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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#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
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(struct tty_ldisc_ops *new_ldisc)
62{
63 unsigned long flags;
64 int ret = 0;
65
66 if (new_ldisc->num < N_TTY || new_ldisc->num >= NR_LDISCS)
67 return -EINVAL;
68
69 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
70 tty_ldiscs[new_ldisc->num] = new_ldisc;
71 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
72
73 return ret;
74}
75EXPORT_SYMBOL(tty_register_ldisc);
76
77/**
78 * tty_unregister_ldisc - unload a line discipline
79 * @ldisc: ldisc number
80 *
81 * Remove a line discipline from the kernel providing it is not
82 * currently in use.
83 *
84 * Locking:
85 * takes tty_ldiscs_lock to guard against ldisc races
86 */
87
88void tty_unregister_ldisc(struct tty_ldisc_ops *ldisc)
89{
90 unsigned long flags;
91
92 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
93 tty_ldiscs[ldisc->num] = NULL;
94 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
95}
96EXPORT_SYMBOL(tty_unregister_ldisc);
97
98static struct tty_ldisc_ops *get_ldops(int disc)
99{
100 unsigned long flags;
101 struct tty_ldisc_ops *ldops, *ret;
102
103 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
104 ret = ERR_PTR(-EINVAL);
105 ldops = tty_ldiscs[disc];
106 if (ldops) {
107 ret = ERR_PTR(-EAGAIN);
108 if (try_module_get(ldops->owner))
109 ret = ldops;
110 }
111 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
112 return ret;
113}
114
115static void put_ldops(struct tty_ldisc_ops *ldops)
116{
117 unsigned long flags;
118
119 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
120 module_put(ldops->owner);
121 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
122}
123
124static int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
125/**
126 * tty_ldisc_get - take a reference to an ldisc
127 * @tty: tty device
128 * @disc: ldisc number
129 *
130 * Takes a reference to a line discipline. Deals with refcounts and
131 * module locking counts.
132 *
133 * Returns: -EINVAL if the discipline index is not [N_TTY..NR_LDISCS] or
134 * if the discipline is not registered
135 * -EAGAIN if request_module() failed to load or register the
136 * discipline
137 * -ENOMEM if allocation failure
138 *
139 * Otherwise, returns a pointer to the discipline and bumps the
140 * ref count
141 *
142 * Locking:
143 * takes tty_ldiscs_lock to guard against ldisc races
144 */
145
146static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
147{
148 struct tty_ldisc *ld;
149 struct tty_ldisc_ops *ldops;
150
151 if (disc < N_TTY || disc >= NR_LDISCS)
152 return ERR_PTR(-EINVAL);
153
154 /*
155 * Get the ldisc ops - we may need to request them to be loaded
156 * dynamically and try again.
157 */
158 ldops = get_ldops(disc);
159 if (IS_ERR(ldops)) {
160 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
161 return ERR_PTR(-EPERM);
162 request_module("tty-ldisc-%d", disc);
163 ldops = get_ldops(disc);
164 if (IS_ERR(ldops))
165 return ERR_CAST(ldops);
166 }
167
168 /*
169 * There is no way to handle allocation failure of only 16 bytes.
170 * Let's simplify error handling and save more memory.
171 */
172 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
173 ld->ops = ldops;
174 ld->tty = tty;
175
176 return ld;
177}
178
179/*
180 * tty_ldisc_put - release the ldisc
181 *
182 * Complement of tty_ldisc_get().
183 */
184static void tty_ldisc_put(struct tty_ldisc *ld)
185{
186 if (WARN_ON_ONCE(!ld))
187 return;
188
189 put_ldops(ld->ops);
190 kfree(ld);
191}
192
193static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
194{
195 return (*pos < NR_LDISCS) ? pos : NULL;
196}
197
198static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
199{
200 (*pos)++;
201 return (*pos < NR_LDISCS) ? pos : NULL;
202}
203
204static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
205{
206}
207
208static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
209{
210 int i = *(loff_t *)v;
211 struct tty_ldisc_ops *ldops;
212
213 ldops = get_ldops(i);
214 if (IS_ERR(ldops))
215 return 0;
216 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
217 put_ldops(ldops);
218 return 0;
219}
220
221const struct seq_operations tty_ldiscs_seq_ops = {
222 .start = tty_ldiscs_seq_start,
223 .next = tty_ldiscs_seq_next,
224 .stop = tty_ldiscs_seq_stop,
225 .show = tty_ldiscs_seq_show,
226};
227
228/**
229 * tty_ldisc_ref_wait - wait for the tty ldisc
230 * @tty: tty device
231 *
232 * Dereference the line discipline for the terminal and take a
233 * reference to it. If the line discipline is in flux then
234 * wait patiently until it changes.
