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linux/drivers/tty/pty.c
Peter Hurley 1a48632ffe pty: Fix input race when closing 
A read() from a pty master may mistakenly indicate EOF (errno == -EIO)
after the pty slave has closed, even though input data remains to be read.
For example,

       pty slave       |        input worker        |    pty master
                       |                            |
                       |                            |   n_tty_read()
pty_write()            |                            |     input avail? no
  add data             |                            |     sleep
  schedule worker  --->|                            |     .
                       |---> flush_to_ldisc()       |     .
pty_close()            |       fill read buffer     |     .
  wait for worker      |       wakeup reader    --->|     .
                       |       read buffer full?    |---> input avail ? yes
                       |<---   yes - exit worker    |     copy 4096 bytes to user
  TTY_OTHER_CLOSED <---|                            |<--- kick worker
                       |                            |

		                **** New read() before worker starts ****

                       |                            |   n_tty_read()
                       |                            |     input avail? no
                       |                            |     TTY_OTHER_CLOSED? yes
                       |                            |     return -EIO

Several conditions are required to trigger this race:
1. the ldisc read buffer must become full so the input worker exits
2. the read() count parameter must be >= 4096 so the ldisc read buffer
   is empty
3. the subsequent read() occurs before the kicked worker has processed
   more input

However, the underlying cause of the race is that data is pipelined, while
tty state is not; ie., data already written by the pty slave end is not
yet visible to the pty master end, but state changes by the pty slave end
are visible to the pty master end immediately.

Pipeline the TTY_OTHER_CLOSED state through input worker to the reader.
1. Introduce TTY_OTHER_DONE which is set by the input worker when
   TTY_OTHER_CLOSED is set and either the input buffers are flushed or
   input processing has completed. Readers/polls are woken when
   TTY_OTHER_DONE is set.
2. Reader/poll checks TTY_OTHER_DONE instead of TTY_OTHER_CLOSED.
3. A new input worker is started from pty_close() after setting
   TTY_OTHER_CLOSED, which ensures the TTY_OTHER_DONE state will be
   set if the last input worker is already finished (or just about to
   exit).

Remove tty_flush_to_ldisc(); no in-tree callers.

Fixes: 52bce7f8d4 ("pty, n_tty: Simplify input processing on final close")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=96311
BugLink: http://bugs.launchpad.net/bugs/1429756
Cc: <stable@vger.kernel.org> # 3.19+
Reported-by: Andy Whitcroft <apw@canonical.com>
Reported-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2015-05-10 19:26:37 +02:00

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/*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* Added support for a Unix98-style ptmx device.
* -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
*
*/
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/fcntl.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/major.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
#include <linux/devpts_fs.h>
#include <linux/slab.h>
#include <linux/mutex.h>
#include <linux/poll.h>
#ifdef CONFIG_UNIX98_PTYS
static struct tty_driver *ptm_driver;
static struct tty_driver *pts_driver;
static DEFINE_MUTEX(devpts_mutex);
#endif
static void pty_close(struct tty_struct *tty, struct file *filp)
{
BUG_ON(!tty);
if (tty->driver->subtype == PTY_TYPE_MASTER)
WARN_ON(tty->count > 1);
else {
if (test_bit(TTY_IO_ERROR, &tty->flags))
return;
if (tty->count > 2)
return;
}
set_bit(TTY_IO_ERROR, &tty->flags);
wake_up_interruptible(&tty->read_wait);
wake_up_interruptible(&tty->write_wait);
spin_lock_irq(&tty->ctrl_lock);
tty->packet = 0;
spin_unlock_irq(&tty->ctrl_lock);
/* Review - krefs on tty_link ?? */
if (!tty->link)
return;
set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
tty_flip_buffer_push(tty->link->port);
wake_up_interruptible(&tty->link->write_wait);
if (tty->driver->subtype == PTY_TYPE_MASTER) {
set_bit(TTY_OTHER_CLOSED, &tty->flags);
#ifdef CONFIG_UNIX98_PTYS
if (tty->driver == ptm_driver) {
mutex_lock(&devpts_mutex);
if (tty->link->driver_data)
devpts_pty_kill(tty->link->driver_data);
mutex_unlock(&devpts_mutex);
}
#endif
tty_vhangup(tty->link);
}
}
/*
* The unthrottle routine is called by the line discipline to signal
* that it can receive more characters. For PTY's, the TTY_THROTTLED
* flag is always set, to force the line discipline to always call the
* unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
* characters in the queue. This is necessary since each time this
* happens, we need to wake up any sleeping processes that could be
* (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
* for the pty buffer to be drained.
