1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/types.h>
3 #include <linux/errno.h>
4 #include <linux/kmod.h>
5 #include <linux/sched.h>
6 #include <linux/interrupt.h>
8 #include <linux/tty_driver.h>
9 #include <linux/file.h>
11 #include <linux/string.h>
12 #include <linux/slab.h>
13 #include <linux/poll.h>
14 #include <linux/proc_fs.h>
15 #include <linux/module.h>
16 #include <linux/device.h>
17 #include <linux/wait.h>
18 #include <linux/bitops.h>
19 #include <linux/seq_file.h>
20 #include <linux/uaccess.h>
21 #include <linux/ratelimit.h>
23 #undef LDISC_DEBUG_HANGUP
25 #ifdef LDISC_DEBUG_HANGUP
26 #define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
28 #define tty_ldisc_debug(tty, f, args...)
31 /* lockdep nested classes for tty->ldisc_sem */
39 * This guards the refcounted line discipline lists. The lock
40 * must be taken with irqs off because there are hangup path
41 * callers who will do ldisc lookups and cannot sleep.
44 static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
45 /* Line disc dispatch table */
46 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
49 * tty_register_ldisc - install a line discipline
51 * @new_ldisc: pointer to the ldisc object
53 * Installs a new line discipline into the kernel. The discipline
54 * is set up as unreferenced and then made available to the kernel
55 * from this point onwards.
58 * takes tty_ldiscs_lock to guard against ldisc races
61 int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
66 if (disc < N_TTY || disc >= NR_LDISCS)
69 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
70 tty_ldiscs[disc] = new_ldisc;
71 new_ldisc->num = disc;
72 new_ldisc->refcount = 0;
73 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
77 EXPORT_SYMBOL(tty_register_ldisc);
80 * tty_unregister_ldisc - unload a line discipline
82 * @new_ldisc: pointer to the ldisc object
84 * Remove a line discipline from the kernel providing it is not
88 * takes tty_ldiscs_lock to guard against ldisc races
91 int tty_unregister_ldisc(int disc)
96 if (disc < N_TTY || disc >= NR_LDISCS)
99 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
100 if (tty_ldiscs[disc]->refcount)
103 tty_ldiscs[disc] = NULL;
104 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
108 EXPORT_SYMBOL(tty_unregister_ldisc);
110 static struct tty_ldisc_ops *get_ldops(int disc)
113 struct tty_ldisc_ops *ldops, *ret;
115 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
116 ret = ERR_PTR(-EINVAL);
117 ldops = tty_ldiscs[disc];
119 ret = ERR_PTR(-EAGAIN);
120 if (try_module_get(ldops->owner)) {
125 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
129 static void put_ldops(struct tty_ldisc_ops *ldops)
133 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
135 module_put(ldops->owner);
136 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
140 * tty_ldisc_get - take a reference to an ldisc
141 * @disc: ldisc number
143 * Takes a reference to a line discipline. Deals with refcounts and
144 * module locking counts.
146 * Returns: -EINVAL if the discipline index is not [N_TTY..NR_LDISCS] or
147 * if the discipline is not registered
148 * -EAGAIN if request_module() failed to load or register the
150 * -ENOMEM if allocation failure
152 * Otherwise, returns a pointer to the discipline and bumps the
156 * takes tty_ldiscs_lock to guard against ldisc races
159 static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
161 struct tty_ldisc *ld;
162 struct tty_ldisc_ops *ldops;
164 if (disc < N_TTY || disc >= NR_LDISCS)
165 return ERR_PTR(-EINVAL);
168 * Get the ldisc ops - we may need to request them to be loaded
169 * dynamically and try again.
171 ldops = get_ldops(disc);
173 request_module("tty-ldisc-%d", disc);
174 ldops = get_ldops(disc);
176 return ERR_CAST(ldops);
180 * There is no way to handle allocation failure of only 16 bytes.
181 * Let's simplify error handling and save more memory.
183 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
191 * tty_ldisc_put - release the ldisc
193 * Complement of tty_ldisc_get().
195 static void tty_ldisc_put(struct tty_ldisc *ld)
197 if (WARN_ON_ONCE(!ld))
204 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
206 return (*pos < NR_LDISCS) ? pos : NULL;
209 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
212 return (*pos < NR_LDISCS) ? pos : NULL;
215 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
219 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
221 int i = *(loff_t *)v;
222 struct tty_ldisc_ops *ldops;
224 ldops = get_ldops(i);
227 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
232 const struct seq_operations tty_ldiscs_seq_ops = {
233 .start = tty_ldiscs_seq_start,
234 .next = tty_ldiscs_seq_next,
235 .stop = tty_ldiscs_seq_stop,
236 .show = tty_ldiscs_seq_show,
240 * tty_ldisc_ref_wait - wait for the tty ldisc
243 * Dereference the line discipline for the terminal and take a
244 * reference to it. If the line discipline is in flux then
245 * wait patiently until it changes.
