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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
23#undef LDISC_DEBUG_HANGUP
24
25#ifdef LDISC_DEBUG_HANGUP
26#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args)
27#else
28#define tty_ldisc_debug(tty, f, args...)
29#endif
30
31/* lockdep nested classes for tty->ldisc_sem */
32enum {
33 LDISC_SEM_NORMAL,
34 LDISC_SEM_OTHER,
35};
36
37
38/*
39 * This guards the refcounted line discipline lists. The lock
40 * must be taken with irqs off because there are hangup path
41 * callers who will do ldisc lookups and cannot sleep.
42 */
43
44static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
45/* Line disc dispatch table */
46static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
47
48/**
49 * tty_register_ldisc - install a line discipline
50 * @disc: ldisc number
51 * @new_ldisc: pointer to the ldisc object
52 *
53 * Installs a new line discipline into the kernel. The discipline
54 * is set up as unreferenced and then made available to the kernel
55 * from this point onwards.
56 *
57 * Locking:
58 * takes tty_ldiscs_lock to guard against ldisc races
59 */
60
61int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
62{
63 unsigned long flags;
64 int ret = 0;
65
66 if (disc < N_TTY || disc >= NR_LDISCS)
67 return -EINVAL;
68
69 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
70 tty_ldiscs[disc] = new_ldisc;
71 new_ldisc->num = disc;
72 new_ldisc->refcount = 0;
73 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
74
75 return ret;
76}
77EXPORT_SYMBOL(tty_register_ldisc);
78
79/**
80 * tty_unregister_ldisc - unload a line discipline
81 * @disc: ldisc number
82 * @new_ldisc: pointer to the ldisc object
83 *
84 * Remove a line discipline from the kernel providing it is not
85 * currently in use.
86 *
87 * Locking:
88 * takes tty_ldiscs_lock to guard against ldisc races
89 */
90
91int tty_unregister_ldisc(int disc)
92{
93 unsigned long flags;
94 int ret = 0;
95
96 if (disc < N_TTY || disc >= NR_LDISCS)
97 return -EINVAL;
98
99 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
100 if (tty_ldiscs[disc]->refcount)
101 ret = -EBUSY;
102 else
103 tty_ldiscs[disc] = NULL;
104 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
105
106 return ret;
107}
108EXPORT_SYMBOL(tty_unregister_ldisc);
109
110static struct tty_ldisc_ops *get_ldops(int disc)
111{
112 unsigned long flags;
113 struct tty_ldisc_ops *ldops, *ret;
114
115 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
116 ret = ERR_PTR(-EINVAL);
117 ldops = tty_ldiscs[disc];
118 if (ldops) {
119 ret = ERR_PTR(-EAGAIN);
120 if (try_module_get(ldops->owner)) {
121 ldops->refcount++;
122 ret = ldops;
123 }
124 }
125 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
126 return ret;
127}
128
129static void put_ldops(struct tty_ldisc_ops *ldops)
130{
131 unsigned long flags;
132
133 raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
134 ldops->refcount--;
135 module_put(ldops->owner);
136 raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
137}
138
139/**
140 * tty_ldisc_get - take a reference to an ldisc
141 * @disc: ldisc number
142 *
143 * Takes a reference to a line discipline. Deals with refcounts and
144 * module locking counts.
145 *
146 * Returns: -EINVAL if the discipline index is not [N_TTY..NR_LDISCS] or
147 * if the discipline is not registered
148 * -EAGAIN if request_module() failed to load or register the
149 * the discipline
150 * -ENOMEM if allocation failure
151 *
152 * Otherwise, returns a pointer to the discipline and bumps the
153 * ref count
154 *
155 * Locking:
156 * takes tty_ldiscs_lock to guard against ldisc races
157 */
158
159#if defined(CONFIG_LDISC_AUTOLOAD)
160 #define INITIAL_AUTOLOAD_STATE 1
161#else
162 #define INITIAL_AUTOLOAD_STATE 0
163#endif
164static int tty_ldisc_autoload = INITIAL_AUTOLOAD_STATE;
165
166static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc)
167{
168 struct tty_ldisc *ld;
169 struct tty_ldisc_ops *ldops;
170
171 if (disc < N_TTY || disc >= NR_LDISCS)
172 return ERR_PTR(-EINVAL);
173
174 /*
175 * Get the ldisc ops - we may need to request them to be loaded
176 * dynamically and try again.
