand->siglock);
70 flush_signal_handlers(current, 1);
71 spin_unlock_irq(&current->sighand->siglock);
72
73 /*
74 * Usermodehelper threads get a copy of userspace init's
75 * fs_struct. Reset umask to the default.
76 */
77 current->fs->umask = 0022;
78
79 /*
80 * Our parent (unbound workqueue) runs with elevated scheduling
81 * priority. Avoid propagating that into the userspace child.
82 */
83 set_user_nice(current, 0);
84
85 retval = -ENOMEM;
86 new = prepare_kernel_cred(current);
87 if (!new)
88 goto out;
89
90 spin_lock(&umh_sysctl_lock);
91 new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
92 new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
93 new->cap_inheritable);
94 spin_unlock(&umh_sysctl_lock);
95
96 if (sub_info->init) {
97 retval = sub_info->init(sub_info, new);
98 if (retval) {
99 abort_creds(new);
100 goto out;
101 }
102 }
103
104 commit_creds(new);
105
106 wait_for_initramfs();
107 retval = kernel_execve(sub_info->path,
108 (const char *const *)sub_info->argv,
109 (const char *const *)sub_info->envp);
110out:
111 sub_info->retval = retval;
112 /*
113 * call_usermodehelper_exec_sync() will call umh_complete
114 * if UHM_WAIT_PROC.
115 */
116 if (!(sub_info->wait & UMH_WAIT_PROC))
117 umh_complete(sub_info);
118 if (!retval)
119 return 0;
120 do_exit(0);
121}
122
123/* Handles UMH_WAIT_PROC. */
124static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
125{
126 pid_t pid;
127
128 /* If SIGCLD is ignored do_wait won't populate the status. */
129 kernel_sigaction(SIGCHLD, SIG_DFL);
130 pid = user_mode_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
131 if (pid < 0)
132 sub_info->retval = pid;
133 else
134 kernel_wait(pid, &sub_info->retval);
135
136 /* Restore default kernel sig handler */
137 kernel_sigaction(SIGCHLD, SIG_IGN);
138 umh_complete(sub_info);
139}
140
141/*
142 * We need to create the usermodehelper kernel thread from a task that is affine
143 * to an optimized set of CPUs (or nohz housekeeping ones) such that they
144 * inherit a widest affinity irrespective of call_usermodehelper() callers with
145 * possibly reduced affinity (eg: per-cpu workqueues). We don't want
146 * usermodehelper targets to contend a busy CPU.
147 *
148 * Unbound workqueues provide such wide affinity and allow to block on
149 * UMH_WAIT_PROC requests without blocking pending request (up to some limit).
150 *
151 * Besides, workqueues provide the privilege level that caller might not have
152 * to perform the usermodehelper request.
153 *
154 */
155static void call_usermodehelper_exec_work(struct work_struct *work)
156{
157 struct subprocess_info *sub_info =
158 container_of(work, struct subprocess_info, work);
159
160 if (sub_info->wait & UMH_WAIT_PROC) {
161 call_usermodehelper_exec_sync(sub_info);
162 } else {
163 pid_t pid;
164 /*
165 * Use CLONE_PARENT to reparent it to kthreadd; we do not
166 * want to pollute current->children, and we need a parent
167 * that always ignores SIGCHLD to ensure auto-reaping.
168 */
169 pid = user_mode_thread(call_usermodehelper_exec_async, sub_info,
170 CLONE_PARENT | SIGCHLD);
171 if (pid < 0) {
172 sub_info->retval = pid;
173 umh_complete(sub_info);
174 }
175 }
176}
177
178/*
179 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
180 * (used for preventing user land processes from being created after the user
181 * land has been frozen during a system-wide hibernation or suspend operation).
182 * Should always be manipulated under umhelper_sem acquired for write.
183 */
184static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
185
186/* Number of helpers running */
187static atomic_t running_helpers = ATOMIC_INIT(0);
188
189/*
190 * Wait queue head used by usermodehelper_disable() to wait for all running
191 * helpers to finish.
192 */
193static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
194
195/*
196 * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
197 * to become 'false'.
198 */
199static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
200
201/*
202 * Time to wait for running_helpers to become zero before the setting of
203 * usermodehelper_disabled in usermodehelper_disable() fails
204 */
205#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
206
207int usermodehelper_read_trylock(void)
208{
209 DEFINE_WAIT(wait);
210 int ret = 0;
211
212 down_read(&umhelper_sem);
213 for (;;) {
214 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
215 TASK_INTERRUPTIBLE);
216 if (!usermodehelper_disabled)
217 break;
218
219 if (usermodehelper_disabled == UMH_DISABLED)
220 ret = -EAGAIN;
221
222 up_read(&umhelper_sem);
223
224 if (ret)
225 break;
226
227 schedule();
228 try_to_freeze();
229
230 down_read(&umhelper_sem);
231 }
232 finish_wait(&usermodehelper_disabled_waitq, &wait);
233 return ret;
234}
235EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
236
237long usermodehelper_read_lock_wait(long timeout)
238{
239 DEFINE_WAIT(wait);
240
241 if (timeout < 0)
242 return -EINVAL;
243
244 down_read(&umhelper_sem);
245 for (;;) {
246 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
247 TASK_UNINTERRUPTIBLE);
248 if (!usermodehelper_disabled)
249 break;
250
251 up_read(&umhelper_sem);
252
253 timeout = schedule_timeout(timeout);
254 if (!timeout)
255 break;
256
257 down_read(&umhelper_sem);
258 }
259 finish_wait(&usermodehelper_disabled_waitq, &wait);
260 return timeout;
261}
262EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
263
264void usermodehelper_read_unlock(void)
265{
266 up_read(&umhelper_sem);
267}
268EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
269
270/**
271 * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
272 * @depth: New value to assign to usermodehelper_disabled.
