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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * fs/timerfd.c
4 *
5 * Copyright (C) 2007 Davide Libenzi <[email protected]>
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
58static void __timerfd_triggered(struct timerfd_ctx *ctx)
59{
60 lockdep_assert_held(&ctx->wqh.lock);
61
62 ctx->expired = 1;
63 ctx->ticks++;
64 wake_up_locked_poll(&ctx->wqh, EPOLLIN);
65}
66
67/*
68 * This gets called when the timer event triggers. We set the "expired"
69 * flag, but we do not re-arm the timer (in case it's necessary,
70 * tintv != 0) until the timer is accessed.
71 */
72static void timerfd_triggered(struct timerfd_ctx *ctx)
73{
74 guard(spinlock_irqsave)(&ctx->wqh.lock);
75 __timerfd_triggered(ctx);
76}
77
78static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
79{
80 struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
81 t.tmr);
82 timerfd_triggered(ctx);
83 return HRTIMER_NORESTART;
84}
85
86static void timerfd_alarmproc(struct alarm *alarm, ktime_t now)
87{
88 struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
89 t.alarm);
90 timerfd_triggered(ctx);
91}
92
93/*
94 * Called when the clock was set to cancel the timers in the cancel
95 * list. This will wake up processes waiting on these timers. The
96 * wake-up requires ctx->ticks to be non zero, therefore we increment
97 * it before calling wake_up_locked().
98 */
99void timerfd_clock_was_set(void)
100{
101 ktime_t moffs = ktime_mono_to_real(0);
102 struct timerfd_ctx *ctx;
103 unsigned long flags;
104
105 rcu_read_lock();
106 list_for_each_entry_rcu(ctx, &cancel_list, clist) {
107 if (!ctx->might_cancel)
108 continue;
109 spin_lock_irqsave(&ctx->wqh.lock, flags);
110 if (ctx->moffs != moffs) {
111 ctx->moffs = KTIME_MAX;
112 ctx->ticks++;
113 wake_up_locked_poll(&ctx->wqh, EPOLLIN);
114 }
115 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
116 }
117 rcu_read_unlock();
118}
119
120static void timerfd_resume_work(struct work_struct *work)
121{
122 timerfd_clock_was_set();
123}
124
125static DECLARE_WORK(timerfd_work, timerfd_resume_work);
126
127/*
128 * Invoked from timekeeping_resume(). Defer the actual update to work so
129 * timerfd_clock_was_set() runs in task context.
130 */
131void timerfd_resume(void)
132{
133 schedule_work(&timerfd_work);
134}
135
136static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
137{
138 if (ctx->might_cancel) {
139 ctx->might_cancel = false;
140 spin_lock(&cancel_lock);
141 list_del_rcu(&ctx->clist);
142 spin_unlock(&cancel_lock);
143 }
144}
145
146static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
147{
148 spin_lock(&ctx->cancel_lock);
149 __timerfd_remove_cancel(ctx);
150 spin_unlock(&ctx->cancel_lock);
151}
152
153static bool timerfd_canceled(struct timerfd_ctx *ctx)
154{
155 if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
156 return false;
157 ctx->moffs = ktime_mono_to_real(0);
158 return true;
159}
160
161static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
162{
163 spin_lock(&ctx->cancel_lock);
164 if ((ctx->clockid == CLOCK_REALTIME ||
165 ctx->clockid == CLOCK_REALTIME_ALARM) &&
166 (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
167 if (!ctx->might_cancel) {
168 ctx->might_cancel = true;
169 spin_lock(&cancel_lock);
170 list_add_rcu(&ctx->clist, &cancel_list);
171 spin_unlock(&cancel_lock);
172 }
173 } else {
174 __timerfd_remove_cancel(ctx);
175 }
176 spin_unlock(&ctx->cancel_lock);
177}
178
179static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
180{
181 ktime_t remaining;
182
183 if (isalarm(ctx))
184 remaining = alarm_expires_remaining(&ctx->t.alarm);
185 else
186 remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
187
188 return remaining < 0 ? 0: remaining;
189}
190
191static void timerfd_alarm_start(struct timerfd_ctx *ctx, ktime_t exp, bool relative)
192{
193 /* Start the timer. If it's expired already, handle the callback. */
194 if (!alarm_start_timer(&ctx->t.alarm, exp, relative))
