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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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7
drivers/tty/pty.c
View File

@ -116,6 +116,12 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
if (tty->stopped)
return 0;
mutex_lock(&tty_mutex);
if (to->magic != TTY_MAGIC) {
mutex_unlock(&tty_mutex);
return -EIO;
}
if (c > 0) {
spin_lock_irqsave(&to->port->lock, flags);
/* Stuff the data into the input queue of the other end */
@ -125,6 +131,7 @@ static int pty_write(struct tty_struct *tty, const unsigned char *buf, int c)
tty_flip_buffer_push(to->port);
spin_unlock_irqrestore(&to->port->lock, flags);
}
mutex_unlock(&tty_mutex);
return c;
}

3
drivers/tty/tty_io.c
View File

@ -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);