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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>
7#include <linux/tty.h>
8#include <linux/tty_driver.h>
9#include <linux/file.h>
10#include <linux/mm.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>
22
23#undef LDISC_DEBUG_HANGUP
24
25#ifdef LDISC_DEBUG_HANGUP
26#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
27#else
28#define tty_ldisc_debug(tty, f, args...)
29#endif
30
31/* lockdep nested classes for tty->ldisc_sem */
32enum {
33 LDISC_SEM_NORMAL,
34 LDISC_SEM_OTHER,
35};
36
37
38/*
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.
42 */
43
44static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
45/* Line disc dispatch table */
46static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
47
48/**
49 * tty_register_ldisc - install a line discipline
50 * @disc: ldisc number
51 * @new_ldisc: pointer to the ldisc object
52 *
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.
56 *
57 * Locking:
58 * takes tty_ldiscs_lock to guard against ldisc races
59 */
60
61int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
62{
63 unsigned long flags;
64 int ret = 0;
65
66 if (disc < N_TTY || disc >= NR_LDISCS)
67 return -EINVAL;
68
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);
74
75 return ret;
76}
77EXPORT_SYMBOL(tty_register_ldisc);
78
79/**
80 * tty_unregister_ldisc - unload a line discipline
81 * @disc: ldisc number
82 * @new_ldisc: pointer to the ldisc object
83 *
84 * Remove a line discipline from the kernel providing it is not
85 * currently in use.
86 *
87 * Locking:
88 * takes tty_ldiscs_lock to guard against ldisc races
89 */
90
91int tty_unregister_ldisc(int disc)
92{
93 unsigned long flags;
94 int ret = 0;
95
96 if (disc < N_TTY || disc >= NR_LDISCS)
97 return -EINVAL;
98
99 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
100 if (tty_ldiscs[disc]->refcount)
101 ret = -EBUSY;
102 else
103 tty_ldiscs[disc] = NULL;
104 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
105
106 return ret;
107}
108EXPORT_SYMBOL(tty_unregister_ldisc);
109
110static struct tty_ldisc_ops *get_ldops(int disc)
111{
112 unsigned long flags;
113 struct tty_ldisc_ops *ldops, *ret;
114
115 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
116 ret = ERR_PTR(-EINVAL);
117 ldops = tty_ldiscs[disc];
118 if (ldops) {
119 ret = ERR_PTR(-EAGAIN);
120 if (try_module_get(ldops->owner)) {
121 ldops->refcount++;
122 ret = ldops;
123 }
124 }
125 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
126 return ret;
127}
128
129static void put_ldops(struct tty_ldisc_ops *ldops)
130{
131 unsigned long flags;
132
133 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
134 ldops->refcount--;
135 module_put(ldops->owner);
136 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
137}
138
139/**
140 * tty_ldisc_get - take a reference to an ldisc
141 * @disc: ldisc number
142 *
143 * Takes a reference to a line discipline. Deals with refcounts and
144 * module locking counts.
145 *
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
149 * the discipline
150 * -ENOMEM if allocation failure
151 *
152 * Otherwise, returns a pointer to the discipline and bumps the
153 * ref count
154 *
155 * Locking:
156 * takes tty_ldiscs_lock to guard against ldisc races
157 */
158
159static int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
160
161static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
162{
163 struct tty_ldisc *ld;
164 struct tty_ldisc_ops *ldops;
165
166 if (disc < N_TTY || disc >= NR_LDISCS)
167 return ERR_PTR(-EINVAL);
168
169 /*
170 * Get the ldisc ops - we may need to request them to be loaded
171 * dynamically and try again.
172 */
173 ldops = get_ldops(disc);
174 if (IS_ERR(ldops)) {
175 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
176 return ERR_PTR(-EPERM);
177 request_module("tty-ldisc-%d", disc);
178 ldops = get_ldops(disc);
179 if (IS_ERR(ldops))
180 return ERR_CAST(ldops);
181 }
182
183 /*
184 * There is no way to handle allocation failure of only 16 bytes.
185 * Let's simplify error handling and save more memory.
186 */
187 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
188 ld->ops = ldops;
189 ld->tty = tty;
190
191 return ld;
192}
193
194/**
195 * tty_ldisc_put - release the ldisc
196 *
197 * Complement of tty_ldisc_get().
198 */
199static void tty_ldisc_put(struct tty_ldisc *ld)
200{
201 if (WARN_ON_ONCE(!ld))
202 return;
203
204 put_ldops(ld->ops);
205 kfree(ld);
206}
207
208static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
209{
210 return (*pos < NR_LDISCS) ? pos : NULL;
211}
212
213static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
214{
215 (*pos)++;
216 return (*pos < NR_LDISCS) ? pos : NULL;
217}
218
219static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
220{
221}
222
223static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
224{
225 int i = *(loff_t *)v;
226 struct tty_ldisc_ops *ldops;
227
228 ldops = get_ldops(i);
229 if (IS_ERR(ldops))
230 return 0;
231 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
232 put_ldops(ldops);
233 return 0;
234}
235
236const struct seq_operations tty_ldiscs_seq_ops = {
237 .start = tty_ldiscs_seq_start,
238 .next = tty_ldiscs_seq_next,
239 .stop = tty_ldiscs_seq_stop,
240 .show = tty_ldiscs_seq_show,
241};
242
243/**
244 * tty_ldisc_ref_wait - wait for the tty ldisc
245 * @tty: tty device
246 *
247 * Dereference the line discipline for the terminal and take a
248 * reference to it. If the line discipline is in flux then
249 * wait patiently until it changes.
250 *
251 * Returns: NULL if the tty has been hungup and not re-opened with
252 * a new file descriptor, otherwise valid ldisc reference
253 *
254 * Note: Must not be called from an IRQ/timer context. The caller
255 * must also be careful not to hold other locks that will deadlock
256 * against a discipline change, such as an existing ldisc reference
257 * (which we check for)
258 *
259 * Note: a file_operations routine (read/poll/write) should use this
260 * function to wait for any ldisc lifetime events to finish.
