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// SPDX-License-Identifier: GPL-2.0-only
/*
* umh - the kernel usermode helper
*/
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/binfmts.h>
#include <linux/syscalls.h>
#include <linux/unistd.h>
#include <linux/kmod.h>
#include <linux/slab.h>
#include <linux/completion.h>
#include <linux/cred.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/workqueue.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/resource.h>
#include <linux/notifier.h>
#include <linux/suspend.h>
#include <linux/rwsem.h>
#include <linux/ptrace.h>
#include <linux/async.h>
#include <linux/uaccess.h>
#include <trace/events/module.h>
#define CAP_BSET (void *)1
#define CAP_PI (void *)2
static kernel_cap_t usermodehelper_bset = CAP_FULL_SET;
static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
static DEFINE_SPINLOCK(umh_sysctl_lock);
static DECLARE_RWSEM(umhelper_sem);
static void call_usermodehelper_freeinfo(struct subprocess_info *info)
{
if (info->cleanup)
(*info->cleanup)(info);
kfree(info);
}
static void umh_complete(struct subprocess_info *sub_info)
{
struct completion *comp = xchg(&sub_info->complete, NULL);
/*
* See call_usermodehelper_exec(). If xchg() returns NULL
* we own sub_info, the UMH_KILLABLE caller has gone away
* or the caller used UMH_NO_WAIT.
*/
if (comp)
complete(comp);
else
call_usermodehelper_freeinfo(sub_info);
}
/*
* This is the task which runs the usermode application
*/
static int call_usermodehelper_exec_async(void *data)
{
struct subprocess_info *sub_info = data;
struct cred *new;
int retval;
spin_lock_irq(¤t->sighand->siglock);
flush_signal_handlers(current, 1);
spin_unlock_irq(¤t->sighand->siglock);
/*
* Our parent (unbound workqueue) runs with elevated scheduling
* priority. Avoid propagating that into the userspace child.
*/
set_user_nice(current, 0);
retval = -ENOMEM;
new = prepare_kernel_cred(current);
if (!new)
goto out;
spin_lock(&umh_sysctl_lock);
new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset);
new->cap_inheritable = cap_intersect(usermodehelper_inheritable,
new->cap_inheritable);
spin_unlock(&umh_sysctl_lock);
if (sub_info->init) {
retval = sub_info->init(sub_info, new);
if (retval) {
abort_creds(new);
goto out;
}
}
commit_creds(new);
retval = kernel_execve(sub_info->path,
(const char *const *)sub_info->argv,
(const char *const *)sub_info->envp);
out:
sub_info->retval = retval;
/*
* call_usermodehelper_exec_sync() will call umh_complete
* if UHM_WAIT_PROC.
*/
if (!(sub_info->wait & UMH_WAIT_PROC))
umh_complete(sub_info);
if (!retval)
return 0;
do_exit(0);
}
/* Handles UMH_WAIT_PROC. */
static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
{
pid_t pid;
/* If SIGCLD is ignored kernel_wait4 won't populate the status. */
kernel_sigaction(SIGCHLD, SIG_DFL);
pid = kernel_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
if (pid < 0) {
sub_info->retval = pid;
} else {
int ret = -ECHILD;
/*
* Normally it is bogus to call wait4() from in-kernel because
* wait4() wants to write the exit code to a userspace address.
* But call_usermodehelper_exec_sync() always runs as kernel
* thread (workqueue) and put_user() to a kernel address works
* OK for kernel threads, due to their having an mm_segment_t
* which spans the entire address space.
*
* Thus the __user pointer cast is valid here.
*/
kernel_wait4(pid, (int __user *)&ret, 0, NULL);
/*
* If ret is 0, either call_usermodehelper_exec_async failed and
* the real error code is already in sub_info->retval or
* sub_info->retval is 0 anyway, so don't mess with it then.
*/
if (ret)
sub_info->retval = ret;
}
/* Restore default kernel sig handler */
kernel_sigaction(SIGCHLD, SIG_IGN);
umh_complete(sub_info);
}
/*
* We need to create the usermodehelper kernel thread from a task that is affine
* to an optimized set of CPUs (or nohz housekeeping ones) such that they
* inherit a widest affinity irrespective of call_usermodehelper() callers with
* possibly reduced affinity (eg: per-cpu workqueues). We don't want
* usermodehelper targets to contend a busy CPU.
*
* Unbound workqueues provide such wide affinity and allow to block on
* UMH_WAIT_PROC requests without blocking pending request (up to some limit).
