drivers/tty/pty.c

   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
  42 static struct tty_driver *ptm_driver;
  43 static struct tty_driver *pts_driver;
  44 static DEFINE_MUTEX(devpts_mutex);
  45 #endif
  46
  47 static 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(TTY_IO_ERROR, &tty->flags);
  58         wake_up_interruptible(&tty->read_wait);
  59         wake_up_interruptible(&tty->write_wait);
  60         spin_lock_irq(&tty->ctrl.lock);
  61         tty->ctrl.packet = false;
  62         spin_unlock_irq(&tty->ctrl.lock);
  63         /* Review - krefs on tty_link ?? */
  64         if (!tty->link)
  65                 return;
  66         set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
  67         wake_up_interruptible(&tty->link->read_wait);
  68         wake_up_interruptible(&tty->link->write_wait);
  69         if (tty->driver->subtype == PTY_TYPE_MASTER) {
  70                 set_bit(TTY_OTHER_CLOSED, &tty->flags);
  71 #ifdef CONFIG_UNIX98_PTYS
  72                 if (tty->driver == ptm_driver) {
  73                         mutex_lock(&devpts_mutex);
  74                         if (tty->link->driver_data)
  75                                 devpts_pty_kill(tty->link->driver_data);
  76                         mutex_unlock(&devpts_mutex);
  77                 }
  78 #endif
  79                 tty_vhangup(tty->link);
  80         }
  81 }
  82
  83 /*
  84  * The unthrottle routine is called by the line discipline to signal
  85  * that it can receive more characters.  For PTY's, the TTY_THROTTLED
  86  * flag is always set, to force the line discipline to always call the
  87  * unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
  88  * characters in the queue.  This is necessary since each time this
  89  * happens, we need to wake up any sleeping processes that could be
  90  * (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
  91  * for the pty buffer to be drained.
  92  */
  93 static void pty_unthrottle(struct tty_struct *tty)
  94 {
  95         tty_wakeup(tty->link);
  96         set_bit(TTY_THROTTLED, &tty->flags);
  97 }
  98
  99 /**
 100  *      pty_write               -       write to a pty
 101  *      @tty: the tty we write from
 102  *      @buf: kernel buffer of data
 103  *      @c: bytes to write
 104  *
 105  *      Our "hardware" write method. Data is coming from the ldisc which
 106  *      may be in a non sleeping state. We simply throw this at the other
 107  *      end of the link as if we were an IRQ handler receiving stuff for
 108  *      the other side of the pty/tty pair.
 109  */
 110
 111 static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
 112 {
 113         struct tty_struct *to = tty->link;
 114         unsigned long flags;
 115
 116         if (tty->flow.stopped)
 117                 return 0;
 118
 119         if (c > 0) {
 120                 spin_lock_irqsave(&to->port->lock, flags);
 121                 /* Stuff the data into the input queue of the other end */
 122                 c = tty_insert_flip_string(to->port, buf, c);
 123                 spin_unlock_irqrestore(&to->port->lock, flags);
 124                 /* And shovel */
 125                 if (c)
 126                         tty_flip_buffer_push(to->port);
 127         }
 128         return c;
 129 }
 130
 131 /**
 132  *      pty_write_room  -       write space
 133  *      @tty: tty we are writing from
 134  *
 135  *      Report how many bytes the ldisc can send into the queue for
 136  *      the other device.