177 */
178 ldops = get_ldops(disc);
179 if (IS_ERR(ldops)) {
180 if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload)
181 return ERR_PTR(-EPERM);
182 request_module("tty-ldisc-%d", disc);
183 ldops = get_ldops(disc);
184 if (IS_ERR(ldops))
185 return ERR_CAST(ldops);
186 }
187
188 /*
189 * There is no way to handle allocation failure of only 16 bytes.
190 * Let's simplify error handling and save more memory.
191 */
192 ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL);
193 ld->ops = ldops;
194 ld->tty = tty;
195
196 return ld;
197}
198
199/**
200 * tty_ldisc_put - release the ldisc
201 *
202 * Complement of tty_ldisc_get().
203 */
204static void tty_ldisc_put(struct tty_ldisc *ld)
205{
206 if (WARN_ON_ONCE(!ld))
207 return;
208
209 put_ldops(ld->ops);
210 kfree(ld);
211}
212
213static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
214{
215 return (*pos < NR_LDISCS) ? pos : NULL;
216}
217
218static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
219{
220 (*pos)++;
221 return (*pos < NR_LDISCS) ? pos : NULL;
222}
223
224static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
225{
226}
227
228static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
229{
230 int i = *(loff_t *)v;
231 struct tty_ldisc_ops *ldops;
232
233 ldops = get_ldops(i);
234 if (IS_ERR(ldops))
235 return 0;
236 seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
237 put_ldops(ldops);
238 return 0;
239}
240
241const struct seq_operations tty_ldiscs_seq_ops = {
242 .start = tty_ldiscs_seq_start,
243 .next = tty_ldiscs_seq_next,
244 .stop = tty_ldiscs_seq_stop,
245 .show = tty_ldiscs_seq_show,
246};
247
248/**
249 * tty_ldisc_ref_wait - wait for the tty ldisc
250 * @tty: tty device
251 *
252 * Dereference the line discipline for the terminal and take a
253 * reference to it. If the line discipline is in flux then
254 * wait patiently until it changes.
255 *
256 * Returns: NULL if the tty has been hungup and not re-opened with
257 * a new file descriptor, otherwise valid ldisc reference
258 *
259 * Note: Must not be called from an IRQ/timer context. The caller
260 * must also be careful not to hold other locks that will deadlock
261 * against a discipline change, such as an existing ldisc reference
262 * (which we check for)
263 *
264 * Note: a file_operations routine (read/poll/write) should use this
265 * function to wait for any ldisc lifetime events to finish.
266 */
267
268struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
269{
270 struct tty_ldisc *ld;
271
272 ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
273 ld = tty->ldisc;
274 if (!ld)
275 ldsem_up_read(&tty->ldisc_sem);
276 return ld;
277}
278EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
279
280/**
281 * tty_ldisc_ref - get the tty ldisc
282 * @tty: tty device
283 *
284 * Dereference the line discipline for the terminal and take a
285 * reference to it. If the line discipline is in flux then
286 * return NULL. Can be called from IRQ and timer functions.
287 */
288
289struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
290{
291 struct tty_ldisc *ld = NULL;
292
293 if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
294 ld = tty->ldisc;
295 if (!ld)
296 ldsem_up_read(&tty->ldisc_sem);
297 }
298 return ld;
299}
300EXPORT_SYMBOL_GPL(tty_ldisc_ref);
301
302/**
303 * tty_ldisc_deref - free a tty ldisc reference
304 * @ld: reference to free up
305 *
306 * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
307 * be called in IRQ context.
