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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#include "tty.h"
23
24#undef LDISC_DEBUG_HANGUP
25
26#ifdef LDISC_DEBUG_HANGUP
27#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
28#else
29#define tty_ldisc_debug(tty, f, args...)
30#endif
31
32/* lockdep nested classes for tty->ldisc_sem */
33enum {
34 LDISC_SEM_NORMAL,
35 LDISC_SEM_OTHER,
36};
37
38
39/*
40 * This guards the refcounted line discipline lists. The lock
41 * must be taken with irqs off because there are hangup path
42 * callers who will do ldisc lookups and cannot sleep.
43 */
44
45static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
46/* Line disc dispatch table */
47static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
48
49/**
50 * tty_register_ldisc - install a line discipline
51 * @new_ldisc: pointer to the ldisc object
52 *
53 * Installs a new line discipline into the kernel. The discipline is set up as
54 * unreferenced and then made available to the kernel from this point onwards.
55 *
56 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
57 */
58int tty_register_ldisc(struct tty_ldisc_ops *new_ldisc)
59{
60 unsigned long flags;
61
62 if (new_ldisc->num < N_TTY || new_ldisc->num >= NR_LDISCS)
63 return -EINVAL;
64
65 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
66 tty_ldiscs[new_ldisc->num] = new_ldisc;
67 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
68
69 return 0;
70}
71EXPORT_SYMBOL(tty_register_ldisc);
72
73/**
74 * tty_unregister_ldisc - unload a line discipline
75 * @ldisc: ldisc number
76 *
77 * Remove a line discipline from the kernel providing it is not currently in
78 * use.
79 *
80 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
81 */
82
83void tty_unregister_ldisc(struct tty_ldisc_ops *ldisc)
84{
85 unsigned long flags;
86
87 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
88 tty_ldiscs[ldisc->num] = NULL;
89 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
90}
91EXPORT_SYMBOL(tty_unregister_ldisc);
92
93static struct tty_ldisc_ops *get_ldops(int disc)
94{
95 unsigned long flags;
96 struct tty_ldisc_ops *ldops, *ret;
97
98 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
99 ret = ERR_PTR(-EINVAL);
100 ldops = tty_ldiscs[disc];
101 if (ldops) {
102 ret = ERR_PTR(-EAGAIN);
103 if (try_module_get(ldops->owner))
104 ret = ldops;
105 }
106 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
107 return ret;
108}
109
110static void put_ldops(struct tty_ldisc_ops *ldops)
111{
112 unsigned long flags;
113
114 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
115 module_put(ldops->owner);
116 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
117}
118
119int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
120
121/**
122 * tty_ldisc_get - take a reference to an ldisc
123 * @tty: tty device
124 * @disc: ldisc number
125 *
126 * Takes a reference to a line discipline. Deals with refcounts and module
127 * locking counts. If the discipline is not available, its module loaded, if
128 * possible.
129 *
130 * Returns:
131 * * -%EINVAL if the discipline index is not [%N_TTY .. %NR_LDISCS] or if the
132 * discipline is not registered
133 * * -%EAGAIN if request_module() failed to load or register the discipline
134 * * -%ENOMEM if allocation failure
135 * * Otherwise, returns a pointer to the discipline and bumps the ref count
136 *
137 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
138 */
139static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
140{
141 struct tty_ldisc *ld;
142 struct tty_ldisc_ops *ldops;
143
144 if (disc < N_TTY || disc >= NR_LDISCS)
145 return ERR_PTR(-EINVAL);
146
147 /*
148 * Get the ldisc ops - we may need to request them to be loaded
149 * dynamically and try again.
150 */
151 ldops = get_ldops(disc);
152 if (IS_ERR(ldops)) {
153 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
154 return ERR_PTR(-EPERM);
155 request_module("tty-ldisc-%d", disc);
156 ldops = get_ldops(disc);
157 if (IS_ERR(ldops))
158 return ERR_CAST(ldops);
159 }
160
161 /*
162 * There is no way to handle allocation failure of only 16 bytes.