 137  */
 138
 139 static unsigned int pty_write_room(struct tty_struct *tty)
 140 {
 141         if (tty->flow.stopped)
 142                 return 0;
 143         return tty_buffer_space_avail(tty->link->port);
 144 }
 145
 146 /* Set the lock flag on a pty */
 147 static int pty_set_lock(struct tty_struct *tty, int __user *arg)
 148 {
 149         int val;
 150
 151         if (get_user(val, arg))
 152                 return -EFAULT;
 153         if (val)
 154                 set_bit(TTY_PTY_LOCK, &tty->flags);
 155         else
 156                 clear_bit(TTY_PTY_LOCK, &tty->flags);
 157         return 0;
 158 }
 159
 160 static int pty_get_lock(struct tty_struct *tty, int __user *arg)
 161 {
 162         int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
 163
 164         return put_user(locked, arg);
 165 }
 166
 167 /* Set the packet mode on a pty */
 168 static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
 169 {
 170         int pktmode;
 171
 172         if (get_user(pktmode, arg))
 173                 return -EFAULT;
 174
 175         spin_lock_irq(&tty->ctrl.lock);
 176         if (pktmode) {
 177                 if (!tty->ctrl.packet) {
 178                         tty->link->ctrl.pktstatus = 0;
 179                         smp_mb();
 180                         tty->ctrl.packet = true;
 181                 }
 182         } else
 183                 tty->ctrl.packet = false;
 184         spin_unlock_irq(&tty->ctrl.lock);
 185
 186         return 0;
 187 }
 188
 189 /* Get the packet mode of a pty */
 190 static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
 191 {
 192         int pktmode = tty->ctrl.packet;
 193
 194         return put_user(pktmode, arg);
 195 }
 196
 197 /* Send a signal to the slave */
 198 static int pty_signal(struct tty_struct *tty, int sig)
 199 {
 200         struct pid *pgrp;
 201
 202         if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
 203                 return -EINVAL;
 204
 205         if (tty->link) {
 206                 pgrp = tty_get_pgrp(tty->link);
 207                 if (pgrp)
 208                         kill_pgrp(pgrp, sig, 1);
 209                 put_pid(pgrp);
 210         }
 211         return 0;
 212 }
 213
 214 static void pty_flush_buffer(struct tty_struct *tty)
 215 {
 216         struct tty_struct *to = tty->link;
 217
 218         if (!to)
 219                 return;
 220
 221         tty_buffer_flush(to, NULL);
 222         if (to->ctrl.packet) {
 223                 spin_lock_irq(&tty->ctrl.lock);
 224                 tty->ctrl.pktstatus |= TIOCPKT_FLUSHWRITE;
 225                 wake_up_interruptible(&to->read_wait);
 226                 spin_unlock_irq(&tty->ctrl.lock);
 227         }
 228 }
 229
 230 static int pty_open(struct tty_struct *tty, struct file *filp)
 231 {
 232         if (!tty || !tty->link)
 233                 return -ENODEV;
 234
 235         if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
 236                 goto out;
 237         if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
 238                 goto out;
 239         if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
 240                 goto out;
 241
 242         clear_bit(TTY_IO_ERROR, &tty->flags);
 243         clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 244         set_bit(TTY_THROTTLED, &tty->flags);
 245         return 0;
 246
 247 out:
 248         set_bit(TTY_IO_ERROR, &tty->flags);
 249         return -EIO;
 250 }
 251
 252 static void pty_set_termios(struct tty_struct *tty,
 253                                         struct ktermios *old_termios)
 254 {
 255         /* See if packet mode change of state. */
 256         if (tty->link && tty->link->ctrl.packet) {
 257                 int extproc = (old_termios->c_lflag & EXTPROC) | L_EXTPROC(tty);
 258                 int old_flow = ((old_termios->c_iflag & IXON) &&
 259                                 (old_termios->c_cc[VSTOP] == '\023') &&
 260                                 (old_termios->c_cc[VSTART] == '\021'));
 261                 int new_flow = (I_IXON(tty) &&
 262                                 STOP_CHAR(tty) == '\023' &&
 263                                 START_CHAR(tty) == '\021');
 264                 if ((old_flow != new_flow) || extproc) {
 265                         spin_lock_irq(&tty->ctrl.lock);
 266                         if (old_flow != new_flow) {
 267                                 tty->ctrl.pktstatus &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
 268                                 if (new_flow)
 269                                         tty->ctrl.pktstatus |= TIOCPKT_DOSTOP;
 270                                 else
 271                                         tty->ctrl.pktstatus |= TIOCPKT_NOSTOP;
 272                         }
 273                         if (extproc)
 274                                 tty->ctrl.pktstatus |= TIOCPKT_IOCTL;
 275                         spin_unlock_irq(&tty->ctrl.lock);
 276                         wake_up_interruptible(&tty->link->read_wait);
 277                 }
 278         }
 279
 280         tty->termios.c_cflag &= ~(CSIZE | PARENB);
 281         tty->termios.c_cflag |= (CS8 | CREAD);
 282 }
 283
 284 /**
 285  *      pty_resize              -       resize event
 286  *      @tty: tty being resized
 287  *      @ws: window size being set.