308 */
309
310void tty_ldisc_deref(struct tty_ldisc *ld)
311{
312 ldsem_up_read(&ld->tty->ldisc_sem);
313}
314EXPORT_SYMBOL_GPL(tty_ldisc_deref);
315
316
317static inline int
318__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
319{
320 return ldsem_down_write(&tty->ldisc_sem, timeout);
321}
322
323static inline int
324__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)
325{
326 return ldsem_down_write_nested(&tty->ldisc_sem,
327 LDISC_SEM_OTHER, timeout);
328}
329
330static inline void __tty_ldisc_unlock(struct tty_struct *tty)
331{
332 ldsem_up_write(&tty->ldisc_sem);
333}
334
335int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
336{
337 int ret;
338
339 /* Kindly asking blocked readers to release the read side */
340 set_bit(TTY_LDISC_CHANGING, &tty->flags);
341 wake_up_interruptible_all(&tty->read_wait);
342 wake_up_interruptible_all(&tty->write_wait);
343
344 ret = __tty_ldisc_lock(tty, timeout);
345 if (!ret)
346 return -EBUSY;
347 set_bit(TTY_LDISC_HALTED, &tty->flags);
348 return 0;
349}
350
351void tty_ldisc_unlock(struct tty_struct *tty)
352{
353 clear_bit(TTY_LDISC_HALTED, &tty->flags);
354 /* Can be cleared here - ldisc_unlock will wake up writers firstly */
355 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
356 __tty_ldisc_unlock(tty);
357}
358
359static int
360tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
361 unsigned long timeout)
362{
363 int ret;
364
365 if (tty < tty2) {
366 ret = __tty_ldisc_lock(tty, timeout);
367 if (ret) {
368 ret = __tty_ldisc_lock_nested(tty2, timeout);
369 if (!ret)
370 __tty_ldisc_unlock(tty);
371 }
372 } else {
373 /* if this is possible, it has lots of implications */
374 WARN_ON_ONCE(tty == tty2);
375 if (tty2 && tty != tty2) {
376 ret = __tty_ldisc_lock(tty2, timeout);
377 if (ret) {
378 ret = __tty_ldisc_lock_nested(tty, timeout);
379 if (!ret)
380 __tty_ldisc_unlock(tty2);
381 }
382 } else
383 ret = __tty_ldisc_lock(tty, timeout);
384 }
385
386 if (!ret)
387 return -EBUSY;
388
389 set_bit(TTY_LDISC_HALTED, &tty->flags);
390 if (tty2)
391 set_bit(TTY_LDISC_HALTED, &tty2->flags);
392 return 0;
393}
394
395static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)
396{
397 tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);
398}
399
400static void tty_ldisc_unlock_pair(struct tty_struct *tty,
401 struct tty_struct *tty2)
402{
403 __tty_ldisc_unlock(tty);
404 if (tty2)
405 __tty_ldisc_unlock(tty2);
406}
407
408/**
409 * tty_ldisc_flush - flush line discipline queue
410 * @tty: tty
411 *
412 * Flush the line discipline queue (if any) and the tty flip buffers
413 * for this tty.
414 */
415
416void tty_ldisc_flush(struct tty_struct *tty)
417{
418 struct tty_ldisc *ld = tty_ldisc_ref(tty);
419
420 tty_buffer_flush(tty, ld);
421 if (ld)
422 tty_ldisc_deref(ld);
423}
424EXPORT_SYMBOL_GPL(tty_ldisc_flush);
425
426/**
427 * tty_set_termios_ldisc - set ldisc field
428 * @tty: tty structure
429 * @disc: line discipline number
430 *
431 * This is probably overkill for real world processors but
432 * they are not on hot paths so a little discipline won't do
433 * any harm.
434 *
435 * The line discipline-related tty_struct fields are reset to
436 * prevent the ldisc driver from re-using stale information for
437 * the new ldisc instance.
438 *
439 * Locking: takes termios_rwsem
440 */
441
442static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
443{
444 down_write(&tty->termios_rwsem);
445 tty->termios.c_line = disc;
446 up_write(&tty->termios_rwsem);
447
448 tty->disc_data = NULL;
449 tty->receive_room = 0;
450}
451
452/**
453 * tty_ldisc_open - open a line discipline
454 * @tty: tty we are opening the ldisc on
455 * @ld: discipline to open
456 *
457 * A helper opening method. Also a convenient debugging and check
458 * point.
459 *
460 * Locking: always called with BTM already held.
461 */
462
463static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
464{
465 WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
466 if (ld->ops->open) {
467 int ret;
468 /* BTM here locks versus a hangup event */
469 ret = ld->ops->open(tty);
470 if (ret)
471 clear_bit(TTY_LDISC_OPEN, &tty->flags);
472
473 tty_ldisc_debug(tty, "%p: opened\n", ld);
474 return ret;
475 }
476 return 0;
477}
478
479/**
480 * tty_ldisc_close - close a line discipline
481 * @tty: tty we are opening the ldisc on
482 * @ld: discipline to close
483 *
484 * A helper close method. Also a convenient debugging and check
485 * point.
