1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 1991, 1992 Linus Torvalds
4 *
5 * Added support for a Unix98-style ptmx device.
6 * -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
7 *
8 */
9
10#include <linux/module.h>
11#include <linux/errno.h>
12#include <linux/interrupt.h>
13#include <linux/tty.h>
14#include <linux/tty_flip.h>
15#include <linux/fcntl.h>
16#include <linux/sched/signal.h>
17#include <linux/string.h>
18#include <linux/major.h>
19#include <linux/mm.h>
20#include <linux/init.h>
21#include <linux/device.h>
22#include <linux/uaccess.h>
23#include <linux/bitops.h>
24#include <linux/devpts_fs.h>
25#include <linux/slab.h>
26#include <linux/mutex.h>
27#include <linux/poll.h>
28#include <linux/mount.h>
29#include <linux/file.h>
30#include <linux/ioctl.h>
31#include <linux/compat.h>
32#include "tty.h"
33
34#undef TTY_DEBUG_HANGUP
35#ifdef TTY_DEBUG_HANGUP
36# define tty_debug_hangup(tty, f, args...) tty_debug(tty, f, ##args)
37#else
38# define tty_debug_hangup(tty, f, args...) do {} while (0)
39#endif
40
41#ifdef CONFIG_UNIX98_PTYS
42static struct tty_driver *ptm_driver;
43static struct tty_driver *pts_driver;
44static DEFINE_MUTEX(devpts_mutex);
45#endif
46
47static void pty_close(struct tty_struct *tty, struct file *filp)
48{
49 if (tty->driver->subtype == PTY_TYPE_MASTER)
50 WARN_ON(tty->count > 1);
51 else {
52 if (tty_io_error(tty))
53 return;
54 if (tty->count > 2)
55 return;
56 }
57 set_bit(nr: TTY_IO_ERROR, addr: &tty->flags);
58 wake_up_interruptible(&tty->read_wait);
59 wake_up_interruptible(&tty->write_wait);
60 scoped_guard(spinlock_irq, &tty->ctrl.lock)
61 tty->ctrl.packet = false;
62 /* Review - krefs on tty_link ?? */
63 if (!tty->link)
64 return;
65 set_bit(nr: TTY_OTHER_CLOSED, addr: &tty->link->flags);
66 wake_up_interruptible(&tty->link->read_wait);
67 wake_up_interruptible(&tty->link->write_wait);
68 if (tty->driver->subtype == PTY_TYPE_MASTER) {
69 set_bit(nr: TTY_OTHER_CLOSED, addr: &tty->flags);
70#ifdef CONFIG_UNIX98_PTYS
71 if (tty->driver == ptm_driver) {
72 guard(mutex)(T: &devpts_mutex);
73 if (tty->link->driver_data)
74 devpts_pty_kill(tty->link->driver_data);
75 }
76#endif
77 tty_vhangup(tty: tty->link);
78 }
79}
80
81/*
82 * The unthrottle routine is called by the line discipline to signal
83 * that it can receive more characters. For PTY's, the TTY_THROTTLED
84 * flag is always set, to force the line discipline to always call the
85 * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
86 * characters in the queue. This is necessary since each time this
87 * happens, we need to wake up any sleeping processes that could be
88 * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
89 * for the pty buffer to be drained.
90 */
91static void pty_unthrottle(struct tty_struct *tty)
92{
93 tty_wakeup(tty: tty->link);
94 set_bit(nr: TTY_THROTTLED, addr: &tty->flags);
95}
96
97/**
98 * pty_write - write to a pty
99 * @tty: the tty we write from
100 * @buf: kernel buffer of data
101 * @c: bytes to write
102 *
103 * Our "hardware" write method. Data is coming from the ldisc which
104 * may be in a non sleeping state. We simply throw this at the other
105 * end of the link as if we were an IRQ handler receiving stuff for
106 * the other side of the pty/tty pair.
