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

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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.

CC: <stable@vger.kernel.org>
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>
This commit is contained in:
Amit Shah 2013-07-29 14:16:13 +09:30 committed by Rusty Russell
parent 2b4fbf029d
commit 057b82be3c
1 changed files with 6 additions and 7 deletions
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13
drivers/char/virtio_console.c
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@ -272,9 +272,12 @@ 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);
@ -1036,14 +1039,10 @@ 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