195 __timerfd_triggered(ctx);
196}
197
198static u64 timerfd_alarm_restart(struct timerfd_ctx *ctx)
199{
200 /* -1 to account for ctx->ticks++ in __timerfd_triggered() */
201 u64 ticks = alarm_forward_now(&ctx->t.alarm, ctx->tintv) - 1;
202
203 timerfd_alarm_start(ctx, alarm_get_expires(&ctx->t.alarm), false);
204 return ticks;
205}
206
207static void timerfd_hrtimer_start(struct timerfd_ctx *ctx, ktime_t exp,
208 const enum hrtimer_mode mode)
209{
210 /* Start the timer. If it's expired already, handle the callback. */
211 if (!hrtimer_start_range_ns_user(&ctx->t.tmr, exp, 0, mode))
212 __timerfd_triggered(ctx);
213}
214
215static u64 timerfd_hrtimer_restart(struct timerfd_ctx *ctx)
216{
217 /* -1 to account for ctx->ticks++ in __timerfd_triggered() */
218 u64 ticks = hrtimer_forward_now(&ctx->t.tmr, ctx->tintv) - 1;
219
220 timerfd_hrtimer_start(ctx, hrtimer_get_expires(&ctx->t.tmr), HRTIMER_MODE_ABS);
221 return ticks;
222}
223
224static u64 timerfd_restart(struct timerfd_ctx *ctx)
225{
226 if (isalarm(ctx))
227 return timerfd_alarm_restart(ctx);
228 return timerfd_hrtimer_restart(ctx);
229}
230
231static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
232 const struct itimerspec64 *ktmr)
233{
234 int clockid = ctx->clockid;
235 enum hrtimer_mode htmode;
236 ktime_t texp;
237
238 htmode = (flags & TFD_TIMER_ABSTIME) ? HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
239
240 texp = timespec64_to_ktime(ktmr->it_value);
241 ctx->expired = 0;
242 ctx->ticks = 0;
243 ctx->tintv = timespec64_to_ktime(ktmr->it_interval);
244
245 if (isalarm(ctx)) {
246 alarm_init(&ctx->t.alarm,
247 ctx->clockid == CLOCK_REALTIME_ALARM ?
248 ALARM_REALTIME : ALARM_BOOTTIME,
249 timerfd_alarmproc);
250 } else {
251 hrtimer_setup(&ctx->t.tmr, timerfd_tmrproc, clockid, htmode);
252 }
253
254 if (texp != 0) {
255 if (flags & TFD_TIMER_ABSTIME)
256 texp = timens_ktime_to_host(clockid, texp);
257 if (isalarm(ctx))
258 timerfd_alarm_start(ctx, texp, !(flags & TFD_TIMER_ABSTIME));
259 else
260 timerfd_hrtimer_start(ctx, texp, htmode);
261
262 if (timerfd_canceled(ctx))
263 return -ECANCELED;
264 }
265
266 ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
267 return 0;
268}
269
270static int timerfd_release(struct inode *inode, struct file *file)
271{
272 struct timerfd_ctx *ctx = file->private_data;
273
274 timerfd_remove_cancel(ctx);
275
276 if (isalarm(ctx))
277 alarm_cancel(&ctx->t.alarm);
278 else
279 hrtimer_cancel(&ctx->t.tmr);
280 kfree_rcu(ctx, rcu);
281 return 0;
282}
283
284static __poll_t timerfd_poll(struct file *file, poll_table *wait)
285{
286 struct timerfd_ctx *ctx = file->private_data;
287 __poll_t events = 0;
288 unsigned long flags;
289
290 poll_wait(file, &ctx->wqh, wait);
291
292 spin_lock_irqsave(&ctx->wqh.lock, flags);
293 if (ctx->ticks)
294 events |= EPOLLIN;
295 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
296
297 return events;
298}
299
300static ssize_t timerfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
301{
302 struct file *file = iocb->ki_filp;
303 struct timerfd_ctx *ctx = file->private_data;
304 ssize_t res;
305 u64 ticks = 0;
306
307 if (iov_iter_count(to) < sizeof(ticks))
308 return -EINVAL;
309
310 spin_lock_irq(&ctx->wqh.lock);
311 if (file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT)
312 res = -EAGAIN;
313 else
314 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
315
316 /*
317 * If clock has changed, we do not care about the
318 * ticks and we do not rearm the timer. Userspace must
319 * reevaluate anyway.
320 */
321 if (timerfd_canceled(ctx)) {
322 ctx->ticks = 0;
323 ctx->expired = 0;
324 res = -ECANCELED;
325 }
326
327 if (ctx->ticks) {
328 unsigned int expired = ctx->expired;
329
330 ticks = ctx->ticks;
331 ctx->expired = 0;
332 ctx->ticks = 0;
333
334 /*
335 * If tintv != 0, this is a periodic timer that needs to be
336 * re-armed. We avoid doing it in the timer callback to avoid
337 * DoS attacks specifying a very short timer period.
