This is a note to let you know that I've just added the patch titled
tty: pty: Fix race condition between release_one_tty and pty_write
to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-testing branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will be merged to the tty-next branch sometime soon,
after it passes testing, and the merge window is open.
If you have any questions about this process, please let me know.
>From b9ca5f8560af244489b4a1bc1ae88b341f24bc95 Mon Sep 17 00:00:00 2001
From: Sahara <keun-o.park@xxxxxxxxxxxxx>
Date: Mon, 11 Feb 2019 11:09:15 +0400
Subject: 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 <keun-o.park@xxxxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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 00099a8439d2..ef72031ab5b9 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 5fa250157025..c27777f3b8c4 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -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);
--
2.21.0