 288  *
 289  *      Update the termios variables and send the necessary signals to
 290  *      peform a terminal resize correctly
 291  */
 292
 293 static int pty_resize(struct tty_struct *tty,  struct winsize *ws)
 294 {
 295         struct pid *pgrp, *rpgrp;
 296         struct tty_struct *pty = tty->link;
 297
 298         /* For a PTY we need to lock the tty side */
 299         mutex_lock(&tty->winsize_mutex);
 300         if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
 301                 goto done;
 302
 303         /* Signal the foreground process group of both ptys */
 304         pgrp = tty_get_pgrp(tty);
 305         rpgrp = tty_get_pgrp(pty);
 306
 307         if (pgrp)
 308                 kill_pgrp(pgrp, SIGWINCH, 1);
 309         if (rpgrp != pgrp && rpgrp)
 310                 kill_pgrp(rpgrp, SIGWINCH, 1);
 311
 312         put_pid(pgrp);
 313         put_pid(rpgrp);
 314
 315         tty->winsize = *ws;
 316         pty->winsize = *ws;     /* Never used so will go away soon */
 317 done:
 318         mutex_unlock(&tty->winsize_mutex);
 319         return 0;
 320 }
 321
 322 /**
 323  *      pty_start - start() handler
 324  *      pty_stop  - stop() handler
 325  *      @tty: tty being flow-controlled
 326  *
 327  *      Propagates the TIOCPKT status to the master pty.
 328  *
 329  *      NB: only the master pty can be in packet mode so only the slave
 330  *          needs start()/stop() handlers
 331  */
 332 static void pty_start(struct tty_struct *tty)
 333 {
 334         unsigned long flags;
 335
 336         if (tty->link && tty->link->ctrl.packet) {
 337                 spin_lock_irqsave(&tty->ctrl.lock, flags);
 338                 tty->ctrl.pktstatus &= ~TIOCPKT_STOP;
 339                 tty->ctrl.pktstatus |= TIOCPKT_START;
 340                 spin_unlock_irqrestore(&tty->ctrl.lock, flags);
 341                 wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
 342         }
 343 }
 344
 345 static void pty_stop(struct tty_struct *tty)
 346 {
 347         unsigned long flags;
 348
 349         if (tty->link && tty->link->ctrl.packet) {
 350                 spin_lock_irqsave(&tty->ctrl.lock, flags);
 351                 tty->ctrl.pktstatus &= ~TIOCPKT_START;
 352                 tty->ctrl.pktstatus |= TIOCPKT_STOP;
 353                 spin_unlock_irqrestore(&tty->ctrl.lock, flags);
 354                 wake_up_interruptible_poll(&tty->link->read_wait, EPOLLIN);
 355         }
 356 }
 357
 358 /**
 359  *      pty_common_install              -       set up the pty pair
 360  *      @driver: the pty driver
 361  *      @tty: the tty being instantiated
 362  *      @legacy: true if this is BSD style
 363  *
 364  *      Perform the initial set up for the tty/pty pair. Called from the
 365  *      tty layer when the port is first opened.
 366  *
 367  *      Locking: the caller must hold the tty_mutex
 368  */
 369 static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
 370                 bool legacy)
 371 {
 372         struct tty_struct *o_tty;
 373         struct tty_port *ports[2];
 374         int idx = tty->index;
 375         int retval = -ENOMEM;
 376
 377         /* Opening the slave first has always returned -EIO */
 378         if (driver->subtype != PTY_TYPE_MASTER)
 379                 return -EIO;
 380
 381         ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
 382         ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
 383         if (!ports[0] || !ports[1])
 384                 goto err;
 385         if (!try_module_get(driver->other->owner)) {
 386                 /* This cannot in fact currently happen */
 387                 goto err;
 388         }
 389         o_tty = alloc_tty_struct(driver->other, idx);
 390         if (!o_tty)
 391                 goto err_put_module;
 392
 393         tty_set_lock_subclass(o_tty);
 394         lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
 395
 396         if (legacy) {
 397                 /* We always use new tty termios data so we can do this
 398                    the easy way .. */
 399                 tty_init_termios(tty);
 400                 tty_init_termios(o_tty);
 401
 402                 driver->other->ttys[idx] = o_tty;
 403                 driver->ttys[idx] = tty;
 404         } else {
 405                 memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
 406                 tty->termios = driver->init_termios;
 407                 memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
 408                 o_tty->termios = driver->other->init_termios;
 409         }
 410
 411         /*
 412          * Everything allocated ... set up the o_tty structure.
