netdev - Re: [PATCH 10/17] netfilter: ipv6: expand skb head in ip6_route_me

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Date:	Mon, 21 Nov 2011 11:29:17 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	kaber@...sh.net
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	ulrich.weber@...hos.com
Subject: Re: [PATCH 10/17] netfilter: ipv6: expand skb head in
 ip6_route_me_harder after oif change

Le lundi 21 novembre 2011 à 06:46 +0100, kaber@...sh.net a écrit :
> From: Patrick McHardy <kaber@...sh.net>
> 
> Expand the skb headroom if the oif changed due to rerouting similar to
> how IPv4 packets are handled.
> 
> Signed-off-by: Patrick McHardy <kaber@...sh.net>
> ---
>  net/ipv6/netfilter.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
> index 30fcee4..d39e954 100644
> --- a/net/ipv6/netfilter.c
> +++ b/net/ipv6/netfilter.c
> @@ -14,6 +14,7 @@ int ip6_route_me_harder(struct sk_buff *skb)
>  {
>  	struct net *net = dev_net(skb_dst(skb)->dev);
>  	const struct ipv6hdr *iph = ipv6_hdr(skb);
> +	unsigned int hh_len;
>  	struct dst_entry *dst;
>  	struct flowi6 fl6 = {
>  		.flowi6_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0,
> @@ -46,6 +47,12 @@ int ip6_route_me_harder(struct sk_buff *skb)
>  	}
>  #endif
>  
> +	/* Change in oif may mean change in hh_len. */
> +	hh_len = skb_dst(skb)->dev->hard_header_len;
> +	if (skb_headroom(skb) < hh_len &&
> +	    pskb_expand_head(skb, hh_len - skb_headroom(skb), 0, GFP_ATOMIC))
> +		return -1;
> +

Hmm, We had a problem recently on Tile arches because of unaligned
accesses.

Had you seen the bug report and proposed patch ?

Fix is to instead do :

	pskb_expand_head(skb,
			 HH_DATA_ALIGN(hh_len - skb_headroom(skb)), 
			 0,
			 GFP_ATOMIC);



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