[PATCH 089/133] virtio: console: fix race in port_fops_open() and port unplug

[Kamal Mostafa]

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

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

From: Amit Shah <amit.shah at redhat.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 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