projects/linux·blob v4.15 · refs

568 lines · 15.2 KiB

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
29#include <trace/events/module.h>
30
31#define CAP_BSET (void *)1
32#define CAP_PI (void *)2
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 * Our parent (unbound workqueue) runs with elevated scheduling
75 * priority. Avoid propagating that into the userspace child.
76 */
77 set_user_nice(current, 0);
78
79 retval = -ENOMEM;
80 new = prepare_kernel_cred(current);
81 if (!new)
82 goto out;
83
84 spin_lock(&umh_sysctl_lock);
85 new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
86 new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
87 new->cap_inheritable);
88 spin_unlock(&umh_sysctl_lock);
89
90 if (sub_info->init) {
91 retval = sub_info->init(sub_info, new);
92 if (retval) {
93 abort_creds(new);
94 goto out;
95 }
96 }
97
98 commit_creds(new);
99
100 retval = do_execve(getname_kernel(sub_info->path),
101 (const char __user *const __user *)sub_info->argv,
102 (const char __user *const __user *)sub_info->envp);
103out:
104 sub_info->retval = retval;
105 /*
106 * call_usermodehelper_exec_sync() will call umh_complete
107 * if UHM_WAIT_PROC.
108 */
109 if (!(sub_info->wait & UMH_WAIT_PROC))
110 umh_complete(sub_info);
111 if (!retval)
112 return 0;
113 do_exit(0);
114}
115
116/* Handles UMH_WAIT_PROC. */
117static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
118{
119 pid_t pid;
120
121 /* If SIGCLD is ignored sys_wait4 won't populate the status. */
122 kernel_sigaction(SIGCHLD, SIG_DFL);
123 pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
124 if (pid < 0) {
125 sub_info->retval = pid;
126 } else {
127 int ret = -ECHILD;
128 /*
129 * Normally it is bogus to call wait4() from in-kernel because
130 * wait4() wants to write the exit code to a userspace address.
131 * But call_usermodehelper_exec_sync() always runs as kernel
132 * thread (workqueue) and put_user() to a kernel address works
133 * OK for kernel threads, due to their having an mm_segment_t
134 * which spans the entire address space.
135 *
136 * Thus the __user pointer cast is valid here.
137 */
138 sys_wait4(pid, (int __user *)&ret, 0, NULL);
139
140 /*
141 * If ret is 0, either call_usermodehelper_exec_async failed and
142 * the real error code is already in sub_info->retval or
143 * sub_info->retval is 0 anyway, so don't mess with it then.
144 */
145 if (ret)
146 sub_info->retval = ret;
147 }
148
149 /* Restore default kernel sig handler */
150 kernel_sigaction(SIGCHLD, SIG_IGN);
151
152 umh_complete(sub_info);
153}
154
155/*
156 * We need to create the usermodehelper kernel thread from a task that is affine
157 * to an optimized set of CPUs (or nohz housekeeping ones) such that they
158 * inherit a widest affinity irrespective of call_usermodehelper() callers with
159 * possibly reduced affinity (eg: per-cpu workqueues). We don't want
160 * usermodehelper targets to contend a busy CPU.
161 *
162 * Unbound workqueues provide such wide affinity and allow to block on
163 * UMH_WAIT_PROC requests without blocking pending request (up to some limit).
164 *
165 * Besides, workqueues provide the privilege level that caller might not have
166 * to perform the usermodehelper request.
167 *
168 */
169static void call_usermodehelper_exec_work(struct work_struct *work)
170{
171 struct subprocess_info *sub_info =
172 container_of(work, struct subprocess_info, work);
173
174 if (sub_info->wait & UMH_WAIT_PROC) {
175 call_usermodehelper_exec_sync(sub_info);
176 } else {
177 pid_t pid;
178 /*
179 * Use CLONE_PARENT to reparent it to kthreadd; we do not
180 * want to pollute current->children, and we need a parent
181 * that always ignores SIGCHLD to ensure auto-reaping.
182 */
183 pid = kernel_thread(call_usermodehelper_exec_async, sub_info,
184 CLONE_PARENT | SIGCHLD);
185 if (pid < 0) {
186 sub_info->retval = pid;
187 umh_complete(sub_info);
188 }
189 }
190}
191
192/*
193 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
194 * (used for preventing user land processes from being created after the user
195 * land has been frozen during a system-wide hibernation or suspend operation).
196 * Should always be manipulated under umhelper_sem acquired for write.
197 */
198static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
199
200/* Number of helpers running */
201static atomic_t running_helpers = ATOMIC_INIT(0);
202
203/*
204 * Wait queue head used by usermodehelper_disable() to wait for all running
205 * helpers to finish.
206 */
207static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
208
209/*
210 * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
211 * to become 'false'.
