path: root/drivers/tty/pty.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  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/signal.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>
#include <linux/mount.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/compat.h>
#include "tty.h"

#undef TTY_DEBUG_HANGUP
#ifdef TTY_DEBUG_HANGUP
# define tty_debug_hangup(tty, f, args...)	tty_debug(tty, f, ##args)
#else
# define tty_debug_hangup(tty, f, args...)	do {} while (0)
#endif

#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)
{
	if (tty->driver->subtype == PTY_TYPE_MASTER)
		WARN_ON(tty->count > 1);
	else {
		if (tty_io_error(tty))
			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->ctrl.packet = false;
	spin_unlock_irq(&tty->ctrl.lock);
	/* Review - krefs on tty_link ?? */
	if (!tty->link)
		return;
	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
	wake_up_interruptible(&tty->link->read_wait);
	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
 *	@c: 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 ssize_t pty_write(struct tty_struct *tty, const u8 *buf, size_t c)
{
	struct tty_struct *to = tty->link;

	if (tty->flow.stopped || !c)
		return 0;

	return tty_insert_flip_string_and_push_buffer(to->port, buf, 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 unsigned int pty_write_room(struct tty_struct *tty)
{
	if (tty->flow.stopped)
		return 0;
	return tty_buffer_space_avail(tty->link->port);
}

/* 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->ctrl.packet) {
			tty->link->ctrl.pktstatus = 0;
			smp_mb();
			tty->ctrl.packet = true;
		}
	} else
		tty->ctrl.packet = false;
	spin_unlock_irq(&tty->ctrl.lock);

	return 0;
}

/* Get the packet mode of a pty */
static int