[ 05/17] virtio: console: fix race with port unplug and open/close

Greg Kroah-Hartman
2013-08-13T06:36:55Z

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

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

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

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@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/char/virtio_console.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -256,9 +256,12 @@ static struct port *find_port_by_devt_in
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);
@@ -789,14 +792,10 @@ static int port_fops_open(struct inode *
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