Wed, Oct 30, 2013 at 02:41:00PM CET, fw@xxxxxxxxx wrote:
>Jiri Pirko <jiri@xxxxxxxxxxx> wrote:
>> Currently, when ipv6 fragment goes through the netfilter, match
>> functions are called on them directly. This might cause match function
>> to fail. So benefit from the fact that nf_defrag_ipv6 constructs
>> reassembled skb for us and use this reassembled skb for matching.
>>
>> This patch fixes for example following situation:
>> On HOSTA do:
>> ip6tables -I INPUT -p icmpv6 -j DROP
>> ip6tables -I INPUT -p icmpv6 -m icmp6 --icmpv6-type 128 -j ACCEPT
>>
>> and on HOSTB you do:
>> ping6 HOSTA -s2000 (MTU is 1500)
>>
>> Incoming echo requests will be filtered out on HOSTA. This issue does
>> not occur with smaller packets than MTU (where fragmentation does not happen).
>
>[..]
>> diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
>> index 44400c2..5421beb0 100644
>> --- a/net/ipv6/netfilter/ip6_tables.c
>> +++ b/net/ipv6/netfilter/ip6_tables.c
>> @@ -328,6 +328,7 @@ ip6t_do_table(struct sk_buff *skb,
>> const struct xt_table_info *private;
>> struct xt_action_param acpar;
>> unsigned int addend;
>> + struct sk_buff *reasm = skb->nfct_reasm ? skb->nfct_reasm : skb;
>>
>> /* Initialization */
>> indev = in ? in->name : nulldevname;
>> @@ -363,7 +364,7 @@ ip6t_do_table(struct sk_buff *skb,
>>
>> IP_NF_ASSERT(e);
>> acpar.thoff = 0;
>> - if (!ip6_packet_match(skb, indev, outdev, &e->ipv6,
>> + if (!ip6_packet_match(reasm, indev, outdev, &e->ipv6,
>> &acpar.thoff, &acpar.fragoff, &acpar.hotdrop)) {
>
>[..]
>
>This is a bit backwards, I think.
>- We gather frags
>- Then we invoke ip6t_do_table for each individual fragment
>
>So basically your patch is equivalent to
>for_each_frag( )
> ip6t_do_table(reassembled_skb)
>
>Which makes no sense to me - why traverse the ruleset n times with the same
>packet?
Because each fragment need to be pushed through separately.
What different approach would you suggest?
Thanks
Jiri
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