]> git.bitcoin.ninja Git - dnssec-prover/commitdiff
Use (and expose) a `ProofBuilder` state machine for proving
authorMatt Corallo <git@bluematt.me>
Mon, 12 Feb 2024 00:03:37 +0000 (00:03 +0000)
committerMatt Corallo <git@bluematt.me>
Mon, 12 Feb 2024 00:03:37 +0000 (00:03 +0000)
This will allow us to expose the state machine we use for building
proofs in, eg, javascript, allowing the construction of proofs
using DoH.

src/query.rs

index 3b1d21775ce2ac8c393b092f0534c3da361e9ca4..1ed76d578b97201fe80af8e87963619960c0aaae 100644 (file)
@@ -17,10 +17,6 @@ use crate::ser::*;
 // this constant instead of a random value.
 const TXID: u16 = 0x4242;
 
-fn emap<V>(v: Result<V, ()>) -> Result<V, Error> {
-       v.map_err(|_| Error::new(ErrorKind::Other, "Bad Response"))
-}
-
 fn build_query(domain: &Name, ty: u16) -> Vec<u8> {
        // TODO: Move to not allocating for the query
        let mut query = Vec::with_capacity(1024);
@@ -40,19 +36,6 @@ fn build_query(domain: &Name, ty: u16) -> Vec<u8> {
        query
 }
 
-fn send_query(stream: &mut TcpStream, domain: &Name, ty: u16) -> Result<(), Error> {
-       let query = build_query(domain, ty);
-       stream.write_all(&query)?;
-       Ok(())
-}
-
-#[cfg(feature = "tokio")]
-async fn send_query_async(stream: &mut TokioTcpStream, domain: &Name, ty: u16) -> Result<(), Error> {
-       let query = build_query(domain, ty);
-       stream.write_all(&query).await?;
-       Ok(())
-}
-
 #[cfg(fuzzing)]
 /// Read some input and parse it as if it came from a server, for fuzzing.
 pub fn fuzz_response(response: &[u8]) {
@@ -60,37 +43,37 @@ pub fn fuzz_response(response: &[u8]) {
        let _ = handle_response(response, &mut proof, &mut names);
 }
 
-fn handle_response(resp: &[u8], proof: &mut Vec<u8>, rrsig_key_names: &mut Vec<Name>) -> Result<u32, Error> {
+fn handle_response(resp: &[u8], proof: &mut Vec<u8>, rrsig_key_names: &mut Vec<Name>) -> Result<u32, ()> {
        let mut read: &[u8] = resp;
-       if emap(read_u16(&mut read))? != TXID { return Err(Error::new(ErrorKind::Other, "bad txid")); }
+       if read_u16(&mut read)? != TXID { return Err(()); }
        // 2 byte transaction ID
-       let flags = emap(read_u16(&mut read))?;
+       let flags = read_u16(&mut read)?;
        if flags & 0b1000_0000_0000_0000 == 0 {
-               return Err(Error::new(ErrorKind::Other, "Missing response flag"));
+               return Err(());
        }
        if flags & 0b0111_1010_0000_0111 != 0 {
-               return Err(Error::new(ErrorKind::Other, "Server indicated error or provided bunk flags"));
+               return Err(());
        }
        if flags & 0b10_0000 == 0 {
-               return Err(Error::new(ErrorKind::Other, "Server indicated data could not be authenticated"));
+               return Err(());
        }
-       let questions = emap(read_u16(&mut read))?;
-       if questions != 1 { return Err(Error::new(ErrorKind::Other, "server responded to multiple Qs")); }
-       let answers = emap(read_u16(&mut read))?;
-       if answers == 0 { return Err(Error::new(ErrorKind::Other, "No answers")); }
-       let _authorities = emap(read_u16(&mut read))?;
-       let _additional = emap(read_u16(&mut read))?;
+       let questions = read_u16(&mut read)?;
+       if questions != 1 { return Err(()); }
+       let answers = read_u16(&mut read)?;
+       if answers == 0 { return Err(()); }
+       let _authorities = read_u16(&mut read)?;
+       let _additional = read_u16(&mut read)?;
 
        for _ in 0..questions {
-               emap(read_wire_packet_name(&mut read, resp))?;
-               emap(read_u16(&mut read))?; // type
-               emap(read_u16(&mut read))?; // class
+               read_wire_packet_name(&mut read, resp)?;
+               read_u16(&mut read)?; // type
+               read_u16(&mut read)?; // class
        }
 
