xref: /openbmc/linux/fs/timerfd.c (revision dbd171df) 
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 
31 struct 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 
49 static LIST_HEAD(cancel_list);
50 static DEFINE_SPINLOCK(cancel_lock);
51 
52 static 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  */
63 static 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 
74 static 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 
82 static 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  */
97 void 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 
118 static void timerfd_resume_work(struct work_struct *work)
119 {
120 	timerfd_clock_was_set();
121 }
122 
123 static 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  */
129 void timerfd_resume(void)
130 {
131 	schedule_work(&timerfd_work);
132 }
133 
134 static 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 
144 static 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 
151 static 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 
159 static 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 
177 static 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 
189 static 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 
235 static 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 
249 static __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 
265 static 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
321 static 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
350 static 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 
384 static 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 
393 static 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 
406 SYSCALL_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 
454 static 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 
526 static 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 
558 SYSCALL_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 
576 SYSCALL_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
586 SYSCALL_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 
603 SYSCALL_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