Quelle timerfd.c Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
*  fs/timerfd.c
*
*  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
*
*
*  Thanks to Thomas Gleixner for code reviews and useful comments.
*
*/

#include <linux/alarmtimer.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/time.h>
#include <linux/hrtimer.h>
#include <linux/anon_inodes.h>
#include <linux/timerfd.h>
#include <linux/syscalls.h>
#include <linux/compat.h>
#include <linux/rcupdate.h>
#include <linux/time_namespace.h>

struct timerfd_ctx {
union {
  struct hrtimer tmr;
  struct alarm alarm;
} t;
ktime_t tintv;
ktime_t moffs;
wait_queue_head_t wqh;
u64 ticks;
int clockid;
short unsigned expired;
short unsigned settime_flags; /* to show in fdinfo */
struct rcu_head rcu;
struct list_head clist;
spinlock_t cancel_lock;
bool might_cancel;
};

static LIST_HEAD(cancel_list);
static DEFINE_SPINLOCK(cancel_lock);

static inline bool isalarm(struct timerfd_ctx *ctx)
{
return ctx->clockid == CLOCK_REALTIME_ALARM ||
  ctx->clockid == CLOCK_BOOTTIME_ALARM;
}

/*
* This gets called when the timer event triggers. We set the "expired"
* flag, but we do not re-arm the timer (in case it's necessary,
* tintv != 0) until the timer is accessed.
*/
static void timerfd_triggered(struct timerfd_ctx *ctx)
{
unsigned long flags;

spin_lock_irqsave(&ctx->wqh.lock, flags);
ctx->expired = 1;
ctx->ticks++;
wake_up_locked_poll(&ctx->wqh, EPOLLIN);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
}

static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
{
struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
            t.tmr);
timerfd_triggered(ctx);
return HRTIMER_NORESTART;
}

static void timerfd_alarmproc(struct alarm *alarm, ktime_t now)
{
struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
            t.alarm);
timerfd_triggered(ctx);
}

/*
* Called when the clock was set to cancel the timers in the cancel
* list. This will wake up processes waiting on these timers. The
* wake-up requires ctx->ticks to be non zero, therefore we increment
* it before calling wake_up_locked().
*/
void timerfd_clock_was_set(void)
{
ktime_t moffs = ktime_mono_to_real(0);
struct timerfd_ctx *ctx;
unsigned long flags;

rcu_read_lock();
list_for_each_entry_rcu(ctx, &cancel_list, clist) {
  if (!ctx->might_cancel)
   continue;
  spin_lock_irqsave(&ctx->wqh.lock, flags);
  if (ctx->moffs != moffs) {
   ctx->moffs = KTIME_MAX;
   ctx->ticks++;
   wake_up_locked_poll(&ctx->wqh, EPOLLIN);
  }
  spin_unlock_irqrestore(&ctx->wqh.lock, flags);
}
rcu_read_unlock();
}

static void timerfd_resume_work(struct work_struct *work)
{
timerfd_clock_was_set();
}

static DECLARE_WORK(timerfd_work, timerfd_resume_work);

/*
* Invoked from timekeeping_resume(). Defer the actual update to work so
* timerfd_clock_was_set() runs in task context.
*/
void timerfd_resume(void)
{
schedule_work(&timerfd_work);
}

static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
if (ctx->might_cancel) {
  ctx->might_cancel = false;
  spin_lock(&cancel_lock);
  list_del_rcu(&ctx->clist);
  spin_unlock(&cancel_lock);
}
}

static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
spin_lock(&ctx->cancel_lock);
__timerfd_remove_cancel(ctx);
spin_unlock(&ctx->cancel_lock);
}

static bool timerfd_canceled(struct timerfd_ctx *ctx)
{
if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
  return false;
ctx->moffs = ktime_mono_to_real(0);
return true;
}

static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
{
spin_lock(&ctx->cancel_lock);
if ((ctx->clockid == CLOCK_REALTIME ||
      ctx->clockid == CLOCK_REALTIME_ALARM) &&
     (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
  if (!ctx->might_cancel) {
   ctx->might_cancel = true;
   spin_lock(&cancel_lock);
   list_add_rcu(&ctx->clist, &cancel_list);
   spin_unlock(&cancel_lock);
  }
} else {
  __timerfd_remove_cancel(ctx);
}
spin_unlock(&ctx->cancel_lock);
}