        // Only read the answers (skip authorities and additional) as that's all we care about.
        let mut min_ttl = u32::MAX;
        for _ in 0..answers {
-               let (rr, ttl) = emap(parse_wire_packet_rr(&mut read, &resp))?;
+               let (rr, ttl) = parse_wire_packet_rr(&mut read, &resp)?;
                write_rr(&rr, ttl, proof);
                min_ttl = cmp::min(min_ttl, ttl);
                if let RR::RRSig(rrsig) = rr { rrsig_key_names.push(rrsig.key_name); }
@@ -98,81 +81,166 @@ fn handle_response(resp: &[u8], proof: &mut Vec<u8>, rrsig_key_names: &mut Vec<N
        Ok(min_ttl)
 }
 
-fn read_response(stream: &mut TcpStream, proof: &mut Vec<u8>, rrsig_key_names: &mut Vec<Name>) -> Result<u32, Error> {
-       let mut len = [0; 2];
-       stream.read_exact(&mut len)?;
-       let mut resp = vec![0; u16::from_be_bytes(len) as usize];
-       stream.read_exact(&mut resp)?;
-       handle_response(&resp, proof, rrsig_key_names)
+const MAX_REQUESTS: usize = 10;
+/// A simple state machine which will generate a series of queries and process the responses until
+/// it has built a DNSSEC proof.
+///
+/// A [`ProofBuilder`] driver starts with [`ProofBuilder::new`], fetching the state machine and
+/// initial query. As long as [`ProofBuilder::awaiting_responses`] returns true, responses should
+/// be read from the resolver. For each query response read from the DNS resolver,
+/// [`ProofBuilder::process_response`] should be called, and each fresh query returned should be
+/// sent to the resolver. Once [`ProofBuilder::awaiting_responses`] returns false,
+/// [`ProofBuilder::finish_proof`] should be called to fetch the resulting proof.
+pub struct ProofBuilder {
+       proof: Vec<u8>,
+       min_ttl: u32,
+       dnskeys_requested: Vec<Name>,
+       pending_queries: usize,
+       queries_made: usize,
+}
+
+impl ProofBuilder {
+       /// Constructs a new [`ProofBuilder`] and an initial query to send to the recursive resolver to
+       /// begin the proof building process.
+       ///
+       /// Given a correctly-functioning resolver the proof will ultimately be able to prove the
+       /// contents of any records with the given `ty`pe at the given `name` (as long as the given
+       /// `ty`pe is supported by this library).
+       ///
+       /// You can find constants for supported standard types in the [`crate::rr`] module.
+       pub fn new(name: &Name, ty: u16) -> (ProofBuilder, Vec<u8>) {
+               let initial_query = build_query(name, ty);
+               (ProofBuilder {
+                       proof: Vec::new(),
+                       min_ttl: u32::MAX,
+                       dnskeys_requested: Vec::with_capacity(MAX_REQUESTS),
+                       pending_queries: 1,
+                       queries_made: 1,
+               }, initial_query)
+       }
+
+       /// Returns true as long as further responses are expected from the resolver.
+       ///
+       /// As long as this returns true, responses should be read from the resolver and passed to
+       /// [`Self::process_response`]. Once this returns false, [`Self::finish_proof`] should be used
+       /// to (possibly) get the final proof.
+       pub fn awaiting_responses(&self) -> bool {
+               self.pending_queries > 0 && self.queries_made <= MAX_REQUESTS
+       }
+
+       /// Processes a query response from the recursive resolver, returning a list of new queries to
+       /// send to the resolver.
+       pub fn process_response(&mut self, resp: &[u8]) -> Result<Vec<Vec<u8>>, ()> {
+               if self.pending_queries == 0 { return Err(()); }
+
+               let mut rrsig_key_names = Vec::new();
+               let min_ttl = handle_response(&resp, &mut self.proof, &mut rrsig_key_names)?;
+               self.min_ttl = cmp::min(self.min_ttl, min_ttl);
+               self.pending_queries -= 1;
+
+               rrsig_key_names.sort_unstable();
+               rrsig_key_names.dedup();
+
+               let mut new_queries = Vec::with_capacity(2);
+               for key_name in rrsig_key_names.drain(..) {
+                       if !self.dnskeys_requested.contains(&key_name) {
+                               new_queries.push(build_query(&key_name, DnsKey::TYPE));
+                               self.pending_queries += 1;
+                               self.queries_made += 1;
+                               self.dnskeys_requested.push(key_name.clone());
+
+                               if key_name.as_str() != "." {
+                                       new_queries.push(build_query(&key_name, DS::TYPE));
+                                       self.pending_queries += 1;
+                                       self.queries_made += 1;
+                               }
+                       }
+               }
+               if self.queries_made <= MAX_REQUESTS {
+                       Ok(new_queries)
+               } else {
+                       Ok(Vec::new())
+               }
+       }
+
+       /// Finalizes the proof, if one is available, and returns it as well as the TTL that should be
+       /// used to cache the proof (i.e. the lowest TTL of all records which were used to build the
+       /// proof).
+       pub fn finish_proof(self) -> Result<(Vec<u8>, u32), ()> {
+               if self.pending_queries > 0 || self.queries_made > MAX_REQUESTS {
+                       Err(())
+               } else {
+                       Ok((self.proof, self.min_ttl))
+               }
+       }
+}
+
+fn send_query(stream: &mut TcpStream, query: &[u8]) -> Result<(), Error> {
+       stream.write_all(&query)?;
+       Ok(())
 }
 
