[pve-devel] [PATCH v1 proxmox 0/3] Fix #5105: Overhaul TLS Handshake Checking Logic

[pve-devel] [PATCH v1 proxmox 0/3] Fix #5105: Overhaul TLS Handshake Checking Logic

[Max Carrara]

Fix #5105: Overhaul TLS Handshake Checking Logic
================================================

This series fixes bug #5105 [1] by overhauling the TLS handshake
checking logic, which is performed when using a connection acceptor
variant with optional TLS.

In the case of PBS (the only place where this is used, to my knowledge),
any requests made over plain HTTP are redirected to the same host, but
clients are instructed to use HTTPS instead.

The TLS handshake checking logic determines whether the client uses HTTP
or HTTPS by peeking into the stream buffer -- if the first 5 received
bytes look like a TLS handshake fragment, the connection is passed on to
OpenSSL before being accepted. Otherwise the connection is assumed to be
unencrypted, i.e. plain HTTP.

However, this logic contains two errors:

  1. The timeout duration is too short - one second is too little
  2. When a timeout occurs, the connection is assumed to be unencrypted
     (and thus plain HTTP)

The patches 01 and 02 are mainly done in preparation for patch 03 (which
contains the actual fix), improving the overall quality of the code and
including the peer's address in error logs.

Please see the individual patches for more information.

Special thanks go to Stefan Hanreich whose advice helped identifying
many individual puzzle pieces comprising this issue.

References
----------

[1]: https://bugzilla.proxmox.com/show_bug.cgi?id=5105

Summary of Changes
------------------

Max Carrara (3):
  rest-server: connection: clean up accept data flow
  rest-server: connection: log peer address on error
  fix #5105: rest-server: connection: overhaul TLS handshake check logic

 proxmox-rest-server/src/connection.rs | 165 +++++++++++++-------------
 1 file changed, 85 insertions(+), 80 deletions(-)

-- 
2.39.2



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[pve-devel] [PATCH v1 proxmox 1/3] rest-server: connection: clean up accept data flow

[Max Carrara]

This adds the structs `AcceptState` and `AcceptFlags` and adapts
relevant method signatures of `AcceptBuilder` accordingly. This makes
it easier to add further parameters in the future.

Signed-off-by: Max Carrara <m.carrara@proxmox.com>
---
 proxmox-rest-server/src/connection.rs | 72 ++++++++++++++-------------
 1 file changed, 38 insertions(+), 34 deletions(-)

diff --git a/proxmox-rest-server/src/connection.rs b/proxmox-rest-server/src/connection.rs
index 34b585cb..243348c0 100644
--- a/proxmox-rest-server/src/connection.rs
+++ b/proxmox-rest-server/src/connection.rs
@@ -255,6 +255,16 @@ impl From<(ClientSender, InsecureClientSender)> for Sender {
     }
 }
 
+struct AcceptState {
+    pub socket: InsecureClientStream,
+    pub acceptor: Arc<Mutex<SslAcceptor>>,
+    pub accept_counter: Arc<()>,
+}
+
+struct AcceptFlags {
+    pub is_debug: bool,
+}
+
 impl AcceptBuilder {
     async fn accept_connections(
         self,
@@ -285,24 +295,26 @@ impl AcceptBuilder {
                 continue;
             }
 
+            let state = AcceptState {
+                socket,
+                acceptor,
+                accept_counter,
+            };
+
+            let flags = AcceptFlags {
+                is_debug: self.debug,
+            };
+
             match sender {
                 Sender::Secure(ref secure_sender) => {
-                    let accept_future = Self::do_accept_tls(
-                        socket,
-                        acceptor,
-                        accept_counter,
-                        self.debug,
-                        secure_sender.clone(),
-                    );
+                    let accept_future = Self::do_accept_tls(state, flags, secure_sender.clone());
 
                     tokio::spawn(accept_future);
                 }
                 Sender::SecureAndInsecure(ref secure_sender, ref insecure_sender) => {
                     let accept_future = Self::do_accept_tls_optional(
-                        socket,
-                        acceptor,
-                        accept_counter,
-                        self.debug,
+                        state,
+                        flags,
                         secure_sender.clone(),
                         insecure_sender.clone(),
                     );
@@ -343,17 +355,11 @@ impl AcceptBuilder {
         Ok(socket)
     }
 