static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
{
ktime_t remaining;

if (isalarm(ctx))
  remaining = alarm_expires_remaining(&ctx->t.alarm);
else
  remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);

return remaining < 0 ? 0: remaining;
}

static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
    const struct itimerspec64 *ktmr)
{
enum hrtimer_mode htmode;
ktime_t texp;
int clockid = ctx->clockid;

htmode = (flags & TFD_TIMER_ABSTIME) ?
  HRTIMER_MODE_ABS: HRTIMER_MODE_REL;

texp = timespec64_to_ktime(ktmr->it_value);
ctx->expired = 0;
ctx->ticks = 0;
ctx->tintv = timespec64_to_ktime(ktmr->it_interval);

if (isalarm(ctx)) {
  alarm_init(&ctx->t.alarm,
      ctx->clockid == CLOCK_REALTIME_ALARM ?
      ALARM_REALTIME : ALARM_BOOTTIME,
      timerfd_alarmproc);
} else {
  hrtimer_setup(&ctx->t.tmr, timerfd_tmrproc, clockid, htmode);
  hrtimer_set_expires(&ctx->t.tmr, texp);
}

if (texp != 0) {
  if (flags & TFD_TIMER_ABSTIME)
   texp = timens_ktime_to_host(clockid, texp);
  if (isalarm(ctx)) {
   if (flags & TFD_TIMER_ABSTIME)
    alarm_start(&ctx->t.alarm, texp);
   else
    alarm_start_relative(&ctx->t.alarm, texp);
  } else {
   hrtimer_start(&ctx->t.tmr, texp, htmode);
  }

  if (timerfd_canceled(ctx))
   return -ECANCELED;
}

ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
return 0;
}

static int timerfd_release(struct inode *inode, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;

timerfd_remove_cancel(ctx);

if (isalarm(ctx))
  alarm_cancel(&ctx->t.alarm);
else
  hrtimer_cancel(&ctx->t.tmr);
kfree_rcu(ctx, rcu);
return 0;
}

static __poll_t timerfd_poll(struct file *file, poll_table *wait)
{
struct timerfd_ctx *ctx = file->private_data;
__poll_t events = 0;
unsigned long flags;

poll_wait(file, &ctx->wqh, wait);

spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ctx->ticks)
  events |= EPOLLIN;
spin_unlock_irqrestore(&ctx->wqh.lock, flags);

return events;
}

static ssize_t timerfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
struct file *file = iocb->ki_filp;
struct timerfd_ctx *ctx = file->private_data;
ssize_t res;
u64 ticks = 0;

if (iov_iter_count(to) < sizeof(ticks))
  return -EINVAL;

spin_lock_irq(&ctx->wqh.lock);
if (file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT)
  res = -EAGAIN;
else
  res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);

/*
* If clock has changed, we do not care about the
* ticks and we do not rearm the timer. Userspace must
* reevaluate anyway.
*/
if (timerfd_canceled(ctx)) {
  ctx->ticks = 0;
  ctx->expired = 0;
  res = -ECANCELED;
}

if (ctx->ticks) {
  ticks = ctx->ticks;

  if (ctx->expired && ctx->tintv) {
   /*
* If tintv != 0, this is a periodic timer that
* needs to be re-armed. We avoid doing it in the timer
* callback to avoid DoS attacks specifying a very
* short timer period.
*/
   if (isalarm(ctx)) {
    ticks += alarm_forward_now(
     &ctx->t.alarm, ctx->tintv) - 1;
    alarm_restart(&ctx->t.alarm);
   } else {
    ticks += hrtimer_forward_now(&ctx->t.tmr,
            ctx->tintv) - 1;
    hrtimer_restart(&ctx->t.tmr);
   }
  }
  ctx->expired = 0;
  ctx->ticks = 0;
}
spin_unlock_irq(&ctx->wqh.lock);
if (ticks) {
  res = copy_to_iter(&ticks, sizeof(ticks), to);
  if (!res)
   res = -EFAULT;
}
return res;
}

