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 
isalarm(struct timerfd_ctx * ctx)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  */
timerfd_triggered(struct timerfd_ctx * ctx)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 
timerfd_tmrproc(struct hrtimer * htmr)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 
timerfd_alarmproc(struct alarm * alarm,ktime_t now)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  */
timerfd_clock_was_set(void)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 
__timerfd_remove_cancel(struct timerfd_ctx * ctx)118 static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
119 {
120 	if (ctx->might_cancel) {
121 		ctx->might_cancel = false;
122 		spin_lock(&cancel_lock);
123 		list_del_rcu(&ctx->clist);
124 		spin_unlock(&cancel_lock);
125 	}
126 }
127 
timerfd_remove_cancel(struct timerfd_ctx * ctx)128 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
129 {
130 	spin_lock(&ctx->cancel_lock);
131 	__timerfd_remove_cancel(ctx);
132 	spin_unlock(&ctx->cancel_lock);
133 }
134 
timerfd_canceled(struct timerfd_ctx * ctx)135 static bool timerfd_canceled(struct timerfd_ctx *ctx)
136 {
137 	if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
138 		return false;
139 	ctx->moffs = ktime_mono_to_real(0);
140 	return true;
141 }
142 
timerfd_setup_cancel(struct timerfd_ctx * ctx,int flags)143 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
144 {
145 	spin_lock(&ctx->cancel_lock);
146 	if ((ctx->clockid == CLOCK_REALTIME ||
147 	     ctx->clockid == CLOCK_REALTIME_ALARM) &&
148 	    (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
149 		if (!ctx->might_cancel) {
150 			ctx->might_cancel = true;
151 			spin_lock(&cancel_lock);
152 			list_add_rcu(&ctx->clist, &cancel_list);
153 			spin_unlock(&cancel_lock);
154 		}
155 	} else {
156 		__timerfd_remove_cancel(ctx);
157 	}
158 	spin_unlock(&ctx->cancel_lock);
159 }
160 
timerfd_get_remaining(struct timerfd_ctx * ctx)161 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
162 {
163 	ktime_t remaining;
164 
165 	if (isalarm(ctx))
166 		remaining = alarm_expires_remaining(&ctx->t.alarm);
167 	else
168 		remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
169 
170 	return remaining < 0 ? 0: remaining;
171 }
172 
timerfd_setup(struct timerfd_ctx * ctx,int flags,const struct itimerspec64 * ktmr)173 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
174 			 const struct itimerspec64 *ktmr)
175 {
176 	enum hrtimer_mode htmode;
177 	ktime_t texp;
178 	int clockid = ctx->clockid;
179 
180 	htmode = (flags & TFD_TIMER_ABSTIME) ?
181 		HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
182 
183 	texp = timespec64_to_ktime(ktmr->it_value);
184 	ctx->expired = 0;
185 	ctx->ticks = 0;
186 	ctx->tintv = timespec64_to_ktime(ktmr->it_interval);
187 
188 	if (isalarm(ctx)) {
189 		alarm_init(&ctx->t.alarm,
190 			   ctx->clockid == CLOCK_REALTIME_ALARM ?
191 			   ALARM_REALTIME : ALARM_BOOTTIME,
192 			   timerfd_alarmproc);
193 	} else {
194 		hrtimer_init(&ctx->t.tmr, clockid, htmode);
195 		hrtimer_set_expires(&ctx->t.tmr, texp);
196 		ctx->t.tmr.function = timerfd_tmrproc;
197 	}
198 
199 	if (texp != 0) {
200 		if (flags & TFD_TIMER_ABSTIME)
201 			texp = timens_ktime_to_host(clockid, texp);
202 		if (isalarm(ctx)) {
203 			if (flags & TFD_TIMER_ABSTIME)
204 				alarm_start(&ctx->t.alarm, texp);
205 			else
206 				alarm_start_relative(&ctx->t.alarm, texp);
207 		} else {
208 			hrtimer_start(&ctx->t.tmr, texp, htmode);
209 		}
210 
211 		if (timerfd_canceled(ctx))
212 			return -ECANCELED;
213 	}
214 
215 	ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
216 	return 0;
217 }
218 
timerfd_release(struct inode * inode,struct file * file)219 static int timerfd_release(struct inode *inode, struct file *file)
