Re: [PATCH v2] openvswitch: Trim off padding before L3+ netfilter processing

[Pravin Shelar <pshelar@ovn.org>]

On Mon, Jan 8, 2018 at 7:02 PM, Ed Swierk <eswierk@skyportsystems.com> wrote:
> On 1/6/18 10:57, Pravin Shelar wrote:
>> On Fri, Jan 5, 2018 at 10:59 PM, Ed Swierk <eswierk@skyportsystems.com> wrote:
>>>
>>>
>>> On Jan 5, 2018 22:17, "Pravin Shelar" <pshelar@ovn.org> wrote:
>>>
>>> On Fri, Jan 5, 2018 at 3:20 PM, Ed Swierk <eswierk@skyportsystems.com>
>>> wrote:
>>>> On Fri, Jan 5, 2018 at 10:14 AM, Ed Swierk <eswierk@skyportsystems.com>
>>>> wrote:
>>>>> On Thu, Jan 4, 2018 at 7:36 PM, Pravin Shelar <pshelar@ovn.org> wrote:
>>>>>> OVS already pull all required headers in skb linear data, so no need
>>>>>> to redo all of it. only check required is the ip-checksum validation.
>>>>>> I think we could avoid it in most of cases by checking skb length to
>>>>>> ipheader length before verifying the ip header-checksum.
>>>>>
>>>>> Shouldn't the IP header checksum be verified even earlier, like in
>>>>> key_extract(), before actually using any of the fields in the IP
>>>>> header?
>>>>
>>>> Something like this for verifying the IP header checksum (not tested):
>>>>
>>> AFAIU openflow does not need this verification, so it is not required
>>> in flow extract.
>>>
>>>
>>> Okay. How about my proposed trimming implementation, caching the pad length
>>> in the ovs cb?
>>>
>> Caching the length is not that simple, OVS actions can change the
>> length. Keeping it consistent with packet would be more work, so lets
>> calculate it in ovs-ct function.
>>
>
> Something like this?
>
Sure, Can you submit formal patch?

> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index a38c80e..282325d 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -4084,6 +4084,8 @@ struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
>                                      unsigned int transport_len,
>                                      __sum16(*skb_chkf)(struct sk_buff *skb));
>
> +int skb_network_trim(struct sk_buff *skb);
> +
>  /**
>   * skb_head_is_locked - Determine if the skb->head is locked down
>   * @skb: skb to check
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 08f5740..c68e927 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4740,6 +4740,41 @@ struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
>  }
>  EXPORT_SYMBOL(skb_checksum_trimmed);
>
> +/**
> + * skb_network_trim - trim skb to length specified by the network header
> + * @skb: the skb to trim
> + *
> + * Trims the skb to the length specified by the network header,
> + * removing any trailing padding. Leaves the skb alone if the protocol
> + * is not IP or IPv6. Frees the skb on error.
> + *
> + * Caller needs to pull the skb to the network header.
> + */
> +int skb_network_trim(struct sk_buff *skb)
> +{
> +       unsigned int len;
> +       int err;
> +
> +       switch (skb->protocol) {
> +       case htons(ETH_P_IP):
> +               len = ntohs(ip_hdr(skb)->tot_len);
> +               break;
> +       case htons(ETH_P_IPV6):
> +               len = sizeof(struct ipv6hdr)
> +                       + ntohs(ipv6_hdr(skb)->payload_len);
> +               break;
> +       default:
> +               len = skb->len;
> +       }
> +
> +       err = pskb_trim_rcsum(skb, len);
> +       if (unlikely(err))
> +               kfree_skb(skb);
> +
> +       return err;
> +}
> +EXPORT_SYMBOL(skb_network_trim);
> +
>  void __skb_warn_lro_forwarding(const struct sk_buff *skb)
>  {
>         net_warn_ratelimited("%s: received packets cannot be forwarded while LRO is enabled\n",
> diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
> index b27c5c6..73418d3 100644
> --- a/net/openvswitch/conntrack.c
> +++ b/net/openvswitch/conntrack.c
> @@ -1112,6 +1112,10 @@ int ovs_ct_execute(struct net *net, struct sk_buff *skb,
>         nh_ofs = skb_network_offset(skb);
>         skb_pull_rcsum(skb, nh_ofs);
>
> +       err = skb_network_trim(skb);
> +       if (err)
> +               return err;
> +
>         if (key->ip.frag != OVS_FRAG_TYPE_NONE) {
>                 err = handle_fragments(net, key, info->zone.id, skb);
>                 if (err)