linux-kernel - Re: [PATCH 4.4 059/268] xen-netfront: Fix race between device setup and open

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Date:   Mon, 11 Jun 2018 15:29:32 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Ross Lagerwall <ross.lagerwall@...rix.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Cc:     stable@...r.kernel.org,
        Sasha Levin <alexander.levin@...rosoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4.4 059/268] xen-netfront: Fix race between device setup
 and open

On Mon, 2018-05-28 at 12:00 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Ross Lagerwall <ross.lagerwall@...rix.com>
> 
> [ Upstream commit f599c64fdf7d9c108e8717fb04bc41c680120da4 ]
[...]
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
[...]
> @@ -1839,6 +1824,7 @@ static int talk_to_netback(struct xenbus
>  		goto out;

This "goto out" is outside the locked section...

>  	}
>  
> +	rtnl_lock();
>  	if (info->queues)
>  		xennet_destroy_queues(info);
>  
> @@ -1849,6 +1835,7 @@ static int talk_to_netback(struct xenbus
>  		info->queues = NULL;
>  		goto out;
>  	}
> +	rtnl_unlock();
>  
>  	/* Create shared ring, alloc event channel -- for each queue */
>  	for (i = 0; i < num_queues; ++i) {
> @@ -1945,8 +1932,10 @@ abort_transaction_no_dev_fatal:
>  	xenbus_transaction_end(xbt, 1);
>   destroy_ring:
>  	xennet_disconnect_backend(info);
> +	rtnl_lock();
>  	xennet_destroy_queues(info);
>   out:
> +	rtnl_unlock();

...so this will be an unmatched unlock.

You need to add another label below the rtnl_unlock().

Ben.

>  	device_unregister(&dev->dev);
>  	return err;
>  }
[...]

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom