proxy: pg17 fixes (#8321)

## Problem

#7809 - we do not support sslnegotiation=direct
#7810 - we do not support negotiating down the protocol extensions.

## Summary of changes

1. Same as postgres, check the first startup packet byte for tls header
`0x16`, and check the ALPN.
2. Tell clients using protocol >3.0 to downgrade

libs/postgres_backend/src/lib.rs

@@ -663,11 +663,17 @@ impl<IO: AsyncRead + AsyncWrite + Unpin> PostgresBackend<IO> {
         assert!(self.state < ProtoState::Authentication);
         let have_tls = self.tls_config.is_some();
         match msg {
-            FeStartupPacket::SslRequest => {
+            FeStartupPacket::SslRequest { direct } => {
                 debug!("SSL requested");
 
-                self.write_message(&BeMessage::EncryptionResponse(have_tls))
-                    .await?;
+                if !direct {
+                    self.write_message(&BeMessage::EncryptionResponse(have_tls))
+                        .await?;
+                } else if !have_tls {
+                    return Err(QueryError::Other(anyhow::anyhow!(
+                        "direct SSL negotiation but no TLS support"
+                    )));
+                }
 
                 if have_tls {
                     self.start_tls().await?;

libs/pq_proto/src/framed.rs

@@ -44,9 +44,9 @@ impl ConnectionError {
 /// Wraps async io `stream`, providing messages to write/flush + read Postgres
 /// messages.
 pub struct Framed<S> {
-    stream: S,
-    read_buf: BytesMut,
-    write_buf: BytesMut,
+    pub stream: S,
+    pub read_buf: BytesMut,
+    pub write_buf: BytesMut,
 }
 
 impl<S> Framed<S> {

libs/pq_proto/src/lib.rs

@@ -39,14 +39,39 @@ pub enum FeMessage {
     PasswordMessage(Bytes),
 }
 
+#[derive(Clone, Copy, PartialEq, PartialOrd)]
+pub struct ProtocolVersion(u32);
+
+impl ProtocolVersion {
+    pub const fn new(major: u16, minor: u16) -> Self {
+        Self((major as u32) << 16 | minor as u32)
+    }
+    pub const fn minor(self) -> u16 {
+        self.0 as u16
+    }
+    pub const fn major(self) -> u16 {
+        (self.0 >> 16) as u16
+    }
+}
+
+impl fmt::Debug for ProtocolVersion {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entry(&self.major())
+            .entry(&self.minor())
+            .finish()
+    }
+}
+
 #[derive(Debug)]
 pub enum FeStartupPacket {
     CancelRequest(CancelKeyData),
-    SslRequest,
+    SslRequest {
+        direct: bool,
+    },
     GssEncRequest,
     StartupMessage {
-        major_version: u32,
-        minor_version: u32,
+        version: ProtocolVersion,
         params: StartupMessageParams,
     },
 }
@@ -301,11 +326,23 @@ impl FeStartupPacket {
     /// different from [`FeMessage::parse`] because startup messages don't have
     /// message type byte; otherwise, its comments apply.
     pub fn parse(buf: &mut BytesMut) -> Result<Option<FeStartupPacket>, ProtocolError> {
+        /// <https://github.com/postgres/postgres/blob/ca481d3c9ab7bf69ff0c8d71ad3951d407f6a33c/src/include/libpq/pqcomm.h#L118>
         const MAX_STARTUP_PACKET_LENGTH: usize = 10000;
-        const RESERVED_INVALID_MAJOR_VERSION: u32 = 1234;
-        const CANCEL_REQUEST_CODE: u32 = 5678;
-        const NEGOTIATE_SSL_CODE: u32 = 5679;
-        const NEGOTIATE_GSS_CODE: u32 = 5680;
+        const RESERVED_INVALID_MAJOR_VERSION: u16 = 1234;
+        /// <https://github.com/postgres/postgres/blob/ca481d3c9ab7bf69ff0c8d71ad3951d407f6a33c/src/include/libpq/pqcomm.h#L132>
+        const CANCEL_REQUEST_CODE: ProtocolVersion = ProtocolVersion::new(1234, 5678);
+        /// <https://github.com/postgres/postgres/blob/ca481d3c9ab7bf69ff0c8d71ad3951d407f6a33c/src/include/libpq/pqcomm.h#L166>
+        const NEGOTIATE_SSL_CODE: ProtocolVersion = ProtocolVersion::new(1234, 5679);
+        /// <https://github.com/postgres/postgres/blob/ca481d3c9ab7bf69ff0c8d71ad3951d407f6a33c/src/include/libpq/pqcomm.h#L167>
+        const NEGOTIATE_GSS_CODE: ProtocolVersion = ProtocolVersion::new(1234, 5680);
+
+        // <https://github.com/postgres/postgres/blob/04bcf9e19a4261fe9c7df37c777592c2e10c32a7/src/backend/tcop/backend_startup.c#L378-L382>
+        // First byte indicates standard SSL handshake message
+        // (It can't be a Postgres startup length because in network byte order
+        // that would be a startup packet hundreds of megabytes long)
+        if buf.first() == Some(&0x16) {
+            return Ok(Some(FeStartupPacket::SslRequest { direct: true }));
+        }
 