*/
static void pty_unthrottle(struct tty_struct *tty)
{
tty_wakeup(tty->link);
set_bit(TTY_THROTTLED, &tty->flags);
}
/**
* pty_write - write to a pty
* @tty: the tty we write from
* @buf: kernel buffer of data
* @count: bytes to write
*
* Our "hardware" write method. Data is coming from the ldisc which
* may be in a non sleeping state. We simply throw this at the other
* end of the link as if we were an IRQ handler receiving stuff for
* the other side of the pty/tty pair.
*/
static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
{
struct tty_struct *to = tty->link;
if (tty->stopped)
return 0;
if (c > 0) {
/* Stuff the data into the input queue of the other end */
c = tty_insert_flip_string(to->port, buf, c);
/* And shovel */
if (c)
tty_flip_buffer_push(to->port);
}
return c;
}
/**
* pty_write_room - write space
* @tty: tty we are writing from
*
* Report how many bytes the ldisc can send into the queue for
* the other device.
*/
static int pty_write_room(struct tty_struct *tty)
{
if (tty->stopped)
return 0;
return tty_buffer_space_avail(tty->link->port);
}
/**
* pty_chars_in_buffer - characters currently in our tx queue
* @tty: our tty
*
* Report how much we have in the transmit queue. As everything is
* instantly at the other end this is easy to implement.
*/
static int pty_chars_in_buffer(struct tty_struct *tty)
{
return 0;
}
/* Set the lock flag on a pty */
static int pty_set_lock(struct tty_struct *tty, int __user *arg)
{
int val;
if (get_user(val, arg))
return -EFAULT;
if (val)
set_bit(TTY_PTY_LOCK, &tty->flags);
else
clear_bit(TTY_PTY_LOCK, &tty->flags);
return 0;
}
static int pty_get_lock(struct tty_struct *tty, int __user *arg)
{
int locked = test_bit(TTY_PTY_LOCK, &tty->flags);
return put_user(locked, arg);
}
/* Set the packet mode on a pty */
static int pty_set_pktmode(struct tty_struct *tty, int __user *arg)
{
int pktmode;
if (get_user(pktmode, arg))
return -EFAULT;
spin_lock_irq(&tty->ctrl_lock);
if (pktmode) {
if (!tty->packet) {
tty->link->ctrl_status = 0;
smp_mb();
tty->packet = 1;
}
} else
tty->packet = 0;
spin_unlock_irq(&tty->ctrl_lock);
return 0;
}
/* Get the packet mode of a pty */
static int pty_get_pktmode(struct tty_struct *tty, int __user *arg)
{
int pktmode = tty->packet;
return put_user(pktmode, arg);
}
/* Send a signal to the slave */
static int pty_signal(struct tty_struct *tty, int sig)
{
struct pid *pgrp;
if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
return -EINVAL;
if (tty->link) {
pgrp = tty_get_pgrp(tty->link);
if (pgrp)
kill_pgrp(pgrp, sig, 1);
put_pid(pgrp);
}
return 0;
}
static void pty_flush_buffer(struct tty_struct *tty)
{
struct tty_struct *to = tty->link;
struct tty_ldisc *ld;
if (!to)
return;
ld = tty_ldisc_ref(to);
tty_buffer_flush(to, ld);
if (ld)
tty_ldisc_deref(ld);
if (to->packet) {
spin_lock_irq(&tty->ctrl_lock);
tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
wake_up_interruptible(&to->read_wait);
spin_unlock_irq(&tty->ctrl_lock);
}
}
static int pty_open(struct tty_struct *tty, struct file *filp)
{
if (!tty || !tty->link)
return -ENODEV;
if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
goto out;
if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
goto out;