 413          */
 414         tty_driver_kref_get(driver->other);
 415         /* Establish the links in both directions */
 416         tty->link   = o_tty;
 417         o_tty->link = tty;
 418         tty_port_init(ports[0]);
 419         tty_port_init(ports[1]);
 420         tty_buffer_set_limit(ports[0], 8192);
 421         tty_buffer_set_limit(ports[1], 8192);
 422         o_tty->port = ports[0];
 423         tty->port = ports[1];
 424         o_tty->port->itty = o_tty;
 425
 426         tty_buffer_set_lock_subclass(o_tty->port);
 427
 428         tty_driver_kref_get(driver);
 429         tty->count++;
 430         o_tty->count++;
 431         return 0;
 432
 433 err_put_module:
 434         module_put(driver->other->owner);
 435 err:
 436         kfree(ports[0]);
 437         kfree(ports[1]);
 438         return retval;
 439 }
 440
 441 static void pty_cleanup(struct tty_struct *tty)
 442 {
 443         tty_port_put(tty->port);
 444 }
 445
 446 /* Traditional BSD devices */
 447 #ifdef CONFIG_LEGACY_PTYS
 448
 449 static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
 450 {
 451         return pty_common_install(driver, tty, true);
 452 }
 453
 454 static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
 455 {
 456         struct tty_struct *pair = tty->link;
 457
 458         driver->ttys[tty->index] = NULL;
 459         if (pair)
 460                 pair->driver->ttys[pair->index] = NULL;
 461 }
 462
 463 static int pty_bsd_ioctl(struct tty_struct *tty,
 464                          unsigned int cmd, unsigned long arg)
 465 {
 466         switch (cmd) {
 467         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 468                 return pty_set_lock(tty, (int __user *) arg);
 469         case TIOCGPTLCK: /* Get PT Lock status */
 470                 return pty_get_lock(tty, (int __user *)arg);
 471         case TIOCPKT: /* Set PT packet mode */
 472                 return pty_set_pktmode(tty, (int __user *)arg);
 473         case TIOCGPKT: /* Get PT packet mode */
 474                 return pty_get_pktmode(tty, (int __user *)arg);
 475         case TIOCSIG:    /* Send signal to other side of pty */
 476                 return pty_signal(tty, (int) arg);
 477         case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
 478                 return -EINVAL;
 479         }
 480         return -ENOIOCTLCMD;
 481 }
 482
 483 #ifdef CONFIG_COMPAT
 484 static long pty_bsd_compat_ioctl(struct tty_struct *tty,
 485                                  unsigned int cmd, unsigned long arg)
 486 {
 487         /*
 488          * PTY ioctls don't require any special translation between 32-bit and
 489          * 64-bit userspace, they are already compatible.
 490          */
 491         return pty_bsd_ioctl(tty, cmd, (unsigned long)compat_ptr(arg));
 492 }
 493 #else
 494 #define pty_bsd_compat_ioctl NULL
 495 #endif
 496
 497 static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
 498 /*
 499  * not really modular, but the easiest way to keep compat with existing
 500  * bootargs behaviour is to continue using module_param here.
 501  */
 502 module_param(legacy_count, int, 0);
 503
 504 /*
 505  * The master side of a pty can do TIOCSPTLCK and thus
 506  * has pty_bsd_ioctl.
