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);
179 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
182 return ERR_PTR(-ENOMEM);
192 * tty_ldisc_put - release the ldisc
194 * Complement of tty_ldisc_get().
196 static void tty_ldisc_put(struct tty_ldisc *ld)
198 if (WARN_ON_ONCE(!ld))
205 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
207 return (*pos < NR_LDISCS) ? pos : NULL;
210 static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
213 return (*pos < NR_LDISCS) ? pos : NULL;
216 static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
220 static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
222 int i = *(loff_t *)v;
223 struct tty_ldisc_ops *ldops;
225 ldops = get_ldops(i);
228 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
233 static const struct seq_operations tty_ldiscs_seq_ops = {
234 .start = tty_ldiscs_seq_start,
235 .next = tty_ldiscs_seq_next,
236 .stop = tty_ldiscs_seq_stop,
237 .show = tty_ldiscs_seq_show,
240 static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
242 return seq_open(file, &tty_ldiscs_seq_ops);
245 const struct file_operations tty_ldiscs_proc_fops = {
246 .owner = THIS_MODULE,
247 .open = proc_tty_ldiscs_open,
250 .release = seq_release,
254 * tty_ldisc_ref_wait - wait for the tty ldisc
257 * Dereference the line discipline for the terminal and take a
258 * reference to it. If the line discipline is in flux then
259 * wait patiently until it changes.
261 * Returns: NULL if the tty has been hungup and not re-opened with
262 * a new file descriptor, otherwise valid ldisc reference
264 * Note: Must not be called from an IRQ/timer context. The caller
265 * must also be careful not to hold other locks that will deadlock
266 * against a discipline change, such as an existing ldisc reference
267 * (which we check for)
269 * Note: a file_operations routine (read/poll/write) should use this
270 * function to wait for any ldisc lifetime events to finish.
273 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
275 struct tty_ldisc *ld;
277 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
280 ldsem_up_read(&tty->ldisc_sem);
283 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
286 * tty_ldisc_ref - get the tty ldisc
289 * Dereference the line discipline for the terminal and take a
290 * reference to it. If the line discipline is in flux then
291 * return NULL. Can be called from IRQ and timer functions.
294 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
296 struct tty_ldisc *ld = NULL;
298 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
301 ldsem_up_read(&tty->ldisc_sem);
305 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
308 * tty_ldisc_deref - free a tty ldisc reference
309 * @ld: reference to free up
311 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
312 * be called in IRQ context.
315 void tty_ldisc_deref(struct tty_ldisc *ld)
317 ldsem_up_read(&ld->tty->ldisc_sem);
319 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
323 __tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
325 return ldsem_down_write(&tty->ldisc_sem, timeout);
329 __tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
331 return ldsem_down_write_nested(&tty->ldisc_sem,
332 LDISC_SEM_OTHER, timeout);
335 static inline void __tty_ldisc_unlock(struct tty_struct *tty)
337 ldsem_up_write(&tty->ldisc_sem);
340 int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
344 ret = __tty_ldisc_lock(tty, timeout);
347 set_bit(TTY_LDISC_HALTED, &tty->flags);
351 void tty_ldisc_unlock(struct tty_struct *tty)
353 clear_bit(TTY_LDISC_HALTED, &tty->flags);
354 __tty_ldisc_unlock(tty);
358 tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
359 unsigned long timeout)
364 ret = __tty_ldisc_lock(tty, timeout);
366 ret = __tty_ldisc_lock_nested(tty2, timeout);
368 __tty_ldisc_unlock(tty);
371 /* if this is possible, it has lots of implications */
372 WARN_ON_ONCE(tty == tty2);
373 if (tty2 && tty != tty2) {
374 ret = __tty_ldisc_lock(tty2, timeout);
376 ret = __tty_ldisc_lock_nested(tty, timeout);
378 __tty_ldisc_unlock(tty2);
381 ret = __tty_ldisc_lock(tty, timeout);
387 set_bit(TTY_LDISC_HALTED, &tty->flags);
389 set_bit(TTY_LDISC_HALTED, &tty2->flags);
393 static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
395 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
398 static void tty_ldisc_unlock_pair(struct tty_struct *tty,
399 struct tty_struct *tty2)
401 __tty_ldisc_unlock(tty);
403 __tty_ldisc_unlock(tty2);
407 * tty_ldisc_flush - flush line discipline queue
410 * Flush the line discipline queue (if any) and the tty flip buffers
414 void tty_ldisc_flush(struct tty_struct *tty)
416 struct tty_ldisc *ld = tty_ldisc_ref(tty);
418 tty_buffer_flush(tty, ld);
422 EXPORT_SYMBOL_GPL(tty_ldisc_flush);
425 * tty_set_termios_ldisc - set ldisc field
426 * @tty: tty structure
427 * @disc: line discipline number
429 * This is probably overkill for real world processors but
430 * they are not on hot paths so a little discipline won't do
433 * The line discipline-related tty_struct fields are reset to
434 * prevent the ldisc driver from re-using stale information for
435 * the new ldisc instance.
