1// SPDX-License-Identifier: GPL-2.0
2/*
3 *  fs/timerfd.c
4 *
5 *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
6 *
7 *
8 *  Thanks to Thomas Gleixner for code reviews and useful comments.
9 *
10 */
11
12#include <linux/alarmtimer.h>
13#include <linux/file.h>
14#include <linux/poll.h>
15#include <linux/init.h>
16#include <linux/fs.h>
17#include <linux/sched.h>
18#include <linux/kernel.h>
19#include <linux/slab.h>
20#include <linux/list.h>
21#include <linux/spinlock.h>
22#include <linux/time.h>
23#include <linux/hrtimer.h>
24#include <linux/anon_inodes.h>
25#include <linux/timerfd.h>
26#include <linux/syscalls.h>
27#include <linux/compat.h>
28#include <linux/rcupdate.h>
29#include <linux/time_namespace.h>
30
31struct timerfd_ctx {
32	union {
33		struct hrtimer tmr;
34		struct alarm alarm;
35	} t;
36	ktime_t tintv;
37	ktime_t moffs;
38	wait_queue_head_t wqh;
39	u64 ticks;
40	int clockid;
41	short unsigned expired;
42	short unsigned settime_flags;	/* to show in fdinfo */
43	struct rcu_head rcu;
44	struct list_head clist;
45	spinlock_t cancel_lock;
46	bool might_cancel;
47};
48
49static LIST_HEAD(cancel_list);
50static DEFINE_SPINLOCK(cancel_lock);
51
52static inline bool isalarm(struct timerfd_ctx *ctx)
53{
54	return ctx->clockid == CLOCK_REALTIME_ALARM ||
55		ctx->clockid == CLOCK_BOOTTIME_ALARM;
56}
57
58/*
59 * This gets called when the timer event triggers. We set the "expired"
60 * flag, but we do not re-arm the timer (in case it's necessary,
61 * tintv != 0) until the timer is accessed.
62 */
63static void timerfd_triggered(struct timerfd_ctx *ctx)
64{
65	unsigned long flags;
66
67	spin_lock_irqsave(&ctx->wqh.lock, flags);
68	ctx->expired = 1;
69	ctx->ticks++;
70	wake_up_locked_poll(&ctx->wqh, EPOLLIN);
71	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
72}
73
74static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
75{
76	struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
77					       t.tmr);
78	timerfd_triggered(ctx);
79	return HRTIMER_NORESTART;
80}
81
82static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
83	ktime_t now)
84{
85	struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
86					       t.alarm);
87	timerfd_triggered(ctx);
88	return ALARMTIMER_NORESTART;
89}
90
91/*
92 * Called when the clock was set to cancel the timers in the cancel
93 * list. This will wake up processes waiting on these timers. The
94 * wake-up requires ctx->ticks to be non zero, therefore we increment
95 * it before calling wake_up_locked().
96 */
97void timerfd_clock_was_set(void)
98{
99	ktime_t moffs = ktime_mono_to_real(0);
100	struct timerfd_ctx *ctx;
101	unsigned long flags;
102
103	rcu_read_lock();
104	list_for_each_entry_rcu(ctx, &cancel_list, clist) {
105		if (!ctx->might_cancel)
106			continue;
107		spin_lock_irqsave(&ctx->wqh.lock, flags);
108		if (ctx->moffs != moffs) {
109			ctx->moffs = KTIME_MAX;
110			ctx->ticks++;
111			wake_up_locked_poll(&ctx->wqh, EPOLLIN);
112		}
113		spin_unlock_irqrestore(&ctx->wqh.lock, flags);
114	}
115	rcu_read_unlock();
116}
117
118static void timerfd_resume_work(struct work_struct *work)
119{
120	timerfd_clock_was_set();
121}
122
123static DECLARE_WORK(timerfd_work, timerfd_resume_work);
124
125/*
126 * Invoked from timekeeping_resume(). Defer the actual update to work so
127 * timerfd_clock_was_set() runs in task context.
