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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 if (tty->ops->ldisc_ok) {
549 retval = tty->ops->ldisc_ok(tty, disc);
550 if (retval)
551 goto out;
552 }
553
554 old_ldisc = tty->ldisc;
555
556 /* Shutdown the old discipline. */
557 tty_ldisc_close(tty, old_ldisc);
558
559 /* Now set up the new line discipline. */
560 tty->ldisc = new_ldisc;
561 tty_set_termios_ldisc(tty, disc);
562
563 retval = tty_ldisc_open(tty, new_ldisc);
564 if (retval < 0) {
565 /* Back to the old one or N_TTY if we can't */
566 tty_ldisc_put(new_ldisc);
567 tty_ldisc_restore(tty, old_ldisc);
568 }
569
570 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
571 down_read(&tty->termios_rwsem);
572 tty->ops->set_ldisc(tty);
573 up_read(&tty->termios_rwsem);
574 }
575
576 /*
577 * At this point we hold a reference to the new ldisc and a
578 * reference to the old ldisc, or we hold two references to
579 * the old ldisc (if it was restored as part of error cleanup
580 * above). In either case, releasing a single reference from
581 * the old ldisc is correct.
582 */
583 new_ldisc = old_ldisc;
584out:
585 tty_ldisc_unlock(tty);
586
587 /*
588 * Restart the work queue in case no characters kick it off. Safe if
589 * already running
590 */
591 tty_buffer_restart_work(tty->port);
592err:
593 tty_ldisc_put(new_ldisc); /* drop the extra reference */
594 tty_unlock(tty);
595 return retval;
596}
597EXPORT_SYMBOL_GPL(tty_set_ldisc);
598
599/**
600 * tty_ldisc_kill - teardown ldisc
601 * @tty: tty being released
602 *
603 * Perform final close of the ldisc and reset @tty->ldisc
604 */
605static void tty_ldisc_kill(struct tty_struct *tty)
606{
607 lockdep_assert_held_write(&tty->ldisc_sem);
608 if (!tty->ldisc)
609 return;
610 /*
611 * Now kill off the ldisc
612 */
613 tty_ldisc_close(tty, tty->ldisc);
614 tty_ldisc_put(tty->ldisc);
615 /* Force an oops if we mess this up */
616 tty->ldisc = NULL;
617}
618
619/**
620 * tty_reset_termios - reset terminal state
621 * @tty: tty to reset
622 *
623 * Restore a terminal to the driver default state.
624 */
625static void tty_reset_termios(struct tty_struct *tty)
626{
627 down_write(&tty->termios_rwsem);
628 tty->termios = tty->driver->init_termios;
629 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
630 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
631 up_write(&tty->termios_rwsem);
632}
633
634
635/**
636 * tty_ldisc_reinit - reinitialise the tty ldisc
637 * @tty: tty to reinit
638 * @disc: line discipline to reinitialize
639 *
640 * Completely reinitialize the line discipline state, by closing the current
641 * instance, if there is one, and opening a new instance. If an error occurs
642 * opening the new non-%N_TTY instance, the instance is dropped and @tty->ldisc
643 * reset to %NULL. The caller can then retry with %N_TTY instead.
644 *
645 * Returns: 0 if successful, otherwise error code < 0
646 */
647int tty_ldisc_reinit(struct tty_struct *tty, int disc)
648{
649 struct tty_ldisc *ld;
650 int retval;
651
652 lockdep_assert_held_write(&tty->ldisc_sem);
653 ld = tty_ldisc_get(tty, disc);
654 if (IS_ERR(ld)) {
655 BUG_ON(disc == N_TTY);
656 return PTR_ERR(ld);
657 }
658
659 if (tty->ldisc) {
660 tty_ldisc_close(tty, tty->ldisc);
661 tty_ldisc_put(tty->ldisc);
662 }
663
664 /* switch the line discipline */
665 tty->ldisc = ld;
666 tty_set_termios_ldisc(tty, disc);
667 retval = tty_ldisc_open(tty, tty->ldisc);
668 if (retval) {
669 tty_ldisc_put(tty->ldisc);
670 tty->ldisc = NULL;
671 }
672 return retval;
673}
674
675/**
676 * tty_ldisc_hangup - hangup ldisc reset
677 * @tty: tty being hung up
678 * @reinit: whether to re-initialise the tty
679 *
680 * Some tty devices reset their termios when they receive a hangup event. In
681 * that situation we must also switch back to %N_TTY properly before we reset
682 * the termios data.
