Re: [PATCH nf] netfilter: bridge: honor frag_max_size when refragmenting

[Florian Westphal <fw@strlen.de>]

Florian Westphal <fw@strlen.de> wrote:
> consider a bridge with mtu 9000, but end host sending smaller
> packets to another host with mtu < 9000.
> 
> In this case, after reassembly, bridge+defrag would refragment,
> and then attempt to send the reassembled packet as long as it
> was below 9k.
> 
> Instead we have to cap by the largest fragment size seen.
> 
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  No Fixes tag, seems this problem has always existed.
>  tested in kvm with both ipv4 and ipv6 and following setup:
> 
>  client (mtu 1500)  --- bridge(mtu 9k) --- client (mtu 1500)
> 
>  bridge (incl. all ports) have 9k mtu.
> 
>  without this patch, ping/ping6 only works for sizes <= 1500
>  and > 9000.

grrr.  it breaks the normal path...

> diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
> index 95087e6e8258..81889afee212 100644
> --- a/net/bridge/br_netfilter_hooks.c
> +++ b/net/bridge/br_netfilter_hooks.c
> @@ -721,18 +721,19 @@ static unsigned int nf_bridge_mtu_reduction(const struct sk_buff *skb)
>  
>  static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
>  {
> -	struct nf_bridge_info *nf_bridge;
> -	unsigned int mtu_reserved;
> +	struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
> +	unsigned int mtu, mtu_reserved;
>  
>  	mtu_reserved = nf_bridge_mtu_reduction(skb);
> +	mtu = nf_bridge->frag_max_size;

This can be 0, I'll send a v2.