[ 3.8.y.z extended stable ] Patch "virtio: console: fix race in port_fops_open() and port unplug" has been added to staging queue

[Kamal Mostafa]

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

    virtio: console: fix race in port_fops_open() and port unplug

to the linux-3.8.y-queue branch of the 3.8.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-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.7.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 4d5f8bc468ba5e5e9d95a440b1a8f180cd5d369a Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah at redhat.com>
Date: Mon, 29 Jul 2013 14:17:13 +0930
Subject: virtio: console: fix race in port_fops_open() and port unplug

commit 671bdea2b9f210566610603ecbb6584c8a201c8c upstream.

Between open() being called and processed, the port can be unplugged.
Check if this happened, and bail out.

A simple test script to reproduce this is:

while true; do for i in $(seq 1 100); do echo $i > /dev/vport0p3; done; done;

This opens and closes the port a lot of times; unplugging the port while
this is happening triggers the bug.

Signed-off-by: Amit Shah <amit.shah at redhat.com>
Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/char/virtio_console.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index ff015e7..4e848c8 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1047,6 +1047,10 @@ static int port_fops_open(struct inode *inode, struct file *filp)

 	/* We get the port with a kref here */
 	port = find_port_by_devt(cdev->dev);
+	if (!port) {
+		/* Port was unplugged before we could proceed */
+		return -ENXIO;
+	}
 	filp->private_data = port;

 	/*
--
1.8.1.2