683 *
684 * Locking: We can take the ldisc mutex as the rest of the code is careful to
685 * allow for this.
686 *
687 * In the pty pair case this occurs in the close() path of the tty itself so we
688 * must be careful about locking rules.
689 */
690void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
691{
692 struct tty_ldisc *ld;
693
694 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
695
696 ld = tty_ldisc_ref(tty);
697 if (ld != NULL) {
698 if (ld->ops->flush_buffer)
699 ld->ops->flush_buffer(tty);
700 tty_driver_flush_buffer(tty);
701 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
702 ld->ops->write_wakeup)
703 ld->ops->write_wakeup(tty);
704 if (ld->ops->hangup)
705 ld->ops->hangup(tty);
706 tty_ldisc_deref(ld);
707 }
708
709 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
710 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
711
712 /*
713 * Shutdown the current line discipline, and reset it to
714 * N_TTY if need be.
715 *
716 * Avoid racing set_ldisc or tty_ldisc_release
717 */
718 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
719
720 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
721 tty_reset_termios(tty);
722
723 if (tty->ldisc) {
724 if (reinit) {
725 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
726 tty_ldisc_reinit(tty, N_TTY) < 0)
727 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
728 } else
729 tty_ldisc_kill(tty);
730 }
731 tty_ldisc_unlock(tty);
732}
733
734/**
735 * tty_ldisc_setup - open line discipline
736 * @tty: tty being shut down
737 * @o_tty: pair tty for pty/tty pairs
738 *
739 * Called during the initial open of a tty/pty pair in order to set up the line
740 * disciplines and bind them to the @tty. This has no locking issues as the
741 * device isn't yet active.
742 */
743int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
744{
745 int retval = tty_ldisc_open(tty, tty->ldisc);
746
747 if (retval)
748 return retval;
749
750 if (o_tty) {
751 /*
752 * Called without o_tty->ldisc_sem held, as o_tty has been
753 * just allocated and no one has a reference to it.
754 */
755 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
756 if (retval) {
757 tty_ldisc_close(tty, tty->ldisc);
758 return retval;
759 }
760 }
761 return 0;
762}
763
764/**
765 * tty_ldisc_release - release line discipline
766 * @tty: tty being shut down (or one end of pty pair)
767 *
768 * Called during the final close of a tty or a pty pair in order to shut down
769 * the line discpline layer. On exit, each tty's ldisc is %NULL.
770 */
771void tty_ldisc_release(struct tty_struct *tty)
772{
773 struct tty_struct *o_tty = tty->link;
774
775 /*
776 * Shutdown this line discipline. As this is the final close,
777 * it does not race with the set_ldisc code path.
778 */
779
780 tty_ldisc_lock_pair(tty, o_tty);
781 tty_ldisc_kill(tty);
782 if (o_tty)
783 tty_ldisc_kill(o_tty);
784 tty_ldisc_unlock_pair(tty, o_tty);
785
786 /*
787 * And the memory resources remaining (buffers, termios) will be
788 * disposed of when the kref hits zero
789 */
790
791 tty_ldisc_debug(tty, "released\n");
792}
793
794/**
795 * tty_ldisc_init - ldisc setup for new tty
796 * @tty: tty being allocated
797 *
798 * Set up the line discipline objects for a newly allocated tty. Note that the
799 * tty structure is not completely set up when this call is made.
