Amit Shah <amit.s...@redhat.com> writes:
> 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.
This fix is clearly correct, but what about the other find_port_by_*
functions?
Applied,
Rusty.
>
> CC: <sta...@vger.kernel.org>
> Reported-by: Mateusz Guzik <mgu...@redhat.com>
> Signed-off-by: Amit Shah <amit.s...@redhat.com>
> ---
> drivers/char/virtio_console.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 1b456fe..291f437 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -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);
> @@ -1019,14 +1022,10 @@ 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
> --
> 1.8.1.4
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