273 *
274 * Change the value of usermodehelper_disabled (under umhelper_sem locked for
275 * writing) and wakeup tasks waiting for it to change.
276 */
277void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
278{
279 down_write(&umhelper_sem);
280 usermodehelper_disabled = depth;
281 wake_up(&usermodehelper_disabled_waitq);
282 up_write(&umhelper_sem);
283}
284
285/**
286 * __usermodehelper_disable - Prevent new helpers from being started.
287 * @depth: New value to assign to usermodehelper_disabled.
288 *
289 * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
290 */
291int __usermodehelper_disable(enum umh_disable_depth depth)
292{
293 long retval;
294
295 if (!depth)
296 return -EINVAL;
297
298 down_write(&umhelper_sem);
299 usermodehelper_disabled = depth;
300 up_write(&umhelper_sem);
301
302 /*
303 * From now on call_usermodehelper_exec() won't start any new
304 * helpers, so it is sufficient if running_helpers turns out to
305 * be zero at one point (it may be increased later, but that
306 * doesn't matter).
307 */
308 retval = wait_event_timeout(running_helpers_waitq,
309 atomic_read(&running_helpers) == 0,
310 RUNNING_HELPERS_TIMEOUT);
311 if (retval)
312 return 0;
313
314 __usermodehelper_set_disable_depth(UMH_ENABLED);
315 return -EAGAIN;
316}
317
318static void helper_lock(void)
319{
320 atomic_inc(&running_helpers);
321 smp_mb__after_atomic();
322}
323
324static void helper_unlock(void)
325{
326 if (atomic_dec_and_test(&running_helpers))
327 wake_up(&running_helpers_waitq);
328}
329
330/**
331 * call_usermodehelper_setup - prepare to call a usermode helper
332 * @path: path to usermode executable
333 * @argv: arg vector for process
334 * @envp: environment for process
335 * @gfp_mask: gfp mask for memory allocation
336 * @init: an init function
337 * @cleanup: a cleanup function
338 * @data: arbitrary context sensitive data
339 *
340 * Returns either %NULL on allocation failure, or a subprocess_info
341 * structure. This should be passed to call_usermodehelper_exec to
342 * exec the process and free the structure.
343 *
344 * The init function is used to customize the helper process prior to
345 * exec. A non-zero return code causes the process to error out, exit,
346 * and return the failure to the calling process
347 *
348 * The cleanup function is just before the subprocess_info is about to
349 * be freed. This can be used for freeing the argv and envp. The
350 * Function must be runnable in either a process context or the
351 * context in which call_usermodehelper_exec is called.
352 */
353struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
354 char **envp, gfp_t gfp_mask,
355 int (*init)(struct subprocess_info *info, struct cred *new),
356 void (*cleanup)(struct subprocess_info *info),
357 void *data)
358{
359 struct subprocess_info *sub_info;
360 sub_info = kzalloc_obj(struct subprocess_info, gfp_mask);
361 if (!sub_info)
362 goto out;
363
364 INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
365
366#ifdef CONFIG_STATIC_USERMODEHELPER
367 sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
368#else
369 sub_info->path = path;
370#endif
371 sub_info->argv = argv;
372 sub_info->envp = envp;
373
374 sub_info->cleanup = cleanup;
375 sub_info->init = init;
376 sub_info->data = data;
377 out:
378 return sub_info;
379}
380EXPORT_SYMBOL(call_usermodehelper_setup);
381
382/**
383 * call_usermodehelper_exec - start a usermode application
384 * @sub_info: information about the subprocess
385 * @wait: wait for the application to finish and return status.
386 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
387 * when the program couldn't be exec'ed. This makes it safe to call
388 * from interrupt context.
389 *
390 * Runs a user-space application. The application is started
391 * asynchronously if wait is not set, and runs as a child of system workqueues.
392 * (ie. it runs with full root capabilities and optimized affinity).
393 *
394 * Note: successful return value does not guarantee the helper was called at
395 * all. You can't rely on sub_info->{init,cleanup} being called even for
396 * UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers
397 * into a successful no-op.
