netdev - Re: [ovs-dev] [PATCH net-next v3 3/8] netfilter: Allow calling into nat helper without skb

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Date:	Fri, 4 Dec 2015 15:45:33 -0800
From:	Pravin Shelar <pshelar@...ira.com>
To:	Pablo Neira Ayuso <pablo@...filter.org>
Cc:	Jarno Rajahalme <jarno@....org>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>, netfilter-devel@...r.kernel.org
Subject: Re: [ovs-dev] [PATCH net-next v3 3/8] netfilter: Allow calling into
 nat helper without skb_dst.g

On Tue, Dec 1, 2015 at 12:51 PM, Pablo Neira Ayuso <pablo@...filter.org> wrote:
> On Wed, Nov 25, 2015 at 04:08:16PM -0800, Jarno Rajahalme wrote:
>> NAT checksum recalculation code assumes existence of skb_dst, which
>> becomes a problem for a later patch in the series ("openvswitch:
>> Interface with NAT.").  Simplify this by removing the check on
>> skb_dst, as the checksum will be dealt with later in the stack.
>>
>> Suggested-by: Pravin Shelar <pshelar@...ira.com>
>> Signed-off-by: Jarno Rajahalme <jarno@....org>
>> ---
>>  net/ipv4/netfilter/nf_nat_l3proto_ipv4.c | 29 ++++++++---------------------
>>  net/ipv6/netfilter/nf_nat_l3proto_ipv6.c | 29 ++++++++---------------------
>>  2 files changed, 16 insertions(+), 42 deletions(-)
>>
>> diff --git a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c b/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
>> index 5075b7e..f8aad03 100644
>> --- a/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
>> +++ b/net/ipv4/netfilter/nf_nat_l3proto_ipv4.c
>> @@ -127,28 +127,15 @@ static void nf_nat_ipv4_csum_recalc(struct sk_buff *skb,
>>                                   u8 proto, void *data, __sum16 *check,
>>                                   int datalen, int oldlen)
>>  {
>> -     const struct iphdr *iph = ip_hdr(skb);
>> -     struct rtable *rt = skb_rtable(skb);
>> -
>>       if (skb->ip_summed != CHECKSUM_PARTIAL) {
>> -             if (!(rt->rt_flags & RTCF_LOCAL) &&
>> -                 (!skb->dev || skb->dev->features & NETIF_F_V4_CSUM)) {
>> -                     skb->ip_summed = CHECKSUM_PARTIAL;
>> -                     skb->csum_start = skb_headroom(skb) +
>> -                                       skb_network_offset(skb) +
>> -                                       ip_hdrlen(skb);
>> -                     skb->csum_offset = (void *)check - data;
>> -                     *check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
>> -                                                 datalen, proto, 0);
>> -             } else {
>> -                     *check = 0;
>> -                     *check = csum_tcpudp_magic(iph->saddr, iph->daddr,
>> -                                                datalen, proto,
>> -                                                csum_partial(data, datalen,
>> -                                                             0));
>> -                     if (proto == IPPROTO_UDP && !*check)
>> -                             *check = CSUM_MANGLED_0;
>> -             }
>> +             const struct iphdr *iph = ip_hdr(skb);
>> +
>> +             skb->ip_summed = CHECKSUM_PARTIAL;
>> +             skb->csum_start = skb_headroom(skb) + skb_network_offset(skb) +
>> +                     ip_hdrlen(skb);
>> +             skb->csum_offset = (void *)check - data;
>> +             *check = ~csum_tcpudp_magic(iph->saddr, iph->daddr, datalen,
>> +                                         proto, 0);
>
> Is this change going to work with traffic that is redirected to the
> localhost?

localhost should handle CHECKSUM_PARTIAL just fine. So I do not see
problem with always converting skb to CHECKSUM_PARTIAL skb.
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