Subject: Re: fake rtable dst patch applied but kernel keeps panicing

From: Massimo Cetra <[email-masked]>
Date: Fri, 20 Apr 2012 12:02:17 +0200

On 19/04/2012 10:45, Eric Dumazet wrote:
> Oh well, at first glance nf_bridge_unshare() is buggy, not sure if this
> can help your bug, but its another step.
>
>
> [PATCH] bridge: fix nf_bridge_unshare()
>
> If memory allocation failed, return an error.
>
> If not, skb->nf_bridge should be updated to point to the copy, not old
> info, or bad things can happen.
>
> Signed-off-by: Eric Dumazet<[email-masked]>
> ---
>   net/bridge/br_netfilter.c |   24 ++++++++++++------------
>   1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
> index dec4f38..b7c2cec 100644
> --- a/net/bridge/br_netfilter.c
> +++ b/net/bridge/br_netfilter.c
> @@ -185,21 +185,20 @@ static inline struct nf_bridge_info *nf_bridge_alloc(struct sk_buff *skb)
>   	return skb->nf_bridge;
>   }
>
> -static inline struct nf_bridge_info *nf_bridge_unshare(struct sk_buff *skb)
> +
> +static inline int nf_bridge_unshare(struct sk_buff *skb)
>   {
> -	struct nf_bridge_info *nf_bridge = skb->nf_bridge;
> +	struct nf_bridge_info *copy, *nf_bridge = skb->nf_bridge;
>
>   	if (atomic_read(&nf_bridge->use)>  1) {
> -		struct nf_bridge_info *tmp = nf_bridge_alloc(skb);
> -
> -		if (tmp) {
> -			memcpy(tmp, nf_bridge, sizeof(struct nf_bridge_info));
> -			atomic_set(&tmp->use, 1);
> -		}
> +		copy = kmemdup(nf_bridge, sizeof(*nf_bridge), GFP_ATOMIC);
> +		if (!copy)
> +			return -ENOMEM;
> +		atomic_set(&copy->use, 1);
>   		nf_bridge_put(nf_bridge);
> -		nf_bridge = tmp;
> +		skb->nf_bridge = copy;
>   	}
> -	return nf_bridge;
> +	return 0;
>   }
>
>   static inline void nf_bridge_push_encap_header(struct sk_buff *skb)
> @@ -744,8 +743,9 @@ static unsigned int br_nf_forward_ip(unsigned int hook, struct sk_buff *skb,
>   		return NF_ACCEPT;
>
>   	/* Need exclusive nf_bridge_info since we might have multiple
> -	 * different physoutdevs. */
> -	if (!nf_bridge_unshare(skb))
> +	 * different physoutdevs.
> +	 */
> +	if (nf_bridge_unshare(skb))
>   		return NF_DROP;
>
>   	parent = bridge_parent(out);
>
>

Hello, Eric,

i applied this patch and Peters last patch to a 3.3.2 kernel.
The result was a bit disappointing because the step was backwards.

Locally, from the same machine, i could ping each IP of each tun 
interface used by any virtual server.

 From the LAN such addresses were not pingable while the ip address of 
the bridge was reachable.

Max