netdev - Re: [PATCH net] net: validate untrusted gso packets

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Message-ID: <186d8595-467f-0337-8197-661c4f19248b@redhat.com>
Date:   Wed, 17 Jan 2018 19:58:24 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] net: validate untrusted gso packets



On 2018年01月17日 12:56, Willem de Bruijn wrote:
>> This just makes that check more strict. Frequency of malicious packets is
>> not really relevant if a single bad packet can cause damage.
>>
>> The alternative to validate on kernel entry is to harden the entire segmentation
>> layer and lower part of the stack. That is much harder to get right and not
>> necessarily cheaper.
>>
>> As a matter of fact, it incurs a cost on all packets, including the common
>> case generated by the protocol stack.
> If packets can be fully validated at the source, we can eventually also
> get rid of the entire SKB_GSO_DODGY and NETIF_F_GSO_ROBUST
> logic. Then virtio packets won't have to enter the segmentation layer
> at all for TSO capable devices.

On the contrary I think, if I read the code correctly, the point is to 
delay the check as much as possible. Then for GSO_ROBUST device, we 
don't even need to do any header check at all. This help for 
performance. What's more, the check should be done layer by layer which 
makes gso_segment a perfect place to do that.

Thanks