On Mon, 31 Jan 2022 at 13:38, Maxim Mikityanskiy <maximmi@xxxxxxxxxx> wrote:
>
> On 2022-01-26 11:45, Lorenz Bauer wrote:
> > On Mon, 24 Jan 2022 at 15:13, Maxim Mikityanskiy <maximmi@xxxxxxxxxx> wrote:
> >>
> >> bpf_tcp_gen_syncookie and bpf_tcp_check_syncookie expect the full length
> >> of the TCP header (with all extensions). Fix the documentation that says
> >> it should be sizeof(struct tcphdr).
> >
> > I don't understand this change, sorry. Are you referring to the fact
> > that the check is len < sizeof(*th) instead of len != sizeof(*th)?
> >
> > Your commit message makes me think that the helpers will access data
> > in the extension headers, which isn't true as far as I can tell.
>
> Yes, they will. See bpf_tcp_gen_syncookie -> tcp_v4_get_syncookie ->
> tcp_get_syncookie_mss -> tcp_parse_mss_option, which iterates over the
> TCP options ("extensions" wasn't the best word I used here). Moreover,
> bpf_tcp_gen_syncookie even checks that th_len == th->doff * 4.
>
> Although bpf_tcp_check_syncookie doesn't need the TCP options and
> doesn't enforce them to be passed, it's still allowed.
Sorry, I was only looking at bpf_tcp_check_syncookie indeed.
Unfortunate, it would be better if that function had a th->doff check
as well. :(
Acked-by: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
