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tty: pty: Fix race condition between release_one_tty and pty_write

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Especially when a linked tty is used such as pty, the linked tty
port's buf works have not been cancelled while master tty port's
buf work has been cancelled. Since release_one_tty and flush_to_ldisc
run in workqueue threads separately, when pty_cleanup happens and
link tty port is freed, flush_to_ldisc tries to access freed port
and port->itty, eventually it causes a panic.
This patch utilizes the magic value with holding the tty_mutex to
check if the tty->link is valid.

Fixes: 2b022ab754 ("pty: cancel pty slave port buf's work in tty_release")
Signed-off-by: Sahara <keun-o.park@darkmatter.ae>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sahara
2019-02-11 11:09:15 +04:00
committed by Greg Kroah-Hartman
parent 75ddbc1fb1
commit b9ca5f8560
2 changed files with 10 additions and 0 deletions
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3
drivers/tty/tty_io.c
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@@ -1448,10 +1448,13 @@ static void release_one_tty(struct work_struct *work)
struct tty_driver *driver = tty->driver;
struct module *owner = driver->owner;
mutex_lock(&tty_mutex);
if (tty->ops->cleanup)
tty->ops->cleanup(tty);
tty->magic = 0;
mutex_unlock(&tty_mutex);
tty_driver_kref_put(driver);
module_put(owner);