Query with a huge question section can lead to crash

[robur-coop]

Query with a huge question section can lead to crash

[hannesm]

thanks for the report :)

I added a regression test (which decodes the frame and afterwards expects error to produce something sensible (and esp. not crash).

the fix I applied is if 450 byte are not sufficient to encode out only the first question. max_udp_size is my sanity guard to not act as an amplifier (which maybe should be tweaked to be a ratio between incoming and outgoing packet) -- given that I don't support any frames with multiple questions, I don't think I need to send the entire question back (please let me know if there's a requirement in some RFC to always send back the entire question section).

[Willy-Tan]

Sending the entire question back isn't a compulsory requirement but RFC5452, a Proposed Standard RFC, advises that the question section in the answer should match the question section from the query to help against spoofed packets. There may be some resolvers implementing this RFC, so that may be an issue, although I don't really know if there are many packets asking for multiples questions in a single query.

I will continue fuzzing in that direction, there may be other cases in which it could happen. The parsing function looks really solid though, I haven't found any bugs here 🤔