220 {
221 	struct timerfd_ctx *ctx = file->private_data;
222 
223 	timerfd_remove_cancel(ctx);
224 
225 	if (isalarm(ctx))
226 		alarm_cancel(&ctx->t.alarm);
227 	else
228 		hrtimer_cancel(&ctx->t.tmr);
229 	kfree_rcu(ctx, rcu);
230 	return 0;
231 }
232 
timerfd_poll(struct file * file,poll_table * wait)233 static __poll_t timerfd_poll(struct file *file, poll_table *wait)
234 {
235 	struct timerfd_ctx *ctx = file->private_data;
236 	__poll_t events = 0;
237 	unsigned long flags;
238 
239 	poll_wait(file, &ctx->wqh, wait);
240 
241 	spin_lock_irqsave(&ctx->wqh.lock, flags);
242 	if (ctx->ticks)
243 		events |= EPOLLIN;
244 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
245 
246 	return events;
247 }
248 
timerfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)249 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
250 			    loff_t *ppos)
251 {
252 	struct timerfd_ctx *ctx = file->private_data;
253 	ssize_t res;
254 	u64 ticks = 0;
255 
256 	if (count < sizeof(ticks))
257 		return -EINVAL;
258 	spin_lock_irq(&ctx->wqh.lock);
259 	if (file->f_flags & O_NONBLOCK)
260 		res = -EAGAIN;
261 	else
262 		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
263 
264 	/*
265 	 * If clock has changed, we do not care about the
266 	 * ticks and we do not rearm the timer. Userspace must
267 	 * reevaluate anyway.
268 	 */
269 	if (timerfd_canceled(ctx)) {
270 		ctx->ticks = 0;
271 		ctx->expired = 0;
272 		res = -ECANCELED;
273 	}
274 
275 	if (ctx->ticks) {
276 		ticks = ctx->ticks;
277 
278 		if (ctx->expired && ctx->tintv) {
279 			/*
280 			 * If tintv != 0, this is a periodic timer that
281 			 * needs to be re-armed. We avoid doing it in the timer
282 			 * callback to avoid DoS attacks specifying a very
283 			 * short timer period.
284 			 */
285 			if (isalarm(ctx)) {
286 				ticks += alarm_forward_now(
287 					&ctx->t.alarm, ctx->tintv) - 1;
288 				alarm_restart(&ctx->t.alarm);
289 			} else {
290 				ticks += hrtimer_forward_now(&ctx->t.tmr,
291 							     ctx->tintv) - 1;
292 				hrtimer_restart(&ctx->t.tmr);
293 			}
294 		}
295 		ctx->expired = 0;
296 		ctx->ticks = 0;
297 	}
298 	spin_unlock_irq(&ctx->wqh.lock);
299 	if (ticks)
300 		res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
301 	return res;
302 }
303 
304 #ifdef CONFIG_PROC_FS
timerfd_show(struct seq_file * m,struct file * file)305 static void timerfd_show(struct seq_file *m, struct file *file)
306 {
307 	struct timerfd_ctx *ctx = file->private_data;
308 	struct timespec64 value, interval;
309 
310 	spin_lock_irq(&ctx->wqh.lock);
311 	value = ktime_to_timespec64(timerfd_get_remaining(ctx));
312 	interval = ktime_to_timespec64(ctx->tintv);
313 	spin_unlock_irq(&ctx->wqh.lock);
314 
315 	seq_printf(m,
316 		   "clockid: %d\n"
317 		   "ticks: %llu\n"
318 		   "settime flags: 0%o\n"
319 		   "it_value: (%llu, %llu)\n"
320 		   "it_interval: (%llu, %llu)\n",
321 		   ctx->clockid,
322 		   (unsigned long long)ctx->ticks,
323 		   ctx->settime_flags,
324 		   (unsigned long long)value.tv_sec,
325 		   (unsigned long long)value.tv_nsec,
326 		   (unsigned long long)interval.tv_sec,
327 		   (unsigned long long)interval.tv_nsec);
328 }
329 #else
330 #define timerfd_show NULL
331 #endif
332 
333 #ifdef CONFIG_CHECKPOINT_RESTORE
timerfd_ioctl(struct file * file,unsigned int cmd,unsigned long arg)334 static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
335 {
336 	struct timerfd_ctx *ctx = file->private_data;
337 	int ret = 0;
338 
339 	switch (cmd) {
340 	case TFD_IOC_SET_TICKS: {
341 		u64 ticks;
342 
343 		if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
344 			return -EFAULT;
345 		if (!ticks)
346 			return -EINVAL;
347 
348 		spin_lock_irq(&ctx->wqh.lock);
