1 /*
2 * fs/timerfd.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 *
6 *
7 * Thanks to Thomas Gleixner for code reviews and useful comments.
8 *
9 */
10
11 #include <linux/alarmtimer.h>
12 #include <linux/file.h>
13 #include <linux/poll.h>
14 #include <linux/init.h>
15 #include <linux/fs.h>
16 #include <linux/sched.h>
17 #include <linux/kernel.h>
18 #include <linux/slab.h>
19 #include <linux/list.h>
20 #include <linux/spinlock.h>
21 #include <linux/time.h>
22 #include <linux/hrtimer.h>
23 #include <linux/anon_inodes.h>
24 #include <linux/timerfd.h>
25 #include <linux/syscalls.h>
26 #include <linux/compat.h>
27 #include <linux/rcupdate.h>
28
29 struct timerfd_ctx {
30 union {
31 struct hrtimer tmr;
32 struct alarm alarm;
33 } t;
34 ktime_t tintv;
35 ktime_t moffs;
36 wait_queue_head_t wqh;
37 u64 ticks;
38 int clockid;
39 short unsigned expired;
40 short unsigned settime_flags; /* to show in fdinfo */
41 struct rcu_head rcu;
42 struct list_head clist;
43 spinlock_t cancel_lock;
44 bool might_cancel;
45 };
46
47 static LIST_HEAD(cancel_list);
48 static DEFINE_SPINLOCK(cancel_lock);
49
isalarm(struct timerfd_ctx * ctx)50 static inline bool isalarm(struct timerfd_ctx *ctx)
51 {
52 return ctx->clockid == CLOCK_REALTIME_ALARM ||
53 ctx->clockid == CLOCK_BOOTTIME_ALARM;
54 }
55
56 /*
57 * This gets called when the timer event triggers. We set the "expired"
58 * flag, but we do not re-arm the timer (in case it's necessary,
59 * tintv.tv64 != 0) until the timer is accessed.
60 */
timerfd_triggered(struct timerfd_ctx * ctx)61 static void timerfd_triggered(struct timerfd_ctx *ctx)
62 {
63 unsigned long flags;
64
65 spin_lock_irqsave(&ctx->wqh.lock, flags);
66 ctx->expired = 1;
67 ctx->ticks++;
68 wake_up_locked(&ctx->wqh);
69 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
70 }
71
timerfd_tmrproc(struct hrtimer * htmr)72 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
73 {
74 struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
75 t.tmr);
76 timerfd_triggered(ctx);
77 return HRTIMER_NORESTART;
78 }
79
timerfd_alarmproc(struct alarm * alarm,ktime_t now)80 static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
81 ktime_t now)
82 {
83 struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
84 t.alarm);
85 timerfd_triggered(ctx);
86 return ALARMTIMER_NORESTART;
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 */
timerfd_clock_was_set(void)95 void timerfd_clock_was_set(void)
96 {
97 ktime_t moffs = ktime_mono_to_real((ktime_t){ .tv64 = 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.tv64 != moffs.tv64) {
107 ctx->moffs.tv64 = KTIME_MAX;
108 ctx->ticks++;
109 wake_up_locked(&ctx->wqh);
110 }
111 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
112 }
113 rcu_read_unlock();
114 }
115
__timerfd_remove_cancel(struct timerfd_ctx * ctx)116 static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
117 {
118 if (ctx->might_cancel) {
119 ctx->might_cancel = false;
120 spin_lock(&cancel_lock);
121 list_del_rcu(&ctx->clist);
122 spin_unlock(&cancel_lock);
123 }
124 }
125
timerfd_remove_cancel(struct timerfd_ctx * ctx)126 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
127 {
128 spin_lock(&ctx->cancel_lock);
129 __timerfd_remove_cancel(ctx);
130 spin_unlock(&ctx->cancel_lock);
131 }
132
timerfd_canceled(struct timerfd_ctx * ctx)133 static bool timerfd_canceled(struct timerfd_ctx *ctx)
134 {
135 if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
136 return false;
137 ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
138 return true;
139 }
140