486 */
487
488static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
489{
490 lockdep_assert_held_write(&tty->ldisc_sem);
491 WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
492 clear_bit(TTY_LDISC_OPEN, &tty->flags);
493 if (ld->ops->close)
494 ld->ops->close(tty);
495 tty_ldisc_debug(tty, "%p: closed\n", ld);
496}
497
498/**
499 * tty_ldisc_failto - helper for ldisc failback
500 * @tty: tty to open the ldisc on
501 * @ld: ldisc we are trying to fail back to
502 *
503 * Helper to try and recover a tty when switching back to the old
504 * ldisc fails and we need something attached.
505 */
506
507static int tty_ldisc_failto(struct tty_struct *tty, int ld)
508{
509 struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
510 int r;
511
512 lockdep_assert_held_write(&tty->ldisc_sem);
513 if (IS_ERR(disc))
514 return PTR_ERR(disc);
515 tty->ldisc = disc;
516 tty_set_termios_ldisc(tty, ld);
517 if ((r = tty_ldisc_open(tty, disc)) < 0)
518 tty_ldisc_put(disc);
519 return r;
520}
521
522/**
523 * tty_ldisc_restore - helper for tty ldisc change
524 * @tty: tty to recover
525 * @old: previous ldisc
526 *
527 * Restore the previous line discipline or N_TTY when a line discipline
528 * change fails due to an open error
529 */
530
531static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
532{
533 /* There is an outstanding reference here so this is safe */
534 if (tty_ldisc_failto(tty, old->ops->num) < 0) {
535 const char *name = tty_name(tty);
536
537 pr_warn("Falling back ldisc for %s.\n", name);
538 /* The traditional behaviour is to fall back to N_TTY, we
539 want to avoid falling back to N_NULL unless we have no
540 choice to avoid the risk of breaking anything */
541 if (tty_ldisc_failto(tty, N_TTY) < 0 &&
542 tty_ldisc_failto(tty, N_NULL) < 0)
543 panic("Couldn't open N_NULL ldisc for %s.", name);
544 }
545}
546
547/**
548 * tty_set_ldisc - set line discipline
549 * @tty: the terminal to set
550 * @ldisc: the line discipline
551 *
552 * Set the discipline of a tty line. Must be called from a process
553 * context. The ldisc change logic has to protect itself against any
554 * overlapping ldisc change (including on the other end of pty pairs),
555 * the close of one side of a tty/pty pair, and eventually hangup.
556 */
557
558int tty_set_ldisc(struct tty_struct *tty, int disc)
559{
560 int retval;
561 struct tty_ldisc *old_ldisc, *new_ldisc;
562
563 new_ldisc = tty_ldisc_get(tty, disc);
564 if (IS_ERR(new_ldisc))
565 return PTR_ERR(new_ldisc);
566
567 tty_lock(tty);
568 retval = tty_ldisc_lock(tty, 5 * HZ);
569 if (retval)
570 goto err;
571
572 if (!tty->ldisc) {
573 retval = -EIO;
574 goto out;
575 }
576
577 /* Check the no-op case */
578 if (tty->ldisc->ops->num == disc)
579 goto out;
580
581 if (test_bit(TTY_HUPPED, &tty->flags)) {
582 /* We were raced by hangup */
583 retval = -EIO;
584 goto out;
585 }
586
587 old_ldisc = tty->ldisc;
588
589 /* Shutdown the old discipline. */
590 tty_ldisc_close(tty, old_ldisc);
591
592 /* Now set up the new line discipline. */
593 tty->ldisc = new_ldisc;
594 tty_set_termios_ldisc(tty, disc);
595
596 retval = tty_ldisc_open(tty, new_ldisc);
597 if (retval < 0) {
598 /* Back to the old one or N_TTY if we can't */
599 tty_ldisc_put(new_ldisc);
600 tty_ldisc_restore(tty, old_ldisc);
601 }
602
603 if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
604 down_read(&tty->termios_rwsem);
605 tty->ops->set_ldisc(tty);
606 up_read(&tty->termios_rwsem);
607 }
608
609 /* At this point we hold a reference to the new ldisc and a
610 reference to the old ldisc, or we hold two references to
611 the old ldisc (if it was restored as part of error cleanup
612 above). In either case, releasing a single reference from
