linux-kernel - [ 06/17] virtio: console: fix race in port_fops

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Message-Id: <20130813063502.259970498@linuxfoundation.org>
Date:	Mon, 12 Aug 2013 23:35:52 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Amit Shah <amit.shah@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: [ 06/17] virtio: console: fix race in port_fops_open() and port unplug

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Amit Shah <amit.shah@...hat.com>

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@...hat.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/char/virtio_console.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -794,6 +794,10 @@ static int port_fops_open(struct inode *
 
 	/* 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;
 
 	/*


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