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>
32 #include <trace/events/module.h>
34 #define CAP_BSET (void *)1
35 #define CAP_PI (void *)2
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
);
42 static void call_usermodehelper_freeinfo(struct subprocess_info
*info
)
45 (*info
->cleanup
)(info
);
49 static void umh_complete(struct subprocess_info
*sub_info
)
51 struct completion
*comp
= xchg(&sub_info
->complete
, NULL
);
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.
60 call_usermodehelper_freeinfo(sub_info
);
64 * This is the task which runs the usermode application
66 static int call_usermodehelper_exec_async(void *data
)
68 struct subprocess_info
*sub_info
= data
;
72 spin_lock_irq(¤t
->sighand
->siglock
);
73 flush_signal_handlers(current
, 1);
74 spin_unlock_irq(¤t
->sighand
->siglock
);
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.
82 current
->fs
->umask
= 0022;
85 * Our parent (unbound workqueue) runs with elevated scheduling
86 * priority. Avoid propagating that into the userspace child.
88 set_user_nice(current
, 0);
91 new = prepare_kernel_cred(current
);
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
);
101 if (sub_info
->init
) {
102 retval
= sub_info
->init(sub_info
, new);
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
);
116 sub_info
->retval
= retval
;
118 * call_usermodehelper_exec_sync() will call umh_complete
121 if (!(sub_info
->wait
& UMH_WAIT_PROC
))
122 umh_complete(sub_info
);
128 /* Handles UMH_WAIT_PROC. */
129 static void call_usermodehelper_exec_sync(struct subprocess_info
*sub_info
)
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
);
137 sub_info
->retval
= pid
;
139 kernel_wait(pid
, &sub_info
->retval
);
141 /* Restore default kernel sig handler */
142 kernel_sigaction(SIGCHLD
, SIG_IGN
);
143 umh_complete(sub_info
);
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.
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).
156 * Besides, workqueues provide the privilege level that caller might not have
157 * to perform the usermodehelper request.
160 static void call_usermodehelper_exec_work(struct work_struct
*work
)
162 struct subprocess_info
*sub_info
=
163 container_of(work
, struct subprocess_info
, work
);
165 if (sub_info
->wait
& UMH_WAIT_PROC
) {
166 call_usermodehelper_exec_sync(sub_info
);
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.
174 pid
= kernel_thread(call_usermodehelper_exec_async
, sub_info
,
175 CLONE_PARENT
| SIGCHLD
);
177 sub_info
->retval
= pid
;
178 umh_complete(sub_info
);
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.
189 static enum umh_disable_depth usermodehelper_disabled
= UMH_DISABLED
;
191 /* Number of helpers running */
192 static atomic_t running_helpers
= ATOMIC_INIT(0);
195 * Wait queue head used by usermodehelper_disable() to wait for all running
198 static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq
);
201 * Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
204 static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq
);
207 * Time to wait for running_helpers to become zero before the setting of
208 * usermodehelper_disabled in usermodehelper_disable() fails
210 #define RUNNING_HELPERS_TIMEOUT (5 * HZ)
212 int usermodehelper_read_trylock(void)
217 down_read(&umhelper_sem
);
219 prepare_to_wait(&usermodehelper_disabled_waitq
, &wait
,
221 if (!usermodehelper_disabled
)
224 if (usermodehelper_disabled
== UMH_DISABLED
)
227 up_read(&umhelper_sem
);
235 down_read(&umhelper_sem
);
237 finish_wait(&usermodehelper_disabled_waitq
, &wait
);
240 EXPORT_SYMBOL_GPL(usermodehelper_read_trylock
);
242 long usermodehelper_read_lock_wait(long timeout
)
249 down_read(&umhelper_sem
);
251 prepare_to_wait(&usermodehelper_disabled_waitq
, &wait
,
252 TASK_UNINTERRUPTIBLE
);
253 if (!usermodehelper_disabled
)
256 up_read(&umhelper_sem
);
258 timeout
= schedule_timeout(timeout
);
262 down_read(&umhelper_sem
);
264 finish_wait(&usermodehelper_disabled_waitq
, &wait
);
267 EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait
);
269 void usermodehelper_read_unlock(void)
271 up_read(&umhelper_sem
);
273 EXPORT_SYMBOL_GPL(usermodehelper_read_unlock
);
276 * __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
277 * @depth: New value to assign to usermodehelper_disabled.
279 * Change the value of usermodehelper_disabled (under umhelper_sem locked for
280 * writing) and wakeup tasks waiting for it to change.
282 void __usermodehelper_set_disable_depth(enum umh_disable_depth depth
)
284 down_write(&umhelper_sem
);
285 usermodehelper_disabled
= depth
;
286 wake_up(&usermodehelper_disabled_waitq
);
287 up_write(&umhelper_sem
);
291 * __usermodehelper_disable - Prevent new helpers from being started.
292 * @depth: New value to assign to usermodehelper_disabled.
