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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 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}
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}