timerfd_setup_cancel(struct timerfd_ctx * ctx,int flags)141 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
142 {
143 spin_lock(&ctx->cancel_lock);
144 if ((ctx->clockid == CLOCK_REALTIME ||
145 ctx->clockid == CLOCK_REALTIME_ALARM) &&
146 (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
147 if (!ctx->might_cancel) {
148 ctx->might_cancel = true;
149 spin_lock(&cancel_lock);
150 list_add_rcu(&ctx->clist, &cancel_list);
151 spin_unlock(&cancel_lock);
152 }
153 } else {
154 __timerfd_remove_cancel(ctx);
155 }
156 spin_unlock(&ctx->cancel_lock);
157 }
158
timerfd_get_remaining(struct timerfd_ctx * ctx)159 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
160 {
161 ktime_t remaining;
162
163 if (isalarm(ctx))
164 remaining = alarm_expires_remaining(&ctx->t.alarm);
165 else
166 remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
167
168 return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
169 }
170
timerfd_setup(struct timerfd_ctx * ctx,int flags,const struct itimerspec * ktmr)171 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
172 const struct itimerspec *ktmr)
173 {
174 enum hrtimer_mode htmode;
175 ktime_t texp;
176 int clockid = ctx->clockid;
177
178 htmode = (flags & TFD_TIMER_ABSTIME) ?
179 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
180
181 texp = timespec_to_ktime(ktmr->it_value);
182 ctx->expired = 0;
183 ctx->ticks = 0;
184 ctx->tintv = timespec_to_ktime(ktmr->it_interval);
185
186 if (isalarm(ctx)) {
187 alarm_init(&ctx->t.alarm,
188 ctx->clockid == CLOCK_REALTIME_ALARM ?
189 ALARM_REALTIME : ALARM_BOOTTIME,
190 timerfd_alarmproc);
191 } else {
192 hrtimer_init(&ctx->t.tmr, clockid, htmode);
193 hrtimer_set_expires(&ctx->t.tmr, texp);
194 ctx->t.tmr.function = timerfd_tmrproc;
195 }
196
197 if (texp.tv64 != 0) {
198 if (isalarm(ctx)) {
199 if (flags & TFD_TIMER_ABSTIME)
200 alarm_start(&ctx->t.alarm, texp);
201 else
202 alarm_start_relative(&ctx->t.alarm, texp);
203 } else {
204 hrtimer_start(&ctx->t.tmr, texp, htmode);
205 }
206
207 if (timerfd_canceled(ctx))
208 return -ECANCELED;
209 }
210
211 ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
212 return 0;
213 }
214
timerfd_release(struct inode * inode,struct file * file)215 static int timerfd_release(struct inode *inode, struct file *file)
216 {
217 struct timerfd_ctx *ctx = file->private_data;
218
219 timerfd_remove_cancel(ctx);
220
221 if (isalarm(ctx))
222 alarm_cancel(&ctx->t.alarm);
223 else
224 hrtimer_cancel(&ctx->t.tmr);
225 kfree_rcu(ctx, rcu);
226 return 0;
227 }
228
timerfd_poll(struct file * file,poll_table * wait)229 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
230 {
231 struct timerfd_ctx *ctx = file->private_data;
232 unsigned int events = 0;
233 unsigned long flags;
234
235 poll_wait(file, &ctx->wqh, wait);
236
237 spin_lock_irqsave(&ctx->wqh.lock, flags);
238 if (ctx->ticks)
239 events |= POLLIN;
240 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
241
242 return events;
243 }
244
timerfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)245 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
246 loff_t *ppos)
247 {
248 struct timerfd_ctx *ctx = file->private_data;
249 ssize_t res;
250 u64 ticks = 0;
251
252 if (count < sizeof(ticks))
253 return -EINVAL;
254 spin_lock_irq(&ctx->wqh.lock);
255 if (file->f_flags & O_NONBLOCK)
256 res = -EAGAIN;
257 else
258 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
259
260 /*
261 * If clock has changed, we do not care about the
262 * ticks and we do not rearm the timer. Userspace must
263 * reevaluate anyway.