235 *
236 * Returns: NULL if the tty has been hungup and not re-opened with
237 * a new file descriptor, otherwise valid ldisc reference
238 *
239 * Note 1: Must not be called from an IRQ/timer context. The caller
240 * must also be careful not to hold other locks that will deadlock
241 * against a discipline change, such as an existing ldisc reference
242 * (which we check for)
243 *
244 * Note 2: a file_operations routine (read/poll/write) should use this
245 * function to wait for any ldisc lifetime events to finish.
246 */
247
248struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
249{
250 struct tty_ldisc *ld;
251
252 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
253 ld = tty->ldisc;
254 if (!ld)
255 ldsem_up_read(&tty->ldisc_sem);
256 return ld;
257}
258EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
259
260/**
261 * tty_ldisc_ref - get the tty ldisc
262 * @tty: tty device
263 *
264 * Dereference the line discipline for the terminal and take a
265 * reference to it. If the line discipline is in flux then
266 * return NULL. Can be called from IRQ and timer functions.
267 */
268
269struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
270{
271 struct tty_ldisc *ld = NULL;
272
273 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
274 ld = tty->ldisc;
275 if (!ld)
276 ldsem_up_read(&tty->ldisc_sem);
277 }
278 return ld;
279}
280EXPORT_SYMBOL_GPL(tty_ldisc_ref);
281
282/**
283 * tty_ldisc_deref - free a tty ldisc reference
284 * @ld: reference to free up
285 *
286 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
287 * be called in IRQ context.
288 */
289
290void tty_ldisc_deref(struct tty_ldisc *ld)
291{
292 ldsem_up_read(&ld->tty->ldisc_sem);
293}
294EXPORT_SYMBOL_GPL(tty_ldisc_deref);
295
296
297static inline int
298__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
299{
300 return ldsem_down_write(&tty->ldisc_sem, timeout);
301}
302
303static inline int
304__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
305{
306 return ldsem_down_write_nested(&tty->ldisc_sem,
307 LDISC_SEM_OTHER, timeout);
308}
309
310static inline void __tty_ldisc_unlock(struct tty_struct *tty)
311{
312 ldsem_up_write(&tty->ldisc_sem);
313}
314
315int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
316{
317 int ret;
318
319 /* Kindly asking blocked readers to release the read side */
320 set_bit(TTY_LDISC_CHANGING, &tty->flags);
321 wake_up_interruptible_all(&tty->read_wait);
322 wake_up_interruptible_all(&tty->write_wait);
323
324 ret = __tty_ldisc_lock(tty, timeout);
325 if (!ret)
326 return -EBUSY;
327 set_bit(TTY_LDISC_HALTED, &tty->flags);
328 return 0;
329}
330
331void tty_ldisc_unlock(struct tty_struct *tty)
332{
333 clear_bit(TTY_LDISC_HALTED, &tty->flags);
334 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
335 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
336 __tty_ldisc_unlock(tty);
337}
338
339static int
340tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
341 unsigned long timeout)
342{
343 int ret;
344
345 if (tty < tty2) {
346 ret = __tty_ldisc_lock(tty, timeout);
347 if (ret) {
348 ret = __tty_ldisc_lock_nested(tty2, timeout);
349 if (!ret)
350 __tty_ldisc_unlock(tty);
351 }
352 } else {
353 /* if this is possible, it has lots of implications */
354 WARN_ON_ONCE(tty == tty2);
355 if (tty2 && tty != tty2) {
356 ret = __tty_ldisc_lock(tty2, timeout);
357 if (ret) {
358 ret = __tty_ldisc_lock_nested(tty, timeout);
359 if (!ret)
360 __tty_ldisc_unlock(tty2);
361 }
362 } else
363 ret = __tty_ldisc_lock(tty, timeout);
364 }
365
366 if (!ret)
367 return -EBUSY;
368
369 set_bit(TTY_LDISC_HALTED, &tty->flags);
370 if (tty2)
371 set_bit(TTY_LDISC_HALTED, &tty2->flags);
372 return 0;
373}
374
375static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
376{
377 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
378}
379
380static void tty_ldisc_unlock_pair(struct tty_struct *tty,
381 struct tty_struct *tty2)
382{
383 __tty_ldisc_unlock(tty);
384 if (tty2)
385 __tty_ldisc_unlock(tty2);
386}
387
388/**
389 * tty_ldisc_flush - flush line discipline queue
390 * @tty: tty
391 *
392 * Flush the line discipline queue (if any) and the tty flip buffers
393 * for this tty.