437 * Locking: takes termios_rwsem
440 static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
442 down_write(&tty->termios_rwsem);
443 tty->termios.c_line = disc;
444 up_write(&tty->termios_rwsem);
446 tty->disc_data = NULL;
447 tty->receive_room = 0;
451 * tty_ldisc_open - open a line discipline
452 * @tty: tty we are opening the ldisc on
453 * @ld: discipline to open
455 * A helper opening method. Also a convenient debugging and check
458 * Locking: always called with BTM already held.
461 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
463 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
466 /* BTM here locks versus a hangup event */
467 ret = ld->ops->open(tty);
469 clear_bit(TTY_LDISC_OPEN, &tty->flags);
471 tty_ldisc_debug(tty, "%p: opened\n", ld);
478 * tty_ldisc_close - close a line discipline
479 * @tty: tty we are opening the ldisc on
480 * @ld: discipline to close
482 * A helper close method. Also a convenient debugging and check
486 static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
488 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
489 clear_bit(TTY_LDISC_OPEN, &tty->flags);
492 tty_ldisc_debug(tty, "%p: closed\n", ld);
496 * tty_ldisc_failto - helper for ldisc failback
497 * @tty: tty to open the ldisc on
498 * @ld: ldisc we are trying to fail back to
500 * Helper to try and recover a tty when switching back to the old
501 * ldisc fails and we need something attached.
504 static int tty_ldisc_failto(struct tty_struct *tty, int ld)
506 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
510 return PTR_ERR(disc);
512 tty_set_termios_ldisc(tty, ld);
513 if ((r = tty_ldisc_open(tty, disc)) < 0)
519 * tty_ldisc_restore - helper for tty ldisc change
520 * @tty: tty to recover
521 * @old: previous ldisc
523 * Restore the previous line discipline or N_TTY when a line discipline
524 * change fails due to an open error
527 static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
529 /* There is an outstanding reference here so this is safe */
530 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
531 const char *name = tty_name(tty);
533 pr_warn("Falling back ldisc for %s.\n", name);
534 /* The traditional behaviour is to fall back to N_TTY, we
535 want to avoid falling back to N_NULL unless we have no
536 choice to avoid the risk of breaking anything */
537 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
538 tty_ldisc_failto(tty, N_NULL) < 0)
539 panic("Couldn't open N_NULL ldisc for %s.", name);
544 * tty_set_ldisc - set line discipline
545 * @tty: the terminal to set
546 * @ldisc: the line discipline
548 * Set the discipline of a tty line. Must be called from a process
549 * context. The ldisc change logic has to protect itself against any
550 * overlapping ldisc change (including on the other end of pty pairs),
551 * the close of one side of a tty/pty pair, and eventually hangup.
554 int tty_set_ldisc(struct tty_struct *tty, int disc)
557 struct tty_ldisc *old_ldisc, *new_ldisc;
559 new_ldisc = tty_ldisc_get(tty, disc);
560 if (IS_ERR(new_ldisc))
561 return PTR_ERR(new_ldisc);
564 retval = tty_ldisc_lock(tty, 5 * HZ);
573 /* Check the no-op case */
574 if (tty->ldisc->ops->num == disc)
577 if (test_bit(TTY_HUPPED, &tty->flags)) {
578 /* We were raced by hangup */
583 old_ldisc = tty->ldisc;
585 /* Shutdown the old discipline. */
586 tty_ldisc_close(tty, old_ldisc);
588 /* Now set up the new line discipline. */
589 tty->ldisc = new_ldisc;
590 tty_set_termios_ldisc(tty, disc);
592 retval = tty_ldisc_open(tty, new_ldisc);
594 /* Back to the old one or N_TTY if we can't */
595 tty_ldisc_put(new_ldisc);
596 tty_ldisc_restore(tty, old_ldisc);
599 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
600 down_read(&tty->termios_rwsem);
601 tty->ops->set_ldisc(tty);
602 up_read(&tty->termios_rwsem);
605 /* At this point we hold a reference to the new ldisc and a
606 reference to the old ldisc, or we hold two references to
607 the old ldisc (if it was restored as part of error cleanup
608 above). In either case, releasing a single reference from
609 the old ldisc is correct. */
610 new_ldisc = old_ldisc;
612 tty_ldisc_unlock(tty);
614 /* Restart the work queue in case no characters kick it off. Safe if
616 tty_buffer_restart_work(tty->port);
618 tty_ldisc_put(new_ldisc); /* drop the extra reference */
622 EXPORT_SYMBOL_GPL(tty_set_ldisc);
625 * tty_ldisc_kill - teardown ldisc
626 * @tty: tty being released
628 * Perform final close of the ldisc and reset tty->ldisc
630 static void tty_ldisc_kill(struct tty_struct *tty)
635 * Now kill off the ldisc
637 tty_ldisc_close(tty, tty->ldisc);
638 tty_ldisc_put(tty->ldisc);
639 /* Force an oops if we mess this up */
644 * tty_reset_termios - reset terminal state
647 * Restore a terminal to the driver default state.
