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 
30 struct timerfd_ctx {
31 	union {
32 		struct hrtimer tmr;
33 		struct alarm alarm;
34 	} t;
35 	ktime_t tintv;
36 	ktime_t moffs;
37 	wait_queue_head_t wqh;
38 	u64 ticks;
39 	int clockid;
40 	short unsigned expired;
41 	short unsigned settime_flags;	/* to show in fdinfo */
42 	struct rcu_head rcu;
43 	struct list_head clist;
44 	spinlock_t cancel_lock;
45 	bool might_cancel;
46 };
47 
48 static LIST_HEAD(cancel_list);
49 static DEFINE_SPINLOCK(cancel_lock);
50 
isalarm(struct timerfd_ctx * ctx)51 static inline bool isalarm(struct timerfd_ctx *ctx)
52 {
53 	return ctx->clockid == CLOCK_REALTIME_ALARM ||
54 		ctx->clockid == CLOCK_BOOTTIME_ALARM;
55 }
56 
57 /*
58  * This gets called when the timer event triggers. We set the "expired"
59  * flag, but we do not re-arm the timer (in case it's necessary,
60  * tintv != 0) until the timer is accessed.
61  */
timerfd_triggered(struct timerfd_ctx * ctx)62 static void timerfd_triggered(struct timerfd_ctx *ctx)
63 {
64 	unsigned long flags;
65 
66 	spin_lock_irqsave(&ctx->wqh.lock, flags);
67 	ctx->expired = 1;
68 	ctx->ticks++;
69 	wake_up_locked_poll(&ctx->wqh, EPOLLIN);
70 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
71 }
72 
timerfd_tmrproc(struct hrtimer * htmr)73 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
74 {
75 	struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
76 					       t.tmr);
77 	timerfd_triggered(ctx);
78 	return HRTIMER_NORESTART;
79 }
80 
timerfd_alarmproc(struct alarm * alarm,ktime_t now)81 static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
82 	ktime_t now)
83 {
84 	struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
85 					       t.alarm);
86 	timerfd_triggered(ctx);
87 	return ALARMTIMER_NORESTART;
88 }
89 
90 /*
91  * Called when the clock was set to cancel the timers in the cancel
92  * list. This will wake up processes waiting on these timers. The
93  * wake-up requires ctx->ticks to be non zero, therefore we increment
94  * it before calling wake_up_locked().
95  */
timerfd_clock_was_set(void)96 void timerfd_clock_was_set(void)
97 {
98 	ktime_t moffs = ktime_mono_to_real(0);
99 	struct timerfd_ctx *ctx;
100 	unsigned long flags;
101 
102 	rcu_read_lock();
103 	list_for_each_entry_rcu(ctx, &cancel_list, clist) {
104 		if (!ctx->might_cancel)
105 			continue;
106 		spin_lock_irqsave(&ctx->wqh.lock, flags);
107 		if (ctx->moffs != moffs) {
108 			ctx->moffs = KTIME_MAX;
109 			ctx->ticks++;
110 			wake_up_locked_poll(&ctx->wqh, EPOLLIN);
111 		}
112 		spin_unlock_irqrestore(&ctx->wqh.lock, flags);
113 	}
114 	rcu_read_unlock();
115 }
116 
__timerfd_remove_cancel(struct timerfd_ctx * ctx)117 static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
118 {
119 	if (ctx->might_cancel) {
120 		ctx->might_cancel = false;
121 		spin_lock(&cancel_lock);
122 		list_del_rcu(&ctx->clist);
123 		spin_unlock(&cancel_lock);
124 	}
125 }
126 
timerfd_remove_cancel(struct timerfd_ctx * ctx)127 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
128 {
129 	spin_lock(&ctx->cancel_lock);
130 	__timerfd_remove_cancel(ctx);
131 	spin_unlock(&ctx->cancel_lock);
132 }
133 
timerfd_canceled(struct timerfd_ctx * ctx)134 static bool timerfd_canceled(struct timerfd_ctx *ctx)
135 {
136 	if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
137 		return false;
138 	ctx->moffs = ktime_mono_to_real(0);
139 	return true;
140 }
141 
timerfd_setup_cancel(struct timerfd_ctx * ctx,int flags)142 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
143 {
144 	spin_lock(&ctx->cancel_lock);
