malformed query can cause assertion failure at encoder.rs:234

[rtmrtmrtmrtm]

If a client sends this DNS request to the hickory 0.24.0 DNS server:

08 00 00 00 00 01 00 00 00 00 00 00 c0 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00

i.e.:
08 00 ID
00 00 flags
00 01 QDCOUNT
00 00 ANCOUNT
00 00 NSCOUNT
00 00 ARCOUNT
c0 00 QNAME
00 00 QTYPE
00 00 QCLASS

hickory-dns fails the 2nd assert here while building the reply message
(really while remembering names for pointers):

pub fn slice_of(&self, start: usize, end: usize) -> &[u8] {
    assert!(start < self.offset);
    assert!(end <= self.buffer.len());
    &self.buffer.buffer()[start..end]
}

The name is eight bytes long, but the current message size (after the
current offset of 12) is only six, because QueriesEmitAndCount::emit()
stored just the six bytes of the original encoded query:

    encoder.emit_vec(self.cached_serialized)?;

So the assert fails.

I've attached a demo program that assumes something like this is
already running:

hickory-dns/target/debug/hickory-dns -d -c hickory-dns/tests/test-data/test_configs/example.toml -z hickory-dns/tests/test-data/test_configs/ -p 24141

hickory1a.txt

[djc]

Thanks for the report! Could you send your test case as a PR adding a unit test in crates/proto/src/rr/serialize/encoder.rs? Bonus points if you can also come up with a fix, but I can probably find some time to fix it myself. 👍