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 31 struct 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 49 static LIST_HEAD(cancel_list); 50 static DEFINE_SPINLOCK(cancel_lock); 51 52 static 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 */ 63 static 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(&ctx->wqh.lock, flags); 72 } 73 74 static 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 82 static 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 */ 97 void timerfd_clock_was_set(void) 98 { 99 ktime_t moffs = ktime_mono_to_real(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(&ctx->wqh.lock, flags); 114 } 115 rcu_read_unlock(); 116 } 117 118 static void timerfd_resume_work(struct work_struct *work) 119 { 120 timerfd_clock_was_set(); 121 } 122 123 static 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 */ 129 void timerfd_resume(void) 130 { 131 schedule_work(&timerfd_work); 132 } 133 134 static void __timerfd_remove_cancel(struct timerfd_ctx *ctx) 135 { 136 if (ctx->might_cancel) { 137 ctx->might_cancel = false; 138 spin_lock(&cancel_lock); 139 list_del_rcu(&ctx->clist); 140 spin_unlock(&cancel_lock); 141 } 142 } 143 144 static void timerfd_remove_cancel(struct timerfd_ctx *ctx) 145 { 146 spin_lock(&ctx->cancel_lock); 147 __timerfd_remove_cancel(ctx); 148 spin_unlock(&ctx->cancel_lock); 149 } 150 151 static 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(0); 156 return true; 157 } 158 159 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags) 160 { 161 spin_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(&cancel_lock); 168 list_add_rcu(&ctx->clist, &cancel_list); 169 spin_unlock(&cancel_lock); 170 } 171 } else { 172 __timerfd_remove_cancel(ctx); 173 } 174 spin_unlock(&ctx->cancel_lock); 175 } 176 177 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx) 178 { 179 ktime_t remaining; 180 181 if (isalarm(ctx)) 182 remaining = alarm_expires_remaining(&ctx->t.alarm); 183 else 184 remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr); 185 186 return remaining < 0 ? 0: remaining; 187 } 188 189 static 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(ktmr->it_value); 200 ctx->expired = 0; 201 ctx->ticks = 0; 202 ctx->tintv = timespec64_to_ktime(ktmr->it_interval); 203 204 if (isalarm(ctx)) { 205 alarm_init(&ctx->t.alarm, 206 ctx->clockid == CLOCK_REALTIME_ALARM ? 207 ALARM_REALTIME : ALARM_BOOTTIME, 208 timerfd_alarmproc); 209 } else { 210 hrtimer_init(&ctx->t.tmr, clockid, htmode); 211 hrtimer_set_expires(&ctx->t.tmr, 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, texp); 218 if (isalarm(ctx)) { 219 if (flags & TFD_TIMER_ABSTIME) 220 alarm_start(&ctx->t.alarm, texp); 221 else 222 alarm_start_relative(&ctx->t.alarm, texp); 223 } else { 224 hrtimer_start(&ctx->t.tmr, texp, 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 } 234 235 static 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(&ctx->t.alarm); 243 else 244 hrtimer_cancel(&ctx->t.tmr); 245 kfree_rcu(ctx, rcu); 246 return 0; 247 } 248 249 static __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(file, &ctx->wqh, wait); 256 257 spin_lock_irqsave(&ctx->wqh.lock, flags); 258 if (ctx->ticks) 259 events |= EPOLLIN; 260 spin_unlock_irqrestore(&ctx->wqh.lock, flags); 261 262 return events; 263 } 264 265 static 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(&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 &ctx->t.alarm, ctx->tintv) - 1; 304 alarm_restart(&ctx->t.alarm); 305 } else { 306 ticks += hrtimer_forward_now(&ctx->t.tmr, 307 ctx->tintv) - 1; 308 hrtimer_restart(&ctx->t.tmr); 309 } 310 } 311 ctx->expired = 0; 312 ctx->ticks = 0; 313 } 314 spin_unlock_irq(&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 321 static 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(&ctx->wqh.lock); 327 value = ktime_to_timespec64(timerfd_get_remaining(ctx)); 328 interval = ktime_to_timespec64(ctx->tintv); 329 spin_unlock_irq(&ctx->wqh.lock); 330 331 seq_printf(m, 332 "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 350 static 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(&ticks, (u64 __user *)arg, sizeof(ticks))) 360 return -EFAULT; 361 if (!ticks) 362 return -EINVAL; 363 364 spin_lock_irq(&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(&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 383 384 static 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 }; 392 393 static 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(f); 400 return -EINVAL; 401 } 402 *p = f; 403 return 0; 404 } 405 406 SYSCALL_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(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(&ctx->t.alarm, 438 ctx->clockid == CLOCK_REALTIME_ALARM ? 439 ALARM_REALTIME : ALARM_BOOTTIME, 440 timerfd_alarmproc); 441 else 442 hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS); 443 444 ctx->moffs = ktime_mono_to_real(0); 445 446 ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx, 447 O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS)); 448 if (ufd < 0) 449 kfree(ctx); 450 451 return ufd; 452 } 453 454 static 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(new)) 464 return -EINVAL; 465 466 ret = timerfd_fget(ufd, &f); 467 if (ret) 468 return ret; 469 ctx = f.file->private_data; 470 471 if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) { 472 fdput(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(&ctx->wqh.lock); 484 485 if (isalarm(ctx)) { 486 if (alarm_try_to_cancel(&ctx->t.alarm) >= 0) 487 break; 488 } else { 489 if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0) 490 break; 491 } 492 spin_unlock_irq(&ctx->wqh.lock); 493 494 if (isalarm(ctx)) 495 hrtimer_cancel_wait_running(&ctx->t.alarm.timer); 496 else 497 hrtimer_cancel_wait_running(&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(&ctx->t.alarm, ctx->tintv); 509 else 510 hrtimer_forward_now(&ctx->t.tmr, 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, new); 520 521 spin_unlock_irq(&ctx->wqh.lock); 522 fdput(f); 523 return ret; 524 } 525 526 static int do_timerfd_gettime(int ufd, struct itimerspec64 *t) 527 { 528 struct fd f; 529 struct timerfd_ctx *ctx; 530 int ret = timerfd_fget(ufd, &f); 531 if (ret) 532 return ret; 533 ctx = f.file->private_data; 534 535 spin_lock_irq(&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 &ctx->t.alarm, ctx->tintv) - 1; 543 alarm_restart(&ctx->t.alarm); 544 } else { 545 ctx->ticks += 546 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv) 547 - 1; 548 hrtimer_restart(&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(&ctx->wqh.lock); 554 fdput(f); 555 return 0; 556 } 557 558 SYSCALL_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(&new, utmr)) 566 return -EFAULT; 567 ret = do_timerfd_settime(ufd, flags, &new, &old); 568 if (ret) 569 return ret; 570 if (otmr && put_itimerspec64(&old, otmr)) 571 return -EFAULT; 572 573 return ret; 574 } 575 576 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct __kernel_itimerspec __user *, otmr) 577 { 578 struct itimerspec64 kotmr; 579 int ret = do_timerfd_gettime(ufd, &kotmr); 580 if (ret) 581 return ret; 582 return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0; 583 } 584 585 #ifdef CONFIG_COMPAT_32BIT_TIME 586 SYSCALL_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(&new, utmr)) 594 return -EFAULT; 595 ret = do_timerfd_settime(ufd, flags, &new, &old); 596 if (ret) 597 return ret; 598 if (otmr && put_old_itimerspec32(&old, otmr)) 599 return -EFAULT; 600 return ret; 601 } 602 603 SYSCALL_DEFINE2(timerfd_gettime32, int, ufd, 604 struct old_itimerspec32 __user *, otmr) 605 { 606 struct itimerspec64 kotmr; 607 int ret = do_timerfd_gettime(ufd, &kotmr); 608 if (ret) 609 return ret; 610 return put_old_itimerspec32(&kotmr, otmr) ? -EFAULT : 0; 611 } 612 #endif 613