On Mon, Mar 28, 2016 at 6:24 PM, Tom Herbert <t...@herbertland.com> wrote:
> On Mon, Mar 28, 2016 at 4:58 PM, Alexander Duyck <adu...@mirantis.com> wrote:
>> This patch should fix the issues seen with a recent fix to prevent
>> tunnel-in-tunnel frames from being generated with GRO. The fix itself is
>> correct for now as long as we do not add any devices that support
>> NETIF_F_GSO_GRE_CSUM. When such a device is added it could have the
>> potential to mess things up due to the fact that the outer transport header
>> points to the outer UDP header and not the GRE header as would be expected.
>>
>> Fixes: fac8e0f579695 ("tunnels: Don't apply GRO to multiple layers of
>> encapsulation.")
>
> This could only fix FOU/GUE. It is very possible someone else could
> happily be doing some other layered encapsulation and never had a
> problem before, so the decision to start enforcing only a single layer
> of encapsulation for GRO would still break them. I still think we
> should revert the patch, and for next version fixes things to that any
> combination/nesting of encapsulation is supported, and if there are
> exceptions to that support they need be clearly documented.
It was pointed out to me that prior to my patch, it was also possible
to remotely cause a stack overflow by filling up a packet with tunnel
headers and letting GRO descend through them over and over again.
Tom, I'm sorry that you don't like how I fixed this issue but there
really, truly is a bug here. I gave you a specific example to be clear
but that doesn't mean that is the only case. I am aware that the bug
is not encountered in all situations and that the fix removes an
optimization in some of those but I think that ensuring correct
behavior must come first.
