Re: [Xen-devel] Xen bug or sky2 device driver bug?

[Jan De Landtsheer <Jan@xxxxxxxxxx>]

Bug exists in linux-vanilla too... sky2 driver is crap (or the NIC
itself for that matter).

On Fri, 2006-08-18 at 10:16 +0200, Gerd Hoffmann wrote:
> > Is it bug of Xen or sky2 device?
> 
> Most likely bridging code, try the patch below (reminds /me that I
> wanted to forward that one to the networking folks ...)
> 
> cheers,
>   Gerd
> 
> plain text document attachment (nf_bridge-header-size)
> Subject: nf_bridge: ethernet header is 14 not 16 bytes
> From: jbeulich@xxxxxxxxxx
> Acked-by: kraxel@xxxxxxx
> References: 150410
> 
> The bridge netfilter code saves two more bytes that it should.
> In most cases it doesn't hurt because many drivers use NET_IP_ALIGN
> to make the IP header aligned, so there are two extra bytes head room
> available.
> 
> Some drivers don't do that though (sky2 for example), so copying
> accesses data outside the skbuff data allocation.  On xen kernels
> this can kill the machine with a page fault due to the way how
> skbuffs are allocated and the memory is managed.
> 
> ---
>  include/linux/netfilter_bridge.h |    2 +-
>  net/bridge/br_netfilter.c        |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> --- linux-2.6.17.orig/include/linux/netfilter_bridge.h
> +++ linux-2.6.17/include/linux/netfilter_bridge.h
> @@ -57,7 +57,7 @@ void nf_bridge_maybe_copy_header(struct 
>                       memcpy(skb->data - 18, skb->nf_bridge->data, 18);
>                       skb_push(skb, 4);
>               } else
> -                     memcpy(skb->data - 16, skb->nf_bridge->data, 16);
> +                     memcpy(skb->data - 14, skb->nf_bridge->data, 14);
>       }
>  }
>  
> --- linux-2.6.17.orig/net/bridge/br_netfilter.c
> +++ linux-2.6.17/net/bridge/br_netfilter.c
> @@ -124,7 +124,7 @@ static inline struct nf_bridge_info *nf_
>  
>  static inline void nf_bridge_save_header(struct sk_buff *skb)
>  {
> -        int header_size = 16;
> +        int header_size = 14;
>  
>       if (skb->protocol == htons(ETH_P_8021Q))
>               header_size = 18;
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