Commit 7f22f6c9 authored Jan 09, 2016 by Peter Hurley Committed by Greg Kroah-Hartman Jan 26, 2016

tty: Retry failed reopen if tty teardown in-progress



A small window exists where a tty reopen will observe the tty
just prior to imminent teardown (tty->count == 0); in this case, open()
returns EIO to userspace.

Instead, retry the open after checking for signals and yielding;
this interruptible retry loop allows teardown to commence and initialize
a new tty on retry. Never retry the BSD master pty reopen; there is no
guarantee the pty pair teardown is imminent since the slave file
descriptors may remain open indefinitely.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Cc: stable <stable@vger.kernel.org> # 4.4
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 0bfd464d

drivers/tty/tty_io.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -1463,13 +1463,13 @@ static int tty_reopen(struct tty_struct *tty)
		{
		struct tty_driver *driver = tty->driver;

		if (!tty->count)
		return -EIO;

		if (driver->type == TTY_DRIVER_TYPE_PTY &&
		driver->subtype == PTY_TYPE_MASTER)
		return -EIO;

		if (!tty->count)
		return -EAGAIN;

		if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
		return -EBUSY;

		@@ -2088,7 +2088,11 @@ retry_open:

		if (IS_ERR(tty)) {
		retval = PTR_ERR(tty);
		if (retval != -EAGAIN \|\| signal_pending(current))
		goto err_file;
		tty_free_file(filp);
		schedule();
		goto retry_open;
		}

		tty_add_file(tty, filp);

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