 507  */
 508 static const struct tty_operations master_pty_ops_bsd = {
 509         .install = pty_install,
 510         .open = pty_open,
 511         .close = pty_close,
 512         .write = pty_write,
 513         .write_room = pty_write_room,
 514         .flush_buffer = pty_flush_buffer,
 515         .unthrottle = pty_unthrottle,
 516         .ioctl = pty_bsd_ioctl,
 517         .compat_ioctl = pty_bsd_compat_ioctl,
 518         .cleanup = pty_cleanup,
 519         .resize = pty_resize,
 520         .remove = pty_remove
 521 };
 522
 523 static const struct tty_operations slave_pty_ops_bsd = {
 524         .install = pty_install,
 525         .open = pty_open,
 526         .close = pty_close,
 527         .write = pty_write,
 528         .write_room = pty_write_room,
 529         .flush_buffer = pty_flush_buffer,
 530         .unthrottle = pty_unthrottle,
 531         .set_termios = pty_set_termios,
 532         .cleanup = pty_cleanup,
 533         .resize = pty_resize,
 534         .start = pty_start,
 535         .stop = pty_stop,
 536         .remove = pty_remove
 537 };
 538
 539 static void __init legacy_pty_init(void)
 540 {
 541         struct tty_driver *pty_driver, *pty_slave_driver;
 542
 543         if (legacy_count <= 0)
 544                 return;
 545
 546         pty_driver = tty_alloc_driver(legacy_count,
 547                         TTY_DRIVER_RESET_TERMIOS |
 548                         TTY_DRIVER_REAL_RAW |
 549                         TTY_DRIVER_DYNAMIC_ALLOC);
 550         if (IS_ERR(pty_driver))
 551                 panic("Couldn't allocate pty driver");
 552
 553         pty_slave_driver = tty_alloc_driver(legacy_count,
 554                         TTY_DRIVER_RESET_TERMIOS |
 555                         TTY_DRIVER_REAL_RAW |
 556                         TTY_DRIVER_DYNAMIC_ALLOC);
 557         if (IS_ERR(pty_slave_driver))
 558                 panic("Couldn't allocate pty slave driver");
 559
 560         pty_driver->driver_name = "pty_master";
 561         pty_driver->name = "pty";
 562         pty_driver->major = PTY_MASTER_MAJOR;
 563         pty_driver->minor_start = 0;
 564         pty_driver->type = TTY_DRIVER_TYPE_PTY;
 565         pty_driver->subtype = PTY_TYPE_MASTER;
 566         pty_driver->init_termios = tty_std_termios;
 567         pty_driver->init_termios.c_iflag = 0;
 568         pty_driver->init_termios.c_oflag = 0;
 569         pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 570         pty_driver->init_termios.c_lflag = 0;
 571         pty_driver->init_termios.c_ispeed = 38400;
 572         pty_driver->init_termios.c_ospeed = 38400;
 573         pty_driver->other = pty_slave_driver;
 574         tty_set_operations(pty_driver, &master_pty_ops_bsd);
 575
 576         pty_slave_driver->driver_name = "pty_slave";
 577         pty_slave_driver->name = "ttyp";
 578         pty_slave_driver->major = PTY_SLAVE_MAJOR;
 579         pty_slave_driver->minor_start = 0;
 580         pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
 581         pty_slave_driver->subtype = PTY_TYPE_SLAVE;
 582         pty_slave_driver->init_termios = tty_std_termios;
 583         pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 584         pty_slave_driver->init_termios.c_ispeed = 38400;
 585         pty_slave_driver->init_termios.c_ospeed = 38400;
 586         pty_slave_driver->other = pty_driver;
 587         tty_set_operations(pty_slave_driver, &slave_pty_ops_bsd);
 588
 589         if (tty_register_driver(pty_driver))
 590                 panic("Couldn't register pty driver");
 591         if (tty_register_driver(pty_slave_driver))
 592                 panic("Couldn't register pty slave driver");
 593 }
 594 #else
 595 static inline void legacy_pty_init(void) { }
 596 #endif
 597
 598 /* Unix98 devices */
 599 #ifdef CONFIG_UNIX98_PTYS
 600 static struct cdev ptmx_cdev;
 601
 602 /**
 603  *      ptm_open_peer - open the peer of a pty
 604  *      @master: the open struct file of the ptmx device node
 605  *      @tty: the master of the pty being opened
 606  *      @flags: the flags for open
 607  *
 608  *      Provide a race free way for userspace to open the slave end of a pty
 609  *      (where they have the master fd and cannot access or trust the mount
 610  *      namespace /dev/pts was mounted inside).