-    async fn do_accept_tls(
-        socket: InsecureClientStream,
-        acceptor: Arc<Mutex<SslAcceptor>>,
-        accept_counter: Arc<()>,
-        debug: bool,
-        secure_sender: ClientSender,
-    ) {
+    async fn do_accept_tls(state: AcceptState, flags: AcceptFlags, secure_sender: ClientSender) {
         let ssl = {
             // limit acceptor_guard scope
             // Acceptor can be reloaded using the command socket "reload-certificate" command
-            let acceptor_guard = acceptor.lock().unwrap();
+            let acceptor_guard = state.acceptor.lock().unwrap();
 
             match openssl::ssl::Ssl::new(acceptor_guard.context()) {
                 Ok(ssl) => ssl,
@@ -364,7 +370,7 @@ impl AcceptBuilder {
             }
         };
 
-        let secure_stream = match tokio_openssl::SslStream::new(ssl, socket) {
+        let secure_stream = match tokio_openssl::SslStream::new(ssl, state.socket) {
             Ok(stream) => stream,
             Err(err) => {
                 log::error!("failed to create SslStream using ssl and connection socket - {err}");
@@ -381,41 +387,39 @@ impl AcceptBuilder {
 
         match result {
             Ok(Ok(())) => {
-                if secure_sender.send(Ok(secure_stream)).await.is_err() && debug {
+                if secure_sender.send(Ok(secure_stream)).await.is_err() && flags.is_debug {
                     log::error!("detected closed connection channel");
                 }
             }
             Ok(Err(err)) => {
-                if debug {
+                if flags.is_debug {
                     log::error!("https handshake failed - {err}");
                 }
             }
             Err(_) => {
-                if debug {
+                if flags.is_debug {
                     log::error!("https handshake timeout");
                 }
             }
         }
 
-        drop(accept_counter); // decrease reference count
+        drop(state.accept_counter); // decrease reference count
     }
 
     async fn do_accept_tls_optional(
-        socket: InsecureClientStream,
-        acceptor: Arc<Mutex<SslAcceptor>>,
-        accept_counter: Arc<()>,
-        debug: bool,
+        state: AcceptState,
+        flags: AcceptFlags,
         secure_sender: ClientSender,
         insecure_sender: InsecureClientSender,
     ) {
         let client_initiates_handshake = {
             #[cfg(feature = "rate-limited-stream")]
-            let socket = socket.inner();
+            let socket_ref = state.socket.inner();
 
             #[cfg(not(feature = "rate-limited-stream"))]
-            let socket = &socket;
+            let socket_ref = &state.socket;
 
-            match Self::wait_for_client_tls_handshake(socket).await {
+            match Self::wait_for_client_tls_handshake(socket_ref).await {
                 Ok(initiates_handshake) => initiates_handshake,
                 Err(err) => {
                     log::error!("error checking for TLS handshake: {err}");
@@ -425,16 +429,16 @@ impl AcceptBuilder {
         };
 
         if !client_initiates_handshake {
-            let insecure_stream = Box::pin(socket);
+            let insecure_stream = Box::pin(state.socket);
 
-            if insecure_sender.send(Ok(insecure_stream)).await.is_err() && debug {
+            if insecure_sender.send(Ok(insecure_stream)).await.is_err() && flags.is_debug {
                 log::error!("detected closed connection channel")
             }
 
             return;
         }
 
-        Self::do_accept_tls(socket, acceptor, accept_counter, debug, secure_sender).await
+        Self::do_accept_tls(state, flags, secure_sender).await
     }
 
     async fn wait_for_client_tls_handshake(incoming_stream: &TcpStream) -> Result<bool, Error> {
-- 
2.39.2



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[pve-devel] [PATCH v1 proxmox 2/3] rest-server: connection: log peer address on error

[Max Carrara]

.. in order to make debugging easier and logs more helpful.

Signed-off-by: Max Carrara <m.carrara@proxmox.com>
---
 proxmox-rest-server/src/connection.rs | 42 ++++++++++++++++-----------
 1 file changed, 25 insertions(+), 17 deletions(-)

diff --git a/proxmox-rest-server/src/connection.rs b/proxmox-rest-server/src/connection.rs
index 243348c0..470021d7 100644
--- a/proxmox-rest-server/src/connection.rs
+++ b/proxmox-rest-server/src/connection.rs
@@ -2,6 +2,7 @@
 //!
 //! Hyper building block.
 