107 */
108
109static ssize_t pty_write(struct tty_struct *tty, const u8 *buf, size_t c)
110{
111 struct tty_struct *to = tty->link;
112
113 if (tty->flow.stopped || !c)
114 return 0;
115
116 return tty_insert_flip_string_and_push_buffer(port: to->port, chars: buf, cnt: c);
117}
118
119/**
120 * pty_write_room - write space
121 * @tty: tty we are writing from
122 *
123 * Report how many bytes the ldisc can send into the queue for
124 * the other device.
125 */
126
127static unsigned int pty_write_room(struct tty_struct *tty)
128{
129 if (tty->flow.stopped)
130 return 0;
131 return tty_buffer_space_avail(port: tty->link->port);
132}
133
134/* Set the lock flag on a pty */
135static int pty_set_lock(struct tty_struct *tty, int __user *arg)
136{
137 int val;
138
139 if (get_user(val, arg))
140 return -EFAULT;
141 if (val)
142 set_bit(nr: TTY_PTY_LOCK, addr: &tty->flags);
143 else
144 clear_bit(nr: TTY_PTY_LOCK, addr: &tty->flags);
145 return 0;
146}
147
148static int pty_get_lock(struct tty_struct *tty, int __user *arg)
149{
150 int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
151
152 return put_user(locked, arg);
153}
154
155/* Set the packet mode on a pty */
156static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
157{
158 int want_pktmode;
159
160 if (get_user(want_pktmode, arg))
161 return -EFAULT;
162
163 guard(spinlock_irq)(l: &tty->ctrl.lock);
164 if (!want_pktmode) {
165 tty->ctrl.packet = false;
166 return 0;
167 }
168
169 if (tty->ctrl.packet)
170 return 0;
171
172 tty->link->ctrl.pktstatus = 0;
173 smp_mb();
174 tty->ctrl.packet = true;
175
176 return 0;
177}
178
179/* Get the packet mode of a pty */
180static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
181{
182 int pktmode = tty->ctrl.packet;
183
184 return put_user(pktmode, arg);
185}
186
187/* Send a signal to the slave */
188static int pty_signal(struct tty_struct *tty, int sig)
189{
190 struct pid *pgrp;
191
192 if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
193 return -EINVAL;
194
195 if (tty->link) {
196 pgrp = tty_get_pgrp(tty: tty->link);
197 if (pgrp)
198 kill_pgrp(pid: pgrp, sig, priv: 1);
199 put_pid(pid: pgrp);
200 }
201 return 0;
202}
203
204static void pty_flush_buffer(struct tty_struct *tty)
205{
206 struct tty_struct *to = tty->link;
207
208 if (!to)
209 return;
210
211 tty_buffer_flush(tty: to, NULL);
212 if (to->ctrl.packet) {
213 guard(spinlock_irq)(l: &tty->ctrl.lock);
214 tty->ctrl.pktstatus |= TIOCPKT_FLUSHWRITE;
215 wake_up_interruptible(&to->read_wait);
216 }
217}
218
219static int pty_open(struct tty_struct *tty, struct file *filp)
220{
221 if (!tty || !tty->link)
222 return -ENODEV;
223
224 if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
225 goto out;
226 if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
227 goto out;
228 if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
229 goto out;
230
231 clear_bit(nr: TTY_IO_ERROR, addr: &tty->flags);
232 clear_bit(nr: TTY_OTHER_CLOSED, addr: &tty->link->flags);
233 set_bit(nr: TTY_THROTTLED, addr: &tty->flags);
234 return 0;
235
236out:
237 set_bit(nr: TTY_IO_ERROR, addr: &tty->flags);
238 return -EIO;
239}
240
241static void pty_set_termios(struct tty_struct *tty,
242 const struct ktermios *old_termios)
243{
244 /* See if packet mode change of state. */
245 if (tty->link && tty->link->ctrl.packet) {
246 int extproc = (old_termios->c_lflag & EXTPROC) | L_EXTPROC(tty);
247 int old_flow = ((old_termios->c_iflag & IXON) &&
248 (old_termios->c_cc[VSTOP] == '\023') &&
249 (old_termios->c_cc[VSTART] == '\021'));
250 int new_flow = (I_IXON(tty) &&
251 STOP_CHAR(tty) == '\023' &&
252 START_CHAR(tty) == '\021');
253 if ((old_flow != new_flow) || extproc) {
254 scoped_guard(spinlock_irq, &tty->ctrl.lock) {
255 if (old_flow != new_flow) {
256 tty->ctrl.pktstatus &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
257 if (new_flow)
258 tty->ctrl.pktstatus |= TIOCPKT_DOSTOP;
259 else
260 tty->ctrl.pktstatus |= TIOCPKT_NOSTOP;
261 }
262 if (extproc)
263 tty->ctrl.pktstatus |= TIOCPKT_IOCTL;
264 }
265 wake_up_interruptible(&tty->link->read_wait);
266 }
267 }
268
269 tty->termios.c_cflag &= ~(CSIZE | PARENB);
270 tty->termios.c_cflag |= (CS8 | CREAD);
271}
272
273/**
274 * pty_resize - resize event
275 * @tty: tty being resized
276 * @ws: window size being set.