145 	if ((ctx->clockid == CLOCK_REALTIME ||
146 	     ctx->clockid == CLOCK_REALTIME_ALARM) &&
147 	    (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
148 		if (!ctx->might_cancel) {
149 			ctx->might_cancel = true;
150 			spin_lock(&cancel_lock);
151 			list_add_rcu(&ctx->clist, &cancel_list);
152 			spin_unlock(&cancel_lock);
153 		}
154 	} else {
155 		__timerfd_remove_cancel(ctx);
156 	}
157 	spin_unlock(&ctx->cancel_lock);
158 }
159 
timerfd_get_remaining(struct timerfd_ctx * ctx)160 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
161 {
162 	ktime_t remaining;
163 
164 	if (isalarm(ctx))
165 		remaining = alarm_expires_remaining(&ctx->t.alarm);
166 	else
167 		remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
168 
169 	return remaining < 0 ? 0: remaining;
170 }
171 
timerfd_setup(struct timerfd_ctx * ctx,int flags,const struct itimerspec64 * ktmr)172 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
173 			 const struct itimerspec64 *ktmr)
174 {
175 	enum hrtimer_mode htmode;
176 	ktime_t texp;
177 	int clockid = ctx->clockid;
178 
179 	htmode = (flags & TFD_TIMER_ABSTIME) ?
180 		HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
181 
182 	texp = timespec64_to_ktime(ktmr->it_value);
183 	ctx->expired = 0;
184 	ctx->ticks = 0;
185 	ctx->tintv = timespec64_to_ktime(ktmr->it_interval);
186 
187 	if (isalarm(ctx)) {
188 		alarm_init(&ctx->t.alarm,
189 			   ctx->clockid == CLOCK_REALTIME_ALARM ?
190 			   ALARM_REALTIME : ALARM_BOOTTIME,
191 			   timerfd_alarmproc);
192 	} else {
193 		hrtimer_init(&ctx->t.tmr, clockid, htmode);
194 		hrtimer_set_expires(&ctx->t.tmr, texp);
195 		ctx->t.tmr.function = timerfd_tmrproc;
196 	}
197 
198 	if (texp != 0) {
199 		if (isalarm(ctx)) {
200 			if (flags & TFD_TIMER_ABSTIME)
201 				alarm_start(&ctx->t.alarm, texp);
202 			else
203 				alarm_start_relative(&ctx->t.alarm, texp);
204 		} else {
205 			hrtimer_start(&ctx->t.tmr, texp, htmode);
206 		}
207 
208 		if (timerfd_canceled(ctx))
209 			return -ECANCELED;
210 	}
211 
212 	ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
213 	return 0;
214 }
215 
timerfd_release(struct inode * inode,struct file * file)216 static int timerfd_release(struct inode *inode, struct file *file)
217 {
218 	struct timerfd_ctx *ctx = file->private_data;
219 
220 	timerfd_remove_cancel(ctx);
221 
222 	if (isalarm(ctx))
223 		alarm_cancel(&ctx->t.alarm);
224 	else
225 		hrtimer_cancel(&ctx->t.tmr);
226 	kfree_rcu(ctx, rcu);
227 	return 0;
228 }
229 
timerfd_poll(struct file * file,poll_table * wait)230 static __poll_t timerfd_poll(struct file *file, poll_table *wait)
231 {
232 	struct timerfd_ctx *ctx = file->private_data;
233 	__poll_t events = 0;
234 	unsigned long flags;
235 
236 	poll_wait(file, &ctx->wqh, wait);
237 
238 	spin_lock_irqsave(&ctx->wqh.lock, flags);
239 	if (ctx->ticks)
240 		events |= EPOLLIN;
241 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
242 
243 	return events;
244 }
245 
timerfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)246 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
247 			    loff_t *ppos)
248 {
249 	struct timerfd_ctx *ctx = file->private_data;
250 	ssize_t res;
251 	u64 ticks = 0;
252 
253 	if (count < sizeof(ticks))
254 		return -EINVAL;
255 	spin_lock_irq(&ctx->wqh.lock);
256 	if (file->f_flags & O_NONBLOCK)
257 		res = -EAGAIN;
258 	else
259 		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
260 
261 	/*
262 	 * If clock has changed, we do not care about the
263 	 * ticks and we do not rearm the timer. Userspace must
264 	 * reevaluate anyway.
