[ 3.5.y.z extended stable ] Patch "virtio: console: fix race with port unplug and open/close" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    virtio: console: fix race with port unplug and open/close

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From f9b84ecbc9f7cb51ed335140629e20e3e499260b Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah at redhat.com>
Date: Mon, 29 Jul 2013 14:16:13 +0930
Subject: [PATCH] virtio: console: fix race with port unplug and open/close

commit 057b82be3ca3d066478e43b162fc082930a746c9 upstream.

There's a window between find_port_by_devt() returning a port and us
taking a kref on the port, where the port could get unplugged.  Fix it
by taking the reference in find_port_by_devt() itself.

Problem reported and analyzed by Mateusz Guzik.

Reported-by: Mateusz Guzik <mguzik at redhat.com>
Signed-off-by: Amit Shah <amit.shah at redhat.com>
Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/char/virtio_console.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 957f293..002357f 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -257,9 +257,12 @@ static struct port *find_port_by_devt_in_portdev(struct ports_device *portdev,
 	unsigned long flags;

 	spin_lock_irqsave(&portdev->ports_lock, flags);
-	list_for_each_entry(port, &portdev->ports, list)
-		if (port->cdev->dev == dev)
+	list_for_each_entry(port, &portdev->ports, list) {
+		if (port->cdev->dev == dev) {
+			kref_get(&port->kref);
 			goto out;
+		}
+	}
 	port = NULL;
 out:
 	spin_unlock_irqrestore(&portdev->ports_lock, flags);
@@ -792,14 +795,10 @@ static int port_fops_open(struct inode *inode, struct file *filp)
 	struct port *port;
 	int ret;

+	/* We get the port with a kref here */
 	port = find_port_by_devt(cdev->dev);
 	filp->private_data = port;

-	/* Prevent against a port getting hot-unplugged at the same time */
-	spin_lock_irq(&port->portdev->ports_lock);
-	kref_get(&port->kref);
-	spin_unlock_irq(&port->portdev->ports_lock);
-
 	/*
 	 * Don't allow opening of console port devices -- that's done
 	 * via /dev/hvc
--
1.8.3.2