264 */
265 if (timerfd_canceled(ctx)) {
266 ctx->ticks = 0;
267 ctx->expired = 0;
268 res = -ECANCELED;
269 }
270
271 if (ctx->ticks) {
272 ticks = ctx->ticks;
273
274 if (ctx->expired && ctx->tintv.tv64) {
275 /*
276 * If tintv.tv64 != 0, this is a periodic timer that
277 * needs to be re-armed. We avoid doing it in the timer
278 * callback to avoid DoS attacks specifying a very
279 * short timer period.
280 */
281 if (isalarm(ctx)) {
282 ticks += alarm_forward_now(
283 &ctx->t.alarm, ctx->tintv) - 1;
284 alarm_restart(&ctx->t.alarm);
285 } else {
286 ticks += hrtimer_forward_now(&ctx->t.tmr,
287 ctx->tintv) - 1;
288 hrtimer_restart(&ctx->t.tmr);
289 }
290 }
291 ctx->expired = 0;
292 ctx->ticks = 0;
293 }
294 spin_unlock_irq(&ctx->wqh.lock);
295 if (ticks)
296 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
297 return res;
298 }
299
300 #ifdef CONFIG_PROC_FS
timerfd_show(struct seq_file * m,struct file * file)301 static void timerfd_show(struct seq_file *m, struct file *file)
302 {
303 struct timerfd_ctx *ctx = file->private_data;
304 struct itimerspec t;
305
306 spin_lock_irq(&ctx->wqh.lock);
307 t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
308 t.it_interval = ktime_to_timespec(ctx->tintv);
309 spin_unlock_irq(&ctx->wqh.lock);
310
311 seq_printf(m,
312 "clockid: %d\n"
313 "ticks: %llu\n"
314 "settime flags: 0%o\n"
315 "it_value: (%llu, %llu)\n"
316 "it_interval: (%llu, %llu)\n",
317 ctx->clockid,
318 (unsigned long long)ctx->ticks,
319 ctx->settime_flags,
320 (unsigned long long)t.it_value.tv_sec,
321 (unsigned long long)t.it_value.tv_nsec,
322 (unsigned long long)t.it_interval.tv_sec,
323 (unsigned long long)t.it_interval.tv_nsec);
324 }
325 #else
326 #define timerfd_show NULL
327 #endif
328
329 #ifdef CONFIG_CHECKPOINT_RESTORE
timerfd_ioctl(struct file * file,unsigned int cmd,unsigned long arg)330 static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
331 {
332 struct timerfd_ctx *ctx = file->private_data;
333 int ret = 0;
334
335 switch (cmd) {
336 case TFD_IOC_SET_TICKS: {
337 u64 ticks;
338
339 if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
340 return -EFAULT;
341 if (!ticks)
342 return -EINVAL;
343
344 spin_lock_irq(&ctx->wqh.lock);
345 if (!timerfd_canceled(ctx)) {
346 ctx->ticks = ticks;
347 wake_up_locked(&ctx->wqh);
348 } else
349 ret = -ECANCELED;
350 spin_unlock_irq(&ctx->wqh.lock);
351 break;
352 }
353 default:
354 ret = -ENOTTY;
355 break;
356 }
357
358 return ret;
359 }
360 #else
361 #define timerfd_ioctl NULL
362 #endif
363
364 static const struct file_operations timerfd_fops = {
365 .release = timerfd_release,
366 .poll = timerfd_poll,
367 .read = timerfd_read,
368 .llseek = noop_llseek,
369 .show_fdinfo = timerfd_show,
370 .unlocked_ioctl = timerfd_ioctl,
371 };
372
timerfd_fget(int fd,struct fd * p)373 static int timerfd_fget(int fd, struct fd *p)
374 {
375 struct fd f = fdget(fd);
376 if (!f.file)
377 return -EBADF;
378 if (f.file->f_op != &timerfd_fops) {
379 fdput(f);
380 return -EINVAL;
381 }
382 *p = f;
383 return 0;
384 }
385
SYSCALL_DEFINE2(timerfd_create,int,clockid,int,flags)386 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
387 {
388 int ufd;
389 struct timerfd_ctx *ctx;
390
391 /* Check the TFD_* constants for consistency. */
392 BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
393 BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
394