800 */
801int tty_ldisc_init(struct tty_struct *tty)
802{
803 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
804
805 if (IS_ERR(ld))
806 return PTR_ERR(ld);
807 tty->ldisc = ld;
808 return 0;
809}
810
811/**
812 * tty_ldisc_deinit - ldisc cleanup for new tty
813 * @tty: tty that was allocated recently
814 *
815 * The tty structure must not be completely set up (tty_ldisc_setup()) when
816 * this call is made.
817 */
818void tty_ldisc_deinit(struct tty_struct *tty)
819{
820 /* no ldisc_sem, tty is being destroyed */
821 if (tty->ldisc)
822 tty_ldisc_put(tty->ldisc);
823 tty->ldisc = NULL;
824}
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 int ret = 0;
62
63 if (new_ldisc->num < N_TTY || new_ldisc->num >= NR_LDISCS)
64 return -EINVAL;
65
66 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
67 tty_ldiscs[new_ldisc->num] = new_ldisc;
68 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
69
70 return ret;
71}
72EXPORT_SYMBOL(tty_register_ldisc);
73
74/**
75 * tty_unregister_ldisc - unload a line discipline
76 * @ldisc: ldisc number
77 *
78 * Remove a line discipline from the kernel providing it is not currently in
79 * use.
80 *
81 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
82 */
83
84void tty_unregister_ldisc(struct tty_ldisc_ops *ldisc)
85{
86 unsigned long flags;
87
88 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
89 tty_ldiscs[ldisc->num] = NULL;
90 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
91}
92EXPORT_SYMBOL(tty_unregister_ldisc);
93
94static struct tty_ldisc_ops *get_ldops(int disc)
95{
96 unsigned long flags;
97 struct tty_ldisc_ops *ldops, *ret;
98
99 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
100 ret = ERR_PTR(-EINVAL);
101 ldops = tty_ldiscs[disc];
102 if (ldops) {
103 ret = ERR_PTR(-EAGAIN);
104 if (try_module_get(ldops->owner))
105 ret = ldops;
106 }
107 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
108 return ret;
109}
110
111static void put_ldops(struct tty_ldisc_ops *ldops)
112{
113 unsigned long flags;
114
115 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
116 module_put(ldops->owner);
117 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
118}
119
120int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD);
121
122/**
123 * tty_ldisc_get - take a reference to an ldisc
124 * @tty: tty device
125 * @disc: ldisc number
126 *
127 * Takes a reference to a line discipline. Deals with refcounts and module
128 * locking counts. If the discipline is not available, its module loaded, if
129 * possible.
130 *
131 * Returns:
132 * * -%EINVAL if the discipline index is not [%N_TTY .. %NR_LDISCS] or if the
133 * discipline is not registered
134 * * -%EAGAIN if request_module() failed to load or register the discipline
135 * * -%ENOMEM if allocation failure
136 * * Otherwise, returns a pointer to the discipline and bumps the ref count
137 *
138 * Locking: takes %tty_ldiscs_lock to guard against ldisc races
139 */
140static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
141{
142 struct tty_ldisc *ld;
143 struct tty_ldisc_ops *ldops;
144
145 if (disc < N_TTY || disc >= NR_LDISCS)
146 return ERR_PTR(-EINVAL);
147
148 /*
149 * Get the ldisc ops - we may need to request them to be loaded
150 * dynamically and try again.
151 */
152 ldops = get_ldops(disc);
153 if (IS_ERR(ldops)) {
154 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
155 return ERR_PTR(-EPERM);
156 request_module("tty-ldisc-%d", disc);
157 ldops = get_ldops(disc);
158 if (IS_ERR(ldops))
159 return ERR_CAST(ldops);
160 }
161
162 /*
163 * There is no way to handle allocation failure of only 16 bytes.
164 * Let's simplify error handling and save more memory.
