netdev - Re: [bpf-next 6/6] selftests/bpf: add test for bpf_tcp_gen

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Message-ID: <CACAyw9-qQ8KbQk6Q6dg0+A337ZbSpot-sHpH_tSxFaQmUfhLyQ@mail.gmail.com>
Date:   Tue, 23 Jul 2019 10:37:29 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Petar Penkov <ppenkov.kernel@...il.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        davem@...emloft.net, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Petar Penkov <ppenkov@...gle.com>
Subject: Re: [bpf-next 6/6] selftests/bpf: add test for bpf_tcp_gen_syncookie

On Tue, 23 Jul 2019 at 01:20, Petar Penkov <ppenkov.kernel@...il.com> wrote:
> +static __always_inline __s64 gen_syncookie(void *data_end, struct bpf_sock *sk,
> +                                          void *iph, __u32 ip_size,
> +                                          struct tcphdr *tcph)
> +{
> +       __u32 thlen = tcph->doff * 4;
> +
> +       if (tcph->syn && !tcph->ack) {
> +               // packet should only have an MSS option
> +               if (thlen != 24)
> +                       return 0;

Just for my own understanding: without this the verifier complains since
thlen is not a known value, even though it is in bounds due to the check below?

> +
> +               if ((void *)tcph + thlen > data_end)
> +                       return 0;
> +
> +               return bpf_tcp_gen_syncookie(sk, iph, ip_size, tcph, thlen);
> +       }
> +       return 0;
> +}
> +

-- 
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

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