261 */
262
263struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
264{
265 struct tty_ldisc *ld;
266
267 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
268 ld = tty->ldisc;
269 if (!ld)
270 ldsem_up_read(&tty->ldisc_sem);
271 return ld;
272}
273EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
274
275/**
276 * tty_ldisc_ref - get the tty ldisc
277 * @tty: tty device
278 *
279 * Dereference the line discipline for the terminal and take a
280 * reference to it. If the line discipline is in flux then
281 * return NULL. Can be called from IRQ and timer functions.
282 */
283
284struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
285{
286 struct tty_ldisc *ld = NULL;
287
288 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
289 ld = tty->ldisc;
290 if (!ld)
291 ldsem_up_read(&tty->ldisc_sem);
292 }
293 return ld;
294}
295EXPORT_SYMBOL_GPL(tty_ldisc_ref);
296
297/**
298 * tty_ldisc_deref - free a tty ldisc reference
299 * @ld: reference to free up
300 *
301 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
302 * be called in IRQ context.
303 */
304
305void tty_ldisc_deref(struct tty_ldisc *ld)
306{
307 ldsem_up_read(&ld->tty->ldisc_sem);
308}
309EXPORT_SYMBOL_GPL(tty_ldisc_deref);
310
311
312static inline int
313__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
314{
315 return ldsem_down_write(&tty->ldisc_sem, timeout);
316}
317
318static inline int
319__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
320{
321 return ldsem_down_write_nested(&tty->ldisc_sem,
322 LDISC_SEM_OTHER, timeout);
323}
324
325static inline void __tty_ldisc_unlock(struct tty_struct *tty)
326{
327 ldsem_up_write(&tty->ldisc_sem);
328}
329
330int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
331{
332 int ret;
333
334 /* Kindly asking blocked readers to release the read side */
335 set_bit(TTY_LDISC_CHANGING, &tty->flags);
336 wake_up_interruptible_all(&tty->read_wait);
337 wake_up_interruptible_all(&tty->write_wait);
338
339 ret = __tty_ldisc_lock(tty, timeout);
340 if (!ret)
341 return -EBUSY;
342 set_bit(TTY_LDISC_HALTED, &tty->flags);
343 return 0;
344}
345
346void tty_ldisc_unlock(struct tty_struct *tty)
347{
348 clear_bit(TTY_LDISC_HALTED, &tty->flags);
349 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
350 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
351 __tty_ldisc_unlock(tty);
352}
353
354static int
355tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
356 unsigned long timeout)
357{
358 int ret;
359
360 if (tty < tty2) {
361 ret = __tty_ldisc_lock(tty, timeout);
362 if (ret) {
363 ret = __tty_ldisc_lock_nested(tty2, timeout);
364 if (!ret)
365 __tty_ldisc_unlock(tty);
366 }
367 } else {
368 /* if this is possible, it has lots of implications */
369 WARN_ON_ONCE(tty == tty2);
370 if (tty2 && tty != tty2) {
371 ret = __tty_ldisc_lock(tty2, timeout);
372 if (ret) {
373 ret = __tty_ldisc_lock_nested(tty, timeout);
374 if (!ret)
375 __tty_ldisc_unlock(tty2);
376 }
377 } else
378 ret = __tty_ldisc_lock(tty, timeout);
379 }
380
381 if (!ret)
382 return -EBUSY;
383
384 set_bit(TTY_LDISC_HALTED, &tty->flags);
385 if (tty2)
386 set_bit(TTY_LDISC_HALTED, &tty2->flags);
387 return 0;
388}
389
390static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
391{
392 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
393}
394
395static void tty_ldisc_unlock_pair(struct tty_struct *tty,
396 struct tty_struct *tty2)
397{
398 __tty_ldisc_unlock(tty);
399 if (tty2)
400 __tty_ldisc_unlock(tty2);
401}
402
403/**
404 * tty_ldisc_flush - flush line discipline queue
405 * @tty: tty
406 *
407 * Flush the line discipline queue (if any) and the tty flip buffers
408 * for this tty.
409 */
410
411void tty_ldisc_flush(struct tty_struct *tty)
412{
413 struct tty_ldisc *ld = tty_ldisc_ref(tty);
414
415 tty_buffer_flush(tty, ld);
416 if (ld)
417 tty_ldisc_deref(ld);
418}
419EXPORT_SYMBOL_GPL(tty_ldisc_flush);
420
421/**
422 * tty_set_termios_ldisc - set ldisc field
423 * @tty: tty structure
424 * @disc: line discipline number
425 *
426 * This is probably overkill for real world processors but
427 * they are not on hot paths so a little discipline won't do
428 * any harm.
429 *
430 * The line discipline-related tty_struct fields are reset to
431 * prevent the ldisc driver from re-using stale information for
432 * the new ldisc instance.
433 *
434 * Locking: takes termios_rwsem
435 */
436
437static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
438{
439 down_write(&tty->termios_rwsem);
440 tty->termios.c_line = disc;
441 up_write(&tty->termios_rwsem);
442
443 tty->disc_data = NULL;
444 tty->receive_room = 0;
445}
446
447/**
448 * tty_ldisc_open - open a line discipline
449 * @tty: tty we are opening the ldisc on
450 * @ld: discipline to open
451 *
452 * A helper opening method. Also a convenient debugging and check
453 * point.
454 *
455 * Locking: always called with BTM already held.