165 */
166 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
167 ld->ops = ldops;
168 ld->tty = tty;
169
170 return ld;
171}
172
173/**
174 * tty_ldisc_put - release the ldisc
175 * @ld: lisdsc to release
176 *
177 * Complement of tty_ldisc_get().
178 */
179static void tty_ldisc_put(struct tty_ldisc *ld)
180{
181 if (WARN_ON_ONCE(!ld))
182 return;
183
184 put_ldops(ld->ops);
185 kfree(ld);
186}
187
188static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
189{
190 return (*pos < NR_LDISCS) ? pos : NULL;
191}
192
193static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
194{
195 (*pos)++;
196 return (*pos < NR_LDISCS) ? pos : NULL;
197}
198
199static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
200{
201}
202
203static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
204{
205 int i = *(loff_t *)v;
206 struct tty_ldisc_ops *ldops;
207
208 ldops = get_ldops(i);
209 if (IS_ERR(ldops))
210 return 0;
211 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
212 put_ldops(ldops);
213 return 0;
214}
215
216const struct seq_operations tty_ldiscs_seq_ops = {
217 .start = tty_ldiscs_seq_start,
218 .next = tty_ldiscs_seq_next,
219 .stop = tty_ldiscs_seq_stop,
220 .show = tty_ldiscs_seq_show,
221};
222
223/**
224 * tty_ldisc_ref_wait - wait for the tty ldisc
225 * @tty: tty device
226 *
227 * Dereference the line discipline for the terminal and take a reference to it.
228 * If the line discipline is in flux then wait patiently until it changes.
229 *
230 * Returns: %NULL if the tty has been hungup and not re-opened with a new file
231 * descriptor, otherwise valid ldisc reference
232 *
233 * Note 1: Must not be called from an IRQ/timer context. The caller must also
234 * be careful not to hold other locks that will deadlock against a discipline
235 * change, such as an existing ldisc reference (which we check for).
236 *
237 * Note 2: a file_operations routine (read/poll/write) should use this function
238 * to wait for any ldisc lifetime events to finish.
239 */
240struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
241{
242 struct tty_ldisc *ld;
243
244 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
245 ld = tty->ldisc;
246 if (!ld)
247 ldsem_up_read(&tty->ldisc_sem);
248 return ld;
249}
250EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
251
252/**
253 * tty_ldisc_ref - get the tty ldisc
254 * @tty: tty device
255 *
256 * Dereference the line discipline for the terminal and take a reference to it.
257 * If the line discipline is in flux then return %NULL. Can be called from IRQ
258 * and timer functions.
259 */
260struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
261{
262 struct tty_ldisc *ld = NULL;
263
264 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
265 ld = tty->ldisc;
266 if (!ld)
267 ldsem_up_read(&tty->ldisc_sem);
268 }
269 return ld;
270}
271EXPORT_SYMBOL_GPL(tty_ldisc_ref);
272
273/**
274 * tty_ldisc_deref - free a tty ldisc reference
275 * @ld: reference to free up
276 *
277 * Undoes the effect of tty_ldisc_ref() or tty_ldisc_ref_wait(). May be called
278 * in IRQ context.