163 * Let's simplify error handling and save more memory.
164 */
165 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
166 ld->ops = ldops;
167 ld->tty = tty;
168
169 return ld;
170}
171
172/**
173 * tty_ldisc_put - release the ldisc
174 * @ld: lisdsc to release
175 *
176 * Complement of tty_ldisc_get().
177 */
178static void tty_ldisc_put(struct tty_ldisc *ld)
179{
180 if (WARN_ON_ONCE(!ld))
181 return;
182
183 put_ldops(ld->ops);
184 kfree(ld);
185}
186
187static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
188{
189 return (*pos < NR_LDISCS) ? pos : NULL;
190}
191
192static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
193{
194 (*pos)++;
195 return (*pos < NR_LDISCS) ? pos : NULL;
196}
197
198static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
199{
200}
201
202static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
203{
204 int i = *(loff_t *)v;
205 struct tty_ldisc_ops *ldops;
206
207 ldops = get_ldops(i);
208 if (IS_ERR(ldops))
209 return 0;
210 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
211 put_ldops(ldops);
212 return 0;
213}
214
215const struct seq_operations tty_ldiscs_seq_ops = {
216 .start = tty_ldiscs_seq_start,
217 .next = tty_ldiscs_seq_next,
218 .stop = tty_ldiscs_seq_stop,
219 .show = tty_ldiscs_seq_show,
220};
221
222/**
223 * tty_ldisc_ref_wait - wait for the tty ldisc
224 * @tty: tty device
225 *
226 * Dereference the line discipline for the terminal and take a reference to it.
227 * If the line discipline is in flux then wait patiently until it changes.
228 *
229 * Returns: %NULL if the tty has been hungup and not re-opened with a new file
230 * descriptor, otherwise valid ldisc reference
231 *
232 * Note 1: Must not be called from an IRQ/timer context. The caller must also
233 * be careful not to hold other locks that will deadlock against a discipline
234 * change, such as an existing ldisc reference (which we check for).
235 *
236 * Note 2: a file_operations routine (read/poll/write) should use this function
237 * to wait for any ldisc lifetime events to finish.
238 */
239struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
240{
241 struct tty_ldisc *ld;
242
243 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
244 ld = tty->ldisc;
245 if (!ld)
246 ldsem_up_read(&tty->ldisc_sem);
247 return ld;
248}
249EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
250
251/**
252 * tty_ldisc_ref - get the tty ldisc
253 * @tty: tty device
254 *
255 * Dereference the line discipline for the terminal and take a reference to it.
256 * If the line discipline is in flux then return %NULL. Can be called from IRQ
257 * and timer functions.
258 */
259struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
260{
261 struct tty_ldisc *ld = NULL;
262
263 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
264 ld = tty->ldisc;
265 if (!ld)
266 ldsem_up_read(&tty->ldisc_sem);
267 }
268 return ld;
269}
270EXPORT_SYMBOL_GPL(tty_ldisc_ref);
271
272/**
273 * tty_ldisc_deref - free a tty ldisc reference
274 * @ld: reference to free up
275 *
276 * Undoes the effect of tty_ldisc_ref() or tty_ldisc_ref_wait(). May be called
277 * in IRQ context.
