1 // SPDX-License-Identifier: GPL-2.0-only
3 * umh - the kernel usermode helper
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 #include <linux/freezer.h>
33 #include <trace/events/module.h>
35 #define CAP_BSET (void *)1
36 #define CAP_PI (void *)2
38 static kernel_cap_t usermodehelper_bset
= CAP_FULL_SET
;
39 static kernel_cap_t usermodehelper_inheritable
= CAP_FULL_SET
;
40 static DEFINE_SPINLOCK(umh_sysctl_lock
);
41 static DECLARE_RWSEM(umhelper_sem
);
43 static void call_usermodehelper_freeinfo(struct subprocess_info
*info
)
46 (*info
->cleanup
)(info
);
50 static void umh_complete(struct subprocess_info
*sub_info
)
52 struct completion
*comp
= xchg(&sub_info
->complete
, NULL
);
54 * See call_usermodehelper_exec(). If xchg() returns NULL
55 * we own sub_info, the UMH_KILLABLE caller has gone away
56 * or the caller used UMH_NO_WAIT.
61 call_usermodehelper_freeinfo(sub_info
);
65 * This is the task which runs the usermode application
67 static int call_usermodehelper_exec_async(void *data
)
69 struct subprocess_info
*sub_info
= data
;
73 spin_lock_irq(¤t
->sighand
->siglock
);
74 flush_signal_handlers(current
, 1);
75 spin_unlock_irq(¤t
->sighand
->siglock
);
78 * Initial kernel threads share ther FS with init, in order to
79 * get the init root directory. But we've now created a new
80 * thread that is going to execve a user process and has its own
81 * 'struct fs_struct'. Reset umask to the default.
83 current
->fs
->umask
= 0022;
86 * Our parent (unbound workqueue) runs with elevated scheduling
87 * priority. Avoid propagating that into the userspace child.
89 set_user_nice(current
, 0);
92 new = prepare_kernel_cred(current
);
96 spin_lock(&umh_sysctl_lock
);
97 new->cap_bset
= cap_intersect(usermodehelper_bset
, new->cap_bset
);
98 new->cap_inheritable
= cap_intersect(usermodehelper_inheritable
,
99 new->cap_inheritable
);
100 spin_unlock(&umh_sysctl_lock
);
102 if (sub_info
->init
) {
103 retval
= sub_info
->init(sub_info
, new);
112 wait_for_initramfs();
113 retval
= kernel_execve(sub_info
->path
,
114 (const char *const *)sub_info
->argv
,
115 (const char *const *)sub_info
->envp
);
117 sub_info
->retval
= retval
;
119 * call_usermodehelper_exec_sync() will call umh_complete
122 if (!(sub_info
->wait
& UMH_WAIT_PROC
))
123 umh_complete(sub_info
);
129 /* Handles UMH_WAIT_PROC. */
130 static void call_usermodehelper_exec_sync(struct subprocess_info
*sub_info
)
134 /* If SIGCLD is ignored do_wait won't populate the status. */
135 kernel_sigaction(SIGCHLD
, SIG_DFL
);
136 pid
= user_mode_thread(call_usermodehelper_exec_async
, sub_info
, SIGCHLD
);
138 sub_info
->retval
= pid
;
140 kernel_wait(pid
, &sub_info
->retval
);
142 /* Restore default kernel sig handler */
143 kernel_sigaction(SIGCHLD
, SIG_IGN
);
144 umh_complete(sub_info
);
148 * We need to create the usermodehelper kernel thread from a task that is affine
149 * to an optimized set of CPUs (or nohz housekeeping ones) such that they
150 * inherit a widest affinity irrespective of call_usermodehelper() callers with
151 * possibly reduced affinity (eg: per-cpu workqueues). We don't want
152 * usermodehelper targets to contend a busy CPU.
154 * Unbound workqueues provide such wide affinity and allow to block on
155 * UMH_WAIT_PROC requests without blocking pending request (up to some limit).
157 * Besides, workqueues provide the privilege level that caller might not have
158 * to perform the usermodehelper request.
161 static void call_usermodehelper_exec_work(struct work_struct
*work
)
163 struct subprocess_info
*sub_info
=
164 container_of(work
, struct subprocess_info
, work
);
166 if (sub_info
->wait
& UMH_WAIT_PROC
) {
167 call_usermodehelper_exec_sync(sub_info
);
171 * Use CLONE_PARENT to reparent it to kthreadd; we do not
172 * want to pollute current->children, and we need a parent
173 * that always ignores SIGCHLD to ensure auto-reaping.
175 pid
= user_mode_thread(call_usermodehelper_exec_async
, sub_info
,
176 CLONE_PARENT
| SIGCHLD
);
178 sub_info
->retval
= pid
;
179 umh_complete(sub_info
);
185 * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
186 * (used for preventing user land processes from being created after the user
187 * land has been frozen during a system-wide hibernation or suspend operation).
188 * Should always be manipulated under umhelper_sem acquired for write.