#ifdef CONFIG_PROC_FS
static void timerfd_show(struct seq_file *m, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;
struct timespec64 value, interval;

spin_lock_irq(&ctx->wqh.lock);
value = ktime_to_timespec64(timerfd_get_remaining(ctx));
interval = ktime_to_timespec64(ctx->tintv);
spin_unlock_irq(&ctx->wqh.lock);

seq_printf(m,
     "clockid: %d\n"
     "ticks: %llu\n"
     "settime flags: 0%o\n"
     "it_value: (%llu, %llu)\n"
     "it_interval: (%llu, %llu)\n",
     ctx->clockid,
     (unsigned long long)ctx->ticks,
     ctx->settime_flags,
     (unsigned long long)value.tv_sec,
     (unsigned long long)value.tv_nsec,
     (unsigned long long)interval.tv_sec,
     (unsigned long long)interval.tv_nsec);
}
#else
#define timerfd_show NULL
#endif

#ifdef CONFIG_CHECKPOINT_RESTORE
static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct timerfd_ctx *ctx = file->private_data;
int ret = 0;

switch (cmd) {
case TFD_IOC_SET_TICKS: {
  u64 ticks;

  if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
   return -EFAULT;
  if (!ticks)
   return -EINVAL;

  spin_lock_irq(&ctx->wqh.lock);
  if (!timerfd_canceled(ctx)) {
   ctx->ticks = ticks;
   wake_up_locked_poll(&ctx->wqh, EPOLLIN);
  } else
   ret = -ECANCELED;
  spin_unlock_irq(&ctx->wqh.lock);
  break;
}
default:
  ret = -ENOTTY;
  break;
}

return ret;
}
#else
#define timerfd_ioctl NULL
#endif

static const struct file_operations timerfd_fops = {
.release = timerfd_release,
.poll  = timerfd_poll,
.read_iter = timerfd_read_iter,
.llseek  = noop_llseek,
.show_fdinfo = timerfd_show,
.unlocked_ioctl = timerfd_ioctl,
};

SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
{
int ufd;
struct timerfd_ctx *ctx;
struct file *file;

/* Check the TFD_* constants for consistency.  */
BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);

if ((flags & ~TFD_CREATE_FLAGS) ||
     (clockid != CLOCK_MONOTONIC &&
      clockid != CLOCK_REALTIME &&
      clockid != CLOCK_REALTIME_ALARM &&
      clockid != CLOCK_BOOTTIME &&
      clockid != CLOCK_BOOTTIME_ALARM))
  return -EINVAL;

if ((clockid == CLOCK_REALTIME_ALARM ||
      clockid == CLOCK_BOOTTIME_ALARM) &&
     !capable(CAP_WAKE_ALARM))
  return -EPERM;

ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
  return -ENOMEM;

init_waitqueue_head(&ctx->wqh);
spin_lock_init(&ctx->cancel_lock);
ctx->clockid = clockid;

if (isalarm(ctx))
  alarm_init(&ctx->t.alarm,
      ctx->clockid == CLOCK_REALTIME_ALARM ?
      ALARM_REALTIME : ALARM_BOOTTIME,
      timerfd_alarmproc);
else
  hrtimer_setup(&ctx->t.tmr, timerfd_tmrproc, clockid, HRTIMER_MODE_ABS);

ctx->moffs = ktime_mono_to_real(0);

ufd = get_unused_fd_flags(flags & TFD_SHARED_FCNTL_FLAGS);
if (ufd < 0) {
  kfree(ctx);
  return ufd;
}

file = anon_inode_getfile_fmode("[timerfd]", &timerfd_fops, ctx,
       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS),
       FMODE_NOWAIT);
if (IS_ERR(file)) {
  put_unused_fd(ufd);
  kfree(ctx);
  return PTR_ERR(file);
}

fd_install(ufd, file);
return ufd;
}

static int do_timerfd_settime(int ufd, int flags,
  const struct itimerspec64 *new,
  struct itimerspec64 *old)
{
struct timerfd_ctx *ctx;
int ret;

if ((flags & ~TFD_SETTIME_FLAGS) ||
   !itimerspec64_valid(new))
  return -EINVAL;