 611  */
 612 int ptm_open_peer(struct file *master, struct tty_struct *tty, int flags)
 613 {
 614         int fd;
 615         struct file *filp;
 616         int retval = -EINVAL;
 617         struct path path;
 618
 619         if (tty->driver != ptm_driver)
 620                 return -EIO;
 621
 622         fd = get_unused_fd_flags(flags);
 623         if (fd < 0) {
 624                 retval = fd;
 625                 goto err;
 626         }
 627
 628         /* Compute the slave's path */
 629         path.mnt = devpts_mntget(master, tty->driver_data);
 630         if (IS_ERR(path.mnt)) {
 631                 retval = PTR_ERR(path.mnt);
 632                 goto err_put;
 633         }
 634         path.dentry = tty->link->driver_data;
 635
 636         filp = dentry_open(&path, flags, current_cred());
 637         mntput(path.mnt);
 638         if (IS_ERR(filp)) {
 639                 retval = PTR_ERR(filp);
 640                 goto err_put;
 641         }
 642
 643         fd_install(fd, filp);
 644         return fd;
 645
 646 err_put:
 647         put_unused_fd(fd);
 648 err:
 649         return retval;
 650 }
 651
 652 static int pty_unix98_ioctl(struct tty_struct *tty,
 653                             unsigned int cmd, unsigned long arg)
 654 {
 655         switch (cmd) {
 656         case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
 657                 return pty_set_lock(tty, (int __user *)arg);
 658         case TIOCGPTLCK: /* Get PT Lock status */
 659                 return pty_get_lock(tty, (int __user *)arg);
 660         case TIOCPKT: /* Set PT packet mode */
 661                 return pty_set_pktmode(tty, (int __user *)arg);
 662         case TIOCGPKT: /* Get PT packet mode */
 663                 return pty_get_pktmode(tty, (int __user *)arg);
 664         case TIOCGPTN: /* Get PT Number */
 665                 return put_user(tty->index, (unsigned int __user *)arg);
 666         case TIOCSIG:    /* Send signal to other side of pty */
 667                 return pty_signal(tty, (int) arg);
 668         }
 669
 670         return -ENOIOCTLCMD;
 671 }
 672
 673 #ifdef CONFIG_COMPAT
 674 static long pty_unix98_compat_ioctl(struct tty_struct *tty,
 675                                  unsigned int cmd, unsigned long arg)
 676 {
 677         /*
 678          * PTY ioctls don't require any special translation between 32-bit and
 679          * 64-bit userspace, they are already compatible.
 680          */
 681         return pty_unix98_ioctl(tty, cmd,
 682                 cmd == TIOCSIG ? arg : (unsigned long)compat_ptr(arg));
 683 }
 684 #else
 685 #define pty_unix98_compat_ioctl NULL
 686 #endif
 687
 688 /**
 689  *      ptm_unix98_lookup       -       find a pty master
 690  *      @driver: ptm driver
 691  *      @file: unused
 692  *      @idx: tty index
 693  *
 694  *      Look up a pty master device. Called under the tty_mutex for now.
 695  *      This provides our locking.
 696  */
 697
 698 static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
 699                 struct file *file, int idx)
 700 {
 701         /* Master must be open via /dev/ptmx */
 702         return ERR_PTR(-EIO);
 703 }
 704
 705 /**
 706  *      pts_unix98_lookup       -       find a pty slave
 707  *      @driver: pts driver
 708  *      @file: file pointer to tty
 709  *      @idx: tty index
 710  *
 711  *      Look up a pty master device. Called under the tty_mutex for now.
 712  *      This provides our locking for the tty pointer.