 #[cfg(feature = "tokio")]
-async fn read_response_async(stream: &mut TokioTcpStream, proof: &mut Vec<u8>, rrsig_key_names: &mut Vec<Name>) -> Result<u32, Error> {
-       let mut len = [0; 2];
-       stream.read_exact(&mut len).await?;
-       let mut resp = vec![0; u16::from_be_bytes(len) as usize];
-       stream.read_exact(&mut resp).await?;
-       handle_response(&resp, proof, rrsig_key_names)
+async fn send_query_async(stream: &mut TokioTcpStream, query: &[u8]) -> Result<(), Error> {
+       stream.write_all(&query).await?;
+       Ok(())
+}
+
+type MsgBuf = [u8; u16::MAX as usize];
+
+fn read_response(stream: &mut TcpStream, response_buf: &mut MsgBuf) -> Result<u16, Error> {
+       let mut len_bytes = [0; 2];
+       stream.read_exact(&mut len_bytes)?;
+       let len = u16::from_be_bytes(len_bytes);
+       stream.read_exact(&mut response_buf[..len as usize])?;
+       Ok(len)
+}
+
+#[cfg(feature = "tokio")]
+async fn read_response_async(stream: &mut TokioTcpStream, response_buf: &mut MsgBuf) -> Result<u16, Error> {
+       let mut len_bytes = [0; 2];
+       stream.read_exact(&mut len_bytes).await?;
+       let len = u16::from_be_bytes(len_bytes);
+       stream.read_exact(&mut response_buf[..len as usize]).await?;
+       Ok(len)
 }
 