247 * Returns: NULL if the tty has been hungup and not re-opened with
248 * a new file descriptor, otherwise valid ldisc reference
250 * Note: Must not be called from an IRQ/timer context. The caller
251 * must also be careful not to hold other locks that will deadlock
252 * against a discipline change, such as an existing ldisc reference
253 * (which we check for)
255 * Note: a file_operations routine (read/poll/write) should use this
256 * function to wait for any ldisc lifetime events to finish.
259 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
261 struct tty_ldisc *ld;
263 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
266 ldsem_up_read(&tty->ldisc_sem);
269 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
272 * tty_ldisc_ref - get the tty ldisc
275 * Dereference the line discipline for the terminal and take a
276 * reference to it. If the line discipline is in flux then
277 * return NULL. Can be called from IRQ and timer functions.
280 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
282 struct tty_ldisc *ld = NULL;
284 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
287 ldsem_up_read(&tty->ldisc_sem);
291 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
294 * tty_ldisc_deref - free a tty ldisc reference
295 * @ld: reference to free up
297 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
298 * be called in IRQ context.
301 void tty_ldisc_deref(struct tty_ldisc *ld)
303 ldsem_up_read(&ld->tty->ldisc_sem);
305 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
309 __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
311 return ldsem_down_write(&tty->ldisc_sem, timeout);
315 __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
317 return ldsem_down_write_nested(&tty->ldisc_sem,
318 LDISC_SEM_OTHER, timeout);
321 static inline void __tty_ldisc_unlock(struct tty_struct *tty)
323 ldsem_up_write(&tty->ldisc_sem);
326 int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
330 /* Kindly asking blocked readers to release the read side */
331 set_bit(TTY_LDISC_CHANGING, &tty->flags);
332 wake_up_interruptible_all(&tty->read_wait);
333 wake_up_interruptible_all(&tty->write_wait);
335 ret = __tty_ldisc_lock(tty, timeout);
338 set_bit(TTY_LDISC_HALTED, &tty->flags);
342 void tty_ldisc_unlock(struct tty_struct *tty)
344 clear_bit(TTY_LDISC_HALTED, &tty->flags);
345 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
346 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
347 __tty_ldisc_unlock(tty);
351 tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
352 unsigned long timeout)
357 ret = __tty_ldisc_lock(tty, timeout);
359 ret = __tty_ldisc_lock_nested(tty2, timeout);
361 __tty_ldisc_unlock(tty);
364 /* if this is possible, it has lots of implications */
365 WARN_ON_ONCE(tty == tty2);
366 if (tty2 && tty != tty2) {
367 ret = __tty_ldisc_lock(tty2, timeout);
369 ret = __tty_ldisc_lock_nested(tty, timeout);
371 __tty_ldisc_unlock(tty2);
374 ret = __tty_ldisc_lock(tty, timeout);
380 set_bit(TTY_LDISC_HALTED, &tty->flags);
382 set_bit(TTY_LDISC_HALTED, &tty2->flags);
386 static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
388 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
391 static void tty_ldisc_unlock_pair(struct tty_struct *tty,
392 struct tty_struct *tty2)
394 __tty_ldisc_unlock(tty);
396 __tty_ldisc_unlock(tty2);
400 * tty_ldisc_flush - flush line discipline queue
403 * Flush the line discipline queue (if any) and the tty flip buffers
407 void tty_ldisc_flush(struct tty_struct *tty)
409 struct tty_ldisc *ld = tty_ldisc_ref(tty);
411 tty_buffer_flush(tty, ld);
415 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
418 * tty_set_termios_ldisc - set ldisc field
419 * @tty: tty structure
420 * @disc: line discipline number
422 * This is probably overkill for real world processors but
423 * they are not on hot paths so a little discipline won't do
426 * The line discipline-related tty_struct fields are reset to
427 * prevent the ldisc driver from re-using stale information for
428 * the new ldisc instance.
430 * Locking: takes termios_rwsem
433 static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
435 down_write(&tty->termios_rwsem);
436 tty->termios.c_line = disc;
437 up_write(&tty->termios_rwsem);
439 tty->disc_data = NULL;
440 tty->receive_room = 0;
444 * tty_ldisc_open - open a line discipline
445 * @tty: tty we are opening the ldisc on
446 * @ld: discipline to open
448 * A helper opening method. Also a convenient debugging and check
451 * Locking: always called with BTM already held.