265 	 */
266 	if (timerfd_canceled(ctx)) {
267 		ctx->ticks = 0;
268 		ctx->expired = 0;
269 		res = -ECANCELED;
270 	}
271 
272 	if (ctx->ticks) {
273 		ticks = ctx->ticks;
274 
275 		if (ctx->expired && ctx->tintv) {
276 			/*
277 			 * If tintv != 0, this is a periodic timer that
278 			 * needs to be re-armed. We avoid doing it in the timer
279 			 * callback to avoid DoS attacks specifying a very
280 			 * short timer period.
281 			 */
282 			if (isalarm(ctx)) {
283 				ticks += alarm_forward_now(
284 					&ctx->t.alarm, ctx->tintv) - 1;
285 				alarm_restart(&ctx->t.alarm);
286 			} else {
287 				ticks += hrtimer_forward_now(&ctx->t.tmr,
288 							     ctx->tintv) - 1;
289 				hrtimer_restart(&ctx->t.tmr);
290 			}
291 		}
292 		ctx->expired = 0;
293 		ctx->ticks = 0;
294 	}
295 	spin_unlock_irq(&ctx->wqh.lock);
296 	if (ticks)
297 		res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
298 	return res;
299 }
300 
301 #ifdef CONFIG_PROC_FS
timerfd_show(struct seq_file * m,struct file * file)302 static void timerfd_show(struct seq_file *m, struct file *file)
303 {
304 	struct timerfd_ctx *ctx = file->private_data;
305 	struct itimerspec t;
306 
307 	spin_lock_irq(&ctx->wqh.lock);
308 	t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
309 	t.it_interval = ktime_to_timespec(ctx->tintv);
310 	spin_unlock_irq(&ctx->wqh.lock);
311 
312 	seq_printf(m,
313 		   "clockid: %d\n"
314 		   "ticks: %llu\n"
315 		   "settime flags: 0%o\n"
316 		   "it_value: (%llu, %llu)\n"
317 		   "it_interval: (%llu, %llu)\n",
318 		   ctx->clockid,
319 		   (unsigned long long)ctx->ticks,
320 		   ctx->settime_flags,
321 		   (unsigned long long)t.it_value.tv_sec,
322 		   (unsigned long long)t.it_value.tv_nsec,
323 		   (unsigned long long)t.it_interval.tv_sec,
324 		   (unsigned long long)t.it_interval.tv_nsec);
325 }
326 #else
327 #define timerfd_show NULL
328 #endif
329 
330 #ifdef CONFIG_CHECKPOINT_RESTORE
timerfd_ioctl(struct file * file,unsigned int cmd,unsigned long arg)331 static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
332 {
333 	struct timerfd_ctx *ctx = file->private_data;
334 	int ret = 0;
335 
336 	switch (cmd) {
337 	case TFD_IOC_SET_TICKS: {
338 		u64 ticks;
339 
340 		if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
341 			return -EFAULT;
342 		if (!ticks)
343 			return -EINVAL;
344 
345 		spin_lock_irq(&ctx->wqh.lock);
346 		if (!timerfd_canceled(ctx)) {
347 			ctx->ticks = ticks;
348 			wake_up_locked_poll(&ctx->wqh, EPOLLIN);
349 		} else
350 			ret = -ECANCELED;
351 		spin_unlock_irq(&ctx->wqh.lock);
352 		break;
353 	}
354 	default:
355 		ret = -ENOTTY;
356 		break;
357 	}
358 
359 	return ret;
360 }
361 #else
362 #define timerfd_ioctl NULL
363 #endif
364 
365 static const struct file_operations timerfd_fops = {
366 	.release	= timerfd_release,
367 	.poll		= timerfd_poll,
368 	.read		= timerfd_read,
369 	.llseek		= noop_llseek,
370 	.show_fdinfo	= timerfd_show,
371 	.unlocked_ioctl	= timerfd_ioctl,
372 };
373 
timerfd_fget(int fd,struct fd * p)374 static int timerfd_fget(int fd, struct fd *p)
