netdev - Re: [Intel-wired-lan] [PATCH V2 RFC 2/2] ixgbe: ixgbe_atr() compute l4_proto only if non-paged data has network/transport headers

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Date:   Mon, 17 Oct 2016 17:16:40 -0400
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Netdev <netdev@...r.kernel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [Intel-wired-lan] [PATCH V2 RFC 2/2] ixgbe: ixgbe_atr() compute
 l4_proto only if non-paged data has network/transport headers

On (10/17/16 12:49), Alexander Duyck wrote:
> >> >         /* Currently only IPv4/IPv6 with TCP is supported */
> >> >         switch (hdr.ipv4->version) {
> >> >         case IPVERSION:
> >> >                 /* access ihl as u8 to avoid unaligned access on ia64 */
> >> >                 hlen = (hdr.network[0] & 0x0F) << 2;
> >> > +               if (skb_tail_pointer(skb) < hdr.network + hlen +
> >> > +                                           sizeof(struct tcphdr))
> >> > +                       return;
> >> >                 l4_proto = hdr.ipv4->protocol;
> >> >                 break;
> >> >         case 6:
> >> >                 hlen = hdr.network - skb->data;
> >> > +               if (skb_tail_pointer(skb) < hdr.network + hlen +
> >> > +                                           sizeof(struct tcphdr))
> >> > +                       return;
> >> >                 l4_proto = ipv6_find_hdr(skb, &hlen, IPPROTO_TCP, NULL, NULL);
> >> >                 hlen -= hdr.network - skb->data;
> >> >                 break;
   :
> >> So you probably need to add a check for "skb_tail_pointer(skb) <
> >> (hdr.network + hlen + 20)".
> >
> > But isnt that the same thing as the checks before l4_proto computation above?
> 
> Sort of.  The problem is IPv6 can include extension headers and that
> can totally mess with us.  So we need to do one more check to verify
> that we have enough space for IPv6 w/ TCP which would be hdr.raw + 20
> + hlenl.

Yes, you are right. So given that I already check that I have
at least 40 bytes past the network header, and ipv6_find_hdr
will pull up exthdrs as needed, my checks are not needed, and the
real ones should happen after we come out of that switch().

--Sowmini