         // need at least 4 bytes with packet len
         if buf.len() < 4 {
@@ -338,12 +375,10 @@ impl FeStartupPacket {
         let mut msg = buf.split_to(len).freeze();
         msg.advance(4); // consume len
 
-        let request_code = msg.get_u32();
-        let req_hi = request_code >> 16;
-        let req_lo = request_code & ((1 << 16) - 1);
+        let request_code = ProtocolVersion(msg.get_u32());
         // StartupMessage, CancelRequest, SSLRequest etc are differentiated by request code.
-        let message = match (req_hi, req_lo) {
-            (RESERVED_INVALID_MAJOR_VERSION, CANCEL_REQUEST_CODE) => {
+        let message = match request_code {
+            CANCEL_REQUEST_CODE => {
                 if msg.remaining() != 8 {
                     return Err(ProtocolError::BadMessage(
                         "CancelRequest message is malformed, backend PID / secret key missing"
@@ -355,21 +390,22 @@ impl FeStartupPacket {
                     cancel_key: msg.get_i32(),
                 })
             }
-            (RESERVED_INVALID_MAJOR_VERSION, NEGOTIATE_SSL_CODE) => {
+            NEGOTIATE_SSL_CODE => {
                 // Requested upgrade to SSL (aka TLS)
-                FeStartupPacket::SslRequest
+                FeStartupPacket::SslRequest { direct: false }
             }
-            (RESERVED_INVALID_MAJOR_VERSION, NEGOTIATE_GSS_CODE) => {
+            NEGOTIATE_GSS_CODE => {
                 // Requested upgrade to GSSAPI
                 FeStartupPacket::GssEncRequest
             }
-            (RESERVED_INVALID_MAJOR_VERSION, unrecognized_code) => {
+            version if version.major() == RESERVED_INVALID_MAJOR_VERSION => {
                 return Err(ProtocolError::Protocol(format!(
-                    "Unrecognized request code {unrecognized_code}"
+                    "Unrecognized request code {}",
+                    version.minor()
                 )));
             }
             // TODO bail if protocol major_version is not 3?
-            (major_version, minor_version) => {
+            version => {
                 // StartupMessage
 
                 let s = str::from_utf8(&msg).map_err(|_e| {
@@ -382,8 +418,7 @@ impl FeStartupPacket {
                 })?;
 
                 FeStartupPacket::StartupMessage {
-                    major_version,
-                    minor_version,
+                    version,
                     params: StartupMessageParams {
                         params: msg.slice_ref(s.as_bytes()),
                     },
@@ -522,6 +557,10 @@ pub enum BeMessage<'a> {
     RowDescription(&'a [RowDescriptor<'a>]),
     XLogData(XLogDataBody<'a>),
     NoticeResponse(&'a str),
+    NegotiateProtocolVersion {
+        version: ProtocolVersion,
+        options: &'a [&'a str],
+    },
     KeepAlive(WalSndKeepAlive),
 }
 
@@ -945,6 +984,18 @@ impl<'a> BeMessage<'a> {
                     buf.put_u8(u8::from(req.request_reply));
                 });
             }
+
+            BeMessage::NegotiateProtocolVersion { version, options } => {
+                buf.put_u8(b'v');
+                write_body(buf, |buf| {
+                    buf.put_u32(version.0);
+                    buf.put_u32(options.len() as u32);
+                    for option in options.iter() {
+                        write_cstr(option, buf)?;
+                    }
+                    Ok(())
+                })?
+            }
         }
         Ok(())
     }