394 */
395
396void tty_ldisc_flush(struct tty_struct *tty)
397{
398 struct tty_ldisc *ld = tty_ldisc_ref(tty);
399
400 tty_buffer_flush(tty, ld);
401 if (ld)
402 tty_ldisc_deref(ld);
403}
404EXPORT_SYMBOL_GPL(tty_ldisc_flush);
405
406/**
407 * tty_set_termios_ldisc - set ldisc field
408 * @tty: tty structure
409 * @disc: line discipline number
410 *
411 * This is probably overkill for real world processors but
412 * they are not on hot paths so a little discipline won't do
413 * any harm.
414 *
415 * The line discipline-related tty_struct fields are reset to
416 * prevent the ldisc driver from re-using stale information for
417 * the new ldisc instance.
418 *
419 * Locking: takes termios_rwsem
420 */
421
422static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
423{
424 down_write(&tty->termios_rwsem);
425 tty->termios.c_line = disc;
426 up_write(&tty->termios_rwsem);
427
428 tty->disc_data = NULL;
429 tty->receive_room = 0;
430}
431
432/**
433 * tty_ldisc_open - open a line discipline
434 * @tty: tty we are opening the ldisc on
435 * @ld: discipline to open
436 *
437 * A helper opening method. Also a convenient debugging and check
438 * point.
439 *
440 * Locking: always called with BTM already held.
441 */
442
443static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
444{
445 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
446 if (ld->ops->open) {
447 int ret;
448 /* BTM here locks versus a hangup event */
449 ret = ld->ops->open(tty);
450 if (ret)
451 clear_bit(TTY_LDISC_OPEN, &tty->flags);
452
453 tty_ldisc_debug(tty, "%p: opened\n", ld);
454 return ret;
455 }
456 return 0;
457}
458
459/**
460 * tty_ldisc_close - close a line discipline
461 * @tty: tty we are opening the ldisc on
462 * @ld: discipline to close
463 *
464 * A helper close method. Also a convenient debugging and check
465 * point.
466 */
467
468static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
469{
470 lockdep_assert_held_write(&tty->ldisc_sem);
471 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
472 clear_bit(TTY_LDISC_OPEN, &tty->flags);
473 if (ld->ops->close)
474 ld->ops->close(tty);
475 tty_ldisc_debug(tty, "%p: closed\n", ld);
476}
477
478/**
479 * tty_ldisc_failto - helper for ldisc failback
480 * @tty: tty to open the ldisc on
481 * @ld: ldisc we are trying to fail back to
482 *
483 * Helper to try and recover a tty when switching back to the old
484 * ldisc fails and we need something attached.
485 */
486
487static int tty_ldisc_failto(struct tty_struct *tty, int ld)
488{
489 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
490 int r;
491
492 lockdep_assert_held_write(&tty->ldisc_sem);
493 if (IS_ERR(disc))
494 return PTR_ERR(disc);
495 tty->ldisc = disc;
496 tty_set_termios_ldisc(tty, ld);
497 r = tty_ldisc_open(tty, disc);
498 if (r < 0)
499 tty_ldisc_put(disc);
500 return r;
501}
502
503/**
504 * tty_ldisc_restore - helper for tty ldisc change
505 * @tty: tty to recover
506 * @old: previous ldisc
507 *
508 * Restore the previous line discipline or N_TTY when a line discipline
509 * change fails due to an open error
510 */
511
512static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
513{
514 /* There is an outstanding reference here so this is safe */
515 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
516 const char *name = tty_name(tty);
517
518 pr_warn("Falling back ldisc for %s.\n", name);
519 /*
520 * The traditional behaviour is to fall back to N_TTY, we
521 * want to avoid falling back to N_NULL unless we have no
522 * choice to avoid the risk of breaking anything
523 */
524 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
525 tty_ldisc_failto(tty, N_NULL) < 0)
526 panic("Couldn't open N_NULL ldisc for %s.", name);
527 }
528}
529
530/**
531 * tty_set_ldisc - set line discipline
532 * @tty: the terminal to set
533 * @disc: the line discipline number
534 *
535 * Set the discipline of a tty line. Must be called from a process
536 * context. The ldisc change logic has to protect itself against any
537 * overlapping ldisc change (including on the other end of pty pairs),
538 * the close of one side of a tty/pty pair, and eventually hangup.