278 */
279void tty_ldisc_deref(struct tty_ldisc *ld)
280{
281 ldsem_up_read(&ld->tty->ldisc_sem);
282}
283EXPORT_SYMBOL_GPL(tty_ldisc_deref);
284
285
286static inline int
287__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
288{
289 return ldsem_down_write(&tty->ldisc_sem, timeout);
290}
291
292static inline int
293__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
294{
295 return ldsem_down_write_nested(&tty->ldisc_sem,
296 LDISC_SEM_OTHER, timeout);
297}
298
299static inline void __tty_ldisc_unlock(struct tty_struct *tty)
300{
301 ldsem_up_write(&tty->ldisc_sem);
302}
303
304int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
305{
306 int ret;
307
308 /* Kindly asking blocked readers to release the read side */
309 set_bit(TTY_LDISC_CHANGING, &tty->flags);
310 wake_up_interruptible_all(&tty->read_wait);
311 wake_up_interruptible_all(&tty->write_wait);
312
313 ret = __tty_ldisc_lock(tty, timeout);
314 if (!ret)
315 return -EBUSY;
316 set_bit(TTY_LDISC_HALTED, &tty->flags);
317 return 0;
318}
319
320void tty_ldisc_unlock(struct tty_struct *tty)
321{
322 clear_bit(TTY_LDISC_HALTED, &tty->flags);
323 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
324 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
325 __tty_ldisc_unlock(tty);
326}
327
328static int
329tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
330 unsigned long timeout)
331{
332 int ret;
333
334 if (tty < tty2) {
335 ret = __tty_ldisc_lock(tty, timeout);
336 if (ret) {
337 ret = __tty_ldisc_lock_nested(tty2, timeout);
338 if (!ret)
339 __tty_ldisc_unlock(tty);
340 }
341 } else {
342 /* if this is possible, it has lots of implications */
343 WARN_ON_ONCE(tty == tty2);
344 if (tty2 && tty != tty2) {
345 ret = __tty_ldisc_lock(tty2, timeout);
346 if (ret) {
347 ret = __tty_ldisc_lock_nested(tty, timeout);
348 if (!ret)
349 __tty_ldisc_unlock(tty2);
350 }
351 } else
352 ret = __tty_ldisc_lock(tty, timeout);
353 }
354
355 if (!ret)
356 return -EBUSY;
357
358 set_bit(TTY_LDISC_HALTED, &tty->flags);
359 if (tty2)
360 set_bit(TTY_LDISC_HALTED, &tty2->flags);
361 return 0;
362}
363
364static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
365{
366 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
367}
368
369static void tty_ldisc_unlock_pair(struct tty_struct *tty,
370 struct tty_struct *tty2)
371{
372 __tty_ldisc_unlock(tty);
373 if (tty2)
374 __tty_ldisc_unlock(tty2);
375}
376
377/**
378 * tty_ldisc_flush - flush line discipline queue
379 * @tty: tty to flush ldisc for
380 *
381 * Flush the line discipline queue (if any) and the tty flip buffers for this
382 * @tty.
383 */
384void tty_ldisc_flush(struct tty_struct *tty)
385{
386 struct tty_ldisc *ld = tty_ldisc_ref(tty);
387
388 tty_buffer_flush(tty, ld);
389 if (ld)
390 tty_ldisc_deref(ld);
391}
392EXPORT_SYMBOL_GPL(tty_ldisc_flush);
393
394/**
395 * tty_set_termios_ldisc - set ldisc field
396 * @tty: tty structure
397 * @disc: line discipline number
398 *
399 * This is probably overkill for real world processors but they are not on hot
400 * paths so a little discipline won't do any harm.
401 *
402 * The line discipline-related tty_struct fields are reset to prevent the ldisc
403 * driver from re-using stale information for the new ldisc instance.
404 *
405 * Locking: takes termios_rwsem
406 */
407static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
408{
409 down_write(&tty->termios_rwsem);
410 tty->termios.c_line = disc;
411 up_write(&tty->termios_rwsem);
412
413 tty->disc_data = NULL;
414 tty->receive_room = 0;
415}
416
417/**
418 * tty_ldisc_open - open a line discipline
419 * @tty: tty we are opening the ldisc on
420 * @ld: discipline to open
421 *
422 * A helper opening method. Also a convenient debugging and check point.
423 *
424 * Locking: always called with BTM already held.