279 */
280void tty_ldisc_deref(struct tty_ldisc *ld)
281{
282 ldsem_up_read(&ld->tty->ldisc_sem);
283}
284EXPORT_SYMBOL_GPL(tty_ldisc_deref);
285
286
287static inline int
288__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
289{
290 return ldsem_down_write(&tty->ldisc_sem, timeout);
291}
292
293static inline int
294__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
295{
296 return ldsem_down_write_nested(&tty->ldisc_sem,
297 LDISC_SEM_OTHER, timeout);
298}
299
300static inline void __tty_ldisc_unlock(struct tty_struct *tty)
301{
302 ldsem_up_write(&tty->ldisc_sem);
303}
304
305int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
306{
307 int ret;
308
309 /* Kindly asking blocked readers to release the read side */
310 set_bit(TTY_LDISC_CHANGING, &tty->flags);
311 wake_up_interruptible_all(&tty->read_wait);
312 wake_up_interruptible_all(&tty->write_wait);
313
314 ret = __tty_ldisc_lock(tty, timeout);
315 if (!ret)
316 return -EBUSY;
317 set_bit(TTY_LDISC_HALTED, &tty->flags);
318 return 0;
319}
320
321void tty_ldisc_unlock(struct tty_struct *tty)
322{
323 clear_bit(TTY_LDISC_HALTED, &tty->flags);
324 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
325 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
326 __tty_ldisc_unlock(tty);
327}
328
329static int
330tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
331 unsigned long timeout)
332{
333 int ret;
334
335 if (tty < tty2) {
336 ret = __tty_ldisc_lock(tty, timeout);
337 if (ret) {
338 ret = __tty_ldisc_lock_nested(tty2, timeout);
339 if (!ret)
340 __tty_ldisc_unlock(tty);
341 }
342 } else {
343 /* if this is possible, it has lots of implications */
344 WARN_ON_ONCE(tty == tty2);
345 if (tty2 && tty != tty2) {
346 ret = __tty_ldisc_lock(tty2, timeout);
347 if (ret) {
348 ret = __tty_ldisc_lock_nested(tty, timeout);
349 if (!ret)
350 __tty_ldisc_unlock(tty2);
351 }
352 } else
353 ret = __tty_ldisc_lock(tty, timeout);
354 }
355
356 if (!ret)
357 return -EBUSY;
358
359 set_bit(TTY_LDISC_HALTED, &tty->flags);
360 if (tty2)
361 set_bit(TTY_LDISC_HALTED, &tty2->flags);
362 return 0;
363}
364
365static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
366{
367 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
368}
369
370static void tty_ldisc_unlock_pair(struct tty_struct *tty,
371 struct tty_struct *tty2)
372{
373 __tty_ldisc_unlock(tty);
374 if (tty2)
375 __tty_ldisc_unlock(tty2);
376}
377
378/**
379 * tty_ldisc_flush - flush line discipline queue
380 * @tty: tty to flush ldisc for
381 *
382 * Flush the line discipline queue (if any) and the tty flip buffers for this
383 * @tty.
384 */
385void tty_ldisc_flush(struct tty_struct *tty)
386{
387 struct tty_ldisc *ld = tty_ldisc_ref(tty);
388
389 tty_buffer_flush(tty, ld);
390 if (ld)
391 tty_ldisc_deref(ld);
392}
393EXPORT_SYMBOL_GPL(tty_ldisc_flush);
394
395/**
396 * tty_set_termios_ldisc - set ldisc field
397 * @tty: tty structure
398 * @disc: line discipline number
399 *
400 * This is probably overkill for real world processors but they are not on hot
401 * paths so a little discipline won't do any harm.
402 *
403 * The line discipline-related tty_struct fields are reset to prevent the ldisc
404 * driver from re-using stale information for the new ldisc instance.
405 *
406 * Locking: takes termios_rwsem
407 */
408static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
409{
410 down_write(&tty->termios_rwsem);
411 tty->termios.c_line = disc;
412 up_write(&tty->termios_rwsem);
413
414 tty->disc_data = NULL;
415 tty->receive_room = 0;
416}
417
418/**
419 * tty_ldisc_open - open a line discipline
420 * @tty: tty we are opening the ldisc on
421 * @ld: discipline to open
422 *
423 * A helper opening method. Also a convenient debugging and check point.
424 *
425 * Locking: always called with BTM already held.
426 */
427static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
428{
429 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
430 if (ld->ops->open) {
431 int ret;
432 /* BTM here locks versus a hangup event */
433 ret = ld->ops->open(tty);
434 if (ret)
435 clear_bit(TTY_LDISC_OPEN, &tty->flags);
436
437 tty_ldisc_debug(tty, "%p: opened\n", ld);
438 return ret;
439 }
440 return 0;
441}
442
443/**
444 * tty_ldisc_close - close a line discipline
445 * @tty: tty we are opening the ldisc on
446 * @ld: discipline to close
447 *
448 * A helper close method. Also a convenient debugging and check point.