613 the old ldisc is correct. */
614 new_ldisc = old_ldisc;
615out:
616 tty_ldisc_unlock(tty);
617
618 /* Restart the work queue in case no characters kick it off. Safe if
619 already running */
620 tty_buffer_restart_work(tty->port);
621err:
622 tty_ldisc_put(new_ldisc); /* drop the extra reference */
623 tty_unlock(tty);
624 return retval;
625}
626EXPORT_SYMBOL_GPL(tty_set_ldisc);
627
628/**
629 * tty_ldisc_kill - teardown ldisc
630 * @tty: tty being released
631 *
632 * Perform final close of the ldisc and reset tty->ldisc
633 */
634static void tty_ldisc_kill(struct tty_struct *tty)
635{
636 lockdep_assert_held_write(&tty->ldisc_sem);
637 if (!tty->ldisc)
638 return;
639 /*
640 * Now kill off the ldisc
641 */
642 tty_ldisc_close(tty, tty->ldisc);
643 tty_ldisc_put(tty->ldisc);
644 /* Force an oops if we mess this up */
645 tty->ldisc = NULL;
646}
647
648/**
649 * tty_reset_termios - reset terminal state
650 * @tty: tty to reset
651 *
652 * Restore a terminal to the driver default state.
653 */
654
655static void tty_reset_termios(struct tty_struct *tty)
656{
657 down_write(&tty->termios_rwsem);
658 tty->termios = tty->driver->init_termios;
659 tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
660 tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
661 up_write(&tty->termios_rwsem);
662}
663
664
665/**
666 * tty_ldisc_reinit - reinitialise the tty ldisc
667 * @tty: tty to reinit
668 * @disc: line discipline to reinitialize
669 *
670 * Completely reinitialize the line discipline state, by closing the
671 * current instance, if there is one, and opening a new instance. If
672 * an error occurs opening the new non-N_TTY instance, the instance
673 * is dropped and tty->ldisc reset to NULL. The caller can then retry
674 * with N_TTY instead.
675 *
676 * Returns 0 if successful, otherwise error code < 0
677 */
678
679int tty_ldisc_reinit(struct tty_struct *tty, int disc)
680{
681 struct tty_ldisc *ld;
682 int retval;
683
684 lockdep_assert_held_write(&tty->ldisc_sem);
685 ld = tty_ldisc_get(tty, disc);
686 if (IS_ERR(ld)) {
687 BUG_ON(disc == N_TTY);
688 return PTR_ERR(ld);
689 }
690
691 if (tty->ldisc) {
692 tty_ldisc_close(tty, tty->ldisc);
693 tty_ldisc_put(tty->ldisc);
694 }
695
696 /* switch the line discipline */
697 tty->ldisc = ld;
698 tty_set_termios_ldisc(tty, disc);
699 retval = tty_ldisc_open(tty, tty->ldisc);
700 if (retval) {
701 tty_ldisc_put(tty->ldisc);
702 tty->ldisc = NULL;
703 }
704 return retval;
705}
706
707/**
708 * tty_ldisc_hangup - hangup ldisc reset
709 * @tty: tty being hung up
710 *
711 * Some tty devices reset their termios when they receive a hangup
712 * event. In that situation we must also switch back to N_TTY properly
713 * before we reset the termios data.
714 *
715 * Locking: We can take the ldisc mutex as the rest of the code is
716 * careful to allow for this.
717 *
718 * In the pty pair case this occurs in the close() path of the
719 * tty itself so we must be careful about locking rules.
720 */
721
722void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
723{
724 struct tty_ldisc *ld;
725
726 tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
727
728 ld = tty_ldisc_ref(tty);
729 if (ld != NULL) {
730 if (ld->ops->flush_buffer)
731 ld->ops->flush_buffer(tty);
732 tty_driver_flush_buffer(tty);
733 if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
734 ld->ops->write_wakeup)
735 ld->ops->write_wakeup(tty);
736 if (ld->ops->hangup)
737 ld->ops->hangup(tty);
738 tty_ldisc_deref(ld);
739 }
740
741 wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT);
742 wake_up_interruptible_poll(&tty->read_wait, EPOLLIN);
743
744 /*
745 * Shutdown the current line discipline, and reset it to
746 * N_TTY if need be.