425 */
426static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
427{
428 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
429 if (ld->ops->open) {
430 int ret;
431 /* BTM here locks versus a hangup event */
432 ret = ld->ops->open(tty);
433 if (ret)
434 clear_bit(TTY_LDISC_OPEN, &tty->flags);
435
436 tty_ldisc_debug(tty, "%p: opened\n", ld);
437 return ret;
438 }
439 return 0;
440}
441
442/**
443 * tty_ldisc_close - close a line discipline
444 * @tty: tty we are opening the ldisc on
445 * @ld: discipline to close
446 *
447 * A helper close method. Also a convenient debugging and check point.
448 */
449static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
450{
451 lockdep_assert_held_write(&tty->ldisc_sem);
452 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
453 clear_bit(TTY_LDISC_OPEN, &tty->flags);
454 if (ld->ops->close)
455 ld->ops->close(tty);
456 tty_ldisc_debug(tty, "%p: closed\n", ld);
457}
458
459/**
460 * tty_ldisc_failto - helper for ldisc failback
461 * @tty: tty to open the ldisc on
462 * @ld: ldisc we are trying to fail back to
463 *
464 * Helper to try and recover a tty when switching back to the old ldisc fails
465 * and we need something attached.
466 */
467static int tty_ldisc_failto(struct tty_struct *tty, int ld)
468{
469 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
470 int r;
471
472 lockdep_assert_held_write(&tty->ldisc_sem);
473 if (IS_ERR(disc))
474 return PTR_ERR(disc);
475 tty->ldisc = disc;
476 tty_set_termios_ldisc(tty, ld);
477 r = tty_ldisc_open(tty, disc);
478 if (r < 0)
479 tty_ldisc_put(disc);
480 return r;
481}
482
483/**
484 * tty_ldisc_restore - helper for tty ldisc change
485 * @tty: tty to recover
486 * @old: previous ldisc
487 *
488 * Restore the previous line discipline or %N_TTY when a line discipline change
489 * fails due to an open error
490 */
491static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
492{
493 /* There is an outstanding reference here so this is safe */
494 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
495 const char *name = tty_name(tty);
496
497 pr_warn("Falling back ldisc for %s.\n", name);
498 /*
499 * The traditional behaviour is to fall back to N_TTY, we
500 * want to avoid falling back to N_NULL unless we have no
501 * choice to avoid the risk of breaking anything
502 */
503 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
504 tty_ldisc_failto(tty, N_NULL) < 0)
505 panic("Couldn't open N_NULL ldisc for %s.", name);
506 }
507}
508
509/**
510 * tty_set_ldisc - set line discipline
511 * @tty: the terminal to set
512 * @disc: the line discipline number
513 *
514 * Set the discipline of a tty line. Must be called from a process context. The
515 * ldisc change logic has to protect itself against any overlapping ldisc
516 * change (including on the other end of pty pairs), the close of one side of a
517 * tty/pty pair, and eventually hangup.
518 */
519int tty_set_ldisc(struct tty_struct *tty, int disc)
520{
521 int retval;
522 struct tty_ldisc *old_ldisc, *new_ldisc;
523
524 new_ldisc = tty_ldisc_get(tty, disc);
525 if (IS_ERR(new_ldisc))
526 return PTR_ERR(new_ldisc);
527
528 tty_lock(tty);
529 retval = tty_ldisc_lock(tty, 5 * HZ);
530 if (retval)
531 goto err;
532
533 if (!tty->ldisc) {
534 retval = -EIO;
535 goto out;
536 }
537
538 /* Check the no-op case */
539 if (tty->ldisc->ops->num == disc)
540 goto out;
541
542 if (test_bit(TTY_HUPPED, &tty->flags)) {
543 /* We were raced by hangup */
544 retval = -EIO;
545 goto out;
546 }
547
548 old_ldisc = tty->ldisc;
549
550 /* Shutdown the old discipline. */
551 tty_ldisc_close(tty, old_ldisc);
552
553 /* Now set up the new line discipline. */
554 tty->ldisc = new_ldisc;
555 tty_set_termios_ldisc(tty, disc);
556
557 retval = tty_ldisc_open(tty, new_ldisc);
558 if (retval < 0) {
559 /* Back to the old one or N_TTY if we can't */
560 tty_ldisc_put(new_ldisc);
561 tty_ldisc_restore(tty, old_ldisc);
562 }
563
564 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
565 down_read(&tty->termios_rwsem);
566 tty->ops->set_ldisc(tty);
567 up_read(&tty->termios_rwsem);
568 }
569
570 /*
571 * At this point we hold a reference to the new ldisc and a
572 * reference to the old ldisc, or we hold two references to
573 * the old ldisc (if it was restored as part of error cleanup
574 * above). In either case, releasing a single reference from
575 * the old ldisc is correct.