if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
goto out;
clear_bit(TTY_IO_ERROR, &tty->flags);
/* TTY_OTHER_CLOSED must be cleared before TTY_OTHER_DONE */
clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
clear_bit(TTY_OTHER_DONE, &tty->link->flags);
set_bit(TTY_THROTTLED, &tty->flags);
return 0;
out:
set_bit(TTY_IO_ERROR, &tty->flags);
return -EIO;
}
static void pty_set_termios(struct tty_struct *tty,
struct ktermios *old_termios)
{
/* See if packet mode change of state. */
if (tty->link && tty->link->packet) {
int extproc = (old_termios->c_lflag & EXTPROC) |
(tty->termios.c_lflag & EXTPROC);
int old_flow = ((old_termios->c_iflag & IXON) &&
(old_termios->c_cc[VSTOP] == '\023') &&
(old_termios->c_cc[VSTART] == '\021'));
int new_flow = (I_IXON(tty) &&
STOP_CHAR(tty) == '\023' &&
START_CHAR(tty) == '\021');
if ((old_flow != new_flow) || extproc) {
spin_lock_irq(&tty->ctrl_lock);
if (old_flow != new_flow) {
tty->ctrl_status &= ~(TIOCPKT_DOSTOP | TIOCPKT_NOSTOP);
if (new_flow)
tty->ctrl_status |= TIOCPKT_DOSTOP;
else
tty->ctrl_status |= TIOCPKT_NOSTOP;
}
if (extproc)
tty->ctrl_status |= TIOCPKT_IOCTL;
spin_unlock_irq(&tty->ctrl_lock);
wake_up_interruptible(&tty->link->read_wait);
}
}
tty->termios.c_cflag &= ~(CSIZE | PARENB);
tty->termios.c_cflag |= (CS8 | CREAD);
}
/**
* pty_do_resize - resize event
* @tty: tty being resized
* @ws: window size being set.
*
* Update the termios variables and send the necessary signals to
* peform a terminal resize correctly
*/
static int pty_resize(struct tty_struct *tty, struct winsize *ws)
{
struct pid *pgrp, *rpgrp;
struct tty_struct *pty = tty->link;
/* For a PTY we need to lock the tty side */
mutex_lock(&tty->winsize_mutex);
if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
goto done;
/* Signal the foreground process group of both ptys */
pgrp = tty_get_pgrp(tty);
rpgrp = tty_get_pgrp(pty);
if (pgrp)
kill_pgrp(pgrp, SIGWINCH, 1);
if (rpgrp != pgrp && rpgrp)
kill_pgrp(rpgrp, SIGWINCH, 1);
put_pid(pgrp);
put_pid(rpgrp);
tty->winsize = *ws;
pty->winsize = *ws; /* Never used so will go away soon */
done:
mutex_unlock(&tty->winsize_mutex);
return 0;
}
/**
* pty_start - start() handler
* pty_stop - stop() handler
* @tty: tty being flow-controlled
*
* Propagates the TIOCPKT status to the master pty.
*
* NB: only the master pty can be in packet mode so only the slave
* needs start()/stop() handlers
*/
static void pty_start(struct tty_struct *tty)
{
unsigned long flags;
if (tty->link && tty->link->packet) {
spin_lock_irqsave(&tty->ctrl_lock, flags);
tty->ctrl_status &= ~TIOCPKT_STOP;
tty->ctrl_status |= TIOCPKT_START;
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
}
}
static void pty_stop(struct tty_struct *tty)
{
unsigned long flags;
if (tty->link && tty->link->packet) {
spin_lock_irqsave(&tty->ctrl_lock, flags);
tty->ctrl_status &= ~TIOCPKT_START;
tty->ctrl_status |= TIOCPKT_STOP;
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
}
}
/**
* pty_common_install - set up the pty pair
* @driver: the pty driver
* @tty: the tty being instantiated
* @legacy: true if this is BSD style
*
* Perform the initial set up for the tty/pty pair. Called from the
* tty layer when the port is first opened.