398 */
399int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
400{
401 unsigned int state = TASK_UNINTERRUPTIBLE;
402 DECLARE_COMPLETION_ONSTACK(done);
403 int retval = 0;
404
405 if (!sub_info->path) {
406 call_usermodehelper_freeinfo(sub_info);
407 return -EINVAL;
408 }
409 helper_lock();
410 if (usermodehelper_disabled) {
411 retval = -EBUSY;
412 goto out;
413 }
414
415 /*
416 * If there is no binary for us to call, then just return and get out of
417 * here. This allows us to set STATIC_USERMODEHELPER_PATH to "" and
418 * disable all call_usermodehelper() calls.
419 */
420 if (strlen(sub_info->path) == 0)
421 goto out;
422
423 /*
424 * Set the completion pointer only if there is a waiter.
425 * This makes it possible to use umh_complete to free
426 * the data structure in case of UMH_NO_WAIT.
427 */
428 sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
429 sub_info->wait = wait;
430
431 queue_work(system_dfl_wq, &sub_info->work);
432 if (wait == UMH_NO_WAIT) /* task has freed sub_info */
433 goto unlock;
434
435 if (wait & UMH_FREEZABLE)
436 state |= TASK_FREEZABLE;
437
438 if (wait & UMH_KILLABLE) {
439 retval = wait_for_completion_state(&done, state | TASK_KILLABLE);
440 if (!retval)
441 goto wait_done;
442
443 /* umh_complete() will see NULL and free sub_info */
444 if (xchg(&sub_info->complete, NULL))
445 goto unlock;
446
447 /*
448 * fallthrough; in case of -ERESTARTSYS now do uninterruptible
449 * wait_for_completion_state(). Since umh_complete() shall call
450 * complete() in a moment if xchg() above returned NULL, this
451 * uninterruptible wait_for_completion_state() will not block
452 * SIGKILL'ed processes for long.
453 */
454 }
455 wait_for_completion_state(&done, state);
456
457wait_done:
458 retval = sub_info->retval;
459out:
460 call_usermodehelper_freeinfo(sub_info);
461unlock:
462 helper_unlock();
463 return retval;
464}
465EXPORT_SYMBOL(call_usermodehelper_exec);
466
467/**
468 * call_usermodehelper() - prepare and start a usermode application
469 * @path: path to usermode executable
470 * @argv: arg vector for process
471 * @envp: environment for process
472 * @wait: wait for the application to finish and return status.
473 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
474 * when the program couldn't be exec'ed. This makes it safe to call
475 * from interrupt context.
476 *
477 * This function is the equivalent to use call_usermodehelper_setup() and
478 * call_usermodehelper_exec().
479 */
480int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
481{
482 struct subprocess_info *info;
483 gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
484
485 info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
486 NULL, NULL, NULL);
487 if (info == NULL)
488 return -ENOMEM;
489
490 return call_usermodehelper_exec(info, wait);
491}
492EXPORT_SYMBOL(call_usermodehelper);
493
494#if defined(CONFIG_SYSCTL)
495static int proc_cap_handler(const struct ctl_table *table, int write,
496 void *buffer, size_t *lenp, loff_t *ppos)
497{
498 struct ctl_table t;
499 unsigned long cap_array[2];
500 kernel_cap_t new_cap, *cap;
501 int err;
502
503 if (write && (!capable(CAP_SETPCAP) ||
504 !capable(CAP_SYS_MODULE)))
505 return -EPERM;
506
507 /*
508 * convert from the global kernel_cap_t to the ulong array to print to
509 * userspace if this is a read.
510 *
511 * Legacy format: capabilities are exposed as two 32-bit values
512 */
513 cap = table->data;
514 spin_lock(&umh_sysctl_lock);
515 cap_array[0] = (u32) cap->val;
516 cap_array[1] = cap->val >> 32;
517 spin_unlock(&umh_sysctl_lock);
518
519 t = *table;
520 t.data = &cap_array;
521
522 /*
523 * actually read or write and array of ulongs from userspace. Remember
524 * these are least significant 32 bits first
525 */
526 err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
527 if (err < 0)
528 return err;
529
530 new_cap.val = (u32)cap_array[0];
531 new_cap.val += (u64)cap_array[1] << 32;
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 *cap = cap_intersect(*cap, new_cap);
539 spin_unlock(&umh_sysctl_lock);
540 }
541
542 return 0;
543}
544
545static const struct ctl_table usermodehelper_table[] = {
546 {
547 .procname = "bset",
548 .data = &usermodehelper_bset,
549 .maxlen = 2 * sizeof(unsigned long),
550 .mode = 0600,
551 .proc_handler = proc_cap_handler,
552 },
553 {
554 .procname = "inheritable",
555 .data = &usermodehelper_inheritable,
556 .maxlen = 2 * sizeof(unsigned long),
557 .mode = 0600,
558 .proc_handler = proc_cap_handler,
559 },
560};
561
562static int __init init_umh_sysctls(void)
563{
564 register_sysctl_init("kernel/usermodehelper", usermodehelper_table);
565 return 0;
566}
567early_initcall(init_umh_sysctls);
568#endif /* CONFIG_SYSCTL */