netdev - Re: [PATCH net] net: Account for all vlan headers in skb_mac_gso

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Message-ID: <1395850483.12610.213.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 26 Mar 2014 09:14:43 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Vlad Yasevich <vyasevic@...hat.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net] net: Account for all vlan headers in
 skb_mac_gso_segment

On Wed, 2014-03-26 at 11:51 -0400, Vlad Yasevich wrote:
> skb_network_protocol() already accounts for multiple vlan
> headers that may be present in the skb.  However, skb_mac_gso_segment()
> doesn't know anything about it and assumes that skb->mac_len
> is set correctly to skip all mac headers.  That may not
> always be the case.  If we are simply forwarding the packet (via
> bridge or macvtap), all vlan headers may not be accounted for.
> 
> A simple solution is to allow skb_network_protocol to return
> the vlan depth it has calculated.  This way skb_mac_gso_segment
> will correctly skip all mac headers.
> 
> Signed-off-by: Vlad Yasevich <vyasevic@...hat.com>
> ---
>  include/linux/netdevice.h |  2 +-
>  net/core/dev.c            | 12 ++++++++----
>  net/core/skbuff.c         |  2 +-
>  3 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index d855794..18b8c1b 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -3015,7 +3015,7 @@ struct sk_buff *skb_gso_segment(struct sk_buff *skb, netdev_features_t features)
>  {
>  	return __skb_gso_segment(skb, features, true);
>  }
> -__be16 skb_network_protocol(struct sk_buff *skb);
> +__be16 skb_network_protocol(struct sk_buff *skb, int *depth);
>  
>  static inline bool can_checksum_protocol(netdev_features_t features,
>  					 __be16 protocol)
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a98f7fa..49c41e6 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2287,7 +2287,7 @@ out:
>  }
>  EXPORT_SYMBOL(skb_checksum_help);
>  
> -__be16 skb_network_protocol(struct sk_buff *skb)
> +__be16 skb_network_protocol(struct sk_buff *skb, int *depth)
>  {
>  	__be16 type = skb->protocol;
>  	int vlan_depth = ETH_HLEN;
> @@ -2314,6 +2314,9 @@ __be16 skb_network_protocol(struct sk_buff *skb)
>  		vlan_depth += VLAN_HLEN;
>  	}
>  
> +	if (depth)
> +		*depth = vlan_depth;

expensive test, just always pass a non NULL pointer, to a dummy stack
variable.

> +
>  	return type;
>  }
>  
> @@ -2327,12 +2330,13 @@ struct sk_buff *skb_mac_gso_segment(struct sk_buff *skb,
>  {
>  	struct sk_buff *segs = ERR_PTR(-EPROTONOSUPPORT);
>  	struct packet_offload *ptype;
> -	__be16 type = skb_network_protocol(skb);
> +	int vlan_depth = 0;
vlan_depth = ETH_HLEN;

> +	__be16 type = skb_network_protocol(skb, &vlan_depth);
>  
>  	if (unlikely(!type))
>  		return ERR_PTR(-EINVAL);
>  
> -	__skb_pull(skb, skb->mac_len);
> +	__skb_pull(skb, vlan_depth > skb->mac_len ? vlan_depth : skb->mac_len);

Please remove this test

	__skb_pull(skb, vlan_depth);




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