Commit 0f40fbbc authored by Brian Bloniarz's avatar Brian Bloniarz Committed by Greg Kroah-Hartman
Browse files

Fix OpenSSH pty regression on close 



OpenSSH expects the (non-blocking) read() of pty master to return
EAGAIN only if it has received all of the slave-side output after
it has received SIGCHLD. This used to work on pre-3.12 kernels.

This fix effectively forces non-blocking read() and poll() to
block for parallel i/o to complete for all ttys. It also unwinds
these changes:

1) f8747d4a
   tty: Fix pty master read() after slave closes

2) 52bce7f8
   pty, n_tty: Simplify input processing on final close

3) 1a48632f
   pty: Fix input race when closing

Inspired by analysis and patch from Marc Aurele La France <tsi@tuyoix.net>

Reported-by: default avatarVolth <openssh@volth.com>
Reported-by: default avatarMarc Aurele La France <tsi@tuyoix.net>
BugLink: https://bugzilla.mindrot.org/show_bug.cgi?id=52
BugLink: https://bugzilla.mindrot.org/show_bug.cgi?id=2492


Signed-off-by: default avatarBrian Bloniarz <brian.bloniarz@gmail.com>
Reviewed-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d11df618

Documentation/serial/tty.txt

+0 −3
Original line number Diff line number Diff line
@@ -210,9 +210,6 @@ TTY_IO_ERROR If set, causes all subsequent userspace read/write 


TTY_OTHER_CLOSED	Device is a pty and the other side has closed.



TTY_OTHER_DONE		Device is a pty and the other side has closed and

			all pending input processing has been completed.



TTY_NO_WRITE_SPLIT	Prevent driver from splitting up writes into

			smaller chunks.

drivers/tty/n_hdlc.c

+2 −2
Original line number Diff line number Diff line
@@ -599,7 +599,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file, 
	add_wait_queue(&tty->read_wait, &wait);



	for (;;) {

		if (test_bit(TTY_OTHER_DONE, &tty->flags)) {

		if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {

			ret = -EIO;

			break;

		}
@@ -827,7 +827,7 @@ static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp, 
		/* set bits for operations that won't block */

		if (n_hdlc->rx_buf_list.head)

			mask |= POLLIN | POLLRDNORM;	/* readable */

		if (test_bit(TTY_OTHER_DONE, &tty->flags))

		if (test_bit(TTY_OTHER_CLOSED, &tty->flags))

			mask |= POLLHUP;

		if (tty_hung_up_p(filp))

			mask |= POLLHUP;

drivers/tty/n_tty.c

+33 −37
Original line number Diff line number Diff line
@@ -1917,18 +1917,6 @@ static inline int input_available_p(struct tty_struct *tty, int poll) 
		return ldata->commit_head - ldata->read_tail >= amt;

}



static inline int check_other_done(struct tty_struct *tty)

{

	int done = test_bit(TTY_OTHER_DONE, &tty->flags);

	if (done) {

		/* paired with cmpxchg() in check_other_closed(); ensures

		 * read buffer head index is not stale

		 */

		smp_mb__after_atomic();

	}

	return done;

}



/**

 *	copy_from_read_buf	-	copy read data directly

 *	@tty: terminal device
@@ -2124,7 +2112,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 
	struct n_tty_data *ldata = tty->disc_data;

	unsigned char __user *b = buf;

	DEFINE_WAIT_FUNC(wait, woken_wake_function);

	int c, done;

	int c;

	int minimum, time;

	ssize_t retval = 0;

	long timeout;
@@ -2183,10 +2171,12 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 
			break;

		}



		done = check_other_done(tty);



		if (!input_available_p(tty, 0)) {

			if (done) {

			up_read(&tty->termios_rwsem);

			tty_buffer_flush_work(tty->port);

			down_read(&tty->termios_rwsem);

			if (!input_available_p(tty, 0)) {

				if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {

					retval = -EIO;

					break;

				}
@@ -2210,6 +2200,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 
				down_read(&tty->termios_rwsem);

				continue;

			}

		}



		if (ldata->icanon && !L_EXTPROC(tty)) {

			retval = canon_copy_from_read_buf(tty, &b, &nr);
@@ -2386,12 +2377,17 @@ static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file, 


	poll_wait(file, &tty->read_wait, wait);

	poll_wait(file, &tty->write_wait, wait);

	if (check_other_done(tty))

		mask |= POLLHUP;

	if (input_available_p(tty, 1))

		mask |= POLLIN | POLLRDNORM;

	else {

		tty_buffer_flush_work(tty->port);

		if (input_available_p(tty, 1))

			mask |= POLLIN | POLLRDNORM;

	}

	if (tty->packet && tty->link->ctrl_status)

		mask |= POLLPRI | POLLIN | POLLRDNORM;

	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))

		mask |= POLLHUP;

	if (tty_hung_up_p(file))

		mask |= POLLHUP;

	if (tty->ops->write && !tty_is_writelocked(tty) &&

drivers/tty/pty.c

+1 −3
Original line number Diff line number Diff line
@@ -59,7 +59,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp) 
	if (!tty->link)

		return;

	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);

	tty_flip_buffer_push(tty->link->port);

	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);
@@ -247,9 +247,7 @@ static int pty_open(struct tty_struct *tty, struct file *filp) 
		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;

drivers/tty/tty_buffer.c

+6 −28
Original line number Diff line number Diff line
@@ -37,29 +37,6 @@ 


#define TTY_BUFFER_PAGE	(((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)



/*

 * If all tty flip buffers have been processed by flush_to_ldisc() or

 * dropped by tty_buffer_flush(), check if the linked pty has been closed.

 * If so, wake the reader/poll to process

 */

static inline void check_other_closed(struct tty_struct *tty)

{

	unsigned long flags, old;



	/* transition from TTY_OTHER_CLOSED => TTY_OTHER_DONE must be atomic */

	for (flags = ACCESS_ONCE(tty->flags);

	     test_bit(TTY_OTHER_CLOSED, &flags);

	     ) {

		old = flags;

		__set_bit(TTY_OTHER_DONE, &flags);

		flags = cmpxchg(&tty->flags, old, flags);

		if (old == flags) {

			wake_up_interruptible(&tty->read_wait);

			break;

		}

	}

}



/**

 *	tty_buffer_lock_exclusive	-	gain exclusive access to buffer

 *	tty_buffer_unlock_exclusive	-	release exclusive access
@@ -254,8 +231,6 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld) 
	if (ld && ld->ops->flush_buffer)

		ld->ops->flush_buffer(tty);



	check_other_closed(tty);



	atomic_dec(&buf->priority);

	mutex_unlock(&buf->lock);

}
@@ -522,10 +497,8 @@ static void flush_to_ldisc(struct work_struct *work) 
		 */

		count = smp_load_acquire(&head->commit) - head->read;

		if (!count) {

			if (next == NULL) {

				check_other_closed(tty);

			if (next == NULL)

				break;

			}

			buf->head = next;

			tty_buffer_free(port, head);

			continue;
@@ -614,3 +587,8 @@ bool tty_buffer_cancel_work(struct tty_port *port) 
{

	return cancel_work_sync(&port->buf.work);

}



void tty_buffer_flush_work(struct tty_port *port)

{

	flush_work(&port->buf.work);

}

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