456 */
457
458static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
459{
460 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
461 if (ld->ops->open) {
462 int ret;
463 /* BTM here locks versus a hangup event */
464 ret = ld->ops->open(tty);
465 if (ret)
466 clear_bit(TTY_LDISC_OPEN, &tty->flags);
467
468 tty_ldisc_debug(tty, "%p: opened\n", ld);
469 return ret;
470 }
471 return 0;
472}
473
474/**
475 * tty_ldisc_close - close a line discipline
476 * @tty: tty we are opening the ldisc on
477 * @ld: discipline to close
478 *
479 * A helper close method. Also a convenient debugging and check
480 * point.
481 */
482
483static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
484{
485 lockdep_assert_held_write(&tty->ldisc_sem);
486 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
487 clear_bit(TTY_LDISC_OPEN, &tty->flags);
488 if (ld->ops->close)
489 ld->ops->close(tty);
490 tty_ldisc_debug(tty, "%p: closed\n", ld);
491}
492
493/**
494 * tty_ldisc_failto - helper for ldisc failback
495 * @tty: tty to open the ldisc on
496 * @ld: ldisc we are trying to fail back to
497 *
498 * Helper to try and recover a tty when switching back to the old
499 * ldisc fails and we need something attached.
500 */
501
502static int tty_ldisc_failto(struct tty_struct *tty, int ld)
503{
504 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
505 int r;
506
507 lockdep_assert_held_write(&tty->ldisc_sem);
508 if (IS_ERR(disc))
509 return PTR_ERR(disc);
510 tty->ldisc = disc;
511 tty_set_termios_ldisc(tty, ld);
512 if ((r = tty_ldisc_open(tty, disc)) < 0)
513 tty_ldisc_put(disc);
514 return r;
515}
516
517/**
518 * tty_ldisc_restore - helper for tty ldisc change
519 * @tty: tty to recover
520 * @old: previous ldisc
521 *
522 * Restore the previous line discipline or N_TTY when a line discipline
523 * change fails due to an open error
524 */
525
526static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
527{
528 /* There is an outstanding reference here so this is safe */
529 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
530 const char *name = tty_name(tty);
531
532 pr_warn("Falling back ldisc for %s.\n", name);
533 /* The traditional behaviour is to fall back to N_TTY, we
534 want to avoid falling back to N_NULL unless we have no
535 choice to avoid the risk of breaking anything */
536 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
537 tty_ldisc_failto(tty, N_NULL) < 0)
538 panic("Couldn't open N_NULL ldisc for %s.", name);
539 }
540}
541
542/**
543 * tty_set_ldisc - set line discipline
544 * @tty: the terminal to set
545 * @ldisc: the line discipline
546 *
547 * Set the discipline of a tty line. Must be called from a process
548 * context. The ldisc change logic has to protect itself against any
549 * overlapping ldisc change (including on the other end of pty pairs),
550 * the close of one side of a tty/pty pair, and eventually hangup.
551 */
552
553int tty_set_ldisc(struct tty_struct *tty, int disc)
554{
555 int retval;
556 struct tty_ldisc *old_ldisc, *new_ldisc;
557
558 new_ldisc = tty_ldisc_get(tty, disc);
559 if (IS_ERR(new_ldisc))
560 return PTR_ERR(new_ldisc);
561
562 tty_lock(tty);
563 retval = tty_ldisc_lock(tty, 5 * HZ);
564 if (retval)
565 goto err;
566
567 if (!tty->ldisc) {
568 retval = -EIO;
569 goto out;
570 }
571
572 /* Check the no-op case */
573 if (tty->ldisc->ops->num == disc)
574 goto out;
575
576 if (test_bit(TTY_HUPPED, &tty->flags)) {
577 /* We were raced by hangup */
578 retval = -EIO;
579 goto out;
580 }
581
582 old_ldisc = tty->ldisc;
583
584 /* Shutdown the old discipline. */
585 tty_ldisc_close(tty, old_ldisc);
586
587 /* Now set up the new line discipline. */
588 tty->ldisc = new_ldisc;
589 tty_set_termios_ldisc(tty, disc);
590
591 retval = tty_ldisc_open(tty, new_ldisc);
592 if (retval < 0) {
593 /* Back to the old one or N_TTY if we can't */
594 tty_ldisc_put(new_ldisc);
595 tty_ldisc_restore(tty, old_ldisc);
596 }
597
598 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
599 down_read(&tty->termios_rwsem);
600 tty->ops->set_ldisc(tty);
601 up_read(&tty->termios_rwsem);
602 }
603
604 /* At this point we hold a reference to the new ldisc and a
605 reference to the old ldisc, or we hold two references to
606 the old ldisc (if it was restored as part of error cleanup
607 above). In either case, releasing a single reference from
608 the old ldisc is correct. */
609 new_ldisc = old_ldisc;
610out:
611 tty_ldisc_unlock(tty);
612
613 /* Restart the work queue in case no characters kick it off. Safe if
614 already running */
615 tty_buffer_restart_work(tty->port);
616err:
617 tty_ldisc_put(new_ldisc); /* drop the extra reference */
618 tty_unlock(tty);
619 return retval;
620}
621EXPORT_SYMBOL_GPL(tty_set_ldisc);
622
623/**
624 * tty_ldisc_kill - teardown ldisc
625 * @tty: tty being released
626 *
627 * Perform final close of the ldisc and reset tty->ldisc
628 */
629static void tty_ldisc_kill(struct tty_struct *tty)
630{
631 lockdep_assert_held_write(&tty->ldisc_sem);
632 if (!tty->ldisc)
633 return;
634 /*
635 * Now kill off the ldisc
636 */
637 tty_ldisc_close(tty, tty->ldisc);
638 tty_ldisc_put(tty->ldisc);
639 /* Force an oops if we mess this up */
640 tty->ldisc = NULL;
641}
642
643/**
644 * tty_reset_termios - reset terminal state
645 * @tty: tty to reset
646 *
647 * Restore a terminal to the driver default state.