+use std::net::SocketAddr;
 use std::os::unix::io::AsRawFd;
 use std::path::PathBuf;
 use std::pin::Pin;
@@ -257,6 +258,7 @@ impl From<(ClientSender, InsecureClientSender)> for Sender {
 
 struct AcceptState {
     pub socket: InsecureClientStream,
+    pub peer: SocketAddr,
     pub acceptor: Arc<Mutex<SslAcceptor>>,
     pub accept_counter: Arc<()>,
 }
@@ -276,9 +278,9 @@ impl AcceptBuilder {
         let mut shutdown_future = crate::shutdown_future().fuse();
 
         loop {
-            let socket = futures::select! {
+            let (socket, peer) = futures::select! {
                 res = self.try_setup_socket(&listener).fuse() => match res {
-                    Ok(socket) => socket,
+                    Ok(socket_peer) => socket_peer,
                     Err(err) => {
                         log::error!("couldn't set up TCP socket: {err}");
                         continue;
@@ -291,12 +293,13 @@ impl AcceptBuilder {
             let accept_counter = Arc::clone(&accept_counter);
 
             if Arc::strong_count(&accept_counter) > self.max_pending_accepts {
-                log::error!("connection rejected - too many open connections");
+                log::error!("[{peer}] connection rejected - too many open connections");
                 continue;
             }
 
             let state = AcceptState {
                 socket,
+                peer,
                 acceptor,
                 accept_counter,
             };
@@ -328,7 +331,7 @@ impl AcceptBuilder {
     async fn try_setup_socket(
         &self,
         listener: &TcpListener,
-    ) -> Result<InsecureClientStream, Error> {
+    ) -> Result<(InsecureClientStream, SocketAddr), Error> {
         let (socket, peer) = match listener.accept().await {
             Ok(connection) => connection,
             Err(error) => {
@@ -338,10 +341,10 @@ impl AcceptBuilder {
 
         socket
             .set_nodelay(true)
-            .context("error while setting TCP_NODELAY on socket")?;
+            .with_context(|| format!("[{peer}] error while setting TCP_NODELAY on socket"))?;
 
         proxmox_sys::linux::socket::set_tcp_keepalive(socket.as_raw_fd(), self.tcp_keepalive_time)
-            .context("error while setting SO_KEEPALIVE on socket")?;
+            .with_context(|| format!("[{peer}] error while setting SO_KEEPALIVE on socket"))?;
 
         #[cfg(feature = "rate-limited-stream")]
         let socket = match self.lookup_rate_limiter.clone() {
@@ -349,13 +352,12 @@ impl AcceptBuilder {
             None => RateLimitedStream::with_limiter(socket, None, None),
         };
 
-        #[cfg(not(feature = "rate-limited-stream"))]
-        let _peer = peer;
-
-        Ok(socket)
+        Ok((socket, peer))
     }
 
     async fn do_accept_tls(state: AcceptState, flags: AcceptFlags, secure_sender: ClientSender) {
+        let peer = state.peer;
+
         let ssl = {
             // limit acceptor_guard scope
             // Acceptor can be reloaded using the command socket "reload-certificate" command
@@ -364,7 +366,9 @@ impl AcceptBuilder {
             match openssl::ssl::Ssl::new(acceptor_guard.context()) {
                 Ok(ssl) => ssl,
                 Err(err) => {
-                    log::error!("failed to create Ssl object from Acceptor context - {err}");
+                    log::error!(
+                        "[{peer}] failed to create Ssl object from Acceptor context - {err}"
+                    );
                     return;
                 }
             }
@@ -373,7 +377,9 @@ impl AcceptBuilder {
         let secure_stream = match tokio_openssl::SslStream::new(ssl, state.socket) {
             Ok(stream) => stream,
             Err(err) => {
-                log::error!("failed to create SslStream using ssl and connection socket - {err}");
+                log::error!(
+                    "[{peer}] failed to create SslStream using ssl and connection socket - {err}"
+                );
                 return;
             }
         };
@@ -388,17 +394,17 @@ impl AcceptBuilder {
         match result {
             Ok(Ok(())) => {
                 if secure_sender.send(Ok(secure_stream)).await.is_err() && flags.is_debug {
-                    log::error!("detected closed connection channel");
+                    log::error!("[{peer}] detected closed connection channel");
                 }
             }
             Ok(Err(err)) => {
                 if flags.is_debug {
-                    log::error!("https handshake failed - {err}");
+                    log::error!("[{peer}] https handshake failed - {err}");
                 }
             }
             Err(_) => {
                 if flags.is_debug {
-                    log::error!("https handshake timeout");
+                    log::error!("[{peer}] https handshake timeout");
                 }
             }
         }
@@ -412,6 +418,8 @@ impl AcceptBuilder {
         secure_sender: ClientSender,
         insecure_sender: InsecureClientSender,
     ) {
+        let peer = state.peer;
+
         let client_initiates_handshake = {
             #[cfg(feature = "rate-limited-stream")]
             let socket_ref = state.socket.inner();
@@ -422,7 +430,7 @@ impl AcceptBuilder {
             match Self::wait_for_client_tls_handshake(socket_ref).await {
                 Ok(initiates_handshake) => initiates_handshake,
                 Err(err) => {
-                    log::error!("error checking for TLS handshake: {err}");
+                    log::error!("[{peer}] error checking for TLS handshake: {err}");
                     return;
                 }
             }
@@ -432,7 +440,7 @@ impl AcceptBuilder {
             let insecure_stream = Box::pin(state.socket);
 