650 static void tty_reset_termios(struct tty_struct *tty)
652 down_write(&tty->termios_rwsem);
653 tty->termios = tty->driver->init_termios;
654 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
655 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
656 up_write(&tty->termios_rwsem);
661 * tty_ldisc_reinit - reinitialise the tty ldisc
662 * @tty: tty to reinit
663 * @disc: line discipline to reinitialize
665 * Completely reinitialize the line discipline state, by closing the
666 * current instance, if there is one, and opening a new instance. If
667 * an error occurs opening the new non-N_TTY instance, the instance
668 * is dropped and tty->ldisc reset to NULL. The caller can then retry
669 * with N_TTY instead.
671 * Returns 0 if successful, otherwise error code < 0
674 int tty_ldisc_reinit(struct tty_struct *tty, int disc)
676 struct tty_ldisc *ld;
679 ld = tty_ldisc_get(tty, disc);
681 BUG_ON(disc == N_TTY);
686 tty_ldisc_close(tty, tty->ldisc);
687 tty_ldisc_put(tty->ldisc);
690 /* switch the line discipline */
692 tty_set_termios_ldisc(tty, disc);
693 retval = tty_ldisc_open(tty, tty->ldisc);
695 tty_ldisc_put(tty->ldisc);
702 * tty_ldisc_hangup - hangup ldisc reset
703 * @tty: tty being hung up
705 * Some tty devices reset their termios when they receive a hangup
706 * event. In that situation we must also switch back to N_TTY properly
707 * before we reset the termios data.
709 * Locking: We can take the ldisc mutex as the rest of the code is
710 * careful to allow for this.
712 * In the pty pair case this occurs in the close() path of the
713 * tty itself so we must be careful about locking rules.
716 void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
718 struct tty_ldisc *ld;
720 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
722 ld = tty_ldisc_ref(tty);
724 if (ld->ops->flush_buffer)
725 ld->ops->flush_buffer(tty);
726 tty_driver_flush_buffer(tty);
727 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
728 ld->ops->write_wakeup)
729 ld->ops->write_wakeup(tty);
731 ld->ops->hangup(tty);
735 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
736 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
739 * Shutdown the current line discipline, and reset it to
742 * Avoid racing set_ldisc or tty_ldisc_release
744 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
746 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
747 tty_reset_termios(tty);
751 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
752 tty_ldisc_reinit(tty, N_TTY) < 0)
753 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
757 tty_ldisc_unlock(tty);
761 * tty_ldisc_setup - open line discipline
762 * @tty: tty being shut down
763 * @o_tty: pair tty for pty/tty pairs
765 * Called during the initial open of a tty/pty pair in order to set up the
766 * line disciplines and bind them to the tty. This has no locking issues
767 * as the device isn't yet active.
770 int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
772 int retval = tty_ldisc_open(tty, tty->ldisc);
777 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
779 tty_ldisc_close(tty, tty->ldisc);
787 * tty_ldisc_release - release line discipline
788 * @tty: tty being shut down (or one end of pty pair)
790 * Called during the final close of a tty or a pty pair in order to shut
791 * down the line discpline layer. On exit, each tty's ldisc is NULL.
794 void tty_ldisc_release(struct tty_struct *tty)
796 struct tty_struct *o_tty = tty->link;
799 * Shutdown this line discipline. As this is the final close,
800 * it does not race with the set_ldisc code path.
803 tty_ldisc_lock_pair(tty, o_tty);
806 tty_ldisc_kill(o_tty);
807 tty_ldisc_unlock_pair(tty, o_tty);
809 /* And the memory resources remaining (buffers, termios) will be
810 disposed of when the kref hits zero */
812 tty_ldisc_debug(tty, "released\n");
814 EXPORT_SYMBOL_GPL(tty_ldisc_release);
817 * tty_ldisc_init - ldisc setup for new tty
818 * @tty: tty being allocated
820 * Set up the line discipline objects for a newly allocated tty. Note that
821 * the tty structure is not completely set up when this call is made.
824 int tty_ldisc_init(struct tty_struct *tty)
826 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
834 * tty_ldisc_deinit - ldisc cleanup for new tty
835 * @tty: tty that was allocated recently
837 * The tty structure must not becompletely set up (tty_ldisc_setup) when
840 void tty_ldisc_deinit(struct tty_struct *tty)
843 tty_ldisc_put(tty->ldisc);