648 */
649
650static void tty_reset_termios(struct tty_struct *tty)
651{
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);
657}
658
659
660/**
661 * tty_ldisc_reinit - reinitialise the tty ldisc
662 * @tty: tty to reinit
663 * @disc: line discipline to reinitialize
664 *
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.
670 *
671 * Returns 0 if successful, otherwise error code < 0
672 */
673
674int tty_ldisc_reinit(struct tty_struct *tty, int disc)
675{
676 struct tty_ldisc *ld;
677 int retval;
678
679 lockdep_assert_held_write(&tty->ldisc_sem);
680 ld = tty_ldisc_get(tty, disc);
681 if (IS_ERR(ld)) {
682 BUG_ON(disc == N_TTY);
683 return PTR_ERR(ld);
684 }
685
686 if (tty->ldisc) {
687 tty_ldisc_close(tty, tty->ldisc);
688 tty_ldisc_put(tty->ldisc);
689 }
690
691 /* switch the line discipline */
692 tty->ldisc = ld;
693 tty_set_termios_ldisc(tty, disc);
694 retval = tty_ldisc_open(tty, tty->ldisc);
695 if (retval) {
696 tty_ldisc_put(tty->ldisc);
697 tty->ldisc = NULL;
698 }
699 return retval;
700}
701
702/**
703 * tty_ldisc_hangup - hangup ldisc reset
704 * @tty: tty being hung up
705 *
706 * Some tty devices reset their termios when they receive a hangup
707 * event. In that situation we must also switch back to N_TTY properly
708 * before we reset the termios data.
709 *
710 * Locking: We can take the ldisc mutex as the rest of the code is
711 * careful to allow for this.
712 *
713 * In the pty pair case this occurs in the close() path of the
714 * tty itself so we must be careful about locking rules.
715 */
716
717void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
718{
719 struct tty_ldisc *ld;
720
721 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
722
723 ld = tty_ldisc_ref(tty);
724 if (ld != NULL) {
725 if (ld->ops->flush_buffer)
726 ld->ops->flush_buffer(tty);
727 tty_driver_flush_buffer(tty);
728 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
729 ld->ops->write_wakeup)
730 ld->ops->write_wakeup(tty);
731 if (ld->ops->hangup)
732 ld->ops->hangup(tty);
733 tty_ldisc_deref(ld);
734 }
735
736 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
737 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
738
739 /*
740 * Shutdown the current line discipline, and reset it to
741 * N_TTY if need be.
742 *
743 * Avoid racing set_ldisc or tty_ldisc_release
744 */
745 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
746
747 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
748 tty_reset_termios(tty);
749
750 if (tty->ldisc) {
751 if (reinit) {
752 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
753 tty_ldisc_reinit(tty, N_TTY) < 0)
754 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
755 } else
756 tty_ldisc_kill(tty);
757 }
758 tty_ldisc_unlock(tty);
759}
760
761/**
762 * tty_ldisc_setup - open line discipline
763 * @tty: tty being shut down
764 * @o_tty: pair tty for pty/tty pairs
765 *
766 * Called during the initial open of a tty/pty pair in order to set up the
767 * line disciplines and bind them to the tty. This has no locking issues
768 * as the device isn't yet active.
769 */
770
771int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
772{
773 int retval = tty_ldisc_open(tty, tty->ldisc);
774 if (retval)
775 return retval;
776
777 if (o_tty) {
778 /*
779 * Called without o_tty->ldisc_sem held, as o_tty has been
780 * just allocated and no one has a reference to it.
781 */
782 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
783 if (retval) {
784 tty_ldisc_close(tty, tty->ldisc);
785 return retval;
786 }
787 }
788 return 0;
789}
790
791/**
792 * tty_ldisc_release - release line discipline
793 * @tty: tty being shut down (or one end of pty pair)
794 *
795 * Called during the final close of a tty or a pty pair in order to shut
796 * down the line discpline layer. On exit, each tty's ldisc is NULL.
797 */
798
799void tty_ldisc_release(struct tty_struct *tty)
800{
801 struct tty_struct *o_tty = tty->link;
802
803 /*
804 * Shutdown this line discipline. As this is the final close,
805 * it does not race with the set_ldisc code path.
806 */
807
808 tty_ldisc_lock_pair(tty, o_tty);
809 tty_ldisc_kill(tty);
810 if (o_tty)
811 tty_ldisc_kill(o_tty);
812 tty_ldisc_unlock_pair(tty, o_tty);
813
814 /* And the memory resources remaining (buffers, termios) will be
815 disposed of when the kref hits zero */
816
817 tty_ldisc_debug(tty, "released\n");
818}
819EXPORT_SYMBOL_GPL(tty_ldisc_release);
820
821/**
822 * tty_ldisc_init - ldisc setup for new tty
823 * @tty: tty being allocated
824 *
825 * Set up the line discipline objects for a newly allocated tty. Note that
826 * the tty structure is not completely set up when this call is made.
827 */
828
829int tty_ldisc_init(struct tty_struct *tty)
830{
831 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
832 if (IS_ERR(ld))
833 return PTR_ERR(ld);
834 tty->ldisc = ld;
835 return 0;
836}
837
838/**
839 * tty_ldisc_deinit - ldisc cleanup for new tty
840 * @tty: tty that was allocated recently
841 *
842 * The tty structure must not becompletely set up (tty_ldisc_setup) when
843 * this call is made.