449 */
450static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
451{
452 lockdep_assert_held_write(&tty->ldisc_sem);
453 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
454 clear_bit(TTY_LDISC_OPEN, &tty->flags);
455 if (ld->ops->close)
456 ld->ops->close(tty);
457 tty_ldisc_debug(tty, "%p: closed\n", ld);
458}
459
460/**
461 * tty_ldisc_failto - helper for ldisc failback
462 * @tty: tty to open the ldisc on
463 * @ld: ldisc we are trying to fail back to
464 *
465 * Helper to try and recover a tty when switching back to the old ldisc fails
466 * and we need something attached.
467 */
468static int tty_ldisc_failto(struct tty_struct *tty, int ld)
469{
470 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
471 int r;
472
473 lockdep_assert_held_write(&tty->ldisc_sem);
474 if (IS_ERR(disc))
475 return PTR_ERR(disc);
476 tty->ldisc = disc;
477 tty_set_termios_ldisc(tty, ld);
478 r = tty_ldisc_open(tty, disc);
479 if (r < 0)
480 tty_ldisc_put(disc);
481 return r;
482}
483
484/**
485 * tty_ldisc_restore - helper for tty ldisc change
486 * @tty: tty to recover
487 * @old: previous ldisc
488 *
489 * Restore the previous line discipline or %N_TTY when a line discipline change
490 * fails due to an open error
491 */
492static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
493{
494 /* There is an outstanding reference here so this is safe */
495 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
496 const char *name = tty_name(tty);
497
498 pr_warn("Falling back ldisc for %s.\n", name);
499 /*
500 * The traditional behaviour is to fall back to N_TTY, we
501 * want to avoid falling back to N_NULL unless we have no
502 * choice to avoid the risk of breaking anything
503 */
504 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
505 tty_ldisc_failto(tty, N_NULL) < 0)
506 panic("Couldn't open N_NULL ldisc for %s.", name);
507 }
508}
509
510/**
511 * tty_set_ldisc - set line discipline
512 * @tty: the terminal to set
513 * @disc: the line discipline number
514 *
515 * Set the discipline of a tty line. Must be called from a process context. The
516 * ldisc change logic has to protect itself against any overlapping ldisc
517 * change (including on the other end of pty pairs), the close of one side of a
518 * tty/pty pair, and eventually hangup.
519 */
520int tty_set_ldisc(struct tty_struct *tty, int disc)
521{
522 int retval;
523 struct tty_ldisc *old_ldisc, *new_ldisc;
524
525 new_ldisc = tty_ldisc_get(tty, disc);
526 if (IS_ERR(new_ldisc))
527 return PTR_ERR(new_ldisc);
528
529 tty_lock(tty);
530 retval = tty_ldisc_lock(tty, 5 * HZ);
531 if (retval)
532 goto err;
533
534 if (!tty->ldisc) {
535 retval = -EIO;
536 goto out;
537 }
538
539 /* Check the no-op case */
540 if (tty->ldisc->ops->num == disc)
541 goto out;
542
543 if (test_bit(TTY_HUPPED, &tty->flags)) {
544 /* We were raced by hangup */
545 retval = -EIO;
546 goto out;
547 }
548
549 old_ldisc = tty->ldisc;
550
551 /* Shutdown the old discipline. */
552 tty_ldisc_close(tty, old_ldisc);
553
554 /* Now set up the new line discipline. */
555 tty->ldisc = new_ldisc;
556 tty_set_termios_ldisc(tty, disc);
557
558 retval = tty_ldisc_open(tty, new_ldisc);
559 if (retval < 0) {
560 /* Back to the old one or N_TTY if we can't */
561 tty_ldisc_put(new_ldisc);
562 tty_ldisc_restore(tty, old_ldisc);
563 }
564
565 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
566 down_read(&tty->termios_rwsem);
567 tty->ops->set_ldisc(tty);
568 up_read(&tty->termios_rwsem);
569 }
570
571 /*
572 * At this point we hold a reference to the new ldisc and a
573 * reference to the old ldisc, or we hold two references to
574 * the old ldisc (if it was restored as part of error cleanup
575 * above). In either case, releasing a single reference from
576 * the old ldisc is correct.