190 static enum umh_disable_depth usermodehelper_disabled
= UMH_DISABLED
;
192 /* Number of helpers running */
193 static atomic_t running_helpers
= ATOMIC_INIT(0);
196 * Wait queue head used by usermodehelper_disable() to wait for all running
199 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq
);
202 * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
205 static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq
);
208 * Time to wait for running_helpers to become zero before the setting of
209 * usermodehelper_disabled in usermodehelper_disable() fails
211 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
213 int usermodehelper_read_trylock(void)
218 down_read(&umhelper_sem
);
220 prepare_to_wait(&usermodehelper_disabled_waitq
, &wait
,
222 if (!usermodehelper_disabled
)
225 if (usermodehelper_disabled
== UMH_DISABLED
)
228 up_read(&umhelper_sem
);
236 down_read(&umhelper_sem
);
238 finish_wait(&usermodehelper_disabled_waitq
, &wait
);
241 EXPORT_SYMBOL_GPL(usermodehelper_read_trylock
);
243 long usermodehelper_read_lock_wait(long timeout
)
250 down_read(&umhelper_sem
);
252 prepare_to_wait(&usermodehelper_disabled_waitq
, &wait
,
253 TASK_UNINTERRUPTIBLE
);
254 if (!usermodehelper_disabled
)
257 up_read(&umhelper_sem
);
259 timeout
= schedule_timeout(timeout
);
263 down_read(&umhelper_sem
);
265 finish_wait(&usermodehelper_disabled_waitq
, &wait
);
268 EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait
);
270 void usermodehelper_read_unlock(void)
272 up_read(&umhelper_sem
);
274 EXPORT_SYMBOL_GPL(usermodehelper_read_unlock
);
277 * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
278 * @depth: New value to assign to usermodehelper_disabled.
280 * Change the value of usermodehelper_disabled (under umhelper_sem locked for
281 * writing) and wakeup tasks waiting for it to change.
283 void __usermodehelper_set_disable_depth(enum umh_disable_depth depth
)
285 down_write(&umhelper_sem
);
286 usermodehelper_disabled
= depth
;
287 wake_up(&usermodehelper_disabled_waitq
);
288 up_write(&umhelper_sem
);
292 * __usermodehelper_disable - Prevent new helpers from being started.
293 * @depth: New value to assign to usermodehelper_disabled.
295 * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
297 int __usermodehelper_disable(enum umh_disable_depth depth
)
304 down_write(&umhelper_sem
);
305 usermodehelper_disabled
= depth
;
306 up_write(&umhelper_sem
);
309 * From now on call_usermodehelper_exec() won't start any new
310 * helpers, so it is sufficient if running_helpers turns out to
311 * be zero at one point (it may be increased later, but that
314 retval
= wait_event_timeout(running_helpers_waitq
,
315 atomic_read(&running_helpers
) == 0,
316 RUNNING_HELPERS_TIMEOUT
);
320 __usermodehelper_set_disable_depth(UMH_ENABLED
);
324 static void helper_lock(void)
326 atomic_inc(&running_helpers
);
327 smp_mb__after_atomic();
330 static void helper_unlock(void)
332 if (atomic_dec_and_test(&running_helpers
))
333 wake_up(&running_helpers_waitq
);
337 * call_usermodehelper_setup - prepare to call a usermode helper
338 * @path: path to usermode executable
339 * @argv: arg vector for process
340 * @envp: environment for process
341 * @gfp_mask: gfp mask for memory allocation
342 * @init: an init function
343 * @cleanup: a cleanup function
344 * @data: arbitrary context sensitive data
346 * Returns either %NULL on allocation failure, or a subprocess_info
347 * structure. This should be passed to call_usermodehelper_exec to
348 * exec the process and free the structure.
350 * The init function is used to customize the helper process prior to
351 * exec. A non-zero return code causes the process to error out, exit,
352 * and return the failure to the calling process
354 * The cleanup function is just before the subprocess_info is about to
355 * be freed. This can be used for freeing the argv and envp. The
356 * Function must be runnable in either a process context or the
357 * context in which call_usermodehelper_exec is called.
359 struct subprocess_info
*call_usermodehelper_setup(const char *path
, char **argv
,
360 char **envp
, gfp_t gfp_mask
,
361 int (*init
)(struct subprocess_info
*info
, struct cred
*new),
362 void (*cleanup
)(struct subprocess_info
*info
),
365 struct subprocess_info
*sub_info
;
366 sub_info
= kzalloc(sizeof(struct subprocess_info
), gfp_mask
);
370 INIT_WORK(&sub_info
->work
, call_usermodehelper_exec_work
);
372 #ifdef CONFIG_STATIC_USERMODEHELPER
373 sub_info
->path
= CONFIG_STATIC_USERMODEHELPER_PATH
;
375 sub_info
->path
= path
;
377 sub_info
->argv
= argv
;
378 sub_info
->envp
= envp
;
380 sub_info
->cleanup
= cleanup
;
381 sub_info
->init
= init
;
382 sub_info
->data
= data
;
386 EXPORT_SYMBOL(call_usermodehelper_setup
);
389 * call_usermodehelper_exec - start a usermode application
390 * @sub_info: information about the subprocess
391 * @wait: wait for the application to finish and return status.
