Quelle umh.c Sprache: C

// 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/fs_struct.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 <linux/initrd.h>
#include <linux/freezer.h>

#include <trace/events/module.h>

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);

/*
* Initial kernel threads share ther FS with init, in order to
* get the init root directory. But we've now created a new
* thread that is going to execve a user process and has its own
* 'struct fs_struct'. Reset umask to the default.
*/
current->fs->umask = 0022;

/*
* 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);

wait_for_initramfs();
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 do_wait won't populate the status. */
kernel_sigaction(SIGCHLD, SIG_DFL);
pid = user_mode_thread(call_usermodehelper_exec_async, sub_info, SIGCHLD);
if (pid < 0)
  sub_info->retval = pid;
else
  kernel_wait(pid, &sub_info->retval);

/* 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 = user_mode_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,
     RUNNING_HELPERS_TIMEOUT);
if (retval)
  return 0;

__usermodehelper_set_disable_depth(UMH_ENABLED);
return -EAGAIN;
}

static void helper_lock(void)
{
atomic_inc(&running_helpers);
smp_mb__after_atomic();
}

static void helper_unlock(void)
{
if (atomic_dec_and_test(&running_helpers))
  wake_up(&running_helpers_waitq);
}

/**
* call_usermodehelper_setup - prepare to call a usermode helper
* @path: path to usermode executable
* @argv: arg vector for process
* @envp: environment for process
* @gfp_mask: gfp mask for memory allocation
* @init: an init function
* @cleanup: a cleanup function
* @data: arbitrary context sensitive data
*
* Returns either %NULL on allocation failure, or a subprocess_info
* structure.  This should be passed to call_usermodehelper_exec to
* exec the process and free the structure.
*
* The init function is used to customize the helper process prior to
* exec.  A non-zero return code causes the process to error out, exit,
* and return the failure to the calling process
*
* The cleanup function is just before the subprocess_info is about to
* be freed.  This can be used for freeing the argv and envp.  The
* Function must be runnable in either a process context or the
* context in which call_usermodehelper_exec is called.
*/
struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
  char **envp, gfp_t gfp_mask,
  int (*init)(struct subprocess_info *info, struct cred *new),
  void (*cleanup)(struct subprocess_info *info),
  void *data)
{
struct subprocess_info *sub_info;
sub_info = kzalloc(sizeof(struct subprocess_info), gfp_mask);
if (!sub_info)
  goto out;

INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);

#ifdef CONFIG_STATIC_USERMODEHELPER
sub_info->path = CONFIG_STATIC_USERMODEHELPER_PATH;
#else
sub_info->path = path;
#endif
sub_info->argv = argv;
sub_info->envp = envp;

sub_info->cleanup = cleanup;
sub_info->init = init;
sub_info->data = data;
  out:
return sub_info;
}
EXPORT_SYMBOL(call_usermodehelper_setup);

/**
* call_usermodehelper_exec - start a usermode application
* @sub_info: information about the subprocess
* @wait: wait for the application to finish and return status.
*        when UMH_NO_WAIT don't wait at all, but you get no useful error back
*        when the program couldn't be exec'ed. This makes it safe to call
*        from interrupt context.
*
* Runs a user-space application.  The application is started
* asynchronously if wait is not set, and runs as a child of system workqueues.
* (ie. it runs with full root capabilities and optimized affinity).
*
* Note: successful return value does not guarantee the helper was called at
* all. You can't rely on sub_info->{init,cleanup} being called even for
* UMH_WAIT_* wait modes as STATIC_USERMODEHELPER_PATH="" turns all helpers
* into a successful no-op.
*/
int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
{
unsigned int state = TASK_UNINTERRUPTIBLE;
DECLARE_COMPLETION_ONSTACK(done);
int retval = 0;

if (!sub_info->path) {
  call_usermodehelper_freeinfo(sub_info);
  return -EINVAL;
}
helper_lock();
if (usermodehelper_disabled) {
  retval = -EBUSY;
  goto out;
}

/*
* If there is no binary for us to call, then just return and get out of
* here.  This allows us to set STATIC_USERMODEHELPER_PATH to "" and
* disable all call_usermodehelper() calls.
*/
if (strlen(sub_info->path) == 0)
  goto out;