577 */
578 new_ldisc = old_ldisc;
579out:
580 tty_ldisc_unlock(tty);
581
582 /*
583 * Restart the work queue in case no characters kick it off. Safe if
584 * already running
585 */
586 tty_buffer_restart_work(tty->port);
587err:
588 tty_ldisc_put(new_ldisc); /* drop the extra reference */
589 tty_unlock(tty);
590 return retval;
591}
592EXPORT_SYMBOL_GPL(tty_set_ldisc);
593
594/**
595 * tty_ldisc_kill - teardown ldisc
596 * @tty: tty being released
597 *
598 * Perform final close of the ldisc and reset @tty->ldisc
599 */
600static void tty_ldisc_kill(struct tty_struct *tty)
601{
602 lockdep_assert_held_write(&tty->ldisc_sem);
603 if (!tty->ldisc)
604 return;
605 /*
606 * Now kill off the ldisc
607 */
608 tty_ldisc_close(tty, tty->ldisc);
609 tty_ldisc_put(tty->ldisc);
610 /* Force an oops if we mess this up */
611 tty->ldisc = NULL;
612}
613
614/**
615 * tty_reset_termios - reset terminal state
616 * @tty: tty to reset
617 *
618 * Restore a terminal to the driver default state.
619 */
620static void tty_reset_termios(struct tty_struct *tty)
621{
622 down_write(&tty->termios_rwsem);
623 tty->termios = tty->driver->init_termios;
624 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
625 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
626 up_write(&tty->termios_rwsem);
627}
628
629
630/**
631 * tty_ldisc_reinit - reinitialise the tty ldisc
632 * @tty: tty to reinit
633 * @disc: line discipline to reinitialize
634 *
635 * Completely reinitialize the line discipline state, by closing the current
636 * instance, if there is one, and opening a new instance. If an error occurs
637 * opening the new non-%N_TTY instance, the instance is dropped and @tty->ldisc
638 * reset to %NULL. The caller can then retry with %N_TTY instead.
639 *
640 * Returns: 0 if successful, otherwise error code < 0
641 */
642int tty_ldisc_reinit(struct tty_struct *tty, int disc)
643{
644 struct tty_ldisc *ld;
645 int retval;
646
647 lockdep_assert_held_write(&tty->ldisc_sem);
648 ld = tty_ldisc_get(tty, disc);
649 if (IS_ERR(ld)) {
650 BUG_ON(disc == N_TTY);
651 return PTR_ERR(ld);
652 }
653
654 if (tty->ldisc) {
655 tty_ldisc_close(tty, tty->ldisc);
656 tty_ldisc_put(tty->ldisc);
657 }
658
659 /* switch the line discipline */
660 tty->ldisc = ld;
661 tty_set_termios_ldisc(tty, disc);
662 retval = tty_ldisc_open(tty, tty->ldisc);
663 if (retval) {
664 tty_ldisc_put(tty->ldisc);
665 tty->ldisc = NULL;
666 }
667 return retval;
668}
669
670/**
671 * tty_ldisc_hangup - hangup ldisc reset
672 * @tty: tty being hung up
673 * @reinit: whether to re-initialise the tty
674 *
675 * Some tty devices reset their termios when they receive a hangup event. In
676 * that situation we must also switch back to %N_TTY properly before we reset
677 * the termios data.
678 *
679 * Locking: We can take the ldisc mutex as the rest of the code is careful to
680 * allow for this.