844 */
845void tty_ldisc_deinit(struct tty_struct *tty)
846{
847 /* no ldisc_sem, tty is being destroyed */
848 if (tty->ldisc)
849 tty_ldisc_put(tty->ldisc);
850 tty->ldisc = NULL;
851}
852
853static struct ctl_table tty_table[] = {
854 {
855 .procname = "ldisc_autoload",
856 .data = &tty_ldisc_autoload,
857 .maxlen = sizeof(tty_ldisc_autoload),
858 .mode = 0644,
859 .proc_handler = proc_dointvec,
860 .extra1 = SYSCTL_ZERO,
861 .extra2 = SYSCTL_ONE,
862 },
863 { }
864};
865
866static struct ctl_table tty_dir_table[] = {
867 {
868 .procname = "tty",
869 .mode = 0555,
870 .child = tty_table,
871 },
872 { }
873};
874
875static struct ctl_table tty_root_table[] = {
876 {
877 .procname = "dev",
878 .mode = 0555,
879 .child = tty_dir_table,
880 },
881 { }
882};
883
884void tty_sysctl_init(void)
885{
886 register_sysctl_table(tty_root_table);
887}
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>
7#include <linux/tty.h>
8#include <linux/tty_driver.h>
9#include <linux/file.h>
10#include <linux/mm.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>
22
23#undef LDISC_DEBUG_HANGUP
24
25#ifdef LDISC_DEBUG_HANGUP
26#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
27#else
28#define tty_ldisc_debug(tty, f, args...)
29#endif
30
31/* lockdep nested classes for tty->ldisc_sem */
32enum {
33 LDISC_SEM_NORMAL,
34 LDISC_SEM_OTHER,
35};
36
37
38/*
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.
42 */
43
44static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
45/* Line disc dispatch table */
46static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
47
48/**
49 * tty_register_ldisc - install a line discipline
50 * @disc: ldisc number
51 * @new_ldisc: pointer to the ldisc object
52 *
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.
56 *
57 * Locking:
58 * takes tty_ldiscs_lock to guard against ldisc races
59 */
60
61int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
62{
63 unsigned long flags;
64 int ret = 0;
65
66 if (disc < N_TTY || disc >= NR_LDISCS)
67 return -EINVAL;
68
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);
74
75 return ret;
76}
77EXPORT_SYMBOL(tty_register_ldisc);
78
79/**
80 * tty_unregister_ldisc - unload a line discipline
81 * @disc: ldisc number
82 * @new_ldisc: pointer to the ldisc object
83 *
84 * Remove a line discipline from the kernel providing it is not
85 * currently in use.
86 *
87 * Locking:
88 * takes tty_ldiscs_lock to guard against ldisc races
89 */
90
91int tty_unregister_ldisc(int disc)
92{
93 unsigned long flags;
94 int ret = 0;
95
96 if (disc < N_TTY || disc >= NR_LDISCS)
97 return -EINVAL;
98
99 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
100 if (tty_ldiscs[disc]->refcount)
101 ret = -EBUSY;
102 else
103 tty_ldiscs[disc] = NULL;
104 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
105
106 return ret;
107}
108EXPORT_SYMBOL(tty_unregister_ldisc);
109
110static struct tty_ldisc_ops *get_ldops(int disc)
111{
112 unsigned long flags;
113 struct tty_ldisc_ops *ldops, *ret;
114
115 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
116 ret = ERR_PTR(-EINVAL);
117 ldops = tty_ldiscs[disc];
118 if (ldops) {
119 ret = ERR_PTR(-EAGAIN);
120 if (try_module_get(ldops->owner)) {
121 ldops->refcount++;
122 ret = ldops;
123 }
124 }
125 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
126 return ret;
127}
128
129static void put_ldops(struct tty_ldisc_ops *ldops)
130{
131 unsigned long flags;
132
133 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
134 ldops->refcount--;
135 module_put(ldops->owner);
136 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
137}
138
139/**
140 * tty_ldisc_get - take a reference to an ldisc
141 * @disc: ldisc number
142 *
143 * Takes a reference to a line discipline. Deals with refcounts and
144 * module locking counts.
145 *
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
149 * the discipline
150 * -ENOMEM if allocation failure
151 *
152 * Otherwise, returns a pointer to the discipline and bumps the
153 * ref count
154 *
155 * Locking:
156 * takes tty_ldiscs_lock to guard against ldisc races
157 */
158
159static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
160{
161 struct tty_ldisc *ld;
162 struct tty_ldisc_ops *ldops;
163
164 if (disc < N_TTY || disc >= NR_LDISCS)
165 return ERR_PTR(-EINVAL);
166
167 /*
168 * Get the ldisc ops - we may need to request them to be loaded
169 * dynamically and try again.
170 */
171 ldops = get_ldops(disc);
172 if (IS_ERR(ldops)) {
173 request_module("tty-ldisc-%d", disc);
174 ldops = get_ldops(disc);
175 if (IS_ERR(ldops))
176 return ERR_CAST(ldops);
177 }
178
179 /*
180 * There is no way to handle allocation failure of only 16 bytes.
181 * Let's simplify error handling and save more memory.
182 */
183 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
184 ld->ops = ldops;
185 ld->tty = tty;
186
187 return ld;
188}
189
190/**
191 * tty_ldisc_put - release the ldisc
192 *
193 * Complement of tty_ldisc_get().
194 */
195static void tty_ldisc_put(struct tty_ldisc *ld)
196{
197 if (WARN_ON_ONCE(!ld))
198 return;
199
200 put_ldops(ld->ops);
201 kfree(ld);
202}
203
204static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
205{
206 return (*pos < NR_LDISCS) ? pos : NULL;
207}
208
209static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
210{
211 (*pos)++;
212 return (*pos < NR_LDISCS) ? pos : NULL;
213}
214
215static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
216{
217}
218
219static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
220{
221 int i = *(loff_t *)v;
222 struct tty_ldisc_ops *ldops;
223
224 ldops = get_ldops(i);
225 if (IS_ERR(ldops))
226 return 0;
227 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
228 put_ldops(ldops);
229 return 0;
230}
231
232static 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,
237};
238
239static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
240{
241 return seq_open(file, &tty_ldiscs_seq_ops);
242}
243
244const struct file_operations tty_ldiscs_proc_fops = {
245 .owner = THIS_MODULE,
246 .open = proc_tty_ldiscs_open,
247 .read = seq_read,
248 .llseek = seq_lseek,
249 .release = seq_release,
250};
251
252/**
253 * tty_ldisc_ref_wait - wait for the tty ldisc
254 * @tty: tty device
255 *
256 * Dereference the line discipline for the terminal and take a
257 * reference to it. If the line discipline is in flux then
258 * wait patiently until it changes.
