Add checking for header sanity

Co-authored-by: Daniel Abramov <inetcrack2@gmail.com>

src/handshake/machine.rs

@@ -20,7 +20,7 @@ pub struct HandshakeMachine<Stream> {
 impl<Stream> HandshakeMachine<Stream> {
     /// Start reading data from the peer.
     pub fn start_read(stream: Stream) -> Self {
-        HandshakeMachine { stream, state: HandshakeState::Reading(ReadBuffer::new()) }
+        Self { stream, state: HandshakeState::Reading(ReadBuffer::new(), AttackCheck::new()) }
     }
     /// Start writing data to the peer.
     pub fn start_write<D: Into<Vec<u8>>>(stream: Stream, data: D) -> Self {
@@ -41,25 +41,31 @@ impl<Stream: Read + Write> HandshakeMachine<Stream> {
     pub fn single_round<Obj: TryParse>(mut self) -> Result<RoundResult<Obj, Stream>> {
         trace!("Doing handshake round.");
         match self.state {
-            HandshakeState::Reading(mut buf) => {
+            HandshakeState::Reading(mut buf, mut attack_check) => {
                 let read = buf.read_from(&mut self.stream).no_block()?;
                 match read {
                     Some(0) => Err(Error::Protocol(ProtocolError::HandshakeIncomplete)),
-                    Some(_) => Ok(if let Some((size, obj)) = Obj::try_parse(Buf::chunk(&buf))? {
-                        buf.advance(size);
-                        RoundResult::StageFinished(StageResult::DoneReading {
-                            result: obj,
-                            stream: self.stream,
-                            tail: buf.into_vec(),
+                    Some(count) => {
+                        attack_check.check_incoming_packet_size(count)?;
+                        // TODO: this is slow for big headers with too many small packets.
+                        // The parser has to be reworked in order to work on streams instead
+                        // of buffers.
+                        Ok(if let Some((size, obj)) = Obj::try_parse(Buf::chunk(&buf))? {
+                            buf.advance(size);
+                            RoundResult::StageFinished(StageResult::DoneReading {
+                                result: obj,
+                                stream: self.stream,
+                                tail: buf.into_vec(),
+                            })
+                        } else {
+                            RoundResult::Incomplete(HandshakeMachine {
+                                state: HandshakeState::Reading(buf, attack_check),
+                                ..self
+                            })
                         })
-                    } else {
-                        RoundResult::Incomplete(HandshakeMachine {
-                            state: HandshakeState::Reading(buf),
-                            ..self
-                        })
-                    }),
+                    }
                     None => Ok(RoundResult::WouldBlock(HandshakeMachine {
-                        state: HandshakeState::Reading(buf),
+                        state: HandshakeState::Reading(buf, attack_check),
                         ..self
                     })),
                 }
@@ -119,7 +125,54 @@ pub trait TryParse: Sized {
 #[derive(Debug)]
 enum HandshakeState {
     /// Reading data from the peer.
-    Reading(ReadBuffer),
+    Reading(ReadBuffer, AttackCheck),
     /// Sending data to the peer.
     Writing(Cursor<Vec<u8>>),
 }
+
+/// Attack mitigation. Contains counters needed to prevent DoS attacks
+/// and reject valid but useless headers.
+#[derive(Debug)]
+pub(crate) struct AttackCheck {
+    /// Number of HTTP header successful reads (TCP packets).
+    number_of_packets: usize,
+    /// Total number of bytes in HTTP header.
+    number_of_bytes: usize,
+}
+
+impl AttackCheck {
+    /// Initialize attack checking for incoming buffer.
+    fn new() -> Self {
+        Self { number_of_packets: 0, number_of_bytes: 0 }
+    }
+
+    /// Check the size of an incoming packet. To be called immediately after `read()`
+    /// passing its returned bytes count as `size`.
+    fn check_incoming_packet_size(&mut self, size: usize) -> Result<()> {
+        self.number_of_packets += 1;
+        self.number_of_bytes += size;
+
+        // TODO: these values are hardcoded. Instead of making them configurable,
+        // rework the way HTTP header is parsed to remove this check at all.
+        const MAX_BYTES: usize = 65536;
+        const MAX_PACKETS: usize = 512;
+        const MIN_PACKET_SIZE: usize = 128;
+        const MIN_PACKET_CHECK_THRESHOLD: usize = 64;
+
+        if self.number_of_bytes > MAX_BYTES {
+            return Err(Error::AttackAttempt);
+        }
+
+        if self.number_of_packets > MAX_PACKETS {
+            return Err(Error::AttackAttempt);
+        }
+
+        if self.number_of_packets > MIN_PACKET_CHECK_THRESHOLD {
+            if self.number_of_packets * MIN_PACKET_SIZE > self.number_of_bytes {
+                return Err(Error::AttackAttempt);
+            }
+        }
+
+        Ok(())
+    }
+}