CLASS(fd, f)(ufd);
if (fd_empty(f))
  return -EBADF;

if (fd_file(f)->f_op != &timerfd_fops)
  return -EINVAL;

ctx = fd_file(f)->private_data;

if (isalarm(ctx) && !capable(CAP_WAKE_ALARM))
  return -EPERM;

timerfd_setup_cancel(ctx, flags);

/*
* We need to stop the existing timer before reprogramming
* it to the new values.
*/
for (;;) {
  spin_lock_irq(&ctx->wqh.lock);

  if (isalarm(ctx)) {
   if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
    break;
  } else {
   if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
    break;
  }
  spin_unlock_irq(&ctx->wqh.lock);

  if (isalarm(ctx))
   hrtimer_cancel_wait_running(&ctx->t.alarm.timer);
  else
   hrtimer_cancel_wait_running(&ctx->t.tmr);
}

/*
* If the timer is expired and it's periodic, we need to advance it
* because the caller may want to know the previous expiration time.
* We do not update "ticks" and "expired" since the timer will be
* re-programmed again in the following timerfd_setup() call.
*/
if (ctx->expired && ctx->tintv) {
  if (isalarm(ctx))
   alarm_forward_now(&ctx->t.alarm, ctx->tintv);
  else
   hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
}

old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
old->it_interval = ktime_to_timespec64(ctx->tintv);

/*
* Re-program the timer to the new value ...
*/
ret = timerfd_setup(ctx, flags, new);

spin_unlock_irq(&ctx->wqh.lock);
return ret;
}

static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
{
struct timerfd_ctx *ctx;
CLASS(fd, f)(ufd);

if (fd_empty(f))
  return -EBADF;
if (fd_file(f)->f_op != &timerfd_fops)
  return -EINVAL;
ctx = fd_file(f)->private_data;

spin_lock_irq(&ctx->wqh.lock);
if (ctx->expired && ctx->tintv) {
  ctx->expired = 0;

  if (isalarm(ctx)) {
   ctx->ticks +=
    alarm_forward_now(
     &ctx->t.alarm, ctx->tintv) - 1;
   alarm_restart(&ctx->t.alarm);
  } else {
   ctx->ticks +=
    hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
    - 1;
   hrtimer_restart(&ctx->t.tmr);
  }
}
t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
t->it_interval = ktime_to_timespec64(ctx->tintv);
spin_unlock_irq(&ctx->wqh.lock);
return 0;
}

SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
  const struct __kernel_itimerspec __user *, utmr,
  struct __kernel_itimerspec __user *, otmr)
{
struct itimerspec64 new, old;
int ret;

if (get_itimerspec64(&new, utmr))
  return -EFAULT;
ret = do_timerfd_settime(ufd, flags, &new, &old);
if (ret)
  return ret;
if (otmr && put_itimerspec64(&old, otmr))
  return -EFAULT;

return ret;
}

SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr)
{
struct itimerspec64 kotmr;
int ret = do_timerfd_gettime(ufd, &kotmr);
if (ret)
  return ret;
return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
}

#ifdef CONFIG_COMPAT_32BIT_TIME
SYSCALL_DEFINE4(timerfd_settime32, int, ufd, int, flags,
  const struct old_itimerspec32 __user *, utmr,
  struct old_itimerspec32 __user *, otmr)
{
struct itimerspec64 new, old;
int ret;

if (get_old_itimerspec32(&new, utmr))
  return -EFAULT;
ret = do_timerfd_settime(ufd, flags, &new, &old);
if (ret)
  return ret;
if (otmr && put_old_itimerspec32(&old, otmr))
  return -EFAULT;
return ret;
}

SYSCALL_DEFINE2(timerfd_gettime32, int, ufd,
  struct old_itimerspec32 __user *, otmr)
{
struct itimerspec64 kotmr;
int ret = do_timerfd_gettime(ufd, &kotmr);
if (ret)
  return ret;
return put_old_itimerspec32(&kotmr, otmr) ? -EFAULT : 0;
}
#endif

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