text: // 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>
  
  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(&ctx->wqh);
  	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 enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
  	ktime_t now)
  {
  	struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
  					       t.alarm);
  	timerfd_triggered(ctx);
  	return ALARMTIMER_NORESTART;
  }
  
  /*
   * 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(&ctx->wqh);
  		}
  		spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  	}
  	rcu_read_unlock();
  }
  
  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_init(&ctx->t.tmr, clockid, htmode);
  		hrtimer_set_expires(&ctx->t.tmr, texp);
  		ctx->t.tmr.function = timerfd_tmrproc;
  	}
  
  	if (texp != 0) {
  		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(struct file *file, char __user *buf, size_t count,
  			    loff_t *ppos)
  {
  	struct timerfd_ctx *ctx = file->private_data;
  	ssize_t res;
  	u64 ticks = 0;
  
  	if (count < sizeof(ticks))
  		return -EINVAL;
  	spin_lock_irq(&ctx->wqh.lock);
  	if (file->f_flags & O_NONBLOCK)
  		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 = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
  	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 itimerspec t;
  
  	spin_lock_irq(&ctx->wqh.lock);
  	t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
  	t.it_interval = ktime_to_timespec(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)t.it_value.tv_sec,
  		   (unsigned long long)t.it_value.tv_nsec,
  		   (unsigned long long)t.it_interval.tv_sec,
  		   (unsigned long long)t.it_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(&ctx->wqh);
  		} 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		= timerfd_read,
  	.llseek		= noop_llseek,
  	.show_fdinfo	= timerfd_show,
  	.unlocked_ioctl	= timerfd_ioctl,
  };
  
  static int timerfd_fget(int fd, struct fd *p)
  {
  	struct fd f = fdget(fd);
  	if (!f.file)
  		return -EBADF;
  	if (f.file->f_op != &timerfd_fops) {
  		fdput(f);
  		return -EINVAL;
  	}
  	*p = f;
  	return 0;
  }
  
  SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
  {
  	int ufd;
  	struct timerfd_ctx *ctx;
  
  	/* 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_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
  
  	ctx->moffs = ktime_mono_to_real(0);
  
  	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
  			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
  	if (ufd < 0)
  		kfree(ctx);
  
  	return ufd;
  }
  
  static int do_timerfd_settime(int ufd, int flags, 
  		const struct itimerspec64 *new,
  		struct itimerspec64 *old)
  {
  	struct fd f;
  	struct timerfd_ctx *ctx;
  	int ret;
  
  	if ((flags & ~TFD_SETTIME_FLAGS) ||
  		 !itimerspec64_valid(new))
  		return -EINVAL;
  
  	ret = timerfd_fget(ufd, &f);
  	if (ret)
  		return ret;
  	ctx = f.file->private_data;
  
  	if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
  		fdput(f);
  		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);
  		cpu_relax();
  	}
  
  	/*
  	 * 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);
  	fdput(f);
  	return ret;
  }
  
  static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
  {
  	struct fd f;
  	struct timerfd_ctx *ctx;
  	int ret = timerfd_fget(ufd, &f);
  	if (ret)
  		return ret;
  	ctx = f.file->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);
  	fdput(f);
  	return 0;
  }
  
  SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
  		const struct itimerspec __user *, utmr,
  		struct 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 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
  COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
  		const struct compat_itimerspec __user *, utmr,
  		struct compat_itimerspec __user *, otmr)
  {
  	struct itimerspec64 new, old;
  	int ret;
  
  	if (get_compat_itimerspec64(&new, utmr))
  		return -EFAULT;
  	ret = do_timerfd_settime(ufd, flags, &new, &old);
  	if (ret)
  		return ret;
  	if (otmr && put_compat_itimerspec64(&old, otmr))
  		return -EFAULT;
  	return ret;
  }
  
  COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
  		struct compat_itimerspec __user *, otmr)
  {
  	struct itimerspec64 kotmr;
  	int ret = do_timerfd_gettime(ufd, &kotmr);
  	if (ret)
  		return ret;
  	return put_compat_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
  }
  #endif
  