 macro_rules! build_proof_impl {
-       ($stream: ident, $send_query: ident, $read_response: ident $(, $async_ok: tt)?) => { {
+       ($stream: ident, $send_query: ident, $read_response: ident, $domain: expr, $ty: expr $(, $async_ok: tt)?) => { {
                // We require the initial query to have already gone out, and assume our resolver will
                // return any CNAMEs all the way to the final record in the response. From there, we just
                // have to take any RRSIGs in the response and walk them up to the root. We do so
                // iteratively, sending DNSKEY and DS lookups after every response, deduplicating requests
                // using `dnskeys_requested`.
-               let mut res = Vec::new(); // The actual proof stream
-               let mut min_ttl = u32::MAX; // Min TTL of any answer record
-               const MAX_REQUESTS: usize = 20;
-               let mut rrsig_key_names = Vec::with_capacity(4); // Last response's RRSIG key_names
-               let mut dnskeys_requested = Vec::with_capacity(MAX_REQUESTS);
-               let mut pending_queries = 1;
-               let mut queries_made = 1;
-               while pending_queries != 0 && queries_made <= MAX_REQUESTS {
-                       let response_min_ttl = $read_response(&mut $stream, &mut res, &mut rrsig_key_names)
+               let (mut builder, initial_query) = ProofBuilder::new($domain, $ty);
+               $send_query(&mut $stream, &initial_query)
+                       $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
+               let mut response_buf = [0; u16::MAX as usize];
+               while builder.awaiting_responses() {
+                       let response_len = $read_response(&mut $stream, &mut response_buf)
                                $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
-                       pending_queries -= 1;
-                       min_ttl = cmp::min(min_ttl, response_min_ttl);
-                       rrsig_key_names.sort_unstable();
-                       rrsig_key_names.dedup();
-                       for key_name in rrsig_key_names.drain(..) {
-                               if !dnskeys_requested.contains(&key_name) {
-                                       $send_query(&mut $stream, &key_name, DnsKey::TYPE)
-                                               $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
-                                       pending_queries += 1;
-                                       queries_made += 1;
-                                       dnskeys_requested.push(key_name.clone());
-
-                                       if key_name.as_str() != "." {
-                                               $send_query(&mut $stream, &key_name, DS::TYPE)
-                                                       $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
-                                               pending_queries += 1;
-                                               queries_made += 1;
-                                       }
-                               }
+                       let new_queries = builder.process_response(&response_buf[..response_len as usize])
+                               .map_err(|()| Error::new(ErrorKind::Other, "Bad response"))?;
+                       for query in new_queries {
+                               $send_query(&mut $stream, &query)
+                                       $(.await?; $async_ok)??; // Either await?; Ok(())?, or just ?
                        }
                }
 
-               if queries_made > MAX_REQUESTS {
-                       Err(Error::new(ErrorKind::Other, "Too many requests required"))
-               } else {
-                       Ok((res, min_ttl))
-               }
+               builder.finish_proof()
+                       .map_err(|()| Error::new(ErrorKind::Other, "Too many requests required"))
        } }
 }
 
 fn build_proof(resolver: SocketAddr, domain: &Name, ty: u16) -> Result<(Vec<u8>, u32), Error> {
        let mut stream = TcpStream::connect(resolver)?;
-       send_query(&mut stream, domain, ty)?;
-       build_proof_impl!(stream, send_query, read_response)
+       build_proof_impl!(stream, send_query, read_response, domain, ty)
 }
 
 #[cfg(feature = "tokio")]
 async fn build_proof_async(resolver: SocketAddr, domain: &Name, ty: u16) -> Result<(Vec<u8>, u32), Error> {
        let mut stream = TokioTcpStream::connect(resolver).await?;
-       send_query_async(&mut stream, domain, ty).await?;
-       build_proof_impl!(stream, send_query_async, read_response_async, { Ok::<(), Error>(()) })
+       build_proof_impl!(stream, send_query_async, read_response_async, domain, ty, { Ok::<(), Error>(()) })
 }
 
 /// Builds a DNSSEC proof for an A record by querying a recursive resolver, returning the proof as