             if insecure_sender.send(Ok(insecure_stream)).await.is_err() && flags.is_debug {
-                log::error!("detected closed connection channel")
+                log::error!("[{peer}] detected closed connection channel")
             }
 
             return;
-- 
2.39.2



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[pve-devel] [PATCH v1 proxmox 3/3] fix #5105: rest-server: connection: overhaul TLS handshake check logic

[Max Carrara]

On rare occasions, the TLS "client hello" message [1] is delayed after
a connection with the server was established, which causes HTTPS
requests to fail before TLS was even negotiated. In these cases, the
server would incorrectly respond with "HTTP/1.1 400 Bad Request"
instead of closing the connection (or similar).

The reasons for the "client hello" being delayed seem to vary; one
user noticed that the issue went away completely after they turned off
UFW [2]. Another user noticed (during private correspondence) that the
issue only appeared when connecting to their PBS instance via WAN, but
not from within their VPN. In the WAN case a firewall was also
present. The same user kindly provided tcpdumps and strace logs on
request.

The issue was finally reproduced with the following Python script:

  import socket
  import time

  HOST: str = ...
  PORT: int = ...

  with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
      sock.connect((HOST, PORT))
      time.sleep(1.5) # simulate firewall / proxy / etc. delay
      sock.sendall(b"\x16\x03\x01\x02\x00")
      data = sock.recv(256)
      print(data)

The additional delay before sending the first 5 bytes of the "client
hello" message causes the handshake checking logic to incorrectly fall
back to plain HTTP.

All of this is fixed by the following:

  1. Increase the timeout duration to 10 seconds (from 1)
  2. Instead of falling back to plain HTTP, refuse to accept the
     connection if the TLS handshake wasn't initiated before the
     timeout limit is reached
  3. Only accept plain HTTP if the first 5 bytes do not correspond to
     a TLS handshake fragment [3]
  4. Do not take the last number of bytes that were in the buffer into
     account; instead, only perform the actual handshake check if
     5 bytes are in the peek buffer

Regarding 1.: This should be generous enough for any client to be able
to initiate a TLS handshake, despite its surrounding circumstances.

Regarding 4.: While this is not 100% related to the issue, altering
this condition simplifies the overall logic and removes a potential
source of unintended behaviour.

[1]: https://www.rfc-editor.org/rfc/rfc8446.html#section-4.1.2
[2]: https://forum.proxmox.com/threads/disable-default-http-redirects-on-8007.142312/post-675352
[3]: https://www.rfc-editor.org/rfc/rfc8446.html#section-4.1.2

Signed-off-by: Max Carrara <m.carrara@proxmox.com>
Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=5105
---
 proxmox-rest-server/src/connection.rs | 69 ++++++++++++---------------
 1 file changed, 31 insertions(+), 38 deletions(-)

diff --git a/proxmox-rest-server/src/connection.rs b/proxmox-rest-server/src/connection.rs
index 470021d7..a2d54b18 100644
--- a/proxmox-rest-server/src/connection.rs
+++ b/proxmox-rest-server/src/connection.rs
@@ -418,70 +418,63 @@ impl AcceptBuilder {
         secure_sender: ClientSender,
         insecure_sender: InsecureClientSender,
     ) {
-        let peer = state.peer;
+        const CLIENT_HANDSHAKE_TIMEOUT: Duration = Duration::from_secs(10);
 
-        let client_initiates_handshake = {
-            #[cfg(feature = "rate-limited-stream")]
-            let socket_ref = state.socket.inner();
+        let peer = state.peer;
 
-            #[cfg(not(feature = "rate-limited-stream"))]
-            let socket_ref = &state.socket;
+        #[cfg(feature = "rate-limited-stream")]
+        let socket_ref = state.socket.inner();
 