*
* Locking: the caller must hold the tty_mutex
*/
static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
bool legacy)
{
struct tty_struct *o_tty;
struct tty_port *ports[2];
int idx = tty->index;
int retval = -ENOMEM;
/* Opening the slave first has always returned -EIO */
if (driver->subtype != PTY_TYPE_MASTER)
return -EIO;
ports[0] = kmalloc(sizeof **ports, GFP_KERNEL);
ports[1] = kmalloc(sizeof **ports, GFP_KERNEL);
if (!ports[0] || !ports[1])
goto err;
if (!try_module_get(driver->other->owner)) {
/* This cannot in fact currently happen */
goto err;
}
o_tty = alloc_tty_struct(driver->other, idx);
if (!o_tty)
goto err_put_module;
tty_set_lock_subclass(o_tty);
lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
if (legacy) {
/* We always use new tty termios data so we can do this
the easy way .. */
retval = tty_init_termios(tty);
if (retval)
goto err_deinit_tty;
retval = tty_init_termios(o_tty);
if (retval)
goto err_free_termios;
driver->other->ttys[idx] = o_tty;
driver->ttys[idx] = tty;
} else {
memset(&tty->termios_locked, 0, sizeof(tty->termios_locked));
tty->termios = driver->init_termios;
memset(&o_tty->termios_locked, 0, sizeof(tty->termios_locked));
o_tty->termios = driver->other->init_termios;
}
/*
* Everything allocated ... set up the o_tty structure.
*/
tty_driver_kref_get(driver->other);
/* Establish the links in both directions */
tty->link = o_tty;
o_tty->link = tty;
tty_port_init(ports[0]);
tty_port_init(ports[1]);
tty_buffer_set_limit(ports[0], 8192);
tty_buffer_set_limit(ports[1], 8192);
o_tty->port = ports[0];
tty->port = ports[1];
o_tty->port->itty = o_tty;
tty_buffer_set_lock_subclass(o_tty->port);
tty_driver_kref_get(driver);
tty->count++;
o_tty->count++;
return 0;
err_free_termios:
if (legacy)
tty_free_termios(tty);
err_deinit_tty:
deinitialize_tty_struct(o_tty);
free_tty_struct(o_tty);
err_put_module:
module_put(driver->other->owner);
err:
kfree(ports[0]);
kfree(ports[1]);
return retval;
}
static void pty_cleanup(struct tty_struct *tty)
{
tty_port_put(tty->port);
}
/* Traditional BSD devices */
#ifdef CONFIG_LEGACY_PTYS
static int pty_install(struct tty_driver *driver, struct tty_struct *tty)
{
return pty_common_install(driver, tty, true);
}
static void pty_remove(struct tty_driver *driver, struct tty_struct *tty)
{
struct tty_struct *pair = tty->link;
driver->ttys[tty->index] = NULL;
if (pair)
pair->driver->ttys[pair->index] = NULL;
}
static int pty_bsd_ioctl(struct tty_struct *tty,
unsigned int cmd, unsigned long arg)
{
switch (cmd) {
case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
return pty_set_lock(tty, (int __user *) arg);
case TIOCGPTLCK: /* Get PT Lock status */
return pty_get_lock(tty, (int __user *)arg);
case TIOCPKT: /* Set PT packet mode */
return pty_set_pktmode(tty, (int __user *)arg);
case TIOCGPKT: /* Get PT packet mode */
return pty_get_pktmode(tty, (int __user *)arg);
case TIOCSIG: /* Send signal to other side of pty */
return pty_signal(tty, (int) arg);
case TIOCGPTN: /* TTY returns ENOTTY, but glibc expects EINVAL here */
return -EINVAL;
}
return -ENOIOCTLCMD;
}
static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
module_param(legacy_count, int, 0);
/*
* The master side of a pty can do TIOCSPTLCK and thus
* has pty_bsd_ioctl.