 713  */
 714
 715 static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
 716                 struct file *file, int idx)
 717 {
 718         struct tty_struct *tty;
 719
 720         mutex_lock(&devpts_mutex);
 721         tty = devpts_get_priv(file->f_path.dentry);
 722         mutex_unlock(&devpts_mutex);
 723         /* Master must be open before slave */
 724         if (!tty)
 725                 return ERR_PTR(-EIO);
 726         return tty;
 727 }
 728
 729 static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
 730 {
 731         return pty_common_install(driver, tty, false);
 732 }
 733
 734 /* this is called once with whichever end is closed last */
 735 static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
 736 {
 737         struct pts_fs_info *fsi;
 738
 739         if (tty->driver->subtype == PTY_TYPE_MASTER)
 740                 fsi = tty->driver_data;
 741         else
 742                 fsi = tty->link->driver_data;
 743
 744         if (fsi) {
 745                 devpts_kill_index(fsi, tty->index);
 746                 devpts_release(fsi);
 747         }
 748 }
 749
 750 static void pty_show_fdinfo(struct tty_struct *tty, struct seq_file *m)
 751 {
 752         seq_printf(m, "tty-index:\t%d\n", tty->index);
 753 }
 754
 755 static const struct tty_operations ptm_unix98_ops = {
 756         .lookup = ptm_unix98_lookup,
 757         .install = pty_unix98_install,
 758         .remove = pty_unix98_remove,
 759         .open = pty_open,
 760         .close = pty_close,
 761         .write = pty_write,
 762         .write_room = pty_write_room,
 763         .flush_buffer = pty_flush_buffer,
 764         .unthrottle = pty_unthrottle,
 765         .ioctl = pty_unix98_ioctl,
 766         .compat_ioctl = pty_unix98_compat_ioctl,
 767         .resize = pty_resize,
 768         .cleanup = pty_cleanup,
 769         .show_fdinfo = pty_show_fdinfo,
 770 };
 771
 772 static const struct tty_operations pty_unix98_ops = {
 773         .lookup = pts_unix98_lookup,
 774         .install = pty_unix98_install,
 775         .remove = pty_unix98_remove,
 776         .open = pty_open,
 777         .close = pty_close,
 778         .write = pty_write,
 779         .write_room = pty_write_room,
 780         .flush_buffer = pty_flush_buffer,
 781         .unthrottle = pty_unthrottle,
 782         .set_termios = pty_set_termios,
 783         .start = pty_start,
 784         .stop = pty_stop,
 785         .cleanup = pty_cleanup,
 786 };
 787
 788 /**
 789  *      ptmx_open               -       open a unix 98 pty master
 790  *      @inode: inode of device file
 791  *      @filp: file pointer to tty
 792  *
 793  *      Allocate a unix98 pty master device from the ptmx driver.
 794  *
 795  *      Locking: tty_mutex protects the init_dev work. tty->count should
 796  *              protect the rest.
 797  *              allocated_ptys_lock handles the list of free pty numbers
 798  */
 799
 800 static int ptmx_open(struct inode *inode, struct file *filp)
 801 {
 802         struct pts_fs_info *fsi;
 803         struct tty_struct *tty;
 804         struct dentry *dentry;
 805         int retval;
 806         int index;
 807
 808         nonseekable_open(inode, filp);
 809
 810         /* We refuse fsnotify events on ptmx, since it's a shared resource */
 811         filp->f_mode |= FMODE_NONOTIFY;
 812
 813         retval = tty_alloc_file(filp);
 814         if (retval)
 815                 return retval;
 816
 817         fsi = devpts_acquire(filp);
 818         if (IS_ERR(fsi)) {
 819                 retval = PTR_ERR(fsi);
 820                 goto out_free_file;
 821         }
 822
 823         /* find a device that is not in use. */
 824         mutex_lock(&devpts_mutex);
 825         index = devpts_new_index(fsi);
 826         mutex_unlock(&devpts_mutex);
 827
 828         retval = index;
 829         if (index < 0)
 830                 goto out_put_fsi;
 831
 832
 833         mutex_lock(&tty_mutex);
 834         tty = tty_init_dev(ptm_driver, index);
 835         /* The tty returned here is locked so we can safely
 836            drop the mutex */
 837         mutex_unlock(&tty_mutex);
 838
 839         retval = PTR_ERR(tty);
 840         if (IS_ERR(tty))
 841                 goto out;
 842
 843         /*
 844          * From here on out, the tty is "live", and the index and
 845          * fsi will be killed/put by the tty_release()
 846          */
