netdev - Re: [PATCH 5/6] net: add and use helpers when adjusting gso

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Date:   Thu, 01 Mar 2018 11:17:44 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, alexei.starovoitov@...il.com
Subject: Re: [PATCH 5/6] net: add and use helpers when adjusting gso_size

Hi Daniel,

>> It means that a user loaded eBPF program can trigger logs full of
>> warnings merely by using this eBPF helper and generating GSO'd SCTP
>> traffic.
>> 
>> Daniel and Alexei, this is a serious problem.  The eBPF helpers
>> mentioned here cannot handle SCTP GSO packets properly, and in fact
>> corrupt them if they adjust the gso_size.
>> 
>> SCTP GSO packets use the GSO_BY_FRAGS scheme and cannot be treated
>> the same way we treat normal GSO packets.
>
> Thanks for Cc, I would have missed it. This patch in combination with
> patch 6/6 seems okay since we reject it in these cases, which is fine
> (although it could be a warn_once), but patch 6/6 is definitely buggy
> in that we leave the skb in a half edited state when leaving the helper.
> Daniel, want me to fix this up from bpf side and route 5/6 and actual
> fix via bpf tree? Otherwise please respin with fixed 6/6.

I'm happy for you to take these two via the bpf tree with whatever
fixes/changes are appropriate - I'm no eBPF expert so my fix was a 'best
guess' only. Let me know if you would like anything respun on my end.

Regards,
Daniel

PS. apologies for missing you on Cc - will make sure you're cced on any
future bpf-related work!
>
> Thanks,
> Daniel