277 *
278 * Update the termios variables and send the necessary signals to
279 * peform a terminal resize correctly
280 */
281
282static int pty_resize(struct tty_struct *tty, struct winsize *ws)
283{
284 struct pid *pgrp, *rpgrp;
285 struct tty_struct *pty = tty->link;
286
287 /* For a PTY we need to lock the tty side */
288 guard(mutex)(T: &tty->winsize_mutex);
289 if (!memcmp(p: ws, q: &tty->winsize, size: sizeof(*ws)))
290 return 0;
291
292 /* Signal the foreground process group of both ptys */
293 pgrp = tty_get_pgrp(tty);
294 rpgrp = tty_get_pgrp(tty: pty);
295
296 if (pgrp)
297 kill_pgrp(pid: pgrp, SIGWINCH, priv: 1);
298 if (rpgrp != pgrp && rpgrp)
299 kill_pgrp(pid: rpgrp, SIGWINCH, priv: 1);
300
301 put_pid(pid: pgrp);
302 put_pid(pid: rpgrp);
303
304 tty->winsize = *ws;
305 pty->winsize = *ws; /* Never used so will go away soon */
306
307 return 0;
308}
309
310/**
311 * pty_start - start() handler
312 * pty_stop - stop() handler
313 * @tty: tty being flow-controlled
314 *
315 * Propagates the TIOCPKT status to the master pty.
316 *
317 * NB: only the master pty can be in packet mode so only the slave
318 * needs start()/stop() handlers
319 */
320static void pty_start(struct tty_struct *tty)
321{
322 if (!tty->link || !tty->link->ctrl.packet)
323 return;
324
325 scoped_guard(spinlock_irqsave, &tty->ctrl.lock) {
326 tty->ctrl.pktstatus &= ~TIOCPKT_STOP;
327 tty->ctrl.pktstatus |= TIOCPKT_START;
328 }
329 wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
330}
331
332static void pty_stop(struct tty_struct *tty)
333{
334 if (!tty->link || !tty->link->ctrl.packet)
335 return;
336
337 scoped_guard(spinlock_irqsave, &tty->ctrl.lock) {
338 tty->ctrl.pktstatus &= ~TIOCPKT_START;
339 tty->ctrl.pktstatus |= TIOCPKT_STOP;
340 }
341 wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
342}
343
344/**
345 * pty_common_install - set up the pty pair
346 * @driver: the pty driver
347 * @tty: the tty being instantiated
348 * @legacy: true if this is BSD style
349 *
350 * Perform the initial set up for the tty/pty pair. Called from the
351 * tty layer when the port is first opened.