576 */
577 new_ldisc = old_ldisc;
578out:
579 tty_ldisc_unlock(tty);
580
581 /*
582 * Restart the work queue in case no characters kick it off. Safe if
583 * already running
584 */
585 tty_buffer_restart_work(tty->port);
586err:
587 tty_ldisc_put(new_ldisc); /* drop the extra reference */
588 tty_unlock(tty);
589 return retval;
590}
591EXPORT_SYMBOL_GPL(tty_set_ldisc);
592
593/**
594 * tty_ldisc_kill - teardown ldisc
595 * @tty: tty being released
596 *
597 * Perform final close of the ldisc and reset @tty->ldisc
598 */
599static void tty_ldisc_kill(struct tty_struct *tty)
600{
601 lockdep_assert_held_write(&tty->ldisc_sem);
602 if (!tty->ldisc)
603 return;
604 /*
605 * Now kill off the ldisc
606 */
607 tty_ldisc_close(tty, tty->ldisc);
608 tty_ldisc_put(tty->ldisc);
609 /* Force an oops if we mess this up */
610 tty->ldisc = NULL;
611}
612
613/**
614 * tty_reset_termios - reset terminal state
615 * @tty: tty to reset
616 *
617 * Restore a terminal to the driver default state.
618 */
619static void tty_reset_termios(struct tty_struct *tty)
620{
621 down_write(&tty->termios_rwsem);
622 tty->termios = tty->driver->init_termios;
623 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
624 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
625 up_write(&tty->termios_rwsem);
626}
627
628
629/**
630 * tty_ldisc_reinit - reinitialise the tty ldisc
631 * @tty: tty to reinit
632 * @disc: line discipline to reinitialize
633 *
634 * Completely reinitialize the line discipline state, by closing the current
635 * instance, if there is one, and opening a new instance. If an error occurs
636 * opening the new non-%N_TTY instance, the instance is dropped and @tty->ldisc
637 * reset to %NULL. The caller can then retry with %N_TTY instead.
638 *
639 * Returns: 0 if successful, otherwise error code < 0
640 */
641int tty_ldisc_reinit(struct tty_struct *tty, int disc)
642{
643 struct tty_ldisc *ld;
644 int retval;
645
646 lockdep_assert_held_write(&tty->ldisc_sem);
647 ld = tty_ldisc_get(tty, disc);
648 if (IS_ERR(ld)) {
649 BUG_ON(disc == N_TTY);
650 return PTR_ERR(ld);
651 }
652
653 if (tty->ldisc) {
654 tty_ldisc_close(tty, tty->ldisc);
655 tty_ldisc_put(tty->ldisc);
656 }
657
658 /* switch the line discipline */
659 tty->ldisc = ld;
660 tty_set_termios_ldisc(tty, disc);
661 retval = tty_ldisc_open(tty, tty->ldisc);
662 if (retval) {
663 tty_ldisc_put(tty->ldisc);
664 tty->ldisc = NULL;
665 }
666 return retval;
667}
668
669/**
670 * tty_ldisc_hangup - hangup ldisc reset
671 * @tty: tty being hung up
672 * @reinit: whether to re-initialise the tty
673 *
674 * Some tty devices reset their termios when they receive a hangup event. In
675 * that situation we must also switch back to %N_TTY properly before we reset
676 * the termios data.
677 *
678 * Locking: We can take the ldisc mutex as the rest of the code is careful to
679 * allow for this.