212 */
213static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
214
215/*
216 * Time to wait for running_helpers to become zero before the setting of
217 * usermodehelper_disabled in usermodehelper_disable() fails
218 */
219#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
220
221int usermodehelper_read_trylock(void)
222{
223 DEFINE_WAIT(wait);
224 int ret = 0;
225
226 down_read(&umhelper_sem);
227 for (;;) {
228 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
229 TASK_INTERRUPTIBLE);
230 if (!usermodehelper_disabled)
231 break;
232
233 if (usermodehelper_disabled == UMH_DISABLED)
234 ret = -EAGAIN;
235
236 up_read(&umhelper_sem);
237
238 if (ret)
239 break;
240
241 schedule();
242 try_to_freeze();
243
244 down_read(&umhelper_sem);
245 }
246 finish_wait(&usermodehelper_disabled_waitq, &wait);
247 return ret;
248}
249EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
250
251long usermodehelper_read_lock_wait(long timeout)
252{
253 DEFINE_WAIT(wait);
254
255 if (timeout < 0)
256 return -EINVAL;
257
258 down_read(&umhelper_sem);
259 for (;;) {
260 prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
261 TASK_UNINTERRUPTIBLE);
262 if (!usermodehelper_disabled)
263 break;
264
265 up_read(&umhelper_sem);
266
267 timeout = schedule_timeout(timeout);
268 if (!timeout)
269 break;
270
271 down_read(&umhelper_sem);
272 }
273 finish_wait(&usermodehelper_disabled_waitq, &wait);
274 return timeout;
275}
276EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
277
278void usermodehelper_read_unlock(void)
279{
280 up_read(&umhelper_sem);
281}
282EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
283
284/**
285 * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
286 * @depth: New value to assign to usermodehelper_disabled.
287 *
288 * Change the value of usermodehelper_disabled (under umhelper_sem locked for
289 * writing) and wakeup tasks waiting for it to change.
290 */
291void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
292{
293 down_write(&umhelper_sem);
294 usermodehelper_disabled = depth;
295 wake_up(&usermodehelper_disabled_waitq);
296 up_write(&umhelper_sem);
297}
298
299/**
300 * __usermodehelper_disable - Prevent new helpers from being started.
301 * @depth: New value to assign to usermodehelper_disabled.
302 *
303 * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
304 */
305int __usermodehelper_disable(enum umh_disable_depth depth)
306{
307 long retval;
308
309 if (!depth)
310 return -EINVAL;
311
312 down_write(&umhelper_sem);
313 usermodehelper_disabled = depth;
314 up_write(&umhelper_sem);
315
316 /*
317 * From now on call_usermodehelper_exec() won't start any new
318 * helpers, so it is sufficient if running_helpers turns out to
319 * be zero at one point (it may be increased later, but that
320 * doesn't matter).
321 */
322 retval = wait_event_timeout(running_helpers_waitq,
323 atomic_read(&running_helpers) == 0,
324 RUNNING_HELPERS_TIMEOUT);
325 if (retval)
326 return 0;
327
328 __usermodehelper_set_disable_depth(UMH_ENABLED);
329 return -EAGAIN;
330}
331
332static void helper_lock(void)
333{
334 atomic_inc(&running_helpers);
335 smp_mb__after_atomic();
336}
337
338static void helper_unlock(void)
339{
340 if (atomic_dec_and_test(&running_helpers))
341 wake_up(&running_helpers_waitq);
342}
343
344/**
345 * call_usermodehelper_setup - prepare to call a usermode helper
346 * @path: path to usermode executable
347 * @argv: arg vector for process
348 * @envp: environment for process
349 * @gfp_mask: gfp mask for memory allocation
350 * @cleanup: a cleanup function
351 * @init: an init function
352 * @data: arbitrary context sensitive data
353 *
354 * Returns either %NULL on allocation failure, or a subprocess_info
355 * structure. This should be passed to call_usermodehelper_exec to
356 * exec the process and free the structure.
357 *
358 * The init function is used to customize the helper process prior to
359 * exec. A non-zero return code causes the process to error out, exit,
360 * and return the failure to the calling process
361 *
362 * The cleanup function is just before ethe subprocess_info is about to
363 * be freed. This can be used for freeing the argv and envp. The
364 * Function must be runnable in either a process context or the
365 * context in which call_usermodehelper_exec is called.
366 */
367struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
368 char **envp, gfp_t gfp_mask,
369 int (*init)(struct subprocess_info *info, struct cred *new),
370 void (*cleanup)(struct subprocess_info *info),
371 void *data)
372{
373 struct subprocess_info *sub_info;
374 sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
375 if (!sub_info)
376 goto out;
377
378 INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
379
380#ifdef CONFIG_STATIC_USERMODEHELPER
381 sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
382#else
383 sub_info->path = path;
384#endif
385 sub_info->argv = argv;
386 sub_info->envp = envp;
387
388 sub_info->cleanup = cleanup;
389 sub_info->init = init;
390 sub_info->data = data;
391 out:
392 return sub_info;
393}
394EXPORT_SYMBOL(call_usermodehelper_setup);
395
396/**
397 * call_usermodehelper_exec - start a usermode application
398 * @sub_info: information about the subprocessa
399 * @wait: wait for the application to finish and return status.