681 *
682 * In the pty pair case this occurs in the close() path of the tty itself so we
683 * must be careful about locking rules.
684 */
685void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
686{
687 struct tty_ldisc *ld;
688
689 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
690
691 ld = tty_ldisc_ref(tty);
692 if (ld != NULL) {
693 if (ld->ops->flush_buffer)
694 ld->ops->flush_buffer(tty);
695 tty_driver_flush_buffer(tty);
696 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
697 ld->ops->write_wakeup)
698 ld->ops->write_wakeup(tty);
699 if (ld->ops->hangup)
700 ld->ops->hangup(tty);
701 tty_ldisc_deref(ld);
702 }
703
704 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
705 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
706
707 /*
708 * Shutdown the current line discipline, and reset it to
709 * N_TTY if need be.
710 *
711 * Avoid racing set_ldisc or tty_ldisc_release
712 */
713 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
714
715 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
716 tty_reset_termios(tty);
717
718 if (tty->ldisc) {
719 if (reinit) {
720 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
721 tty_ldisc_reinit(tty, N_TTY) < 0)
722 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
723 } else
724 tty_ldisc_kill(tty);
725 }
726 tty_ldisc_unlock(tty);
727}
728
729/**
730 * tty_ldisc_setup - open line discipline
731 * @tty: tty being shut down
732 * @o_tty: pair tty for pty/tty pairs
733 *
734 * Called during the initial open of a tty/pty pair in order to set up the line
735 * disciplines and bind them to the @tty. This has no locking issues as the
736 * device isn't yet active.
737 */
738int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
739{
740 int retval = tty_ldisc_open(tty, tty->ldisc);
741
742 if (retval)
743 return retval;
744
745 if (o_tty) {
746 /*
747 * Called without o_tty->ldisc_sem held, as o_tty has been
748 * just allocated and no one has a reference to it.
749 */
750 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
751 if (retval) {
752 tty_ldisc_close(tty, tty->ldisc);
753 return retval;
754 }
755 }
756 return 0;
757}
758
759/**
760 * tty_ldisc_release - release line discipline
761 * @tty: tty being shut down (or one end of pty pair)
762 *
763 * Called during the final close of a tty or a pty pair in order to shut down
764 * the line discpline layer. On exit, each tty's ldisc is %NULL.
765 */
766void tty_ldisc_release(struct tty_struct *tty)
767{
768 struct tty_struct *o_tty = tty->link;
769
770 /*
771 * Shutdown this line discipline. As this is the final close,
772 * it does not race with the set_ldisc code path.
773 */
774
775 tty_ldisc_lock_pair(tty, o_tty);
776 tty_ldisc_kill(tty);
777 if (o_tty)
778 tty_ldisc_kill(o_tty);
779 tty_ldisc_unlock_pair(tty, o_tty);
780
781 /*
782 * And the memory resources remaining (buffers, termios) will be
783 * disposed of when the kref hits zero
784 */
785
786 tty_ldisc_debug(tty, "released\n");
787}
788
789/**
790 * tty_ldisc_init - ldisc setup for new tty
791 * @tty: tty being allocated
792 *
793 * Set up the line discipline objects for a newly allocated tty. Note that the
794 * tty structure is not completely set up when this call is made.
795 */
796int tty_ldisc_init(struct tty_struct *tty)
797{
798 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
799
800 if (IS_ERR(ld))
801 return PTR_ERR(ld);
802 tty->ldisc = ld;
803 return 0;
804}
805
806/**
807 * tty_ldisc_deinit - ldisc cleanup for new tty
808 * @tty: tty that was allocated recently
809 *
810 * The tty structure must not be completely set up (tty_ldisc_setup()) when
811 * this call is made.
812 */
813void tty_ldisc_deinit(struct tty_struct *tty)
814{
815 /* no ldisc_sem, tty is being destroyed */
816 if (tty->ldisc)
817 tty_ldisc_put(tty->ldisc);
818 tty->ldisc = NULL;
819}