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(lock: &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(mono: 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(lock: &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(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(lock: &cancel_lock);
139 list_del_rcu(entry: &ctx->clist);
140 spin_unlock(lock: &cancel_lock);
141 }
142}
143
144static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
145{
146 spin_lock(lock: &ctx->cancel_lock);
147 __timerfd_remove_cancel(ctx);
148 spin_unlock(lock: &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(mono: 0);
156 return true;
157}
158
159static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
160{
161 spin_lock(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(lock: &cancel_lock);
168 list_add_rcu(new: &ctx->clist, head: &cancel_list);
169 spin_unlock(lock: &cancel_lock);
170 }
171 } else {
172 __timerfd_remove_cancel(ctx);
173 }
174 spin_unlock(lock: &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(alarm: &ctx->t.alarm);
183 else
184 remaining = hrtimer_expires_remaining_adjusted(timer: &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(ts: ktmr->it_value);
200 ctx->expired = 0;
201 ctx->ticks = 0;
202 ctx->tintv = timespec64_to_ktime(ts: ktmr->it_interval);
203
204 if (isalarm(ctx)) {
205 alarm_init(alarm: &ctx->t.alarm,
206 type: ctx->clockid == CLOCK_REALTIME_ALARM ?
207 ALARM_REALTIME : ALARM_BOOTTIME,
208 function: timerfd_alarmproc);
209 } else {
210 hrtimer_init(timer: &ctx->t.tmr, which_clock: clockid, mode: htmode);
211 hrtimer_set_expires(timer: &ctx->t.tmr, time: 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, tim: texp);
218 if (isalarm(ctx)) {
219 if (flags & TFD_TIMER_ABSTIME)
220 alarm_start(alarm: &ctx->t.alarm, start: texp);
221 else
222 alarm_start_relative(alarm: &ctx->t.alarm, start: texp);
223 } else {
224 hrtimer_start(timer: &ctx->t.tmr, tim: texp, mode: 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(alarm: &ctx->t.alarm);
243 else
244 hrtimer_cancel(timer: &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(filp: file, wait_address: &ctx->wqh, p: wait);
256
257 spin_lock_irqsave(&ctx->wqh.lock, flags);
258 if (ctx->ticks)
259 events |= EPOLLIN;
260 spin_unlock_irqrestore(lock: &ctx->wqh.lock, flags);
261
262 return events;
263}
264
265static 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(lock: &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 alarm: &ctx->t.alarm, interval: ctx->tintv) - 1;
304 alarm_restart(alarm: &ctx->t.alarm);
305 } else {
306 ticks += hrtimer_forward_now(timer: &ctx->t.tmr,
307 interval: ctx->tintv) - 1;
308 hrtimer_restart(timer: &ctx->t.tmr);
309 }
310 }
311 ctx->expired = 0;
312 ctx->ticks = 0;
313 }
314 spin_unlock_irq(lock: &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
321static 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(lock: &ctx->wqh.lock);
327 value = ktime_to_timespec64(timerfd_get_remaining(ctx));
328 interval = ktime_to_timespec64(ctx->tintv);
329 spin_unlock_irq(lock: &ctx->wqh.lock);
330
331 seq_printf(m,
332 fmt: "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
350static 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(to: &ticks, from: (u64 __user *)arg, n: sizeof(ticks)))
360 return -EFAULT;
361 if (!ticks)
362 return -EINVAL;
363
364 spin_lock_irq(lock: &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(lock: &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
384static 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
393static 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(fd: f);
400 return -EINVAL;
401 }
402 *p = f;
403 return 0;
404}
405
406SYSCALL_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(size: 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(alarm: &ctx->t.alarm,
438 type: ctx->clockid == CLOCK_REALTIME_ALARM ?
439 ALARM_REALTIME : ALARM_BOOTTIME,
440 function: timerfd_alarmproc);
441 else
442 hrtimer_init(timer: &ctx->t.tmr, which_clock: clockid, mode: HRTIMER_MODE_ABS);
443
444 ctx->moffs = ktime_mono_to_real(mono: 0);
445
446 ufd = anon_inode_getfd(name: "[timerfd]", fops: &timerfd_fops, priv: ctx,
447 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
448 if (ufd < 0)
449 kfree(objp: ctx);
450
451 return ufd;
452}
453
454static 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(its: new))
464 return -EINVAL;
465
466 ret = timerfd_fget(fd: ufd, p: &f);
467 if (ret)
468 return ret;
469 ctx = f.file->private_data;
470
471 if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
472 fdput(fd: 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(lock: &ctx->wqh.lock);
484
485 if (isalarm(ctx)) {
486 if (alarm_try_to_cancel(alarm: &ctx->t.alarm) >= 0)
487 break;
488 } else {
489 if (hrtimer_try_to_cancel(timer: &ctx->t.tmr) >= 0)
490 break;
491 }
492 spin_unlock_irq(lock: &ctx->wqh.lock);
493
494 if (isalarm(ctx))
495 hrtimer_cancel_wait_running(timer: &ctx->t.alarm.timer);
496 else
497 hrtimer_cancel_wait_running(timer: &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(alarm: &ctx->t.alarm, interval: ctx->tintv);
509 else
510 hrtimer_forward_now(timer: &ctx->t.tmr, interval: 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, ktmr: new);
520
521 spin_unlock_irq(lock: &ctx->wqh.lock);
522 fdput(fd: f);
523 return ret;
524}
525
526static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
527{
528 struct fd f;
529 struct timerfd_ctx *ctx;
530 int ret = timerfd_fget(fd: ufd, p: &f);
531 if (ret)
532 return ret;
533 ctx = f.file->private_data;
534
535 spin_lock_irq(lock: &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 alarm: &ctx->t.alarm, interval: ctx->tintv) - 1;
543 alarm_restart(alarm: &ctx->t.alarm);
544 } else {
545 ctx->ticks +=
546 hrtimer_forward_now(timer: &ctx->t.tmr, interval: ctx->tintv)
547 - 1;
548 hrtimer_restart(timer: &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(lock: &ctx->wqh.lock);
554 fdput(fd: f);
555 return 0;
556}
557
558SYSCALL_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(it: &new, uit: utmr))
566 return -EFAULT;
567 ret = do_timerfd_settime(ufd, flags, new: &new, old: &old);
568 if (ret)
569 return ret;
570 if (otmr && put_itimerspec64(it: &old, uit: otmr))
571 return -EFAULT;
572
573 return ret;
574}
575
576SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr)
577{
578 struct itimerspec64 kotmr;
579 int ret = do_timerfd_gettime(ufd, t: &kotmr);
580 if (ret)
581 return ret;
582 return put_itimerspec64(it: &kotmr, uit: otmr) ? -EFAULT : 0;
583}
584
585#ifdef CONFIG_COMPAT_32BIT_TIME
586SYSCALL_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(its: &new, uits: utmr))
594 return -EFAULT;
595 ret = do_timerfd_settime(ufd, flags, new: &new, old: &old);
596 if (ret)
597 return ret;
598 if (otmr && put_old_itimerspec32(its: &old, uits: otmr))
599 return -EFAULT;
600 return ret;
601}
602
603SYSCALL_DEFINE2(timerfd_gettime32, int, ufd,
604 struct old_itimerspec32 __user *, otmr)
605{
606 struct itimerspec64 kotmr;
607 int ret = do_timerfd_gettime(ufd, t: &kotmr);
608 if (ret)
609 return ret;
610 return put_old_itimerspec32(its: &kotmr, uits: otmr) ? -EFAULT : 0;
611}
612#endif
613

source code of linux/fs/timerfd.c