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_iter(struct kiocb *iocb, struct iov_iter *to)
266{
267	struct file *file = iocb->ki_filp;
268	struct timerfd_ctx *ctx = file->private_data;
269	ssize_t res;
270	u64 ticks = 0;
271
272	if (iov_iter_count(to) < sizeof(ticks))
273		return -EINVAL;
274
275	spin_lock_irq(&ctx->wqh.lock);
276	if (file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT)
277		res = -EAGAIN;
278	else
279		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
280
281	/*
282	 * If clock has changed, we do not care about the
283	 * ticks and we do not rearm the timer. Userspace must
284	 * reevaluate anyway.
285	 */
286	if (timerfd_canceled(ctx)) {
287		ctx->ticks = 0;
288		ctx->expired = 0;
289		res = -ECANCELED;
290	}
291
292	if (ctx->ticks) {
293		ticks = ctx->ticks;
294
295		if (ctx->expired && ctx->tintv) {
296			/*
297			 * If tintv != 0, this is a periodic timer that
298			 * needs to be re-armed. We avoid doing it in the timer
299			 * callback to avoid DoS attacks specifying a very
300			 * short timer period.
301			 */
302			if (isalarm(ctx)) {
303				ticks += alarm_forward_now(
304					&ctx->t.alarm, ctx->tintv) - 1;
305				alarm_restart(&ctx->t.alarm);
306			} else {
307				ticks += hrtimer_forward_now(&ctx->t.tmr,
308							     ctx->tintv) - 1;
309				hrtimer_restart(&ctx->t.tmr);
310			}
311		}
312		ctx->expired = 0;
313		ctx->ticks = 0;
314	}
315	spin_unlock_irq(&ctx->wqh.lock);
316	if (ticks) {
317		res = copy_to_iter(&ticks, sizeof(ticks), to);
318		if (!res)
319			res = -EFAULT;
320	}
321	return res;
322}
323
324#ifdef CONFIG_PROC_FS
325static void timerfd_show(struct seq_file *m, struct file *file)
326{
327	struct timerfd_ctx *ctx = file->private_data;
328	struct timespec64 value, interval;
329
330	spin_lock_irq(&ctx->wqh.lock);
331	value = ktime_to_timespec64(timerfd_get_remaining(ctx));
332	interval = ktime_to_timespec64(ctx->tintv);
333	spin_unlock_irq(&ctx->wqh.lock);
334
335	seq_printf(m,
336		   "clockid: %d\n"
337		   "ticks: %llu\n"
338		   "settime flags: 0%o\n"
339		   "it_value: (%llu, %llu)\n"
340		   "it_interval: (%llu, %llu)\n",
341		   ctx->clockid,
342		   (unsigned long long)ctx->ticks,
343		   ctx->settime_flags,
344		   (unsigned long long)value.tv_sec,
345		   (unsigned long long)value.tv_nsec,
346		   (unsigned long long)interval.tv_sec,
347		   (unsigned long long)interval.tv_nsec);
348}
349#else
350#define timerfd_show NULL
351#endif
352
353#ifdef CONFIG_CHECKPOINT_RESTORE
354static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
355{
356	struct timerfd_ctx *ctx = file->private_data;
357	int ret = 0;
358
359	switch (cmd) {
360	case TFD_IOC_SET_TICKS: {
361		u64 ticks;
362
363		if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
364			return -EFAULT;
365		if (!ticks)
366			return -EINVAL;
367
368		spin_lock_irq(&ctx->wqh.lock);
369		if (!timerfd_canceled(ctx)) {
370			ctx->ticks = ticks;
371			wake_up_locked_poll(&ctx->wqh, EPOLLIN);
372		} else
373			ret = -ECANCELED;
374		spin_unlock_irq(&ctx->wqh.lock);
375		break;
376	}
377	default:
378		ret = -ENOTTY;
379		break;
380	}
381
382	return ret;
383}
384#else
385#define timerfd_ioctl NULL
386#endif
387
388static const struct file_operations timerfd_fops = {
389	.release	= timerfd_release,
390	.poll		= timerfd_poll,
391	.read_iter	= timerfd_read_iter,
392	.llseek		= noop_llseek,
393	.show_fdinfo	= timerfd_show,
394	.unlocked_ioctl	= timerfd_ioctl,
395};
396
397static int timerfd_fget(int fd, struct fd *p)
398{
399	struct fd f = fdget(fd);
400	if (!f.file)
401		return -EBADF;
402	if (f.file->f_op != &timerfd_fops) {
403		fdput(f);
404		return -EINVAL;
405	}
406	*p = f;
407	return 0;
408}
409
410SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
411{
412	int ufd;
413	struct timerfd_ctx *ctx;
414	struct file *file;
415
416	/* Check the TFD_* constants for consistency.  */
417	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
418	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
419
420	if ((flags & ~TFD_CREATE_FLAGS) ||
421	    (clockid != CLOCK_MONOTONIC &&
422	     clockid != CLOCK_REALTIME &&
423	     clockid != CLOCK_REALTIME_ALARM &&
424	     clockid != CLOCK_BOOTTIME &&
425	     clockid != CLOCK_BOOTTIME_ALARM))
426		return -EINVAL;
427
428	if ((clockid == CLOCK_REALTIME_ALARM ||
429	     clockid == CLOCK_BOOTTIME_ALARM) &&
430	    !capable(CAP_WAKE_ALARM))
431		return -EPERM;
432
433	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
434	if (!ctx)
435		return -ENOMEM;
436
437	init_waitqueue_head(&ctx->wqh);
438	spin_lock_init(&ctx->cancel_lock);
439	ctx->clockid = clockid;
440
441	if (isalarm(ctx))
442		alarm_init(&ctx->t.alarm,
443			   ctx->clockid == CLOCK_REALTIME_ALARM ?
