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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 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}