539 */
540
541int tty_set_ldisc(struct tty_struct *tty, int disc)
542{
543 int retval;
544 struct tty_ldisc *old_ldisc, *new_ldisc;
545
546 new_ldisc = tty_ldisc_get(tty, disc);
547 if (IS_ERR(new_ldisc))
548 return PTR_ERR(new_ldisc);
549
550 tty_lock(tty);
551 retval = tty_ldisc_lock(tty, 5 * HZ);
552 if (retval)
553 goto err;
554
555 if (!tty->ldisc) {
556 retval = -EIO;
557 goto out;
558 }
559
560 /* Check the no-op case */
561 if (tty->ldisc->ops->num == disc)
562 goto out;
563
564 if (test_bit(TTY_HUPPED, &tty->flags)) {
565 /* We were raced by hangup */
566 retval = -EIO;
567 goto out;
568 }
569
570 old_ldisc = tty->ldisc;
571
572 /* Shutdown the old discipline. */
573 tty_ldisc_close(tty, old_ldisc);
574
575 /* Now set up the new line discipline. */
576 tty->ldisc = new_ldisc;
577 tty_set_termios_ldisc(tty, disc);
578
579 retval = tty_ldisc_open(tty, new_ldisc);
580 if (retval < 0) {
581 /* Back to the old one or N_TTY if we can't */
582 tty_ldisc_put(new_ldisc);
583 tty_ldisc_restore(tty, old_ldisc);
584 }
585
586 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
587 down_read(&tty->termios_rwsem);
588 tty->ops->set_ldisc(tty);
589 up_read(&tty->termios_rwsem);
590 }
591
592 /*
593 * At this point we hold a reference to the new ldisc and a
594 * reference to the old ldisc, or we hold two references to
595 * the old ldisc (if it was restored as part of error cleanup
596 * above). In either case, releasing a single reference from
597 * the old ldisc is correct.
598 */
599 new_ldisc = old_ldisc;
600out:
601 tty_ldisc_unlock(tty);
602
603 /*
604 * Restart the work queue in case no characters kick it off. Safe if
605 * already running
606 */
607 tty_buffer_restart_work(tty->port);
608err:
609 tty_ldisc_put(new_ldisc); /* drop the extra reference */
610 tty_unlock(tty);
611 return retval;
612}
613EXPORT_SYMBOL_GPL(tty_set_ldisc);
614
615/**
616 * tty_ldisc_kill - teardown ldisc
617 * @tty: tty being released
618 *
619 * Perform final close of the ldisc and reset tty->ldisc
620 */
621static void tty_ldisc_kill(struct tty_struct *tty)
622{
623 lockdep_assert_held_write(&tty->ldisc_sem);
624 if (!tty->ldisc)
625 return;
626 /*
627 * Now kill off the ldisc
628 */
629 tty_ldisc_close(tty, tty->ldisc);
630 tty_ldisc_put(tty->ldisc);
631 /* Force an oops if we mess this up */
632 tty->ldisc = NULL;
633}
634
635/**
636 * tty_reset_termios - reset terminal state
637 * @tty: tty to reset
638 *
639 * Restore a terminal to the driver default state.
640 */
641
642static void tty_reset_termios(struct tty_struct *tty)
643{
644 down_write(&tty->termios_rwsem);
645 tty->termios = tty->driver->init_termios;
646 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
647 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
648 up_write(&tty->termios_rwsem);
649}
650
651
652/**
653 * tty_ldisc_reinit - reinitialise the tty ldisc
654 * @tty: tty to reinit
655 * @disc: line discipline to reinitialize
656 *
657 * Completely reinitialize the line discipline state, by closing the
658 * current instance, if there is one, and opening a new instance. If
659 * an error occurs opening the new non-N_TTY instance, the instance
660 * is dropped and tty->ldisc reset to NULL. The caller can then retry
661 * with N_TTY instead.
662 *
663 * Returns 0 if successful, otherwise error code < 0
664 */
665
666int tty_ldisc_reinit(struct tty_struct *tty, int disc)
667{
668 struct tty_ldisc *ld;
669 int retval;
670
671 lockdep_assert_held_write(&tty->ldisc_sem);
672 ld = tty_ldisc_get(tty, disc);
673 if (IS_ERR(ld)) {
674 BUG_ON(disc == N_TTY);
675 return PTR_ERR(ld);
676 }
677
678 if (tty->ldisc) {
679 tty_ldisc_close(tty, tty->ldisc);
680 tty_ldisc_put(tty->ldisc);
681 }
682
683 /* switch the line discipline */
684 tty->ldisc = ld;
685 tty_set_termios_ldisc(tty, disc);
686 retval = tty_ldisc_open(tty, tty->ldisc);
687 if (retval) {
688 tty_ldisc_put(tty->ldisc);
689 tty->ldisc = NULL;
690 }
691 return retval;
692}
693
694/**
695 * tty_ldisc_hangup - hangup ldisc reset
696 * @tty: tty being hung up
697 * @reinit: whether to re-initialise the tty
698 *
699 * Some tty devices reset their termios when they receive a hangup
700 * event. In that situation we must also switch back to N_TTY properly
701 * before we reset the termios data.
