On Mon, 31 Jan 2022 at 13:38, Maxim Mikityanskiy [off-list ref] wrote:

On 2022-01-26 11:45, Lorenz Bauer wrote:

quoted

On Mon, 24 Jan 2022 at 15:13, Maxim Mikityanskiy [off-list ref] wrote:

quoted

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 <redacted>

-- 
Lorenz Bauer  |  Systems Engineer
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