259 *
260 * Returns: NULL if the tty has been hungup and not re-opened with
261 * a new file descriptor, otherwise valid ldisc reference
262 *
263 * Note: Must not be called from an IRQ/timer context. The caller
264 * must also be careful not to hold other locks that will deadlock
265 * against a discipline change, such as an existing ldisc reference
266 * (which we check for)
267 *
268 * Note: a file_operations routine (read/poll/write) should use this
269 * function to wait for any ldisc lifetime events to finish.
270 */
271
272struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
273{
274 struct tty_ldisc *ld;
275
276 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
277 ld = tty->ldisc;
278 if (!ld)
279 ldsem_up_read(&tty->ldisc_sem);
280 return ld;
281}
282EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
283
284/**
285 * tty_ldisc_ref - get the tty ldisc
286 * @tty: tty device
287 *
288 * Dereference the line discipline for the terminal and take a
289 * reference to it. If the line discipline is in flux then
290 * return NULL. Can be called from IRQ and timer functions.
291 */
292
293struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
294{
295 struct tty_ldisc *ld = NULL;
296
297 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
298 ld = tty->ldisc;
299 if (!ld)
300 ldsem_up_read(&tty->ldisc_sem);
301 }
302 return ld;
303}
304EXPORT_SYMBOL_GPL(tty_ldisc_ref);
305
306/**
307 * tty_ldisc_deref - free a tty ldisc reference
308 * @ld: reference to free up
309 *
310 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
311 * be called in IRQ context.
312 */
313
314void tty_ldisc_deref(struct tty_ldisc *ld)
315{
316 ldsem_up_read(&ld->tty->ldisc_sem);
317}
318EXPORT_SYMBOL_GPL(tty_ldisc_deref);
319
320
321static inline int
322__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
323{
324 return ldsem_down_write(&tty->ldisc_sem, timeout);
325}
326
327static inline int
328__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
329{
330 return ldsem_down_write_nested(&tty->ldisc_sem,
331 LDISC_SEM_OTHER, timeout);
332}
333
334static inline void __tty_ldisc_unlock(struct tty_struct *tty)
335{
336 ldsem_up_write(&tty->ldisc_sem);
337}
338
339int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
340{
341 int ret;
342
343 ret = __tty_ldisc_lock(tty, timeout);
344 if (!ret)
345 return -EBUSY;
346 set_bit(TTY_LDISC_HALTED, &tty->flags);
347 return 0;
348}
349
350void tty_ldisc_unlock(struct tty_struct *tty)
351{
352 clear_bit(TTY_LDISC_HALTED, &tty->flags);
353 __tty_ldisc_unlock(tty);
354}
355
356static int
357tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
358 unsigned long timeout)
359{
360 int ret;
361
362 if (tty < tty2) {
363 ret = __tty_ldisc_lock(tty, timeout);
364 if (ret) {
365 ret = __tty_ldisc_lock_nested(tty2, timeout);
366 if (!ret)
367 __tty_ldisc_unlock(tty);
368 }
369 } else {
370 /* if this is possible, it has lots of implications */
371 WARN_ON_ONCE(tty == tty2);
372 if (tty2 && tty != tty2) {
373 ret = __tty_ldisc_lock(tty2, timeout);
374 if (ret) {
375 ret = __tty_ldisc_lock_nested(tty, timeout);
376 if (!ret)
377 __tty_ldisc_unlock(tty2);
378 }
379 } else
380 ret = __tty_ldisc_lock(tty, timeout);
381 }
382
383 if (!ret)
384 return -EBUSY;
385
386 set_bit(TTY_LDISC_HALTED, &tty->flags);
387 if (tty2)
388 set_bit(TTY_LDISC_HALTED, &tty2->flags);
389 return 0;
390}
391
392static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
393{
394 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
395}
396
397static void tty_ldisc_unlock_pair(struct tty_struct *tty,
398 struct tty_struct *tty2)
399{
400 __tty_ldisc_unlock(tty);
401 if (tty2)
402 __tty_ldisc_unlock(tty2);
403}
404
405/**
406 * tty_ldisc_flush - flush line discipline queue
407 * @tty: tty
408 *
409 * Flush the line discipline queue (if any) and the tty flip buffers
410 * for this tty.
411 */
412
413void tty_ldisc_flush(struct tty_struct *tty)
414{
415 struct tty_ldisc *ld = tty_ldisc_ref(tty);
416
417 tty_buffer_flush(tty, ld);
418 if (ld)
419 tty_ldisc_deref(ld);
420}
421EXPORT_SYMBOL_GPL(tty_ldisc_flush);
422
423/**
424 * tty_set_termios_ldisc - set ldisc field
425 * @tty: tty structure
426 * @disc: line discipline number
427 *
428 * This is probably overkill for real world processors but
429 * they are not on hot paths so a little discipline won't do
430 * any harm.
431 *
432 * The line discipline-related tty_struct fields are reset to
433 * prevent the ldisc driver from re-using stale information for
434 * the new ldisc instance.
435 *
436 * Locking: takes termios_rwsem
437 */
438
439static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
440{
441 down_write(&tty->termios_rwsem);
442 tty->termios.c_line = disc;
443 up_write(&tty->termios_rwsem);
444
445 tty->disc_data = NULL;
446 tty->receive_room = 0;
447}
448
449/**
450 * tty_ldisc_open - open a line discipline
451 * @tty: tty we are opening the ldisc on
452 * @ld: discipline to open
453 *
454 * A helper opening method. Also a convenient debugging and check
455 * point.
