From 3a65ec01f8849c3e11267794b9d1c70ef32d13e3 Mon Sep 17 00:00:00 2001 From: Sahara Date: Sun, 3 Feb 2019 09:27:28 +0400 Subject: [PATCH] tty: pty: Fix race condition between release_one_tty and pty_write 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: 2b022ab7542d ("pty: cancel pty slave port buf's work in tty_release") Signed-off-by: Sahara --- drivers/tty/pty.c | 7 +++++++ drivers/tty/tty_io.c | 3 +++ 2 files changed, 10 insertions(+) diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index 00099a84..ef72031 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -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; } diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 23c6fd2..6c4a206 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1446,10 +1446,13 @@ 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); -- 2.7.4