395 if ((flags & ~TFD_CREATE_FLAGS) ||
396 (clockid != CLOCK_MONOTONIC &&
397 clockid != CLOCK_REALTIME &&
398 clockid != CLOCK_REALTIME_ALARM &&
399 clockid != CLOCK_BOOTTIME &&
400 clockid != CLOCK_BOOTTIME_ALARM))
401 return -EINVAL;
402
403 if (!capable(CAP_WAKE_ALARM) &&
404 (clockid == CLOCK_REALTIME_ALARM ||
405 clockid == CLOCK_BOOTTIME_ALARM))
406 return -EPERM;
407
408 ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
409 if (!ctx)
410 return -ENOMEM;
411
412 init_waitqueue_head(&ctx->wqh);
413 spin_lock_init(&ctx->cancel_lock);
414 ctx->clockid = clockid;
415
416 if (isalarm(ctx))
417 alarm_init(&ctx->t.alarm,
418 ctx->clockid == CLOCK_REALTIME_ALARM ?
419 ALARM_REALTIME : ALARM_BOOTTIME,
420 timerfd_alarmproc);
421 else
422 hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
423
424 ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
425
426 ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
427 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
428 if (ufd < 0)
429 kfree(ctx);
430
431 return ufd;
432 }
433
do_timerfd_settime(int ufd,int flags,const struct itimerspec * new,struct itimerspec * old)434 static int do_timerfd_settime(int ufd, int flags,
435 const struct itimerspec *new,
436 struct itimerspec *old)
437 {
438 struct fd f;
439 struct timerfd_ctx *ctx;
440 int ret;
441
442 if ((flags & ~TFD_SETTIME_FLAGS) ||
443 !timespec_valid(&new->it_value) ||
444 !timespec_valid(&new->it_interval))
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 (!capable(CAP_WAKE_ALARM) && isalarm(ctx)) {
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.tv64) {
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_timespec(timerfd_get_remaining(ctx));
491 old->it_interval = ktime_to_timespec(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 itimerspec * t)503 static int do_timerfd_gettime(int ufd, struct itimerspec *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.tv64) {
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_timespec(timerfd_get_remaining(ctx));
529 t->it_interval = ktime_to_timespec(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 itimerspec __user *,utmr,struct itimerspec __user *,otmr)535 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
536 const struct itimerspec __user *, utmr,
537 struct itimerspec __user *, otmr)
538 {
539 struct itimerspec new, old;
540 int ret;
541
542 if (copy_from_user(&new, utmr, sizeof(new)))
543 return -EFAULT;
544 ret = do_timerfd_settime(ufd, flags, &new, &old);
545 if (ret)
546 return ret;
547 if (otmr && copy_to_user(otmr, &old, sizeof(old)))
548 return -EFAULT;
549
550 return ret;
551 }
552
SYSCALL_DEFINE2(timerfd_gettime,int,ufd,struct itimerspec __user *,otmr)553 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
554 {
555 struct itimerspec kotmr;
556 int ret = do_timerfd_gettime(ufd, &kotmr);
557 if (ret)
558 return ret;
559 return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
560 }
561
562 #ifdef CONFIG_COMPAT
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 itimerspec new, old;
568 int ret;
569
570 if (get_compat_itimerspec(&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_itimerspec(otmr, &old))
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 itimerspec kotmr;
584 int ret = do_timerfd_gettime(ufd, &kotmr);
585 if (ret)
586 return ret;
587 return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
588 }
589 #endif
590