338 */
339 if (expired && ctx->tintv)
340 ticks += timerfd_restart(ctx);
341 }
342 spin_unlock_irq(&ctx->wqh.lock);
343 if (ticks) {
344 res = copy_to_iter(&ticks, sizeof(ticks), to);
345 if (!res)
346 res = -EFAULT;
347 }
348 return res;
349}
350
351#ifdef CONFIG_PROC_FS
352static void timerfd_show(struct seq_file *m, struct file *file)
353{
354 struct timerfd_ctx *ctx = file->private_data;
355 struct timespec64 value, interval;
356
357 spin_lock_irq(&ctx->wqh.lock);
358 value = ktime_to_timespec64(timerfd_get_remaining(ctx));
359 interval = ktime_to_timespec64(ctx->tintv);
360 spin_unlock_irq(&ctx->wqh.lock);
361
362 seq_printf(m,
363 "clockid: %d\n"
364 "ticks: %llu\n"
365 "settime flags: 0%o\n"
366 "it_value: (%llu, %llu)\n"
367 "it_interval: (%llu, %llu)\n",
368 ctx->clockid,
369 (unsigned long long)ctx->ticks,
370 ctx->settime_flags,
371 (unsigned long long)value.tv_sec,
372 (unsigned long long)value.tv_nsec,
373 (unsigned long long)interval.tv_sec,
374 (unsigned long long)interval.tv_nsec);
375}
376#else
377#define timerfd_show NULL
378#endif
379
380#ifdef CONFIG_CHECKPOINT_RESTORE
381static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
382{
383 struct timerfd_ctx *ctx = file->private_data;
384 int ret = 0;
385
386 switch (cmd) {
387 case TFD_IOC_SET_TICKS: {
388 u64 ticks;
389
390 if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
391 return -EFAULT;
392 if (!ticks)
393 return -EINVAL;
394
395 spin_lock_irq(&ctx->wqh.lock);
396 if (!timerfd_canceled(ctx)) {
397 ctx->ticks = ticks;
398 wake_up_locked_poll(&ctx->wqh, EPOLLIN);
399 } else
400 ret = -ECANCELED;
401 spin_unlock_irq(&ctx->wqh.lock);
402 break;
403 }
404 default:
405 ret = -ENOTTY;
406 break;
407 }
408
409 return ret;
410}
411#else
412#define timerfd_ioctl NULL
413#endif
414
415static const struct file_operations timerfd_fops = {
416 .release = timerfd_release,
417 .poll = timerfd_poll,
418 .read_iter = timerfd_read_iter,
419 .llseek = noop_llseek,
420 .show_fdinfo = timerfd_show,
421 .unlocked_ioctl = timerfd_ioctl,
422};
423
424SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
425{
426 struct timerfd_ctx *ctx __free(kfree) = NULL;
427 int ret;
428
429 /* Check the TFD_* constants for consistency. */
430 BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
431 BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
432
433 if ((flags & ~TFD_CREATE_FLAGS) ||
434 (clockid != CLOCK_MONOTONIC &&
435 clockid != CLOCK_REALTIME &&
436 clockid != CLOCK_REALTIME_ALARM &&
437 clockid != CLOCK_BOOTTIME &&
438 clockid != CLOCK_BOOTTIME_ALARM))
439 return -EINVAL;
440
441 if ((clockid == CLOCK_REALTIME_ALARM ||
442 clockid == CLOCK_BOOTTIME_ALARM) &&
443 !capable(CAP_WAKE_ALARM))
444 return -EPERM;
445
446 ctx = kzalloc_obj(*ctx);
447 if (!ctx)
448 return -ENOMEM;
449
450 init_waitqueue_head(&ctx->wqh);
451 spin_lock_init(&ctx->cancel_lock);
452 ctx->clockid = clockid;
453
454 if (isalarm(ctx))
455 alarm_init(&ctx->t.alarm,
456 ctx->clockid == CLOCK_REALTIME_ALARM ?