*
* Besides, workqueues provide the privilege level that caller might not have
* to perform the usermodehelper request.
*
*/
static void call_usermodehelper_exec_work(struct work_struct *work)
{
struct subprocess_info *sub_info =
container_of(work, struct subprocess_info, work);
if (sub_info->wait & UMH_WAIT_PROC) {
call_usermodehelper_exec_sync(sub_info);
} else {
pid_t pid;
/*
* Use CLONE_PARENT to reparent it to kthreadd; we do not
* want to pollute current->children, and we need a parent
* that always ignores SIGCHLD to ensure auto-reaping.
*/
pid = kernel_thread(call_usermodehelper_exec_async, sub_info,
CLONE_PARENT | SIGCHLD);
if (pid < 0) {
sub_info->retval = pid;
umh_complete(sub_info);
}
}
}
/*
* If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
* (used for preventing user land processes from being created after the user
* land has been frozen during a system-wide hibernation or suspend operation).
* Should always be manipulated under umhelper_sem acquired for write.
*/
static enum umh_disable_depth usermodehelper_disabled = UMH_DISABLED;
/* Number of helpers running */
static atomic_t running_helpers = ATOMIC_INIT(0);
/*
* Wait queue head used by usermodehelper_disable() to wait for all running
* helpers to finish.
*/
static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
/*
* Used by usermodehelper_read_lock_wait() to wait for usermodehelper_disabled
* to become 'false'.
*/
static DECLARE_WAIT_QUEUE_HEAD(usermodehelper_disabled_waitq);
/*
* Time to wait for running_helpers to become zero before the setting of
* usermodehelper_disabled in usermodehelper_disable() fails
*/
#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
int usermodehelper_read_trylock(void)
{
DEFINE_WAIT(wait);
int ret = 0;
down_read(&umhelper_sem);
for (;;) {
prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
TASK_INTERRUPTIBLE);
if (!usermodehelper_disabled)
break;
if (usermodehelper_disabled == UMH_DISABLED)
ret = -EAGAIN;
up_read(&umhelper_sem);
if (ret)
break;
schedule();
try_to_freeze();
down_read(&umhelper_sem);
}
finish_wait(&usermodehelper_disabled_waitq, &wait);
return ret;
}
EXPORT_SYMBOL_GPL(usermodehelper_read_trylock);
long usermodehelper_read_lock_wait(long timeout)
{
DEFINE_WAIT(wait);
if (timeout < 0)
return -EINVAL;
down_read(&umhelper_sem);
for (;;) {
prepare_to_wait(&usermodehelper_disabled_waitq, &wait,
TASK_UNINTERRUPTIBLE);
if (!usermodehelper_disabled)
break;
up_read(&umhelper_sem);
timeout = schedule_timeout(timeout);
if (!timeout)
break;
down_read(&umhelper_sem);
}
finish_wait(&usermodehelper_disabled_waitq, &wait);
return timeout;
}
EXPORT_SYMBOL_GPL(usermodehelper_read_lock_wait);
void usermodehelper_read_unlock(void)
{
up_read(&umhelper_sem);
}
EXPORT_SYMBOL_GPL(usermodehelper_read_unlock);
/**
* __usermodehelper_set_disable_depth - Modify usermodehelper_disabled.
* @depth: New value to assign to usermodehelper_disabled.
*
* Change the value of usermodehelper_disabled (under umhelper_sem locked for
* writing) and wakeup tasks waiting for it to change.
*/
void __usermodehelper_set_disable_depth(enum umh_disable_depth depth)
{
down_write(&umhelper_sem);
usermodehelper_disabled = depth;
wake_up(&usermodehelper_disabled_waitq);
up_write(&umhelper_sem);
}
/**
* __usermodehelper_disable - Prevent new helpers from being started.
* @depth: New value to assign to usermodehelper_disabled.
*
* Set usermodehelper_disabled to @depth and wait for running helpers to exit.
*/
int __usermodehelper_disable(enum umh_disable_depth depth)
{
long retval;
if (!depth)
return -EINVAL;
down_write(&umhelper_sem);
usermodehelper_disabled = depth;
up_write(&umhelper_sem);
/*
* From now on call_usermodehelper_exec() won't start any new
* helpers, so it is sufficient if running_helpers turns out to
* be zero at one point (it may be increased later, but that
* doesn't matter).
*/
retval = wait_event_timeout(running_helpers_waitq,
atomic_read(&running_helpers) == 0,
RU
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