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