454 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
456 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
459 /* BTM here locks versus a hangup event */
460 ret = ld->ops->open(tty);
462 clear_bit(TTY_LDISC_OPEN, &tty->flags);
464 tty_ldisc_debug(tty, "%p: opened\n", ld);
471 * tty_ldisc_close - close a line discipline
472 * @tty: tty we are opening the ldisc on
473 * @ld: discipline to close
475 * A helper close method. Also a convenient debugging and check
479 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
481 lockdep_assert_held_exclusive(&tty->ldisc_sem);
482 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
483 clear_bit(TTY_LDISC_OPEN, &tty->flags);
486 tty_ldisc_debug(tty, "%p: closed\n", ld);
490 * tty_ldisc_failto - helper for ldisc failback
491 * @tty: tty to open the ldisc on
492 * @ld: ldisc we are trying to fail back to
494 * Helper to try and recover a tty when switching back to the old
495 * ldisc fails and we need something attached.
498 static int tty_ldisc_failto(struct tty_struct *tty, int ld)
500 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
503 lockdep_assert_held_exclusive(&tty->ldisc_sem);
505 return PTR_ERR(disc);
507 tty_set_termios_ldisc(tty, ld);
508 if ((r = tty_ldisc_open(tty, disc)) < 0)
514 * tty_ldisc_restore - helper for tty ldisc change
515 * @tty: tty to recover
516 * @old: previous ldisc
518 * Restore the previous line discipline or N_TTY when a line discipline
519 * change fails due to an open error
522 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
524 /* There is an outstanding reference here so this is safe */
525 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
526 const char *name = tty_name(tty);
528 pr_warn("Falling back ldisc for %s.\n", name);
529 /* The traditional behaviour is to fall back to N_TTY, we
530 want to avoid falling back to N_NULL unless we have no
531 choice to avoid the risk of breaking anything */
532 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
533 tty_ldisc_failto(tty, N_NULL) < 0)
534 panic("Couldn't open N_NULL ldisc for %s.", name);
539 * tty_set_ldisc - set line discipline
540 * @tty: the terminal to set
541 * @ldisc: the line discipline
543 * Set the discipline of a tty line. Must be called from a process
544 * context. The ldisc change logic has to protect itself against any
545 * overlapping ldisc change (including on the other end of pty pairs),
546 * the close of one side of a tty/pty pair, and eventually hangup.
549 int tty_set_ldisc(struct tty_struct *tty, int disc)
552 struct tty_ldisc *old_ldisc, *new_ldisc;
554 new_ldisc = tty_ldisc_get(tty, disc);
555 if (IS_ERR(new_ldisc))
556 return PTR_ERR(new_ldisc);
559 retval = tty_ldisc_lock(tty, 5 * HZ);
568 /* Check the no-op case */
569 if (tty->ldisc->ops->num == disc)
572 if (test_bit(TTY_HUPPED, &tty->flags)) {
573 /* We were raced by hangup */
578 old_ldisc = tty->ldisc;
580 /* Shutdown the old discipline. */
581 tty_ldisc_close(tty, old_ldisc);
583 /* Now set up the new line discipline. */
584 tty->ldisc = new_ldisc;
585 tty_set_termios_ldisc(tty, disc);
587 retval = tty_ldisc_open(tty, new_ldisc);
589 /* Back to the old one or N_TTY if we can't */
590 tty_ldisc_put(new_ldisc);
591 tty_ldisc_restore(tty, old_ldisc);
594 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
595 down_read(&tty->termios_rwsem);
596 tty->ops->set_ldisc(tty);
597 up_read(&tty->termios_rwsem);
600 /* At this point we hold a reference to the new ldisc and a
601 reference to the old ldisc, or we hold two references to
602 the old ldisc (if it was restored as part of error cleanup
603 above). In either case, releasing a single reference from
604 the old ldisc is correct. */
605 new_ldisc = old_ldisc;
607 tty_ldisc_unlock(tty);
609 /* Restart the work queue in case no characters kick it off. Safe if
611 tty_buffer_restart_work(tty->port);
613 tty_ldisc_put(new_ldisc); /* drop the extra reference */
617 EXPORT_SYMBOL_GPL(tty_set_ldisc);
620 * tty_ldisc_kill - teardown ldisc
621 * @tty: tty being released
623 * Perform final close of the ldisc and reset tty->ldisc
625 static void tty_ldisc_kill(struct tty_struct *tty)
627 lockdep_assert_held_exclusive(&tty->ldisc_sem);
631 * Now kill off the ldisc
633 tty_ldisc_close(tty, tty->ldisc);
634 tty_ldisc_put(tty->ldisc);
635 /* Force an oops if we mess this up */
640 * tty_reset_termios - reset terminal state
643 * Restore a terminal to the driver default state.
