RE: [RFC PATCH] lro: ip fragment checking

[Brandeburg, Jesse]

Ben Hutchings wrote:
> On Mon, 2008-11-24 at 16:56 +0100, Jan-Bernd Themann wrote:
>> Currently there is no checking in the LRO receive path whether
>> TCP packets are ip fragmented. We should not consider
>> those packets for aggregation.
>> I'm not sure if this checking is actually required. Does anyone
>> know if it is possible to get fragmented TCP packets without
>> the tcp stack changing the MSS size?
>> This patch introduces explicit checking. Any objections?
> 
> LRO depends on the hardware performing TCP checksum offload, and the
> TCP checksum cannot be verified for IP fragments in isolation.  So I
> think drivers should not be passing fragments into inet_lro or should
> reject them in its get_frag_header() or get_skb_header() method. 
> Certainly sfc doesn't pass fragments into inet_lro because they have
> not been checksummed.

The fragments, definitely will not have checksums offloaded, but
what about the first packet in the chain?  I haven't verified in
ixgbe or igb whether or not it could try and aggregate a packet
with MF set if it was the first fragment in a series of IP fragments.--
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