352 *
353 * Locking: the caller must hold the tty_mutex
354 */
355static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
356 bool legacy)
357{
358 struct tty_struct *o_tty;
359 struct tty_port *ports[2];
360 int idx = tty->index;
361 int retval = -ENOMEM;
362
363 /* Opening the slave first has always returned -EIO */
364 if (driver->subtype != PTY_TYPE_MASTER)
365 return -EIO;
366
367 ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
368 ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
369 if (!ports[0] || !ports[1])
370 goto err;
371 if (!try_module_get(module: driver->other->owner)) {
372 /* This cannot in fact currently happen */
373 goto err;
374 }
375 o_tty = alloc_tty_struct(driver: driver->other, idx);
376 if (!o_tty)
377 goto err_put_module;
378
379 tty_set_lock_subclass(tty: o_tty);
380 lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
381
382 if (legacy) {
383 /* We always use new tty termios data so we can do this
384 the easy way .. */
385 tty_init_termios(tty);
386 tty_init_termios(tty: o_tty);
387
388 driver->other->ttys[idx] = o_tty;
389 driver->ttys[idx] = tty;
390 } else {
391 memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
392 tty->termios = driver->init_termios;
393 memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
394 o_tty->termios = driver->other->init_termios;
395 }
396
397 /*
398 * Everything allocated ... set up the o_tty structure.
399 */
400 tty_driver_kref_get(d: driver->other);
401 /* Establish the links in both directions */
402 tty->link = o_tty;
403 o_tty->link = tty;
404 tty_port_init(port: ports[0]);
405 tty_port_init(port: ports[1]);
406 tty_buffer_set_limit(port: ports[0], limit: 8192);
407 tty_buffer_set_limit(port: ports[1], limit: 8192);
408 o_tty->port = ports[0];
409 tty->port = ports[1];
410 o_tty->port->itty = o_tty;
411
412 tty_buffer_set_lock_subclass(port: o_tty->port);
413
414 tty_driver_kref_get(d: driver);
415 tty->count++;
416 o_tty->count++;
417 return 0;
418
419err_put_module:
420 module_put(module: driver->other->owner);
421err:
422 kfree(objp: ports[0]);
423 kfree(objp: ports[1]);
424 return retval;
425}
426
427static void pty_cleanup(struct tty_struct *tty)
428{
429 tty_port_put(port: tty->port);
430}
431
432/* Traditional BSD devices */
433#ifdef CONFIG_LEGACY_PTYS
434
435static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
436{
437 return pty_common_install(driver, tty, legacy: true);
438}
439
440static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
441{
442 struct tty_struct *pair = tty->link;
443
444 driver->ttys[tty->index] = NULL;
445 if (pair)
446 pair->driver->ttys[pair->index] = NULL;
447}
448
449static int pty_bsd_ioctl(struct tty_struct *tty,
450 unsigned int cmd, unsigned long arg)
451{
452 switch (cmd) {
453 case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
454 return pty_set_lock(tty, arg: (int __user *) arg);
455 case TIOCGPTLCK: /* Get PT Lock status */
456 return pty_get_lock(tty, arg: (int __user *)arg);
457 case TIOCPKT: /* Set PT packet mode */
458 return pty_set_pktmode(tty, arg: (int __user *)arg);
459 case TIOCGPKT: /* Get PT packet mode */
460 return pty_get_pktmode(tty, arg: (int __user *)arg);
461 case TIOCSIG: /* Send signal to other side of pty */
462 return pty_signal(tty, sig: (int) arg);
463 case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
464 return -EINVAL;
465 }
466 return -ENOIOCTLCMD;
467}
468
469#ifdef CONFIG_COMPAT
470static long pty_bsd_compat_ioctl(struct tty_struct *tty,
471 unsigned int cmd, unsigned long arg)
472{
473 /*
474 * PTY ioctls don't require any special translation between 32-bit and
475 * 64-bit userspace, they are already compatible.
476 */
477 return pty_bsd_ioctl(tty, cmd, arg: (unsigned long)compat_ptr(uptr: arg));
478}
479#else
480#define pty_bsd_compat_ioctl NULL
481#endif
482
483static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
484/*
485 * not really modular, but the easiest way to keep compat with existing
486 * bootargs behaviour is to continue using module_param here.