*/
static const struct tty_operations master_pty_ops_bsd = {
.install = pty_install,
.open = pty_open,
.close = pty_close,
.write = pty_write,
.write_room = pty_write_room,
.flush_buffer = pty_flush_buffer,
.chars_in_buffer = pty_chars_in_buffer,
.unthrottle = pty_unthrottle,
.ioctl = pty_bsd_ioctl,
.cleanup = pty_cleanup,
.resize = pty_resize,
.remove = pty_remove
};
static const struct tty_operations slave_pty_ops_bsd = {
.install = pty_install,
.open = pty_open,
.close = pty_close,
.write = pty_write,
.write_room = pty_write_room,
.flush_buffer = pty_flush_buffer,
.chars_in_buffer = pty_chars_in_buffer,
.unthrottle = pty_unthrottle,
.set_termios = pty_set_termios,
.cleanup = pty_cleanup,
.resize = pty_resize,
.start = pty_start,
.stop = pty_stop,
.remove = pty_remove
};
static void __init legacy_pty_init(void)
{
struct tty_driver *pty_driver, *pty_slave_driver;
if (legacy_count <= 0)
return;
pty_driver = tty_alloc_driver(legacy_count,
TTY_DRIVER_RESET_TERMIOS |
TTY_DRIVER_REAL_RAW |
TTY_DRIVER_DYNAMIC_ALLOC);
if (IS_ERR(pty_driver))
panic("Couldn't allocate pty driver");
pty_slave_driver = tty_alloc_driver(legacy_count,
TTY_DRIVER_RESET_TERMIOS |
TTY_DRIVER_REAL_RAW |
TTY_DRIVER_DYNAMIC_ALLOC);
if (IS_ERR(pty_slave_driver))
panic("Couldn't allocate pty slave driver");
pty_driver->driver_name = "pty_master";
pty_driver->name = "pty";
pty_driver->major = PTY_MASTER_MAJOR;
pty_driver->minor_start = 0;
pty_driver->type = TTY_DRIVER_TYPE_PTY;
pty_driver->subtype = PTY_TYPE_MASTER;
pty_driver->init_termios = tty_std_termios;
pty_driver->init_termios.c_iflag = 0;
pty_driver->init_termios.c_oflag = 0;
pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
pty_driver->init_termios.c_lflag = 0;
pty_driver->init_termios.c_ispeed = 38400;
pty_driver->init_termios.c_ospeed = 38400;
pty_driver->other = pty_slave_driver;
tty_set_operations(pty_driver, &master_pty_ops_bsd);
pty_slave_driver->driver_name = "pty_slave";
pty_slave_driver->name = "ttyp";
pty_slave_driver->major = PTY_SLAVE_MAJOR;
pty_slave_driver->minor_start = 0;
pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
pty_slave_driver->subtype = PTY_TYPE_SLAVE;
pty_slave_driver->init_termios = tty_std_termios;
pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
pty_slave_driver->init_termios.c_ispeed = 38400;
pty_slave_driver->init_termios.c_ospeed = 38400;
pty_slave_driver->other = pty_driver;
tty_set_operations(pty_slave_driver, &slave_pty_ops_bsd);
if (tty_register_driver(pty_driver))
panic("Couldn't register pty driver");
if (tty_register_driver(pty_slave_driver))
panic("Couldn't register pty slave driver");
}
#else
static inline void legacy_pty_init(void) { }
#endif
/* Unix98 devices */
#ifdef CONFIG_UNIX98_PTYS
static struct cdev ptmx_cdev;
static int pty_unix98_ioctl(struct tty_struct *tty,
unsigned int cmd, unsigned long arg)
{
switch (cmd) {
case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
return pty_set_lock(tty, (int __user *)arg);
case TIOCGPTLCK: /* Get PT Lock status */
return pty_get_lock(tty, (int __user *)arg);
case TIOCPKT: /* Set PT packet mode */
return pty_set_pktmode(tty, (int __user *)arg);
case TIOCGPKT: /* Get PT packet mode */
return pty_get_pktmode(tty, (int __user *)arg);
case TIOCGPTN: /* Get PT Number */
return put_user(tty->index, (unsigned int __user *)arg);
case TIOCSIG: /* Send signal to other side of pty */
return pty_signal(tty, (int) arg);
}
return -ENOIOCTLCMD;
}
/**
* ptm_unix98_lookup - find a pty master
* @driver: ptm driver
* @idx: tty index
*
* Look up a pty master device. Called under the tty_mutex for now.
