netdev - Re: [RFC net-next] ipip: Add room for custom tunnel header

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Date:	Thu, 08 Aug 2013 09:00:58 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Kristian Evensen <kristian.evensen@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC net-next] ipip: Add room for custom tunnel header

On Thu, 2013-08-08 at 15:52 +0200, Kristian Evensen wrote:
> Hello,

...

> Signed-off-by: Kristian Evensen <kristian.evensen@...il.com>
> ---
>  include/uapi/linux/if_tunnel.h |    1 +
>  net/ipv4/ipip.c                |    5 ++++-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/if_tunnel.h b/include/uapi/linux/if_tunnel.h
> index aee73d0..039bbc3 100644
> --- a/include/uapi/linux/if_tunnel.h
> +++ b/include/uapi/linux/if_tunnel.h
> @@ -35,6 +35,7 @@ struct ip_tunnel_parm {
>  	__be32			i_key;
>  	__be32			o_key;
>  	struct iphdr		iph;
> +	int                     hlen;
>  };
>  
>  enum {
> diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
> index 51fc2a1..9705aa1 100644
> --- a/net/ipv4/ipip.c
> +++ b/net/ipv4/ipip.c
> @@ -226,6 +226,9 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
>  		skb->encapsulation = 1;
>  	}
>  
> +	if (tunnel->hlen > 0)
> +		skb_push(skb, tunnel->hlen);


What happens if hlen is bigger than available headroom ?

hlen comes from userspace and there is no safety check, right ?

What guarantee do we have _something_ will fill the bytes ?
(We do not want to leak prior content of those bytes to the wire)



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