487 */
488module_param(legacy_count, int, 0);
489
490/*
491 * The master side of a pty can do TIOCSPTLCK and thus
492 * has pty_bsd_ioctl.
493 */
494static const struct tty_operations master_pty_ops_bsd = {
495 .install = pty_install,
496 .open = pty_open,
497 .close = pty_close,
498 .write = pty_write,
499 .write_room = pty_write_room,
500 .flush_buffer = pty_flush_buffer,
501 .unthrottle = pty_unthrottle,
502 .ioctl = pty_bsd_ioctl,
503 .compat_ioctl = pty_bsd_compat_ioctl,
504 .cleanup = pty_cleanup,
505 .resize = pty_resize,
506 .remove = pty_remove
507};
508
509static const struct tty_operations slave_pty_ops_bsd = {
510 .install = pty_install,
511 .open = pty_open,
512 .close = pty_close,
513 .write = pty_write,
514 .write_room = pty_write_room,
515 .flush_buffer = pty_flush_buffer,
516 .unthrottle = pty_unthrottle,
517 .set_termios = pty_set_termios,
518 .cleanup = pty_cleanup,
519 .resize = pty_resize,
520 .start = pty_start,
521 .stop = pty_stop,
522 .remove = pty_remove
523};
524
525static void __init legacy_pty_init(void)
526{
527 struct tty_driver *pty_driver, *pty_slave_driver;
528
529 if (legacy_count <= 0)
530 return;
531
532 pty_driver = tty_alloc_driver(legacy_count,
533 TTY_DRIVER_RESET_TERMIOS |
534 TTY_DRIVER_REAL_RAW |
535 TTY_DRIVER_DYNAMIC_ALLOC);
536 if (IS_ERR(ptr: pty_driver))
537 panic(fmt: "Couldn't allocate pty driver");
538
539 pty_slave_driver = tty_alloc_driver(legacy_count,
540 TTY_DRIVER_RESET_TERMIOS |
541 TTY_DRIVER_REAL_RAW |
542 TTY_DRIVER_DYNAMIC_ALLOC);
543 if (IS_ERR(ptr: pty_slave_driver))
544 panic(fmt: "Couldn't allocate pty slave driver");
545
546 pty_driver->driver_name = "pty_master";
547 pty_driver->name = "pty";
548 pty_driver->major = PTY_MASTER_MAJOR;
549 pty_driver->minor_start = 0;
550 pty_driver->type = TTY_DRIVER_TYPE_PTY;
551 pty_driver->subtype = PTY_TYPE_MASTER;
552 pty_driver->init_termios = tty_std_termios;
553 pty_driver->init_termios.c_iflag = 0;
554 pty_driver->init_termios.c_oflag = 0;
555 pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
556 pty_driver->init_termios.c_lflag = 0;
557 pty_driver->init_termios.c_ispeed = 38400;
558 pty_driver->init_termios.c_ospeed = 38400;
559 pty_driver->other = pty_slave_driver;
560 tty_set_operations(driver: pty_driver, op: &master_pty_ops_bsd);
561
562 pty_slave_driver->driver_name = "pty_slave";
563 pty_slave_driver->name = "ttyp";
564 pty_slave_driver->major = PTY_SLAVE_MAJOR;
565 pty_slave_driver->minor_start = 0;
566 pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
567 pty_slave_driver->subtype = PTY_TYPE_SLAVE;
568 pty_slave_driver->init_termios = tty_std_termios;
569 pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
570 pty_slave_driver->init_termios.c_ispeed = 38400;
571 pty_slave_driver->init_termios.c_ospeed = 38400;
572 pty_slave_driver->other = pty_driver;
573 tty_set_operations(driver: pty_slave_driver, op: &slave_pty_ops_bsd);
574
575 if (tty_register_driver(driver: pty_driver))
576 panic(fmt: "Couldn't register pty driver");
577 if (tty_register_driver(driver: pty_slave_driver))
578 panic(fmt: "Couldn't register pty slave driver");
579}
580#else
581static inline void legacy_pty_init(void) { }
582#endif
583
584/* Unix98 devices */
585#ifdef CONFIG_UNIX98_PTYS
586static struct cdev ptmx_cdev;
587
588static struct file *ptm_open_peer_file(struct file *master,
589 struct tty_struct *tty, int flags)
590{
591 struct path path;
592 struct file *file;
593
594 /* Compute the slave's path */
595 path.mnt = devpts_mntget(master, tty->driver_data);
596 if (IS_ERR(ptr: path.mnt))
597 return ERR_CAST(ptr: path.mnt);
598 path.dentry = tty->link->driver_data;
599
600 file = dentry_open(path: &path, flags, current_cred());
601 mntput(mnt: path.mnt);
602 return file;
603}
604
605/**
606 * ptm_open_peer - open the peer of a pty
607 * @master: the open struct file of the ptmx device node
608 * @tty: the master of the pty being opened
609 * @flags: the flags for open
610 *
611 * Provide a race free way for userspace to open the slave end of a pty
612 * (where they have the master fd and cannot access or trust the mount
613 * namespace /dev/pts was mounted inside).