128 */
129void timerfd_resume(void)
130{
131	schedule_work(&timerfd_work);
132}
133
134static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
135{
136	if (ctx->might_cancel) {
137		ctx->might_cancel = false;
138		spin_lock(&cancel_lock);
139		list_del_rcu(&ctx->clist);
140		spin_unlock(&cancel_lock);
141	}
142}
143
144static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
145{
146	spin_lock(&ctx->cancel_lock);
147	__timerfd_remove_cancel(ctx);
148	spin_unlock(&ctx->cancel_lock);
149}
150
151static bool timerfd_canceled(struct timerfd_ctx *ctx)
152{
153	if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
154		return false;
155	ctx->moffs = ktime_mono_to_real(0);
156	return true;
157}
158
159static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
160{
161	spin_lock(&ctx->cancel_lock);
162	if ((ctx->clockid == CLOCK_REALTIME ||
163	     ctx->clockid == CLOCK_REALTIME_ALARM) &&
164	    (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
165		if (!ctx->might_cancel) {
166			ctx->might_cancel = true;
167			spin_lock(&cancel_lock);
168			list_add_rcu(&ctx->clist, &cancel_list);
169			spin_unlock(&cancel_lock);
170		}
171	} else {
172		__timerfd_remove_cancel(ctx);
173	}
174	spin_unlock(&ctx->cancel_lock);
175}
176
177static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
178{
179	ktime_t remaining;
180
181	if (isalarm(ctx))
182		remaining = alarm_expires_remaining(&ctx->t.alarm);
183	else
184		remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
185
186	return remaining < 0 ? 0: remaining;
187}
188
189static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
190			 const struct itimerspec64 *ktmr)
191{
192	enum hrtimer_mode htmode;
193	ktime_t texp;
194	int clockid = ctx->clockid;
195
196	htmode = (flags & TFD_TIMER_ABSTIME) ?
197		HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
198
199	texp = timespec64_to_ktime(ktmr->it_value);
200	ctx->expired = 0;
201	ctx->ticks = 0;
202	ctx->tintv = timespec64_to_ktime(ktmr->it_interval);
203
204	if (isalarm(ctx)) {
205		alarm_init(&ctx->t.alarm,
206			   ctx->clockid == CLOCK_REALTIME_ALARM ?
207			   ALARM_REALTIME : ALARM_BOOTTIME,
208			   timerfd_alarmproc);
209	} else {
210		hrtimer_init(&ctx->t.tmr, clockid, htmode);
211		hrtimer_set_expires(&ctx->t.tmr, texp);
212		ctx->t.tmr.function = timerfd_tmrproc;
213	}
214
215	if (texp != 0) {
216		if (flags & TFD_TIMER_ABSTIME)
217			texp = timens_ktime_to_host(clockid, texp);
218		if (isalarm(ctx)) {
219			if (flags & TFD_TIMER_ABSTIME)
220				alarm_start(&ctx->t.alarm, texp);
221			else
222				alarm_start_relative(&ctx->t.alarm, texp);
223		} else {
224			hrtimer_start(&ctx->t.tmr, texp, htmode);
225		}
226
227		if (timerfd_canceled(ctx))
228			return -ECANCELED;
229	}
230
231	ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
232	return 0;
233}
234
235static int timerfd_release(struct inode *inode, struct file *file)
236{
237	struct timerfd_ctx *ctx = file->private_data;
238
239	timerfd_remove_cancel(ctx);
240
241	if (isalarm(ctx))
242		alarm_cancel(&ctx->t.alarm);
243	else
244		hrtimer_cancel(&ctx->t.tmr);
245	kfree_rcu(ctx, rcu);
246	return 0;
247}
248
249static __poll_t timerfd_poll(struct file *file, poll_table *wait)
250{
251	struct timerfd_ctx *ctx = file->private_data;
252	__poll_t events = 0;
253	unsigned long flags;
254
255	poll_wait(file, &ctx->wqh, wait);
256
257	spin_lock_irqsave(&ctx->wqh.lock, flags);
258	if (ctx->ticks)
259		events |= EPOLLIN;
260	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
261
262	return events;
263}
264
265static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
266			    loff_t *ppos)
267{
268	struct timerfd_ctx *ctx = file->private_data;
269	ssize_t res;
270	u64 ticks = 0;
271
272	if (count < sizeof(ticks))
273		return -EINVAL;
274	spin_lock_irq(&ctx->wqh.lock);
275	if (file->f_flags & O_NONBLOCK)
276		res = -EAGAIN;
277	else
278		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
279
280	/*
281	 * If clock has changed, we do not care about the
282	 * ticks and we do not rearm the timer. Userspace must
283	 * reevaluate anyway.
284	 */
285	if (timerfd_canceled(ctx)) {
286		ctx->ticks = 0;
287		ctx->expired = 0;
288		res = -ECANCELED;
289	}
290
291	if (ctx->ticks) {
292		ticks = ctx->ticks;
293
294		if (ctx->expired && ctx->tintv) {
295			/*
296			 * If tintv != 0, this is a periodic timer that
297			 * needs to be re-armed. We avoid doing it in the timer
298			 * callback to avoid DoS attacks specifying a very
299			 * short timer period.
300			 */
301			if (isalarm(ctx)) {
302				ticks += alarm_forward_now(
303					&ctx->t.alarm, ctx->tintv) - 1;
304				alarm_restart(&ctx->t.alarm);
305			} else {
306				ticks += hrtimer_forward_now(&ctx->t.tmr,
307							     ctx->tintv) - 1;
308				hrtimer_restart(&ctx->t.tmr);
309			}
310		}
311		ctx->expired = 0;
312		ctx->ticks = 0;
313	}
314	spin_unlock_irq(&ctx->wqh.lock);
315	if (ticks)
316		res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
317	return res;
318}
319
320#ifdef CONFIG_PROC_FS
321static void timerfd_show(struct seq_file *m, struct file *file)
322{
323	struct timerfd_ctx *ctx = file->private_data;
324	struct timespec64 value, interval;
325
326	spin_lock_irq(&ctx->wqh.lock);
327	value = ktime_to_timespec64(timerfd_get_remaining(ctx));
328	interval = ktime_to_timespec64(ctx->tintv);
329	spin_unlock_irq(&ctx->wqh.lock);
330
331	seq_printf(m,
332		   "clockid: %d\n"
333		   "ticks: %llu\n"
334		   "settime flags: 0%o\n"
335		   "it_value: (%llu, %llu)\n"
336		   "it_interval: (%llu, %llu)\n",
337		   ctx->clockid,
338		   (unsigned long long)ctx->ticks,
339		   ctx->settime_flags,
340		   (unsigned long long)value.tv_sec,
341		   (unsigned long long)value.tv_nsec,
342		   (unsigned long long)interval.tv_sec,
343		   (unsigned long long)interval.tv_nsec);
344}
345#else
346#define timerfd_show NULL
347#endif
348
349#ifdef CONFIG_CHECKPOINT_RESTORE
350static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
351{
352	struct timerfd_ctx *ctx = file->private_data;
353	int ret = 0;
354
355	switch (cmd) {
356	case TFD_IOC_SET_TICKS: {
357		u64 ticks;
358
359		if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
360			return -EFAULT;
361		if (!ticks)
362			return -EINVAL;
363
364		spin_lock_irq(&ctx->wqh.lock);
365		if (!timerfd_canceled(ctx)) {
366			ctx->ticks = ticks;
367			wake_up_locked_poll(&ctx->wqh, EPOLLIN);
368		} else
369			ret = -ECANCELED;
370		spin_unlock_irq(&ctx->wqh.lock);
371		break;
372	}
373	default:
374		ret = -ENOTTY;
375		break;
376	}
377
378	return ret;
379}
380#else
381#define timerfd_ioctl NULL
382#endif
383
384static const struct file_operations timerfd_fops = {
385	.release	= timerfd_release,
386	.poll		= timerfd_poll,
387	.read		= timerfd_read,
388	.llseek		= noop_llseek,
389	.show_fdinfo	= timerfd_show,
390	.unlocked_ioctl	= timerfd_ioctl,
391};
392
393static int timerfd_fget(int fd, struct fd *p)
394{
395	struct fd f = fdget(fd);
396	if (!f.file)
397		return -EBADF;
398	if (f.file->f_op != &timerfd_fops) {
399		fdput(f);
400		return -EINVAL;
401	}
402	*p = f;
403	return 0;
404}
405
406SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
407{
408	int ufd;
409	struct timerfd_ctx *ctx;
410
411	/* Check the TFD_* constants for consistency.  */
412	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
413	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
414
415	if ((flags & ~TFD_CREATE_FLAGS) ||
416	    (clockid != CLOCK_MONOTONIC &&
417	     clockid != CLOCK_REALTIME &&
418	     clockid != CLOCK_REALTIME_ALARM &&
419	     clockid != CLOCK_BOOTTIME &&
420	     clockid != CLOCK_BOOTTIME_ALARM))
421		return -EINVAL;
422
423	if ((clockid == CLOCK_REALTIME_ALARM ||
424	     clockid == CLOCK_BOOTTIME_ALARM) &&
425	    !capable(CAP_WAKE_ALARM))
426		return -EPERM;
427
428	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
429	if (!ctx)
430		return -ENOMEM;
431
432	init_waitqueue_head(&ctx->wqh);
433	spin_lock_init(&ctx->cancel_lock);
434	ctx->clockid = clockid;
435
436	if (isalarm(ctx))
437		alarm_init(&ctx->t.alarm,
438			   ctx->clockid == CLOCK_REALTIME_ALARM ?