646 static void tty_reset_termios(struct tty_struct *tty)
648 down_write(&tty->termios_rwsem);
649 tty->termios = tty->driver->init_termios;
650 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
651 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
652 up_write(&tty->termios_rwsem);
657 * tty_ldisc_reinit - reinitialise the tty ldisc
658 * @tty: tty to reinit
659 * @disc: line discipline to reinitialize
661 * Completely reinitialize the line discipline state, by closing the
662 * current instance, if there is one, and opening a new instance. If
663 * an error occurs opening the new non-N_TTY instance, the instance
664 * is dropped and tty->ldisc reset to NULL. The caller can then retry
665 * with N_TTY instead.
667 * Returns 0 if successful, otherwise error code < 0
670 int tty_ldisc_reinit(struct tty_struct *tty, int disc)
672 struct tty_ldisc *ld;
675 lockdep_assert_held_exclusive(&tty->ldisc_sem);
676 ld = tty_ldisc_get(tty, disc);
678 BUG_ON(disc == N_TTY);
683 tty_ldisc_close(tty, tty->ldisc);
684 tty_ldisc_put(tty->ldisc);
687 /* switch the line discipline */
689 tty_set_termios_ldisc(tty, disc);
690 retval = tty_ldisc_open(tty, tty->ldisc);
692 tty_ldisc_put(tty->ldisc);
699 * tty_ldisc_hangup - hangup ldisc reset
700 * @tty: tty being hung up
702 * Some tty devices reset their termios when they receive a hangup
703 * event. In that situation we must also switch back to N_TTY properly
704 * before we reset the termios data.
706 * Locking: We can take the ldisc mutex as the rest of the code is
707 * careful to allow for this.
709 * In the pty pair case this occurs in the close() path of the
710 * tty itself so we must be careful about locking rules.
713 void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
715 struct tty_ldisc *ld;
717 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
719 ld = tty_ldisc_ref(tty);
721 if (ld->ops->flush_buffer)
722 ld->ops->flush_buffer(tty);
723 tty_driver_flush_buffer(tty);
724 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
725 ld->ops->write_wakeup)
726 ld->ops->write_wakeup(tty);
728 ld->ops->hangup(tty);
732 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
733 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
736 * Shutdown the current line discipline, and reset it to
739 * Avoid racing set_ldisc or tty_ldisc_release
741 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
743 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
744 tty_reset_termios(tty);
748 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
749 tty_ldisc_reinit(tty, N_TTY) < 0)
750 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
754 tty_ldisc_unlock(tty);
758 * tty_ldisc_setup - open line discipline
759 * @tty: tty being shut down
760 * @o_tty: pair tty for pty/tty pairs
762 * Called during the initial open of a tty/pty pair in order to set up the
763 * line disciplines and bind them to the tty. This has no locking issues
764 * as the device isn't yet active.
767 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
769 int retval = tty_ldisc_open(tty, tty->ldisc);
775 * Called without o_tty->ldisc_sem held, as o_tty has been
776 * just allocated and no one has a reference to it.
778 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
780 tty_ldisc_close(tty, tty->ldisc);
788 * tty_ldisc_release - release line discipline
789 * @tty: tty being shut down (or one end of pty pair)
791 * Called during the final close of a tty or a pty pair in order to shut
792 * down the line discpline layer. On exit, each tty's ldisc is NULL.
795 void tty_ldisc_release(struct tty_struct *tty)
797 struct tty_struct *o_tty = tty->link;
800 * Shutdown this line discipline. As this is the final close,
801 * it does not race with the set_ldisc code path.
804 tty_ldisc_lock_pair(tty, o_tty);
807 tty_ldisc_kill(o_tty);
808 tty_ldisc_unlock_pair(tty, o_tty);
810 /* And the memory resources remaining (buffers, termios) will be
811 disposed of when the kref hits zero */
813 tty_ldisc_debug(tty, "released\n");
815 EXPORT_SYMBOL_GPL(tty_ldisc_release);
818 * tty_ldisc_init - ldisc setup for new tty
819 * @tty: tty being allocated
821 * Set up the line discipline objects for a newly allocated tty. Note that
822 * the tty structure is not completely set up when this call is made.
825 int tty_ldisc_init(struct tty_struct *tty)
827 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
835 * tty_ldisc_deinit - ldisc cleanup for new tty
836 * @tty: tty that was allocated recently
838 * The tty structure must not becompletely set up (tty_ldisc_setup) when
841 void tty_ldisc_deinit(struct tty_struct *tty)
843 /* no ldisc_sem, tty is being destroyed */
845 tty_ldisc_put(tty->ldisc);