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