/*
* Set the completion pointer only if there is a waiter.
* This makes it possible to use umh_complete to free
* the data structure in case of UMH_NO_WAIT.
*/
sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done;
sub_info->wait = wait;

queue_work(system_unbound_wq, &sub_info->work);
if (wait == UMH_NO_WAIT) /* task has freed sub_info */
  goto unlock;

if (wait & UMH_FREEZABLE)
  state |= TASK_FREEZABLE;

if (wait & UMH_KILLABLE) {
  retval = wait_for_completion_state(&done, state | TASK_KILLABLE);
  if (!retval)
   goto wait_done;

  /* umh_complete() will see NULL and free sub_info */
  if (xchg(&sub_info->complete, NULL))
   goto unlock;

  /*
* fallthrough; in case of -ERESTARTSYS now do uninterruptible
* wait_for_completion_state(). Since umh_complete() shall call
* complete() in a moment if xchg() above returned NULL, this
* uninterruptible wait_for_completion_state() will not block
* SIGKILL'ed processes for long.
*/
}
wait_for_completion_state(&done, state);

wait_done:
retval = sub_info->retval;
out:
call_usermodehelper_freeinfo(sub_info);
unlock:
helper_unlock();
return retval;
}
EXPORT_SYMBOL(call_usermodehelper_exec);

/**
* call_usermodehelper() - prepare and start a usermode application
* @path: path to usermode executable
* @argv: arg vector for process
* @envp: environment for process
* @wait: wait for the application to finish and return status.
*        when UMH_NO_WAIT don't wait at all, but you get no useful error back
*        when the program couldn't be exec'ed. This makes it safe to call
*        from interrupt context.
*
* This function is the equivalent to use call_usermodehelper_setup() and
* call_usermodehelper_exec().
*/
int call_usermodehelper(const char *path, char **argv, char **envp, int wait)
{
struct subprocess_info *info;
gfp_t gfp_mask = (wait == UMH_NO_WAIT) ? GFP_ATOMIC : GFP_KERNEL;

info = call_usermodehelper_setup(path, argv, envp, gfp_mask,
      NULL, NULL, NULL);
if (info == NULL)
  return -ENOMEM;

return call_usermodehelper_exec(info, wait);
}
EXPORT_SYMBOL(call_usermodehelper);

#if defined(CONFIG_SYSCTL)
static int proc_cap_handler(const struct ctl_table *table, int write,
    void *buffer, size_t *lenp, loff_t *ppos)
{
struct ctl_table t;
unsigned long cap_array[2];
kernel_cap_t new_cap, *cap;
int err;

if (write && (!capable(CAP_SETPCAP) ||
        !capable(CAP_SYS_MODULE)))
  return -EPERM;

/*
* convert from the global kernel_cap_t to the ulong array to print to
* userspace if this is a read.
*
* Legacy format: capabilities are exposed as two 32-bit values
*/
cap = table->data;
spin_lock(&umh_sysctl_lock);
cap_array[0] = (u32) cap->val;
cap_array[1] = cap->val >> 32;
spin_unlock(&umh_sysctl_lock);

t = *table;
t.data = &cap_array;

/*
* actually read or write and array of ulongs from userspace.  Remember
* these are least significant 32 bits first
*/
err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos);
if (err < 0)
  return err;

new_cap.val = (u32)cap_array[0];
new_cap.val += (u64)cap_array[1] << 32;

/*
* Drop everything not in the new_cap (but don't add things)
*/
if (write) {
  spin_lock(&umh_sysctl_lock);
  *cap = cap_intersect(*cap, new_cap);
  spin_unlock(&umh_sysctl_lock);
}

return 0;
}

static const struct ctl_table usermodehelper_table[] = {
{
  .procname = "bset",
  .data  = &usermodehelper_bset,
  .maxlen  = 2 * sizeof(unsigned long),
  .mode  = 0600,
  .proc_handler = proc_cap_handler,
},
{
  .procname = "inheritable",
  .data  = &usermodehelper_inheritable,
  .maxlen  = 2 * sizeof(unsigned long),
  .mode  = 0600,
  .proc_handler = proc_cap_handler,
},
};

static int __init init_umh_sysctls(void)
{
register_sysctl_init("kernel/usermodehelper", usermodehelper_table);
return 0;
}
early_initcall(init_umh_sysctls);
#endif /* CONFIG_SYSCTL */

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