 847         set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
 848         tty->driver_data = fsi;
 849
 850         tty_add_file(tty, filp);
 851
 852         dentry = devpts_pty_new(fsi, index, tty->link);
 853         if (IS_ERR(dentry)) {
 854                 retval = PTR_ERR(dentry);
 855                 goto err_release;
 856         }
 857         tty->link->driver_data = dentry;
 858
 859         retval = ptm_driver->ops->open(tty, filp);
 860         if (retval)
 861                 goto err_release;
 862
 863         tty_debug_hangup(tty, "opening (count=%d)\n", tty->count);
 864
 865         tty_unlock(tty);
 866         return 0;
 867 err_release:
 868         tty_unlock(tty);
 869         // This will also put-ref the fsi
 870         tty_release(inode, filp);
 871         return retval;
 872 out:
 873         devpts_kill_index(fsi, index);
 874 out_put_fsi:
 875         devpts_release(fsi);
 876 out_free_file:
 877         tty_free_file(filp);
 878         return retval;
 879 }
 880
 881 static struct file_operations ptmx_fops __ro_after_init;
 882
 883 static void __init unix98_pty_init(void)
 884 {
 885         ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
 886                         TTY_DRIVER_RESET_TERMIOS |
 887                         TTY_DRIVER_REAL_RAW |
 888                         TTY_DRIVER_DYNAMIC_DEV |
 889                         TTY_DRIVER_DEVPTS_MEM |
 890                         TTY_DRIVER_DYNAMIC_ALLOC);
 891         if (IS_ERR(ptm_driver))
 892                 panic("Couldn't allocate Unix98 ptm driver");
 893         pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
 894                         TTY_DRIVER_RESET_TERMIOS |
 895                         TTY_DRIVER_REAL_RAW |
 896                         TTY_DRIVER_DYNAMIC_DEV |
 897                         TTY_DRIVER_DEVPTS_MEM |
 898                         TTY_DRIVER_DYNAMIC_ALLOC);
 899         if (IS_ERR(pts_driver))
 900                 panic("Couldn't allocate Unix98 pts driver");
 901
 902         ptm_driver->driver_name = "pty_master";
 903         ptm_driver->name = "ptm";
 904         ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
 905         ptm_driver->minor_start = 0;
 906         ptm_driver->type = TTY_DRIVER_TYPE_PTY;
 907         ptm_driver->subtype = PTY_TYPE_MASTER;
 908         ptm_driver->init_termios = tty_std_termios;
 909         ptm_driver->init_termios.c_iflag = 0;
 910         ptm_driver->init_termios.c_oflag = 0;
 911         ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 912         ptm_driver->init_termios.c_lflag = 0;
 913         ptm_driver->init_termios.c_ispeed = 38400;
 914         ptm_driver->init_termios.c_ospeed = 38400;
 915         ptm_driver->other = pts_driver;
 916         tty_set_operations(ptm_driver, &ptm_unix98_ops);
 917
 918         pts_driver->driver_name = "pty_slave";
 919         pts_driver->name = "pts";
 920         pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
 921         pts_driver->minor_start = 0;
 922         pts_driver->type = TTY_DRIVER_TYPE_PTY;
 923         pts_driver->subtype = PTY_TYPE_SLAVE;
 924         pts_driver->init_termios = tty_std_termios;
 925         pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
 926         pts_driver->init_termios.c_ispeed = 38400;
 927         pts_driver->init_termios.c_ospeed = 38400;
 928         pts_driver->other = ptm_driver;
 929         tty_set_operations(pts_driver, &pty_unix98_ops);
 930
 931         if (tty_register_driver(ptm_driver))
 932                 panic("Couldn't register Unix98 ptm driver");
 933         if (tty_register_driver(pts_driver))
 934                 panic("Couldn't register Unix98 pts driver");
 935
 936         /* Now create the /dev/ptmx special device */
 937         tty_default_fops(&ptmx_fops);
 938         ptmx_fops.open = ptmx_open;
 939
 940         cdev_init(&ptmx_cdev, &ptmx_fops);
 941         if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
 942             register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
 943                 panic("Couldn't register /dev/ptmx driver");
 944         device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
 945 }
 946
 947 #else
 948 static inline void unix98_pty_init(void) { }
 949 #endif
 950
 951 static int __init pty_init(void)
 952 {
 953         legacy_pty_init();
 954         unix98_pty_init();
 955         return 0;
 956 }
 957 device_initcall(pty_init);