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TOMOYO Linux Cross Reference
Linux/fs/timerfd.c

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  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 
 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 != 0) until the timer is accessed.
 60  */
 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 
 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 
 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  */
 95 void timerfd_clock_was_set(void)
 96 {
 97         ktime_t moffs = ktime_mono_to_real(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(&ctx->wqh);
110                 }
111                 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
112         }
113         rcu_read_unlock();
114 }
115 
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 
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 
133 static bool timerfd_canceled(struct timerfd_ctx *ctx)
134 {
135         if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
136                 return false;
137         ctx->moffs = ktime_mono_to_real(0);
138         return true;
139 }
140 
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 
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 < 0 ? 0: remaining;
169 }
170 
171 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
172                          const struct itimerspec64 *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 = timespec64_to_ktime(ktmr->it_value);
182         ctx->expired = 0;
183         ctx->ticks = 0;
184         ctx->tintv = timespec64_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 != 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 
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 
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 
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) {
275                         /*
276                          * If tintv != 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
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
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 
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 
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 ((clockid == CLOCK_REALTIME_ALARM ||
404              clockid == CLOCK_BOOTTIME_ALARM) &&
405             !capable(CAP_WAKE_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(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 
434 static int do_timerfd_settime(int ufd, int flags, 
435                 const struct itimerspec64 *new,
436                 struct itimerspec64 *old)
437 {
438         struct fd f;
439         struct timerfd_ctx *ctx;
440         int ret;
441 
442         if ((flags & ~TFD_SETTIME_FLAGS) ||
443                  !itimerspec64_valid(new))
444                 return -EINVAL;
445 
446         ret = timerfd_fget(ufd, &f);
447         if (ret)
448                 return ret;
449         ctx = f.file->private_data;
450 
451         if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
452                 fdput(f);
453                 return -EPERM;
454         }
455 
456         timerfd_setup_cancel(ctx, flags);
457 
458         /*
459          * We need to stop the existing timer before reprogramming
460          * it to the new values.
461          */
462         for (;;) {
463                 spin_lock_irq(&ctx->wqh.lock);
464 
465                 if (isalarm(ctx)) {
466                         if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
467                                 break;
468                 } else {
469                         if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
470                                 break;
471                 }
472                 spin_unlock_irq(&ctx->wqh.lock);
473                 cpu_relax();
474         }
475 
476         /*
477          * If the timer is expired and it's periodic, we need to advance it
478          * because the caller may want to know the previous expiration time.
479          * We do not update "ticks" and "expired" since the timer will be
480          * re-programmed again in the following timerfd_setup() call.
481          */
482         if (ctx->expired && ctx->tintv) {
483                 if (isalarm(ctx))
484                         alarm_forward_now(&ctx->t.alarm, ctx->tintv);
485                 else
486                         hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
487         }
488 
489         old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
490         old->it_interval = ktime_to_timespec64(ctx->tintv);
491 
492         /*
493          * Re-program the timer to the new value ...
494          */
495         ret = timerfd_setup(ctx, flags, new);
496 
497         spin_unlock_irq(&ctx->wqh.lock);
498         fdput(f);
499         return ret;
500 }
501 
502 static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
503 {
504         struct fd f;
505         struct timerfd_ctx *ctx;
506         int ret = timerfd_fget(ufd, &f);
507         if (ret)
508                 return ret;
509         ctx = f.file->private_data;
510 
511         spin_lock_irq(&ctx->wqh.lock);
512         if (ctx->expired && ctx->tintv) {
513                 ctx->expired = 0;
514 
515                 if (isalarm(ctx)) {
516                         ctx->ticks +=
517                                 alarm_forward_now(
518                                         &ctx->t.alarm, ctx->tintv) - 1;
519                         alarm_restart(&ctx->t.alarm);
520                 } else {
521                         ctx->ticks +=
522                                 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
523                                 - 1;
524                         hrtimer_restart(&ctx->t.tmr);
525                 }
526         }
527         t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
528         t->it_interval = ktime_to_timespec64(ctx->tintv);
529         spin_unlock_irq(&ctx->wqh.lock);
530         fdput(f);
531         return 0;
532 }
533 
534 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
535                 const struct itimerspec __user *, utmr,
536                 struct itimerspec __user *, otmr)
537 {
538         struct itimerspec64 new, old;
539         int ret;
540 
541         if (get_itimerspec64(&new, utmr))
542                 return -EFAULT;
543         ret = do_timerfd_settime(ufd, flags, &new, &old);
544         if (ret)
545                 return ret;
546         if (otmr && put_itimerspec64(&old, otmr))
547                 return -EFAULT;
548 
549         return ret;
550 }
551 
552 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
553 {
554         struct itimerspec64 kotmr;
555         int ret = do_timerfd_gettime(ufd, &kotmr);
556         if (ret)
557                 return ret;
558         return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
559 }
560 
561 #ifdef CONFIG_COMPAT
562 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
563                 const struct compat_itimerspec __user *, utmr,
564                 struct compat_itimerspec __user *, otmr)
565 {
566         struct itimerspec64 new, old;
567         int ret;
568 
569         if (get_compat_itimerspec64(&new, utmr))
570                 return -EFAULT;
571         ret = do_timerfd_settime(ufd, flags, &new, &old);
572         if (ret)
573                 return ret;
574         if (otmr && put_compat_itimerspec64(&old, otmr))
575                 return -EFAULT;
576         return ret;
577 }
578 
579 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
580                 struct compat_itimerspec __user *, otmr)
581 {
582         struct itimerspec64 kotmr;
583         int ret = do_timerfd_gettime(ufd, &kotmr);
584         if (ret)
585                 return ret;
586         return put_compat_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
587 }
588 #endif
589 

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