456 *
457 * Locking: always called with BTM already held.
458 */
459
460static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
461{
462 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
463 if (ld->ops->open) {
464 int ret;
465 /* BTM here locks versus a hangup event */
466 ret = ld->ops->open(tty);
467 if (ret)
468 clear_bit(TTY_LDISC_OPEN, &tty->flags);
469
470 tty_ldisc_debug(tty, "%p: opened\n", ld);
471 return ret;
472 }
473 return 0;
474}
475
476/**
477 * tty_ldisc_close - close a line discipline
478 * @tty: tty we are opening the ldisc on
479 * @ld: discipline to close
480 *
481 * A helper close method. Also a convenient debugging and check
482 * point.
483 */
484
485static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
486{
487 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
488 clear_bit(TTY_LDISC_OPEN, &tty->flags);
489 if (ld->ops->close)
490 ld->ops->close(tty);
491 tty_ldisc_debug(tty, "%p: closed\n", ld);
492}
493
494/**
495 * tty_ldisc_failto - helper for ldisc failback
496 * @tty: tty to open the ldisc on
497 * @ld: ldisc we are trying to fail back to
498 *
499 * Helper to try and recover a tty when switching back to the old
500 * ldisc fails and we need something attached.
501 */
502
503static int tty_ldisc_failto(struct tty_struct *tty, int ld)
504{
505 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
506 int r;
507
508 if (IS_ERR(disc))
509 return PTR_ERR(disc);
510 tty->ldisc = disc;
511 tty_set_termios_ldisc(tty, ld);
512 if ((r = tty_ldisc_open(tty, disc)) < 0)
513 tty_ldisc_put(disc);
514 return r;
515}
516
517/**
518 * tty_ldisc_restore - helper for tty ldisc change
519 * @tty: tty to recover
520 * @old: previous ldisc
521 *
522 * Restore the previous line discipline or N_TTY when a line discipline
523 * change fails due to an open error
524 */
525
526static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
527{
528 /* There is an outstanding reference here so this is safe */
529 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
530 const char *name = tty_name(tty);
531
532 pr_warn("Falling back ldisc for %s.\n", name);
533 /* The traditional behaviour is to fall back to N_TTY, we
534 want to avoid falling back to N_NULL unless we have no
535 choice to avoid the risk of breaking anything */
536 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
537 tty_ldisc_failto(tty, N_NULL) < 0)
538 panic("Couldn't open N_NULL ldisc for %s.", name);
539 }
540}
541
542/**
543 * tty_set_ldisc - set line discipline
544 * @tty: the terminal to set
545 * @ldisc: the line discipline
546 *
547 * Set the discipline of a tty line. Must be called from a process
548 * context. The ldisc change logic has to protect itself against any
549 * overlapping ldisc change (including on the other end of pty pairs),
550 * the close of one side of a tty/pty pair, and eventually hangup.
551 */
552
553int tty_set_ldisc(struct tty_struct *tty, int disc)
554{
555 int retval;
556 struct tty_ldisc *old_ldisc, *new_ldisc;
557
558 new_ldisc = tty_ldisc_get(tty, disc);
559 if (IS_ERR(new_ldisc))
560 return PTR_ERR(new_ldisc);
561
562 tty_lock(tty);
563 retval = tty_ldisc_lock(tty, 5 * HZ);
564 if (retval)
565 goto err;
566
567 if (!tty->ldisc) {
568 retval = -EIO;
569 goto out;
570 }
571
572 /* Check the no-op case */
573 if (tty->ldisc->ops->num == disc)
574 goto out;
575
576 if (test_bit(TTY_HUPPED, &tty->flags)) {
577 /* We were raced by hangup */
578 retval = -EIO;
579 goto out;
580 }
581
582 old_ldisc = tty->ldisc;
583
584 /* Shutdown the old discipline. */
585 tty_ldisc_close(tty, old_ldisc);
586
587 /* Now set up the new line discipline. */
588 tty->ldisc = new_ldisc;
589 tty_set_termios_ldisc(tty, disc);
590
591 retval = tty_ldisc_open(tty, new_ldisc);
592 if (retval < 0) {
593 /* Back to the old one or N_TTY if we can't */
594 tty_ldisc_put(new_ldisc);
595 tty_ldisc_restore(tty, old_ldisc);
596 }
597
598 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
599 down_read(&tty->termios_rwsem);
600 tty->ops->set_ldisc(tty);
601 up_read(&tty->termios_rwsem);
602 }
603
604 /* At this point we hold a reference to the new ldisc and a
605 reference to the old ldisc, or we hold two references to
606 the old ldisc (if it was restored as part of error cleanup
607 above). In either case, releasing a single reference from
608 the old ldisc is correct. */
609 new_ldisc = old_ldisc;
610out:
611 tty_ldisc_unlock(tty);
612
613 /* Restart the work queue in case no characters kick it off. Safe if
614 already running */
615 tty_buffer_restart_work(tty->port);
616err:
617 tty_ldisc_put(new_ldisc); /* drop the extra reference */
618 tty_unlock(tty);
619 return retval;
620}
621EXPORT_SYMBOL_GPL(tty_set_ldisc);
622
623/**
624 * tty_ldisc_kill - teardown ldisc
625 * @tty: tty being released
626 *
627 * Perform final close of the ldisc and reset tty->ldisc
628 */
629static void tty_ldisc_kill(struct tty_struct *tty)
630{
631 if (!tty->ldisc)
632 return;
633 /*
634 * Now kill off the ldisc
635 */
636 tty_ldisc_close(tty, tty->ldisc);
637 tty_ldisc_put(tty->ldisc);
638 /* Force an oops if we mess this up */
639 tty->ldisc = NULL;
640}
641
642/**
643 * tty_reset_termios - reset terminal state
644 * @tty: tty to reset
645 *
646 * Restore a terminal to the driver default state.