439			   ALARM_REALTIME : ALARM_BOOTTIME,
440			   timerfd_alarmproc);
441	else
442		hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
443
444	ctx->moffs = ktime_mono_to_real(0);
445
446	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
447			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
448	if (ufd < 0)
449		kfree(ctx);
450
451	return ufd;
452}
453
454static int do_timerfd_settime(int ufd, int flags,
455		const struct itimerspec64 *new,
456		struct itimerspec64 *old)
457{
458	struct fd f;
459	struct timerfd_ctx *ctx;
460	int ret;
461
462	if ((flags & ~TFD_SETTIME_FLAGS) ||
463		 !itimerspec64_valid(new))
464		return -EINVAL;
465
466	ret = timerfd_fget(ufd, &f);
467	if (ret)
468		return ret;
469	ctx = f.file->private_data;
470
471	if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
472		fdput(f);
473		return -EPERM;
474	}
475
476	timerfd_setup_cancel(ctx, flags);
477
478	/*
479	 * We need to stop the existing timer before reprogramming
480	 * it to the new values.
481	 */
482	for (;;) {
483		spin_lock_irq(&ctx->wqh.lock);
484
485		if (isalarm(ctx)) {
486			if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
487				break;
488		} else {
489			if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
490				break;
491		}
492		spin_unlock_irq(&ctx->wqh.lock);
493
494		if (isalarm(ctx))
495			hrtimer_cancel_wait_running(&ctx->t.alarm.timer);
496		else
497			hrtimer_cancel_wait_running(&ctx->t.tmr);
498	}
499
500	/*
501	 * If the timer is expired and it's periodic, we need to advance it
502	 * because the caller may want to know the previous expiration time.
503	 * We do not update "ticks" and "expired" since the timer will be
504	 * re-programmed again in the following timerfd_setup() call.
505	 */
506	if (ctx->expired && ctx->tintv) {
507		if (isalarm(ctx))
508			alarm_forward_now(&ctx->t.alarm, ctx->tintv);
509		else
510			hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
511	}
512
513	old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
514	old->it_interval = ktime_to_timespec64(ctx->tintv);
515
516	/*
517	 * Re-program the timer to the new value ...
518	 */
519	ret = timerfd_setup(ctx, flags, new);
520
521	spin_unlock_irq(&ctx->wqh.lock);
522	fdput(f);
523	return ret;
524}
525
526static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
527{
528	struct fd f;
529	struct timerfd_ctx *ctx;
530	int ret = timerfd_fget(ufd, &f);
531	if (ret)
532		return ret;
533	ctx = f.file->private_data;
534
535	spin_lock_irq(&ctx->wqh.lock);
536	if (ctx->expired && ctx->tintv) {
537		ctx->expired = 0;
538
539		if (isalarm(ctx)) {
540			ctx->ticks +=
541				alarm_forward_now(
542					&ctx->t.alarm, ctx->tintv) - 1;
543			alarm_restart(&ctx->t.alarm);
544		} else {
545			ctx->ticks +=
546				hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
547				- 1;
548			hrtimer_restart(&ctx->t.tmr);
549		}
550	}
551	t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
552	t->it_interval = ktime_to_timespec64(ctx->tintv);
553	spin_unlock_irq(&ctx->wqh.lock);
554	fdput(f);
555	return 0;
556}
557
558SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
559		const struct __kernel_itimerspec __user *, utmr,
560		struct __kernel_itimerspec __user *, otmr)
561{
562	struct itimerspec64 new, old;
563	int ret;
564
565	if (get_itimerspec64(&new, utmr))
566		return -EFAULT;
567	ret = do_timerfd_settime(ufd, flags, &new, &old);
568	if (ret)
569		return ret;
570	if (otmr && put_itimerspec64(&old, otmr))
571		return -EFAULT;
572
573	return ret;
574}
575
576SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr)
577{
578	struct itimerspec64 kotmr;
579	int ret = do_timerfd_gettime(ufd, &kotmr);
580	if (ret)
581		return ret;
582	return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
583}
584
585#ifdef CONFIG_COMPAT_32BIT_TIME
586SYSCALL_DEFINE4(timerfd_settime32, int, ufd, int, flags,
587		const struct old_itimerspec32 __user *, utmr,
588		struct old_itimerspec32 __user *, otmr)
589{
590	struct itimerspec64 new, old;
591	int ret;
592
593	if (get_old_itimerspec32(&new, utmr))
594		return -EFAULT;
595	ret = do_timerfd_settime(ufd, flags, &new, &old);
596	if (ret)
597		return ret;
598	if (otmr && put_old_itimerspec32(&old, otmr))
599		return -EFAULT;
600	return ret;
601}
602
603SYSCALL_DEFINE2(timerfd_gettime32, int, ufd,
604		struct old_itimerspec32 __user *, otmr)
605{
606	struct itimerspec64 kotmr;
607	int ret = do_timerfd_gettime(ufd, &kotmr);
608	if (ret)
609		return ret;
610	return put_old_itimerspec32(&kotmr, otmr) ? -EFAULT : 0;
611}
612#endif
613