375 {
376 	struct fd f = fdget(fd);
377 	if (!f.file)
378 		return -EBADF;
379 	if (f.file->f_op != &timerfd_fops) {
380 		fdput(f);
381 		return -EINVAL;
382 	}
383 	*p = f;
384 	return 0;
385 }
386 
SYSCALL_DEFINE2(timerfd_create,int,clockid,int,flags)387 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
388 {
389 	int ufd;
390 	struct timerfd_ctx *ctx;
391 
392 	/* Check the TFD_* constants for consistency.  */
393 	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
394 	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
395 
396 	if ((flags & ~TFD_CREATE_FLAGS) ||
397 	    (clockid != CLOCK_MONOTONIC &&
398 	     clockid != CLOCK_REALTIME &&
399 	     clockid != CLOCK_REALTIME_ALARM &&
400 	     clockid != CLOCK_BOOTTIME &&
401 	     clockid != CLOCK_BOOTTIME_ALARM))
402 		return -EINVAL;
403 
404 	if ((clockid == CLOCK_REALTIME_ALARM ||
405 	     clockid == CLOCK_BOOTTIME_ALARM) &&
406 	    !capable(CAP_WAKE_ALARM))
407 		return -EPERM;
408 
409 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
410 	if (!ctx)
411 		return -ENOMEM;
412 
413 	init_waitqueue_head(&ctx->wqh);
414 	spin_lock_init(&ctx->cancel_lock);
415 	ctx->clockid = clockid;
416 
417 	if (isalarm(ctx))
418 		alarm_init(&ctx->t.alarm,
419 			   ctx->clockid == CLOCK_REALTIME_ALARM ?
420 			   ALARM_REALTIME : ALARM_BOOTTIME,
421 			   timerfd_alarmproc);
422 	else
423 		hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
424 
425 	ctx->moffs = ktime_mono_to_real(0);
426 
427 	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
428 			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
429 	if (ufd < 0)
430 		kfree(ctx);
431 
432 	return ufd;
433 }
434 
do_timerfd_settime(int ufd,int flags,const struct itimerspec64 * new,struct itimerspec64 * old)435 static int do_timerfd_settime(int ufd, int flags,
436 		const struct itimerspec64 *new,
437 		struct itimerspec64 *old)
438 {
439 	struct fd f;
440 	struct timerfd_ctx *ctx;
441 	int ret;
442 
443 	if ((flags & ~TFD_SETTIME_FLAGS) ||
444 		 !itimerspec64_valid(new))
445 		return -EINVAL;
446 
447 	ret = timerfd_fget(ufd, &f);
448 	if (ret)
449 		return ret;
450 	ctx = f.file->private_data;
451 
452 	if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
453 		fdput(f);
454 		return -EPERM;
455 	}
456 
457 	timerfd_setup_cancel(ctx, flags);
458 
459 	/*
460 	 * We need to stop the existing timer before reprogramming
461 	 * it to the new values.
462 	 */
463 	for (;;) {
464 		spin_lock_irq(&ctx->wqh.lock);
465 
466 		if (isalarm(ctx)) {
467 			if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
468 				break;
469 		} else {
470 			if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
471 				break;
472 		}
473 		spin_unlock_irq(&ctx->wqh.lock);
474 		cpu_relax();
475 	}
476 
477 	/*
478 	 * If the timer is expired and it's periodic, we need to advance it
479 	 * because the caller may want to know the previous expiration time.
480 	 * We do not update "ticks" and "expired" since the timer will be
481 	 * re-programmed again in the following timerfd_setup() call.