444			   ALARM_REALTIME : ALARM_BOOTTIME,
445			   timerfd_alarmproc);
446	else
447		hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
448
449	ctx->moffs = ktime_mono_to_real(0);
450
451	ufd = get_unused_fd_flags(flags & TFD_SHARED_FCNTL_FLAGS);
452	if (ufd < 0) {
453		kfree(ctx);
454		return ufd;
455	}
456
457	file = anon_inode_getfile("[timerfd]", &timerfd_fops, ctx,
458				    O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
459	if (IS_ERR(file)) {
460		put_unused_fd(ufd);
461		kfree(ctx);
462		return PTR_ERR(file);
463	}
464
465	file->f_mode |= FMODE_NOWAIT;
466	fd_install(ufd, file);
467	return ufd;
468}
469
470static int do_timerfd_settime(int ufd, int flags,
471		const struct itimerspec64 *new,
472		struct itimerspec64 *old)
473{
474	struct fd f;
475	struct timerfd_ctx *ctx;
476	int ret;
477
478	if ((flags & ~TFD_SETTIME_FLAGS) ||
479		 !itimerspec64_valid(new))
480		return -EINVAL;
481
482	ret = timerfd_fget(ufd, &f);
483	if (ret)
484		return ret;
485	ctx = f.file->private_data;
486
487	if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
488		fdput(f);
489		return -EPERM;
490	}
491
492	timerfd_setup_cancel(ctx, flags);
493
494	/*
495	 * We need to stop the existing timer before reprogramming
496	 * it to the new values.
497	 */
498	for (;;) {
499		spin_lock_irq(&ctx->wqh.lock);
500
501		if (isalarm(ctx)) {
502			if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
503				break;
504		} else {
505			if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
506				break;
507		}
508		spin_unlock_irq(&ctx->wqh.lock);
509
510		if (isalarm(ctx))
511			hrtimer_cancel_wait_running(&ctx->t.alarm.timer);
512		else
513			hrtimer_cancel_wait_running(&ctx->t.tmr);
514	}
515
516	/*
517	 * If the timer is expired and it's periodic, we need to advance it
518	 * because the caller may want to know the previous expiration time.
519	 * We do not update "ticks" and "expired" since the timer will be
520	 * re-programmed again in the following timerfd_setup() call.
521	 */
522	if (ctx->expired && ctx->tintv) {
523		if (isalarm(ctx))
524			alarm_forward_now(&ctx->t.alarm, ctx->tintv);
525		else
526			hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
527	}
528
529	old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
530	old->it_interval = ktime_to_timespec64(ctx->tintv);
531
532	/*
533	 * Re-program the timer to the new value ...
534	 */
535	ret = timerfd_setup(ctx, flags, new);
536
537	spin_unlock_irq(&ctx->wqh.lock);
538	fdput(f);
539	return ret;
540}
541
542static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
543{
544	struct fd f;
545	struct timerfd_ctx *ctx;
546	int ret = timerfd_fget(ufd, &f);
547	if (ret)
548		return ret;
549	ctx = f.file->private_data;
550
551	spin_lock_irq(&ctx->wqh.lock);
552	if (ctx->expired && ctx->tintv) {
553		ctx->expired = 0;
554
555		if (isalarm(ctx)) {
556			ctx->ticks +=
557				alarm_forward_now(
558					&ctx->t.alarm, ctx->tintv) - 1;
559			alarm_restart(&ctx->t.alarm);
560		} else {
561			ctx->ticks +=
562				hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
563				- 1;
564			hrtimer_restart(&ctx->t.tmr);
565		}
566	}
567	t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
568	t->it_interval = ktime_to_timespec64(ctx->tintv);
569	spin_unlock_irq(&ctx->wqh.lock);
570	fdput(f);
571	return 0;
572}
573
574SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
575		const struct __kernel_itimerspec __user *, utmr,
576		struct __kernel_itimerspec __user *, otmr)
577{
578	struct itimerspec64 new, old;
579	int ret;
580
581	if (get_itimerspec64(&new, utmr))
582		return -EFAULT;
583	ret = do_timerfd_settime(ufd, flags, &new, &old);
584	if (ret)
585		return ret;
586	if (otmr && put_itimerspec64(&old, otmr))
587		return -EFAULT;
588
589	return ret;
590}
591
592SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr)
593{
594	struct itimerspec64 kotmr;
595	int ret = do_timerfd_gettime(ufd, &kotmr);
596	if (ret)
597		return ret;
598	return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
599}
600
601#ifdef CONFIG_COMPAT_32BIT_TIME
602SYSCALL_DEFINE4(timerfd_settime32, int, ufd, int, flags,
603		const struct old_itimerspec32 __user *, utmr,
604		struct old_itimerspec32 __user *, otmr)
605{
606	struct itimerspec64 new, old;
607	int ret;
608
609	if (get_old_itimerspec32(&new, utmr))
610		return -EFAULT;
611	ret = do_timerfd_settime(ufd, flags, &new, &old);
612	if (ret)
613		return ret;
614	if (otmr && put_old_itimerspec32(&old, otmr))
615		return -EFAULT;
616	return ret;
617}
618
619SYSCALL_DEFINE2(timerfd_gettime32, int, ufd,
620		struct old_itimerspec32 __user *, otmr)
621{
622	struct itimerspec64 kotmr;
623	int ret = do_timerfd_gettime(ufd, &kotmr);
624	if (ret)
625		return ret;
626	return put_old_itimerspec32(&kotmr, otmr) ? -EFAULT : 0;
627}
628#endif
629