392 * when UMH_NO_WAIT don't wait at all, but you get no useful error back
393 * when the program couldn't be exec'ed. This makes it safe to call
394 * from interrupt context.
396 * Runs a user-space application. The application is started
397 * asynchronously if wait is not set, and runs as a child of system workqueues.
398 * (ie. it runs with full root capabilities and optimized affinity).
400 * Note: successful return value does not guarantee the helper was called at
401 * all. You can't rely on sub_info->{init,cleanup} being called even for
402 * UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers
403 * into a successful no-op.
405 int call_usermodehelper_exec(struct subprocess_info
*sub_info
, int wait
)
407 unsigned int state
= TASK_UNINTERRUPTIBLE
;
408 DECLARE_COMPLETION_ONSTACK(done
);
411 if (!sub_info
->path
) {
412 call_usermodehelper_freeinfo(sub_info
);
416 if (usermodehelper_disabled
) {
422 * If there is no binary for us to call, then just return and get out of
423 * here. This allows us to set STATIC_USERMODEHELPER_PATH to "" and
424 * disable all call_usermodehelper() calls.
426 if (strlen(sub_info
->path
) == 0)
430 * Set the completion pointer only if there is a waiter.
431 * This makes it possible to use umh_complete to free
432 * the data structure in case of UMH_NO_WAIT.
434 sub_info
->complete
= (wait
== UMH_NO_WAIT
) ? NULL
: &done
;
435 sub_info
->wait
= wait
;
437 queue_work(system_unbound_wq
, &sub_info
->work
);
438 if (wait
== UMH_NO_WAIT
) /* task has freed sub_info */
441 if (wait
& UMH_KILLABLE
)
442 state
|= TASK_KILLABLE
;
444 if (wait
& UMH_FREEZABLE
)
445 state
|= TASK_FREEZABLE
;
447 retval
= wait_for_completion_state(&done
, state
);
451 if (wait
& UMH_KILLABLE
) {
452 /* umh_complete() will see NULL and free sub_info */
453 if (xchg(&sub_info
->complete
, NULL
))
458 retval
= sub_info
->retval
;
460 call_usermodehelper_freeinfo(sub_info
);
465 EXPORT_SYMBOL(call_usermodehelper_exec
);
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.
477 * This function is the equivalent to use call_usermodehelper_setup() and
478 * call_usermodehelper_exec().
480 int call_usermodehelper(const char *path
, char **argv
, char **envp
, int wait
)
482 struct subprocess_info
*info
;
483 gfp_t gfp_mask
= (wait
== UMH_NO_WAIT
) ? GFP_ATOMIC
: GFP_KERNEL
;
485 info
= call_usermodehelper_setup(path
, argv
, envp
, gfp_mask
,
490 return call_usermodehelper_exec(info
, wait
);
492 EXPORT_SYMBOL(call_usermodehelper
);
494 static int proc_cap_handler(struct ctl_table
*table
, int write
,
495 void *buffer
, size_t *lenp
, loff_t
*ppos
)
498 unsigned long cap_array
[_KERNEL_CAPABILITY_U32S
];
499 kernel_cap_t new_cap
;
502 if (write
&& (!capable(CAP_SETPCAP
) ||
503 !capable(CAP_SYS_MODULE
)))
507 * convert from the global kernel_cap_t to the ulong array to print to
508 * userspace if this is a read.
510 spin_lock(&umh_sysctl_lock
);
511 for (i
= 0; i
< _KERNEL_CAPABILITY_U32S
; i
++) {
512 if (table
->data
== CAP_BSET
)
513 cap_array
[i
] = usermodehelper_bset
.cap
[i
];
514 else if (table
->data
== CAP_PI
)
515 cap_array
[i
] = usermodehelper_inheritable
.cap
[i
];
519 spin_unlock(&umh_sysctl_lock
);
525 * actually read or write and array of ulongs from userspace. Remember
526 * these are least significant 32 bits first
528 err
= proc_doulongvec_minmax(&t
, write
, buffer
, lenp
, ppos
);
533 * convert from the sysctl array of ulongs to the kernel_cap_t
534 * internal representation
536 for (i
= 0; i
< _KERNEL_CAPABILITY_U32S
; i
++)
537 new_cap
.cap
[i
] = cap_array
[i
];
540 * Drop everything not in the new_cap (but don't add things)
543 spin_lock(&umh_sysctl_lock
);
544 if (table
->data
== CAP_BSET
)
545 usermodehelper_bset
= cap_intersect(usermodehelper_bset
, new_cap
);
546 if (table
->data
== CAP_PI
)
547 usermodehelper_inheritable
= cap_intersect(usermodehelper_inheritable
, new_cap
);
548 spin_unlock(&umh_sysctl_lock
);
554 struct ctl_table usermodehelper_table
[] = {
558 .maxlen
= _KERNEL_CAPABILITY_U32S
* sizeof(unsigned long),
560 .proc_handler
= proc_cap_handler
,
563 .procname
= "inheritable",
565 .maxlen
= _KERNEL_CAPABILITY_U32S
* sizeof(unsigned long),
567 .proc_handler
= proc_cap_handler
,