294 * Set usermodehelper_disabled to @depth and wait for running helpers to exit.
296 int __usermodehelper_disable(enum umh_disable_depth depth
)
303 down_write(&umhelper_sem
);
304 usermodehelper_disabled
= depth
;
305 up_write(&umhelper_sem
);
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
313 retval
= wait_event_timeout(running_helpers_waitq
,
314 atomic_read(&running_helpers
) == 0,
315 RUNNING_HELPERS_TIMEOUT
);
319 __usermodehelper_set_disable_depth(UMH_ENABLED
);
323 static void helper_lock(void)
325 atomic_inc(&running_helpers
);
326 smp_mb__after_atomic();
329 static void helper_unlock(void)
331 if (atomic_dec_and_test(&running_helpers
))
332 wake_up(&running_helpers_waitq
);
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
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.
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
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.
358 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
),
364 struct subprocess_info
*sub_info
;
365 sub_info
= kzalloc(sizeof(struct subprocess_info
), gfp_mask
);
369 INIT_WORK(&sub_info
->work
, call_usermodehelper_exec_work
);
371 #ifdef CONFIG_STATIC_USERMODEHELPER
372 sub_info
->path
= CONFIG_STATIC_USERMODEHELPER_PATH
;
374 sub_info
->path
= path
;
376 sub_info
->argv
= argv
;
377 sub_info
->envp
= envp
;
379 sub_info
->cleanup
= cleanup
;
380 sub_info
->init
= init
;
381 sub_info
->data
= data
;
385 EXPORT_SYMBOL(call_usermodehelper_setup
);
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.
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).
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.
404 int call_usermodehelper_exec(struct subprocess_info
*sub_info
, int wait
)
406 DECLARE_COMPLETION_ONSTACK(done
);
409 if (!sub_info
->path
) {
410 call_usermodehelper_freeinfo(sub_info
);
414 if (usermodehelper_disabled
) {
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.
424 if (strlen(sub_info
->path
) == 0)
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.
432 sub_info
->complete
= (wait
== UMH_NO_WAIT
) ? NULL
: &done
;
433 sub_info
->wait
= wait
;
435 queue_work(system_unbound_wq
, &sub_info
->work
);
436 if (wait
== UMH_NO_WAIT
) /* task has freed sub_info */
439 if (wait
& UMH_KILLABLE
) {
440 retval
= wait_for_completion_killable(&done
);
444 /* umh_complete() will see NULL and free sub_info */
445 if (xchg(&sub_info
->complete
, NULL
))
447 /* fallthrough, umh_complete() was already called */
450 wait_for_completion(&done
);
452 retval
= sub_info
->retval
;
454 call_usermodehelper_freeinfo(sub_info
);
459 EXPORT_SYMBOL(call_usermodehelper_exec
);
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.
471 * This function is the equivalent to use call_usermodehelper_setup() and
472 * call_usermodehelper_exec().
474 int call_usermodehelper(const char *path
, char **argv
, char **envp
, int wait
)
476 struct subprocess_info
*info
;
477 gfp_t gfp_mask
= (wait
== UMH_NO_WAIT
) ? GFP_ATOMIC
: GFP_KERNEL
;
479 info
= call_usermodehelper_setup(path
, argv
, envp
, gfp_mask
,
484 return call_usermodehelper_exec(info
, wait
);
486 EXPORT_SYMBOL(call_usermodehelper
);
488 static int proc_cap_handler(struct ctl_table
*table
, int write
,
489 void *buffer
, size_t *lenp
, loff_t
*ppos
)
492 unsigned long cap_array
[_KERNEL_CAPABILITY_U32S
];
493 kernel_cap_t new_cap
;
496 if (write
&& (!capable(CAP_SETPCAP
) ||
497 !capable(CAP_SYS_MODULE
)))
501 * convert from the global kernel_cap_t to the ulong array to print to
502 * userspace if this is a read.
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
];
513 spin_unlock(&umh_sysctl_lock
);
519 * actually read or write and array of ulongs from userspace. Remember
520 * these are least significant 32 bits first
522 err
= proc_doulongvec_minmax(&t
, write
, buffer
, lenp
, ppos
);
527 * convert from the sysctl array of ulongs to the kernel_cap_t
528 * internal representation
530 for (i
= 0; i
< _KERNEL_CAPABILITY_U32S
; i
++)
531 new_cap
.cap
[i
] = cap_array
[i
];
534 * Drop everything not in the new_cap (but don't add things)
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
);
548 struct ctl_table usermodehelper_table
[] = {
552 .maxlen
= _KERNEL_CAPABILITY_U32S
* sizeof(unsigned long),
554 .proc_handler
= proc_cap_handler
,
557 .procname
= "inheritable",
559 .maxlen
= _KERNEL_CAPABILITY_U32S
* sizeof(unsigned long),
561 .proc_handler
= proc_cap_handler
,