614 */
615int ptm_open_peer(struct file *master, struct tty_struct *tty, int flags)
616{
617 if (tty->driver != ptm_driver)
618 return -EIO;
619
620 return FD_ADD(flags, ptm_open_peer_file(master, tty, flags));
621}
622
623static int pty_unix98_ioctl(struct tty_struct *tty,
624 unsigned int cmd, unsigned long arg)
625{
626 switch (cmd) {
627 case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
628 return pty_set_lock(tty, arg: (int __user *)arg);
629 case TIOCGPTLCK: /* Get PT Lock status */
630 return pty_get_lock(tty, arg: (int __user *)arg);
631 case TIOCPKT: /* Set PT packet mode */
632 return pty_set_pktmode(tty, arg: (int __user *)arg);
633 case TIOCGPKT: /* Get PT packet mode */
634 return pty_get_pktmode(tty, arg: (int __user *)arg);
635 case TIOCGPTN: /* Get PT Number */
636 return put_user(tty->index, (unsigned int __user *)arg);
637 case TIOCSIG: /* Send signal to other side of pty */
638 return pty_signal(tty, sig: (int) arg);
639 }
640
641 return -ENOIOCTLCMD;
642}
643
644#ifdef CONFIG_COMPAT
645static long pty_unix98_compat_ioctl(struct tty_struct *tty,
646 unsigned int cmd, unsigned long arg)
647{
648 /*
649 * PTY ioctls don't require any special translation between 32-bit and
650 * 64-bit userspace, they are already compatible.
651 */
652 return pty_unix98_ioctl(tty, cmd,
653 arg: cmd == TIOCSIG ? arg : (unsigned long)compat_ptr(uptr: arg));
654}
655#else
656#define pty_unix98_compat_ioctl NULL
657#endif
658
659/**
660 * ptm_unix98_lookup - find a pty master
661 * @driver: ptm driver
662 * @file: unused
663 * @idx: tty index
664 *
665 * Look up a pty master device. Called under the tty_mutex for now.
666 * This provides our locking.
667 */
668
669static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
670 struct file *file, int idx)
671{
672 /* Master must be open via /dev/ptmx */
673 return ERR_PTR(error: -EIO);
674}
675
676/**
677 * pts_unix98_lookup - find a pty slave
678 * @driver: pts driver
679 * @file: file pointer to tty
680 * @idx: tty index
681 *
682 * Look up a pty master device. Called under the tty_mutex for now.
683 * This provides our locking for the tty pointer.