400 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
401 * when the program couldn't be exec'ed. This makes it safe to call
402 * from interrupt context.
403 *
404 * Runs a user-space application. The application is started
405 * asynchronously if wait is not set, and runs as a child of system workqueues.
406 * (ie. it runs with full root capabilities and optimized affinity).
407 */
408int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
409{
410 DECLARE_COMPLETION_ONSTACK(done);
411 int retval = 0;
412
413 if (!sub_info->path) {
414 call_usermodehelper_freeinfo(sub_info);
415 return -EINVAL;
416 }
417 helper_lock();
418 if (usermodehelper_disabled) {
419 retval = -EBUSY;
420 goto out;
421 }
422
423 /*
424 * If there is no binary for us to call, then just return and get out of
425 * here. This allows us to set STATIC_USERMODEHELPER_PATH to "" and
426 * disable all call_usermodehelper() calls.
427 */
428 if (strlen(sub_info->path) == 0)
429 goto out;
430
431 /*
432 * Set the completion pointer only if there is a waiter.
433 * This makes it possible to use umh_complete to free
434 * the data structure in case of UMH_NO_WAIT.
435 */
436 sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
437 sub_info->wait = wait;
438
439 queue_work(system_unbound_wq, &sub_info->work);
440 if (wait == UMH_NO_WAIT) /* task has freed sub_info */
441 goto unlock;
442
443 if (wait & UMH_KILLABLE) {
444 retval = wait_for_completion_killable(&done);
445 if (!retval)
446 goto wait_done;
447
448 /* umh_complete() will see NULL and free sub_info */
449 if (xchg(&sub_info->complete, NULL))
450 goto unlock;
451 /* fallthrough, umh_complete() was already called */
452 }
453
454 wait_for_completion(&done);
455wait_done:
456 retval = sub_info->retval;
457out:
458 call_usermodehelper_freeinfo(sub_info);
459unlock:
460 helper_unlock();
461 return retval;
462}
463EXPORT_SYMBOL(call_usermodehelper_exec);
464
465/**
466 * call_usermodehelper() - prepare and start a usermode application
467 * @path: path to usermode executable
468 * @argv: arg vector for process
469 * @envp: environment for process
470 * @wait: wait for the application to finish and return status.
471 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
472 * when the program couldn't be exec'ed. This makes it safe to call
473 * from interrupt context.
474 *
475 * This function is the equivalent to use call_usermodehelper_setup() and
476 * call_usermodehelper_exec().
477 */
478int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
479{
480 struct subprocess_info *info;
481 gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;
482
483 info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
484 NULL, NULL, NULL);
485 if (info == NULL)
486 return -ENOMEM;
487
488 return call_usermodehelper_exec(info, wait);
489}
490EXPORT_SYMBOL(call_usermodehelper);
491
492static int proc_cap_handler(struct ctl_table *table, int write,
493 void __user *buffer, size_t *lenp, loff_t *ppos)
494{
495 struct ctl_table t;
496 unsigned long cap_array[_KERNEL_CAPABILITY_U32S];
497 kernel_cap_t new_cap;
498 int err, i;
499
500 if (write && (!capable(CAP_SETPCAP) ||
501 !capable(CAP_SYS_MODULE)))
502 return -EPERM;
503
504 /*
505 * convert from the global kernel_cap_t to the ulong array to print to
506 * userspace if this is a read.
507 */
508 spin_lock(&umh_sysctl_lock);
509 for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) {
510 if (table->data == CAP_BSET)
511 cap_array[i] = usermodehelper_bset.cap[i];
512 else if (table->data == CAP_PI)
513 cap_array[i] = usermodehelper_inheritable.cap[i];
514 else
515 BUG();
516 }
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 /*
531 * convert from the sysctl array of ulongs to the kernel_cap_t
532 * internal representation
533 */
534 for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++)
535 new_cap.cap[i] = cap_array[i];
536
537 /*
538 * Drop everything not in the new_cap (but don't add things)
539 */
540 if (write) {
541 spin_lock(&umh_sysctl_lock);
542 if (table->data == CAP_BSET)
543 usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
544 if (table->data == CAP_PI)
545 usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
546 spin_unlock(&umh_sysctl_lock);
547 }
548
549 return 0;
550}
551
552struct ctl_table usermodehelper_table[] = {
553 {
554 .procname = "bset",
555 .data = CAP_BSET,
556 .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
557 .mode = 0600,
558 .proc_handler = proc_cap_handler,
559 },
560 {
561 .procname = "inheritable",
562 .data = CAP_PI,
563 .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long),
564 .mode = 0600,
565 .proc_handler = proc_cap_handler,
566 },
567 { }
568};