netdev - Re: [PATCH net v2] ipv6/netfilter: Discard first fragment not including all headers

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Date:   Fri, 6 Nov 2020 08:58:15 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Georg Kohmann <geokohma@...co.com>
Cc:     netdev@...r.kernel.org, pablo@...filter.org, kadlec@...filter.org,
        fw@...len.de, davem@...emloft.net, kuznet@....inr.ac.ru,
        yoshfuji@...ux-ipv6.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org
Subject: Re: [PATCH net v2] ipv6/netfilter: Discard first fragment not
 including all headers

On Fri,  6 Nov 2020 14:08:03 +0100 Georg Kohmann wrote:
> diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
> index c8cf1bb..e6173f5 100644
> --- a/net/ipv6/reassembly.c
> +++ b/net/ipv6/reassembly.c
> @@ -325,7 +325,7 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
>  	const struct ipv6hdr *hdr = ipv6_hdr(skb);
>  	struct net *net = dev_net(skb_dst(skb)->dev);
>  	__be16 frag_off;
> -	int iif, offset;
> +	int iif;
>  	u8 nexthdr;
>  
>  	if (IP6CB(skb)->flags & IP6SKB_FRAGMENTED)
> @@ -362,24 +362,11 @@ static int ipv6_frag_rcv(struct sk_buff *skb)
>  	 * the source of the fragment, with the Pointer field set to zero.
>  	 */
>  	nexthdr = hdr->nexthdr;
> -	offset = ipv6_skip_exthdr(skb, skb_transport_offset(skb), &nexthdr, &frag_off);
> -	if (offset >= 0) {
> -		/* Check some common protocols' header */
> -		if (nexthdr == IPPROTO_TCP)
> -			offset += sizeof(struct tcphdr);
> -		else if (nexthdr == IPPROTO_UDP)
> -			offset += sizeof(struct udphdr);
> -		else if (nexthdr == IPPROTO_ICMPV6)
> -			offset += sizeof(struct icmp6hdr);
> -		else
> -			offset += 1;
> -
> -		if (!(frag_off & htons(IP6_OFFSET)) && offset > skb->len) {
> -			__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
> -					IPSTATS_MIB_INHDRERRORS);
> -			icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);
> -			return -1;
> -		}
> +	if (!ipv6_frag_validate(skb, skb_transport_offset(skb), &nexthdr)) {
> +		__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev),
> +				IPSTATS_MIB_INHDRERRORS);
> +		icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);
> +		return -1;
>  	}

net/ipv6/reassembly.c: In function ‘ipv6_frag_rcv’:
net/ipv6/reassembly.c:327:9: warning: unused variable ‘frag_off’ [-Wunused-variable]
  327 |  __be16 frag_off;
      |         ^~~~~~~~