684 */
685
686static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
687 struct file *file, int idx)
688{
689 guard(mutex)(T: &devpts_mutex);
690 /* Master must be open before slave */
691 return devpts_get_priv(file->f_path.dentry) ? : ERR_PTR(error: -EIO);
692}
693
694static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
695{
696 return pty_common_install(driver, tty, legacy: false);
697}
698
699/* this is called once with whichever end is closed last */
700static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
701{
702 struct pts_fs_info *fsi;
703
704 if (tty->driver->subtype == PTY_TYPE_MASTER)
705 fsi = tty->driver_data;
706 else
707 fsi = tty->link->driver_data;
708
709 if (fsi) {
710 devpts_kill_index(fsi, tty->index);
711 devpts_release(fsi);
712 }
713}
714
715static void pty_show_fdinfo(struct tty_struct *tty, struct seq_file *m)
716{
717 seq_printf(m, fmt: "tty-index:\t%d\n", tty->index);
718}
719
720static const struct tty_operations ptm_unix98_ops = {
721 .lookup = ptm_unix98_lookup,
722 .install = pty_unix98_install,
723 .remove = pty_unix98_remove,
724 .open = pty_open,
725 .close = pty_close,
726 .write = pty_write,
727 .write_room = pty_write_room,
728 .flush_buffer = pty_flush_buffer,
729 .unthrottle = pty_unthrottle,
730 .ioctl = pty_unix98_ioctl,
731 .compat_ioctl = pty_unix98_compat_ioctl,
732 .resize = pty_resize,
733 .cleanup = pty_cleanup,
734 .show_fdinfo = pty_show_fdinfo,
735};
736
737static const struct tty_operations pty_unix98_ops = {
738 .lookup = pts_unix98_lookup,
739 .install = pty_unix98_install,
740 .remove = pty_unix98_remove,
741 .open = pty_open,
742 .close = pty_close,
743 .write = pty_write,
744 .write_room = pty_write_room,
745 .flush_buffer = pty_flush_buffer,
746 .unthrottle = pty_unthrottle,
747 .set_termios = pty_set_termios,
748 .start = pty_start,
749 .stop = pty_stop,
750 .cleanup = pty_cleanup,
751};
752
753/**
754 * ptmx_open - open a unix 98 pty master
755 * @inode: inode of device file
756 * @filp: file pointer to tty
757 *
758 * Allocate a unix98 pty master device from the ptmx driver.
759 *
760 * Locking: tty_mutex protects the init_dev work. tty->count should
761 * protect the rest.
762 * allocated_ptys_lock handles the list of free pty numbers
763 */
764
765static int ptmx_open(struct inode *inode, struct file *filp)
766{
767 struct pts_fs_info *fsi;
768 struct tty_struct *tty;
769 struct dentry *dentry;
770 int retval;
771 int index;
772
773 nonseekable_open(inode, filp);
774
775 /* We refuse fsnotify events on ptmx, since it's a shared resource */
776 file_set_fsnotify_mode(file: filp, FMODE_NONOTIFY);
777
778 retval = tty_alloc_file(file: filp);
779 if (retval)
780 return retval;
781
782 fsi = devpts_acquire(filp);
783 if (IS_ERR(ptr: fsi)) {
784 retval = PTR_ERR(ptr: fsi);
785 goto out_free_file;
786 }
787
788 /* find a device that is not in use. */
789 scoped_guard(mutex, &devpts_mutex)
790 index = devpts_new_index(fsi);
791
792 retval = index;
793 if (index < 0)
794 goto out_put_fsi;
795
796
797 /* The tty returned here is locked so we can safely drop the mutex */
798 scoped_guard(mutex, &tty_mutex)
799 tty = tty_init_dev(driver: ptm_driver, idx: index);
800
801 retval = PTR_ERR(ptr: tty);
802 if (IS_ERR(ptr: tty))
803 goto out;
804
805 /*
806 * From here on out, the tty is "live", and the index and
807 * fsi will be killed/put by the tty_release()
808 */
809 set_bit(nr: TTY_PTY_LOCK, addr: &tty->flags); /* LOCK THE SLAVE */
810 tty->driver_data = fsi;
811
812 tty_add_file(tty, file: filp);