482 	 */
483 	if (ctx->expired && ctx->tintv) {
484 		if (isalarm(ctx))
485 			alarm_forward_now(&ctx->t.alarm, ctx->tintv);
486 		else
487 			hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
488 	}
489 
490 	old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
491 	old->it_interval = ktime_to_timespec64(ctx->tintv);
492 
493 	/*
494 	 * Re-program the timer to the new value ...
495 	 */
496 	ret = timerfd_setup(ctx, flags, new);
497 
498 	spin_unlock_irq(&ctx->wqh.lock);
499 	fdput(f);
500 	return ret;
501 }
502 
do_timerfd_gettime(int ufd,struct itimerspec64 * t)503 static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
504 {
505 	struct fd f;
506 	struct timerfd_ctx *ctx;
507 	int ret = timerfd_fget(ufd, &f);
508 	if (ret)
509 		return ret;
510 	ctx = f.file->private_data;
511 
512 	spin_lock_irq(&ctx->wqh.lock);
513 	if (ctx->expired && ctx->tintv) {
514 		ctx->expired = 0;
515 
516 		if (isalarm(ctx)) {
517 			ctx->ticks +=
518 				alarm_forward_now(
519 					&ctx->t.alarm, ctx->tintv) - 1;
520 			alarm_restart(&ctx->t.alarm);
521 		} else {
522 			ctx->ticks +=
523 				hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
524 				- 1;
525 			hrtimer_restart(&ctx->t.tmr);
526 		}
527 	}
528 	t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
529 	t->it_interval = ktime_to_timespec64(ctx->tintv);
530 	spin_unlock_irq(&ctx->wqh.lock);
531 	fdput(f);
532 	return 0;
533 }
534 
SYSCALL_DEFINE4(timerfd_settime,int,ufd,int,flags,const struct __kernel_itimerspec __user *,utmr,struct __kernel_itimerspec __user *,otmr)535 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
536 		const struct __kernel_itimerspec __user *, utmr,
537 		struct __kernel_itimerspec __user *, otmr)
538 {
539 	struct itimerspec64 new, old;
540 	int ret;
541 
542 	if (get_itimerspec64(&new, utmr))
543 		return -EFAULT;
544 	ret = do_timerfd_settime(ufd, flags, &new, &old);
545 	if (ret)
546 		return ret;
547 	if (otmr && put_itimerspec64(&old, otmr))
548 		return -EFAULT;
549 
550 	return ret;
551 }
552 
SYSCALL_DEFINE2(timerfd_gettime,int,ufd,struct __kernel_itimerspec __user *,otmr)553 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr)
554 {
555 	struct itimerspec64 kotmr;
556 	int ret = do_timerfd_gettime(ufd, &kotmr);
557 	if (ret)
558 		return ret;
559 	return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
560 }
561 
562 #ifdef CONFIG_COMPAT_32BIT_TIME
COMPAT_SYSCALL_DEFINE4(timerfd_settime,int,ufd,int,flags,const struct compat_itimerspec __user *,utmr,struct compat_itimerspec __user *,otmr)563 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
564 		const struct compat_itimerspec __user *, utmr,
565 		struct compat_itimerspec __user *, otmr)
566 {
567 	struct itimerspec64 new, old;
568 	int ret;
569 
570 	if (get_compat_itimerspec64(&new, utmr))
571 		return -EFAULT;
572 	ret = do_timerfd_settime(ufd, flags, &new, &old);
573 	if (ret)
574 		return ret;
575 	if (otmr && put_compat_itimerspec64(&old, otmr))
576 		return -EFAULT;
577 	return ret;
578 }
579 
COMPAT_SYSCALL_DEFINE2(timerfd_gettime,int,ufd,struct compat_itimerspec __user *,otmr)580 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
581 		struct compat_itimerspec __user *, otmr)
582 {
583 	struct itimerspec64 kotmr;
584 	int ret = do_timerfd_gettime(ufd, &kotmr);
585 	if (ret)
586 		return ret;
587 	return put_compat_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
588 }
589 #endif
590