702 *
703 * Locking: We can take the ldisc mutex as the rest of the code is
704 * careful to allow for this.
705 *
706 * In the pty pair case this occurs in the close() path of the
707 * tty itself so we must be careful about locking rules.
708 */
709
710void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
711{
712 struct tty_ldisc *ld;
713
714 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
715
716 ld = tty_ldisc_ref(tty);
717 if (ld != NULL) {
718 if (ld->ops->flush_buffer)
719 ld->ops->flush_buffer(tty);
720 tty_driver_flush_buffer(tty);
721 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
722 ld->ops->write_wakeup)
723 ld->ops->write_wakeup(tty);
724 if (ld->ops->hangup)
725 ld->ops->hangup(tty);
726 tty_ldisc_deref(ld);
727 }
728
729 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
730 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
731
732 /*
733 * Shutdown the current line discipline, and reset it to
734 * N_TTY if need be.
735 *
736 * Avoid racing set_ldisc or tty_ldisc_release
737 */
738 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
739
740 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
741 tty_reset_termios(tty);
742
743 if (tty->ldisc) {
744 if (reinit) {
745 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
746 tty_ldisc_reinit(tty, N_TTY) < 0)
747 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
748 } else
749 tty_ldisc_kill(tty);
750 }
751 tty_ldisc_unlock(tty);
752}
753
754/**
755 * tty_ldisc_setup - open line discipline
756 * @tty: tty being shut down
757 * @o_tty: pair tty for pty/tty pairs
758 *
759 * Called during the initial open of a tty/pty pair in order to set up the
760 * line disciplines and bind them to the tty. This has no locking issues
761 * as the device isn't yet active.
762 */
763
764int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
765{
766 int retval = tty_ldisc_open(tty, tty->ldisc);
767
768 if (retval)
769 return retval;
770
771 if (o_tty) {
772 /*
773 * Called without o_tty->ldisc_sem held, as o_tty has been
774 * just allocated and no one has a reference to it.
775 */
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 /*
809 * And the memory resources remaining (buffers, termios) will be
810 * disposed of when the kref hits zero
811 */
812
813 tty_ldisc_debug(tty, "released\n");
814}
815EXPORT_SYMBOL_GPL(tty_ldisc_release);
816
817/**
818 * tty_ldisc_init - ldisc setup for new tty
819 * @tty: tty being allocated
820 *
821 * Set up the line discipline objects for a newly allocated tty. Note that
822 * the tty structure is not completely set up when this call is made.
823 */
824
825int tty_ldisc_init(struct tty_struct *tty)
826{
827 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
828
829 if (IS_ERR(ld))
830 return PTR_ERR(ld);
831 tty->ldisc = ld;
832 return 0;
833}
834
835/**
836 * tty_ldisc_deinit - ldisc cleanup for new tty
837 * @tty: tty that was allocated recently
838 *
839 * The tty structure must not becompletely set up (tty_ldisc_setup) when
840 * this call is made.
841 */
842void tty_ldisc_deinit(struct tty_struct *tty)
843{
844 /* no ldisc_sem, tty is being destroyed */
845 if (tty->ldisc)
846 tty_ldisc_put(tty->ldisc);
847 tty->ldisc = NULL;
848}
849
850static struct ctl_table tty_table[] = {
851 {
852 .procname = "ldisc_autoload",
853 .data = &tty_ldisc_autoload,
854 .maxlen = sizeof(tty_ldisc_autoload),
855 .mode = 0644,
856 .proc_handler = proc_dointvec,
857 .extra1 = SYSCTL_ZERO,
858 .extra2 = SYSCTL_ONE,
859 },
860 { }
861};
862
863static struct ctl_table tty_dir_table[] = {
864 {
865 .procname = "tty",
866 .mode = 0555,
867 .child = tty_table,
868 },
869 { }
870};
871
872static struct ctl_table tty_root_table[] = {
873 {
874 .procname = "dev",
875 .mode = 0555,
876 .child = tty_dir_table,
877 },
878 { }
879};
880
881void tty_sysctl_init(void)
882{
883 register_sysctl_table(tty_root_table);
884}