457 ALARM_REALTIME : ALARM_BOOTTIME,
458 timerfd_alarmproc);
459 else
460 hrtimer_setup(&ctx->t.tmr, timerfd_tmrproc, clockid, HRTIMER_MODE_ABS);
461
462 ctx->moffs = ktime_mono_to_real(0);
463
464 ret = FD_ADD(flags & TFD_SHARED_FCNTL_FLAGS,
465 anon_inode_getfile_fmode("[timerfd]", &timerfd_fops, ctx,
466 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS),
467 FMODE_NOWAIT));
468 if (ret >= 0)
469 retain_and_null_ptr(ctx);
470 return ret;
471}
472
473static int do_timerfd_settime(int ufd, int flags,
474 const struct itimerspec64 *new,
475 struct itimerspec64 *old)
476{
477 struct timerfd_ctx *ctx;
478 int ret;
479
480 if ((flags & ~TFD_SETTIME_FLAGS) ||
481 !itimerspec64_valid(new))
482 return -EINVAL;
483
484 CLASS(fd, f)(ufd);
485 if (fd_empty(f))
486 return -EBADF;
487
488 if (fd_file(f)->f_op != &timerfd_fops)
489 return -EINVAL;
490
491 ctx = fd_file(f)->private_data;
492
493 if (isalarm(ctx) && !capable(CAP_WAKE_ALARM))
494 return -EPERM;
495
496 timerfd_setup_cancel(ctx, flags);
497
498 /*
499 * We need to stop the existing timer before reprogramming
500 * it to the new values.
501 */
502 for (;;) {
503 spin_lock_irq(&ctx->wqh.lock);
504
505 if (isalarm(ctx)) {
506 if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
507 break;
508 } else {
509 if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
510 break;
511 }
512 spin_unlock_irq(&ctx->wqh.lock);
513
514 if (isalarm(ctx))
515 hrtimer_cancel_wait_running(&ctx->t.alarm.timer);
516 else
517 hrtimer_cancel_wait_running(&ctx->t.tmr);
518 }
519
520 /*
521 * If the timer is expired and it's periodic, we need to advance it
522 * because the caller may want to know the previous expiration time.
523 * We do not update "ticks" and "expired" since the timer will be
524 * re-programmed again in the following timerfd_setup() call.
525 */
526 if (ctx->expired && ctx->tintv) {
527 if (isalarm(ctx))
528 alarm_forward_now(&ctx->t.alarm, ctx->tintv);
529 else
530 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
531 }
532
533 old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
534 old->it_interval = ktime_to_timespec64(ctx->tintv);
535
536 /*
537 * Re-program the timer to the new value ...
538 */
539 ret = timerfd_setup(ctx, flags, new);
540
541 spin_unlock_irq(&ctx->wqh.lock);
542 return ret;
543}
544
545static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
546{
547 struct timerfd_ctx *ctx;
548 CLASS(fd, f)(ufd);
549
550 if (fd_empty(f))
551 return -EBADF;
552 if (fd_file(f)->f_op != &timerfd_fops)
553 return -EINVAL;
554 ctx = fd_file(f)->private_data;
555
556 spin_lock_irq(&ctx->wqh.lock);
557 if (ctx->expired && ctx->tintv) {
558 ctx->expired = 0;
559 ctx->ticks += timerfd_restart(ctx);
560 }
561 t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
562 t->it_interval = ktime_to_timespec64(ctx->tintv);
563 spin_unlock_irq(&ctx->wqh.lock);
564 return 0;
565}
566
567SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
568 const struct __kernel_itimerspec __user *, utmr,
569 struct __kernel_itimerspec __user *, otmr)
570{
571 struct itimerspec64 new, old;
572 int ret;
573
574 if (get_itimerspec64(&new, utmr))
575 return -EFAULT;
576 ret = do_timerfd_settime(ufd, flags, &new, &old);
577 if (ret)
578 return ret;
579 if (otmr && put_itimerspec64(&old, otmr))
580 return -EFAULT;
581
582 return ret;
583}
584
585SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr)
586{
587 struct itimerspec64 kotmr;
588 int ret = do_timerfd_gettime(ufd, &kotmr);
589 if (ret)
590 return ret;
591 return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
592}
593
594#ifdef CONFIG_COMPAT_32BIT_TIME
595SYSCALL_DEFINE4(timerfd_settime32, int, ufd, int, flags,
596 const struct old_itimerspec32 __user *, utmr,
597 struct old_itimerspec32 __user *, otmr)
598{
599 struct itimerspec64 new, old;
600 int ret;
601
602 if (get_old_itimerspec32(&new, utmr))
603 return -EFAULT;
604 ret = do_timerfd_settime(ufd, flags, &new, &old);
605 if (ret)
606 return ret;
607 if (otmr && put_old_itimerspec32(&old, otmr))
608 return -EFAULT;
609 return ret;
610}
611
612SYSCALL_DEFINE2(timerfd_gettime32, int, ufd,
613 struct old_itimerspec32 __user *, otmr)
614{
615 struct itimerspec64 kotmr;
616 int ret = do_timerfd_gettime(ufd, &kotmr);
617 if (ret)
618 return ret;
619 return put_old_itimerspec32(&kotmr, otmr) ? -EFAULT : 0;
620}
621#endif