680 *
681 * In the pty pair case this occurs in the close() path of the tty itself so we
682 * must be careful about locking rules.
683 */
684void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
685{
686 struct tty_ldisc *ld;
687
688 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
689
690 ld = tty_ldisc_ref(tty);
691 if (ld != NULL) {
692 if (ld->ops->flush_buffer)
693 ld->ops->flush_buffer(tty);
694 tty_driver_flush_buffer(tty);
695 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
696 ld->ops->write_wakeup)
697 ld->ops->write_wakeup(tty);
698 if (ld->ops->hangup)
699 ld->ops->hangup(tty);
700 tty_ldisc_deref(ld);
701 }
702
703 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
704 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
705
706 /*
707 * Shutdown the current line discipline, and reset it to
708 * N_TTY if need be.
709 *
710 * Avoid racing set_ldisc or tty_ldisc_release
711 */
712 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
713
714 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
715 tty_reset_termios(tty);
716
717 if (tty->ldisc) {
718 if (reinit) {
719 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
720 tty_ldisc_reinit(tty, N_TTY) < 0)
721 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
722 } else
723 tty_ldisc_kill(tty);
724 }
725 tty_ldisc_unlock(tty);
726}
727
728/**
729 * tty_ldisc_setup - open line discipline
730 * @tty: tty being shut down
731 * @o_tty: pair tty for pty/tty pairs
732 *
733 * Called during the initial open of a tty/pty pair in order to set up the line
734 * disciplines and bind them to the @tty. This has no locking issues as the
735 * device isn't yet active.
736 */
737int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
738{
739 int retval = tty_ldisc_open(tty, tty->ldisc);
740
741 if (retval)
742 return retval;
743
744 if (o_tty) {
745 /*
746 * Called without o_tty->ldisc_sem held, as o_tty has been
747 * just allocated and no one has a reference to it.
748 */
749 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
750 if (retval) {
751 tty_ldisc_close(tty, tty->ldisc);
752 return retval;
753 }
754 }
755 return 0;
756}
757
758/**
759 * tty_ldisc_release - release line discipline
760 * @tty: tty being shut down (or one end of pty pair)
761 *
762 * Called during the final close of a tty or a pty pair in order to shut down
763 * the line discpline layer. On exit, each tty's ldisc is %NULL.
764 */
765void tty_ldisc_release(struct tty_struct *tty)
766{
767 struct tty_struct *o_tty = tty->link;
768
769 /*
770 * Shutdown this line discipline. As this is the final close,
771 * it does not race with the set_ldisc code path.
772 */
773
774 tty_ldisc_lock_pair(tty, o_tty);
775 tty_ldisc_kill(tty);
776 if (o_tty)
777 tty_ldisc_kill(o_tty);
778 tty_ldisc_unlock_pair(tty, o_tty);
779
780 /*
781 * And the memory resources remaining (buffers, termios) will be
782 * disposed of when the kref hits zero
783 */
784
785 tty_ldisc_debug(tty, "released\n");
786}
787
788/**
789 * tty_ldisc_init - ldisc setup for new tty
790 * @tty: tty being allocated
791 *
792 * Set up the line discipline objects for a newly allocated tty. Note that the
793 * tty structure is not completely set up when this call is made.
794 */
795int tty_ldisc_init(struct tty_struct *tty)
796{
797 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
798
799 if (IS_ERR(ld))
800 return PTR_ERR(ld);
801 tty->ldisc = ld;
802 return 0;
803}
804
805/**
806 * tty_ldisc_deinit - ldisc cleanup for new tty
807 * @tty: tty that was allocated recently
808 *
809 * The tty structure must not be completely set up (tty_ldisc_setup()) when
810 * this call is made.
811 */
812void tty_ldisc_deinit(struct tty_struct *tty)
813{
814 /* no ldisc_sem, tty is being destroyed */
815 if (tty->ldisc)
816 tty_ldisc_put(tty->ldisc);
817 tty->ldisc = NULL;
818}
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}