netdev - Re: [PATCH net] bridge: check iface upper dev when setting master via ioctl

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Date:   Thu, 26 Apr 2018 17:00:08 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+de73361ee4971b6e6f75@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net] bridge: check iface upper dev when setting master via
 ioctl

On 26/04/18 16:56, Hangbin Liu wrote:
> When we set a bond slave's master to bridge via ioctl, we only check
> the IFF_BRIDGE_PORT flag. Although we will find the slave's real master
> at netdev_master_upper_dev_link() later, it already does some settings
> and allocates some resources. So it would be better to return as early
> as possible.
> 
> Reported-by: syzbot+de73361ee4971b6e6f75@...kaller.appspotmail.com
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
>  net/bridge/br_if.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
> index 82c1a6f..176de8a9 100644
> --- a/net/bridge/br_if.c
> +++ b/net/bridge/br_if.c
> @@ -518,8 +518,8 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
>  		return -ELOOP;
>  	}
>  
> -	/* Device is already being bridged */
> -	if (br_port_exists(dev))
> +	/* Device has master upper dev */
> +	if (netdev_has_any_upper_dev(dev))
>  		return -EBUSY;
>  
>  	/* No bridging devices that dislike that (e.g. wireless) */
> 

Not all upper devs are masters. This can break some setups.