* This provides our locking.
*/
static struct tty_struct *ptm_unix98_lookup(struct tty_driver *driver,
struct inode *ptm_inode, int idx)
{
/* Master must be open via /dev/ptmx */
return ERR_PTR(-EIO);
}
/**
* pts_unix98_lookup - find a pty slave
* @driver: pts driver
* @idx: tty index
*
* Look up a pty master device. Called under the tty_mutex for now.
* This provides our locking for the tty pointer.
*/
static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver,
struct inode *pts_inode, int idx)
{
struct tty_struct *tty;
mutex_lock(&devpts_mutex);
tty = devpts_get_priv(pts_inode);
mutex_unlock(&devpts_mutex);
/* Master must be open before slave */
if (!tty)
return ERR_PTR(-EIO);
return tty;
}
/* We have no need to install and remove our tty objects as devpts does all
the work for us */
static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
{
return pty_common_install(driver, tty, false);
}
static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
{
}
/* this is called once with whichever end is closed last */
static void pty_unix98_shutdown(struct tty_struct *tty)
{
devpts_kill_index(tty->driver_data, tty->index);
}
static const struct tty_operations ptm_unix98_ops = {
.lookup = ptm_unix98_lookup,
.install = pty_unix98_install,
.remove = pty_unix98_remove,
.open = pty_open,
.close = pty_close,
.write = pty_write,
.write_room = pty_write_room,
.flush_buffer = pty_flush_buffer,
.chars_in_buffer = pty_chars_in_buffer,
.unthrottle = pty_unthrottle,
.ioctl = pty_unix98_ioctl,
.resize = pty_resize,
.shutdown = pty_unix98_shutdown,
.cleanup = pty_cleanup
};
static const struct tty_operations pty_unix98_ops = {
.lookup = pts_unix98_lookup,
.install = pty_unix98_install,
.remove = pty_unix98_remove,
.open = pty_open,
.close = pty_close,
.write = pty_write,
.write_room = pty_write_room,
.flush_buffer = pty_flush_buffer,
.chars_in_buffer = pty_chars_in_buffer,
.unthrottle = pty_unthrottle,
.set_termios = pty_set_termios,
.start = pty_start,
.stop = pty_stop,
.shutdown = pty_unix98_shutdown,
.cleanup = pty_cleanup,
};
/**
* ptmx_open - open a unix 98 pty master
* @inode: inode of device file
* @filp: file pointer to tty
*
* Allocate a unix98 pty master device from the ptmx driver.
*
* Locking: tty_mutex protects the init_dev work. tty->count should
* protect the rest.
* allocated_ptys_lock handles the list of free pty numbers
*/
static int ptmx_open(struct inode *inode, struct file *filp)
{
struct tty_struct *tty;
struct inode *slave_inode;
int retval;
int index;
nonseekable_open(inode, filp);
/* We refuse fsnotify events on ptmx, since it's a shared resource */
filp->f_mode |= FMODE_NONOTIFY;
retval = tty_alloc_file(filp);
if (retval)
return retval;
/* find a device that is not in use. */
mutex_lock(&devpts_mutex);
index = devpts_new_index(inode);
if (index < 0) {
retval = index;
mutex_unlock(&devpts_mutex);
goto err_file;
}
mutex_unlock(&devpts_mutex);
mutex_lock(&tty_mutex);
tty = tty_init_dev(ptm_driver, index);
if (IS_ERR(tty)) {
retval = PTR_ERR(tty);
goto out;
}
/* The tty returned here is locked so we can safely
drop the mutex */
mutex_unlock(&tty_mutex);
set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
tty->driver_data = inode;
tty_add_file(tty, filp);
slave_inode = devpts_pty_new(inode,
MKDEV(UNIX98_PTY_SLAVE_MAJOR, index), index,
tty->link);
if (IS_ERR(slave_inode)) {
retval = PTR_ERR(slave_inode);
goto err_release;
}
tty->link->driver_data = slave_inode;
retval = ptm_driver->ops->open(tty, filp);
if (retval)
goto err_release;
tty_unlock(tty);
return 0;
err_release:
tty_unlock(tty);
tty_release(inode, filp);
return retval;
out:
mutex_unlock(&tty_mutex);
devpts_kill_index(inode, index);
err_file:
tty_free_file(filp);
return retval;
}
static struct file_operations ptmx_fops;
static void __init unix98_pty_init(void)
{
ptm_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
TTY_DRIVER_RESET_TERMIOS |
TTY_DRIVER_REAL_RAW |
TTY_DRIVER_DYNAMIC_DEV |
TTY_DRIVER_DEVPTS_MEM |
TTY_DRIVER_DYNAMIC_ALLOC);
if (IS_ERR(ptm_driver))
panic("Couldn't allocate Unix98 ptm driver");
pts_driver = tty_alloc_driver(NR_UNIX98_PTY_MAX,
TTY_DRIVER_RESET_TERMIOS |
TTY_DRIVER_REAL_RAW |
TTY_DRIVER_DYNAMIC_DEV |
TTY_DRIVER_DEVPTS_MEM |
TTY_DRIVER_DYNAMIC_ALLOC);
if (IS_ERR(pts_driver))
panic("Couldn't allocate Unix98 pts driver");
ptm_driver->driver_name = "pty_master";
ptm_driver->name = "ptm";
ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
ptm_driver->minor_start = 0;
ptm_driver->type = TTY_DRIVER_TYPE_PTY;
ptm_driver->subtype = PTY_TYPE_MASTER;
ptm_driver->init_termios = tty_std_termios;
ptm_driver->init_termios.c_iflag = 0;
ptm_driver->init_termios.c_oflag = 0;
ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
ptm_driver->init_termios.c_lflag = 0;
ptm_driver->init_termios.c_ispeed = 38400;
ptm_driver->init_termios.c_ospeed = 38400;
ptm_driver->other = pts_driver;
tty_set_operations(ptm_driver, &ptm_unix98_ops);
pts_driver->driver_name = "pty_slave";
pts_driver->name = "pts";
pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
pts_driver->minor_start = 0;
pts_driver->type = TTY_DRIVER_TYPE_PTY;
pts_driver->subtype = PTY_TYPE_SLAVE;
pts_driver->init_termios = tty_std_termios;
pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
pts_driver->init_termios.c_ispeed = 38400;
pts_driver->init_termios.c_ospeed = 38400;
pts_driver->other = ptm_driver;
tty_set_operations(pts_driver, &pty_unix98_ops);
if (tty_register_driver(ptm_driver))
panic("Couldn't register Unix98 ptm driver");
if (tty_register_driver(pts_driver))
panic("Couldn't register Unix98 pts driver");
/* Now create the /dev/ptmx special device */
tty_default_fops(&ptmx_fops);
ptmx_fops.open = ptmx_open;
cdev_init(&ptmx_cdev, &ptmx_fops);
if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
panic("Couldn't register /dev/ptmx driver");
device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
}
#else
static inline void unix98_pty_init(void) { }
#endif
static int __init pty_init(void)
{
legacy_pty_init();
unix98_pty_init();
return 0;
}
module_init(pty_init);
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