349 		if (!timerfd_canceled(ctx)) {
350 			ctx->ticks = ticks;
351 			wake_up_locked_poll(&ctx->wqh, EPOLLIN);
352 		} else
353 			ret = -ECANCELED;
354 		spin_unlock_irq(&ctx->wqh.lock);
355 		break;
356 	}
357 	default:
358 		ret = -ENOTTY;
359 		break;
360 	}
361 
362 	return ret;
363 }
364 #else
365 #define timerfd_ioctl NULL
366 #endif
367 
368 static const struct file_operations timerfd_fops = {
369 	.release	= timerfd_release,
370 	.poll		= timerfd_poll,
371 	.read		= timerfd_read,
372 	.llseek		= noop_llseek,
373 	.show_fdinfo	= timerfd_show,
374 	.unlocked_ioctl	= timerfd_ioctl,
375 };
376 
timerfd_fget(int fd,struct fd * p)377 static int timerfd_fget(int fd, struct fd *p)
378 {
379 	struct fd f = fdget(fd);
380 	if (!f.file)
381 		return -EBADF;
382 	if (f.file->f_op != &timerfd_fops) {
383 		fdput(f);
384 		return -EINVAL;
385 	}
386 	*p = f;
387 	return 0;
388 }
389 
SYSCALL_DEFINE2(timerfd_create,int,clockid,int,flags)390 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
391 {
392 	int ufd;
393 	struct timerfd_ctx *ctx;
394 
395 	/* Check the TFD_* constants for consistency.  */
396 	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
397 	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
398 
399 	if ((flags & ~TFD_CREATE_FLAGS) ||
400 	    (clockid != CLOCK_MONOTONIC &&
401 	     clockid != CLOCK_REALTIME &&
402 	     clockid != CLOCK_REALTIME_ALARM &&
403 	     clockid != CLOCK_BOOTTIME &&
404 	     clockid != CLOCK_BOOTTIME_ALARM))
405 		return -EINVAL;
406 
407 	if ((clockid == CLOCK_REALTIME_ALARM ||
408 	     clockid == CLOCK_BOOTTIME_ALARM) &&
409 	    !capable(CAP_WAKE_ALARM))
410 		return -EPERM;
411 
412 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
413 	if (!ctx)
414 		return -ENOMEM;
415 
416 	init_waitqueue_head(&ctx->wqh);
417 	spin_lock_init(&ctx->cancel_lock);
418 	ctx->clockid = clockid;
419 
420 	if (isalarm(ctx))
421 		alarm_init(&ctx->t.alarm,
422 			   ctx->clockid == CLOCK_REALTIME_ALARM ?
423 			   ALARM_REALTIME : ALARM_BOOTTIME,
424 			   timerfd_alarmproc);
425 	else
426 		hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
427 
428 	ctx->moffs = ktime_mono_to_real(0);
429 
430 	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
431 			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
432 	if (ufd < 0)
433 		kfree(ctx);
434 
435 	return ufd;
436 }
437 
do_timerfd_settime(int ufd,int flags,const struct itimerspec64 * new,struct itimerspec64 * old)438 static int do_timerfd_settime(int ufd, int flags,
439 		const struct itimerspec64 *new,
440 		struct itimerspec64 *old)
441 {
442 	struct fd f;
443 	struct timerfd_ctx *ctx;
444 	int ret;
445 
446 	if ((flags & ~TFD_SETTIME_FLAGS) ||
447 		 !itimerspec64_valid(new))
448 		return -EINVAL;
449 
450 	ret = timerfd_fget(ufd, &f);
451 	if (ret)
452 		return ret;
453 	ctx = f.file->private_data;
454 
455 	if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
456 		fdput(f);
457 		return -EPERM;
458 	}
459 
460 	timerfd_setup_cancel(ctx, flags);
461 
462 	/*
463 	 * We need to stop the existing timer before reprogramming
464 	 * it to the new values.
465 	 */
466 	for (;;) {
467 		spin_lock_irq(&ctx->wqh.lock);
468 
469 		if (isalarm(ctx)) {
470 			if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
471 				break;
472 		} else {
473 			if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
474 				break;
475 		}
476 		spin_unlock_irq(&ctx->wqh.lock);
477 
478 		if (isalarm(ctx))
479 			hrtimer_cancel_wait_running(&ctx->t.alarm.timer);
480 		else
481 			hrtimer_cancel_wait_running(&ctx->t.tmr);
482 	}
483 
484 	/*
485 	 * If the timer is expired and it's periodic, we need to advance it
486 	 * because the caller may want to know the previous expiration time.