647 */
648
649static void tty_reset_termios(struct tty_struct *tty)
650{
651 down_write(&tty->termios_rwsem);
652 tty->termios = tty->driver->init_termios;
653 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
654 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
655 up_write(&tty->termios_rwsem);
656}
657
658
659/**
660 * tty_ldisc_reinit - reinitialise the tty ldisc
661 * @tty: tty to reinit
662 * @disc: line discipline to reinitialize
663 *
664 * Completely reinitialize the line discipline state, by closing the
665 * current instance, if there is one, and opening a new instance. If
666 * an error occurs opening the new non-N_TTY instance, the instance
667 * is dropped and tty->ldisc reset to NULL. The caller can then retry
668 * with N_TTY instead.
669 *
670 * Returns 0 if successful, otherwise error code < 0
671 */
672
673int tty_ldisc_reinit(struct tty_struct *tty, int disc)
674{
675 struct tty_ldisc *ld;
676 int retval;
677
678 ld = tty_ldisc_get(tty, disc);
679 if (IS_ERR(ld)) {
680 BUG_ON(disc == N_TTY);
681 return PTR_ERR(ld);
682 }
683
684 if (tty->ldisc) {
685 tty_ldisc_close(tty, tty->ldisc);
686 tty_ldisc_put(tty->ldisc);
687 }
688
689 /* switch the line discipline */
690 tty->ldisc = ld;
691 tty_set_termios_ldisc(tty, disc);
692 retval = tty_ldisc_open(tty, tty->ldisc);
693 if (retval) {
694 tty_ldisc_put(tty->ldisc);
695 tty->ldisc = NULL;
696 }
697 return retval;
698}
699
700/**
701 * tty_ldisc_hangup - hangup ldisc reset
702 * @tty: tty being hung up
703 *
704 * Some tty devices reset their termios when they receive a hangup
705 * event. In that situation we must also switch back to N_TTY properly
706 * before we reset the termios data.
707 *
708 * Locking: We can take the ldisc mutex as the rest of the code is
709 * careful to allow for this.
710 *
711 * In the pty pair case this occurs in the close() path of the
712 * tty itself so we must be careful about locking rules.
713 */
714
715void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
716{
717 struct tty_ldisc *ld;
718
719 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
720
721 ld = tty_ldisc_ref(tty);
722 if (ld != NULL) {
723 if (ld->ops->flush_buffer)
724 ld->ops->flush_buffer(tty);
725 tty_driver_flush_buffer(tty);
726 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
727 ld->ops->write_wakeup)
728 ld->ops->write_wakeup(tty);
729 if (ld->ops->hangup)
730 ld->ops->hangup(tty);
731 tty_ldisc_deref(ld);
732 }
733
734 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
735 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
736
737 /*
738 * Shutdown the current line discipline, and reset it to
739 * N_TTY if need be.
740 *
741 * Avoid racing set_ldisc or tty_ldisc_release
742 */
743 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
744
745 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
746 tty_reset_termios(tty);
747
748 if (tty->ldisc) {
749 if (reinit) {
750 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
751 tty_ldisc_reinit(tty, N_TTY) < 0)
752 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
753 } else
754 tty_ldisc_kill(tty);
755 }
756 tty_ldisc_unlock(tty);
757}
758
759/**
760 * tty_ldisc_setup - open line discipline
761 * @tty: tty being shut down
762 * @o_tty: pair tty for pty/tty pairs
763 *
764 * Called during the initial open of a tty/pty pair in order to set up the
765 * line disciplines and bind them to the tty. This has no locking issues
766 * as the device isn't yet active.
767 */
768
769int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
770{
771 int retval = tty_ldisc_open(tty, tty->ldisc);
772 if (retval)
773 return retval;
774
775 if (o_tty) {
776 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
777 if (retval) {
778 tty_ldisc_close(tty, tty->ldisc);
779 return retval;
780 }
781 }
782 return 0;
783}
784
785/**
786 * tty_ldisc_release - release line discipline
787 * @tty: tty being shut down (or one end of pty pair)
788 *
789 * Called during the final close of a tty or a pty pair in order to shut
790 * down the line discpline layer. On exit, each tty's ldisc is NULL.
791 */
792
793void tty_ldisc_release(struct tty_struct *tty)
794{
795 struct tty_struct *o_tty = tty->link;
796
797 /*
798 * Shutdown this line discipline. As this is the final close,
799 * it does not race with the set_ldisc code path.
800 */
801
802 tty_ldisc_lock_pair(tty, o_tty);
803 tty_ldisc_kill(tty);
804 if (o_tty)
805 tty_ldisc_kill(o_tty);
806 tty_ldisc_unlock_pair(tty, o_tty);
807
808 /* And the memory resources remaining (buffers, termios) will be
809 disposed of when the kref hits zero */
810
811 tty_ldisc_debug(tty, "released\n");
812}
813EXPORT_SYMBOL_GPL(tty_ldisc_release);
814
815/**
816 * tty_ldisc_init - ldisc setup for new tty
817 * @tty: tty being allocated
818 *
819 * Set up the line discipline objects for a newly allocated tty. Note that
820 * the tty structure is not completely set up when this call is made.
821 */
822
823int tty_ldisc_init(struct tty_struct *tty)
824{
825 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
826 if (IS_ERR(ld))
827 return PTR_ERR(ld);
828 tty->ldisc = ld;
829 return 0;
830}
831
832/**
833 * tty_ldisc_deinit - ldisc cleanup for new tty
834 * @tty: tty that was allocated recently
835 *
836 * The tty structure must not becompletely set up (tty_ldisc_setup) when
837 * this call is made.
838 */
839void tty_ldisc_deinit(struct tty_struct *tty)
840{
841 if (tty->ldisc)
842 tty_ldisc_put(tty->ldisc);
843 tty->ldisc = NULL;
844}