747 *
748 * Avoid racing set_ldisc or tty_ldisc_release
749 */
750 tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
751
752 if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
753 tty_reset_termios(tty);
754
755 if (tty->ldisc) {
756 if (reinit) {
757 if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
758 tty_ldisc_reinit(tty, N_TTY) < 0)
759 WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
760 } else
761 tty_ldisc_kill(tty);
762 }
763 tty_ldisc_unlock(tty);
764}
765
766/**
767 * tty_ldisc_setup - open line discipline
768 * @tty: tty being shut down
769 * @o_tty: pair tty for pty/tty pairs
770 *
771 * Called during the initial open of a tty/pty pair in order to set up the
772 * line disciplines and bind them to the tty. This has no locking issues
773 * as the device isn't yet active.
774 */
775
776int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
777{
778 int retval = tty_ldisc_open(tty, tty->ldisc);
779 if (retval)
780 return retval;
781
782 if (o_tty) {
783 /*
784 * Called without o_tty->ldisc_sem held, as o_tty has been
785 * just allocated and no one has a reference to it.
786 */
787 retval = tty_ldisc_open(o_tty, o_tty->ldisc);
788 if (retval) {
789 tty_ldisc_close(tty, tty->ldisc);
790 return retval;
791 }
792 }
793 return 0;
794}
795
796/**
797 * tty_ldisc_release - release line discipline
798 * @tty: tty being shut down (or one end of pty pair)
799 *
800 * Called during the final close of a tty or a pty pair in order to shut
801 * down the line discpline layer. On exit, each tty's ldisc is NULL.
802 */
803
804void tty_ldisc_release(struct tty_struct *tty)
805{
806 struct tty_struct *o_tty = tty->link;
807
808 /*
809 * Shutdown this line discipline. As this is the final close,
810 * it does not race with the set_ldisc code path.
811 */
812
813 tty_ldisc_lock_pair(tty, o_tty);
814 tty_ldisc_kill(tty);
815 if (o_tty)
816 tty_ldisc_kill(o_tty);
817 tty_ldisc_unlock_pair(tty, o_tty);
818
819 /* And the memory resources remaining (buffers, termios) will be
820 disposed of when the kref hits zero */
821
822 tty_ldisc_debug(tty, "released\n");
823}
824EXPORT_SYMBOL_GPL(tty_ldisc_release);
825
826/**
827 * tty_ldisc_init - ldisc setup for new tty
828 * @tty: tty being allocated
829 *
830 * Set up the line discipline objects for a newly allocated tty. Note that
831 * the tty structure is not completely set up when this call is made.
832 */
833
834int tty_ldisc_init(struct tty_struct *tty)
835{
836 struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
837 if (IS_ERR(ld))
838 return PTR_ERR(ld);
839 tty->ldisc = ld;
840 return 0;
841}
842
843/**
844 * tty_ldisc_deinit - ldisc cleanup for new tty
845 * @tty: tty that was allocated recently
846 *
847 * The tty structure must not becompletely set up (tty_ldisc_setup) when
848 * this call is made.
849 */
850void tty_ldisc_deinit(struct tty_struct *tty)
851{
852 /* no ldisc_sem, tty is being destroyed */
853 if (tty->ldisc)
854 tty_ldisc_put(tty->ldisc);
855 tty->ldisc = NULL;
856}
857
858static struct ctl_table tty_table[] = {
859 {
860 .procname = "ldisc_autoload",
861 .data = &tty_ldisc_autoload,
862 .maxlen = sizeof(tty_ldisc_autoload),
863 .mode = 0644,
864 .proc_handler = proc_dointvec,
865 .extra1 = SYSCTL_ZERO,
866 .extra2 = SYSCTL_ONE,
867 },
868 { }
869};
870
871static struct ctl_table tty_dir_table[] = {
872 {
873 .procname = "tty",
874 .mode = 0555,
875 .child = tty_table,
876 },
877 { }
878};
879
880static struct ctl_table tty_root_table[] = {
881 {
882 .procname = "dev",
883 .mode = 0555,
884 .child = tty_dir_table,
885 },
886 { }
887};
888
889void tty_sysctl_init(void)
890{
891 register_sysctl_table(tty_root_table);
892}
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}