813
814 dentry = devpts_pty_new(fsi, index, tty->link);
815 if (IS_ERR(ptr: dentry)) {
816 retval = PTR_ERR(ptr: dentry);
817 goto err_release;
818 }
819 tty->link->driver_data = dentry;
820
821 retval = ptm_driver->ops->open(tty, filp);
822 if (retval)
823 goto err_release;
824
825 tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);
826
827 tty_unlock(tty);
828 return 0;
829err_release:
830 tty_unlock(tty);
831 // This will also put-ref the fsi
832 tty_release(inode, filp);
833 return retval;
834out:
835 devpts_kill_index(fsi, index);
836out_put_fsi:
837 devpts_release(fsi);
838out_free_file:
839 tty_free_file(file: filp);
840 return retval;
841}
842
843static struct file_operations ptmx_fops __ro_after_init;
844
845static void __init unix98_pty_init(void)
846{
847 ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
848 TTY_DRIVER_RESET_TERMIOS |
849 TTY_DRIVER_REAL_RAW |
850 TTY_DRIVER_DYNAMIC_DEV |
851 TTY_DRIVER_DEVPTS_MEM |
852 TTY_DRIVER_DYNAMIC_ALLOC);
853 if (IS_ERR(ptr: ptm_driver))
854 panic(fmt: "Couldn't allocate Unix98 ptm driver");
855 pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
856 TTY_DRIVER_RESET_TERMIOS |
857 TTY_DRIVER_REAL_RAW |
858 TTY_DRIVER_DYNAMIC_DEV |
859 TTY_DRIVER_DEVPTS_MEM |
860 TTY_DRIVER_DYNAMIC_ALLOC);
861 if (IS_ERR(ptr: pts_driver))
862 panic(fmt: "Couldn't allocate Unix98 pts driver");
863
864 ptm_driver->driver_name = "pty_master";
865 ptm_driver->name = "ptm";
866 ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
867 ptm_driver->minor_start = 0;
868 ptm_driver->type = TTY_DRIVER_TYPE_PTY;
869 ptm_driver->subtype = PTY_TYPE_MASTER;
870 ptm_driver->init_termios = tty_std_termios;
871 ptm_driver->init_termios.c_iflag = 0;
872 ptm_driver->init_termios.c_oflag = 0;
873 ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
874 ptm_driver->init_termios.c_lflag = 0;
875 ptm_driver->init_termios.c_ispeed = 38400;
876 ptm_driver->init_termios.c_ospeed = 38400;
877 ptm_driver->other = pts_driver;
878 tty_set_operations(driver: ptm_driver, op: &ptm_unix98_ops);
879
880 pts_driver->driver_name = "pty_slave";
881 pts_driver->name = "pts";
882 pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
883 pts_driver->minor_start = 0;
884 pts_driver->type = TTY_DRIVER_TYPE_PTY;
885 pts_driver->subtype = PTY_TYPE_SLAVE;
886 pts_driver->init_termios = tty_std_termios;
887 pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
888 pts_driver->init_termios.c_ispeed = 38400;
889 pts_driver->init_termios.c_ospeed = 38400;
890 pts_driver->other = ptm_driver;
891 tty_set_operations(driver: pts_driver, op: &pty_unix98_ops);
892
893 if (tty_register_driver(driver: ptm_driver))
894 panic(fmt: "Couldn't register Unix98 ptm driver");
895 if (tty_register_driver(driver: pts_driver))
896 panic(fmt: "Couldn't register Unix98 pts driver");
897
898 /* Now create the /dev/ptmx special device */
899 tty_default_fops(fops: &ptmx_fops);
900 ptmx_fops.open = ptmx_open;
901
902 cdev_init(&ptmx_cdev, &ptmx_fops);
903 if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
904 register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
905 panic(fmt: "Couldn't register /dev/ptmx driver");
906 device_create(cls: &tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, fmt: "ptmx");
907}
908
909#else
910static inline void unix98_pty_init(void) { }
911#endif
912
913static int __init pty_init(void)
914{
915 legacy_pty_init();
916 unix98_pty_init();
917 return 0;
918}
919device_initcall(pty_init);
920

source code of linux/drivers/tty/pty.c