487 	 * We do not update "ticks" and "expired" since the timer will be
488 	 * re-programmed again in the following timerfd_setup() call.
489 	 */
490 	if (ctx->expired && ctx->tintv) {
491 		if (isalarm(ctx))
492 			alarm_forward_now(&ctx->t.alarm, ctx->tintv);
493 		else
494 			hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
495 	}
496 
497 	old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
498 	old->it_interval = ktime_to_timespec64(ctx->tintv);
499 
500 	/*
501 	 * Re-program the timer to the new value ...
502 	 */
503 	ret = timerfd_setup(ctx, flags, new);
504 
505 	spin_unlock_irq(&ctx->wqh.lock);
506 	fdput(f);
507 	return ret;
508 }
509 
do_timerfd_gettime(int ufd,struct itimerspec64 * t)510 static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
511 {
512 	struct fd f;
513 	struct timerfd_ctx *ctx;
514 	int ret = timerfd_fget(ufd, &f);
515 	if (ret)
516 		return ret;
517 	ctx = f.file->private_data;
518 
519 	spin_lock_irq(&ctx->wqh.lock);
520 	if (ctx->expired && ctx->tintv) {
521 		ctx->expired = 0;
522 
523 		if (isalarm(ctx)) {
524 			ctx->ticks +=
525 				alarm_forward_now(
526 					&ctx->t.alarm, ctx->tintv) - 1;
527 			alarm_restart(&ctx->t.alarm);
528 		} else {
529 			ctx->ticks +=
530 				hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
531 				- 1;
532 			hrtimer_restart(&ctx->t.tmr);
533 		}
534 	}
535 	t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
536 	t->it_interval = ktime_to_timespec64(ctx->tintv);
537 	spin_unlock_irq(&ctx->wqh.lock);
538 	fdput(f);
539 	return 0;
540 }
541 
SYSCALL_DEFINE4(timerfd_settime,int,ufd,int,flags,const struct __kernel_itimerspec __user *,utmr,struct __kernel_itimerspec __user *,otmr)542 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
543 		const struct __kernel_itimerspec __user *, utmr,
544 		struct __kernel_itimerspec __user *, otmr)
545 {
546 	struct itimerspec64 new, old;
547 	int ret;
548 
549 	if (get_itimerspec64(&new, utmr))
550 		return -EFAULT;
551 	ret = do_timerfd_settime(ufd, flags, &new, &old);
552 	if (ret)
553 		return ret;
554 	if (otmr && put_itimerspec64(&old, otmr))
555 		return -EFAULT;
556 
557 	return ret;
558 }
559 
SYSCALL_DEFINE2(timerfd_gettime,int,ufd,struct __kernel_itimerspec __user *,otmr)560 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr)
561 {
562 	struct itimerspec64 kotmr;
563 	int ret = do_timerfd_gettime(ufd, &kotmr);
564 	if (ret)
565 		return ret;
566 	return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
567 }
568 
569 #ifdef CONFIG_COMPAT_32BIT_TIME
SYSCALL_DEFINE4(timerfd_settime32,int,ufd,int,flags,const struct old_itimerspec32 __user *,utmr,struct old_itimerspec32 __user *,otmr)570 SYSCALL_DEFINE4(timerfd_settime32, int, ufd, int, flags,
571 		const struct old_itimerspec32 __user *, utmr,
572 		struct old_itimerspec32 __user *, otmr)
573 {
574 	struct itimerspec64 new, old;
575 	int ret;
576 
577 	if (get_old_itimerspec32(&new, utmr))
578 		return -EFAULT;
579 	ret = do_timerfd_settime(ufd, flags, &new, &old);
580 	if (ret)
581 		return ret;
582 	if (otmr && put_old_itimerspec32(&old, otmr))
583 		return -EFAULT;
584 	return ret;
585 }
586 
SYSCALL_DEFINE2(timerfd_gettime32,int,ufd,struct old_itimerspec32 __user *,otmr)587 SYSCALL_DEFINE2(timerfd_gettime32, int, ufd,
588 		struct old_itimerspec32 __user *, otmr)
589 {
590 	struct itimerspec64 kotmr;
591 	int ret = do_timerfd_gettime(ufd, &kotmr);
592 	if (ret)
593 		return ret;
594 	return put_old_itimerspec32(&kotmr, otmr) ? -EFAULT : 0;
595 }
596 #endif
597