-            match Self::wait_for_client_tls_handshake(socket_ref).await {
-                Ok(initiates_handshake) => initiates_handshake,
-                Err(err) => {
-                    log::error!("[{peer}] error checking for TLS handshake: {err}");
-                    return;
-                }
-            }
-        };
+        #[cfg(not(feature = "rate-limited-stream"))]
+        let socket_ref = &state.socket;
 
-        if !client_initiates_handshake {
-            let insecure_stream = Box::pin(state.socket);
+        let handshake_res =
+            Self::wait_for_client_tls_handshake(socket_ref, CLIENT_HANDSHAKE_TIMEOUT).await;
 
-            if insecure_sender.send(Ok(insecure_stream)).await.is_err() && flags.is_debug {
-                log::error!("[{peer}] detected closed connection channel")
+        match handshake_res {
+            Ok(true) => {
+                Self::do_accept_tls(state, flags, secure_sender).await;
             }
+            Ok(false) => {
+                let insecure_stream = Box::pin(state.socket);
 
-            return;
+                if let Err(send_err) = insecure_sender.send(Ok(insecure_stream)).await {
+                    log::error!("[{peer}] failed to accept connection - connection channel closed: {send_err}");
+                }
+            }
+            Err(err) => {
+                log::error!("[{peer}] failed to check for TLS handshake: {err}");
+            }
         }
-
-        Self::do_accept_tls(state, flags, secure_sender).await
     }
 
-    async fn wait_for_client_tls_handshake(incoming_stream: &TcpStream) -> Result<bool, Error> {
-        const MS_TIMEOUT: u64 = 1000;
-        const BYTES_BUF_SIZE: usize = 128;
+    async fn wait_for_client_tls_handshake(
+        incoming_stream: &TcpStream,
+        timeout: Duration,
+    ) -> Result<bool, Error> {
+        const HANDSHAKE_BYTES_LEN: usize = 5;
 
-        let mut buf = [0; BYTES_BUF_SIZE];
-        let mut last_peek_size = 0;
+        let mut buf = [0; HANDSHAKE_BYTES_LEN];
 
         let future = async {
             loop {
                 let peek_size = incoming_stream
                     .peek(&mut buf)
                     .await
-                    .context("couldn't peek into incoming tcp stream")?;
-
-                if contains_tls_handshake_fragment(&buf) {
-                    return Ok(true);
-                }
+                    .context("couldn't peek into incoming TCP stream")?;
 
-                // No more new data came in
-                if peek_size == last_peek_size {
-                    return Ok(false);
+                if peek_size == HANDSHAKE_BYTES_LEN {
+                    return Ok(contains_tls_handshake_fragment(&buf));
                 }
 
-                last_peek_size = peek_size;
-
                 // explicitly yield to event loop; this future otherwise blocks ad infinitum
                 tokio::task::yield_now().await;
             }
         };
 
-        tokio::time::timeout(Duration::from_millis(MS_TIMEOUT), future)
+        tokio::time::timeout(timeout, future)
             .await
-            .unwrap_or(Ok(false))
+            .context("timed out while waiting for client to initiate TLS handshake")?
     }
 }
 
-- 
2.39.2



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Re: [pve-devel] [PATCH v1 proxmox 0/3] Fix #5105: Overhaul TLS Handshake Checking Logic

[Max Carrara]

On Fri Jul 5, 2024 at 6:20 PM CEST, Max Carrara wrote:
> Fix #5105: Overhaul TLS Handshake Checking Logic
> ================================================

Oh, woops - this should've gone to pbs-devel. Will send it there;
disregard this series, please. Was a bit too quick on the trigger on
Friday it seems ;)

>
> This series fixes bug #5105 [1] by overhauling the TLS handshake
> checking logic, which is performed when using a connection acceptor
> variant with optional TLS.
>
> In the case of PBS (the only place where this is used, to my knowledge),
> any requests made over plain HTTP are redirected to the same host, but
> clients are instructed to use HTTPS instead.
>
> The TLS handshake checking logic determines whether the client uses HTTP
> or HTTPS by peeking into the stream buffer -- if the first 5 received
> bytes look like a TLS handshake fragment, the connection is passed on to
> OpenSSL before being accepted. Otherwise the connection is assumed to be
> unencrypted, i.e. plain HTTP.
>
> However, this logic contains two errors:
>
>   1. The timeout duration is too short - one second is too little
>   2. When a timeout occurs, the connection is assumed to be unencrypted
>      (and thus plain HTTP)
>
> The patches 01 and 02 are mainly done in preparation for patch 03 (which
> contains the actual fix), improving the overall quality of the code and
> including the peer's address in error logs.
>
> Please see the individual patches for more information.
>
> Special thanks go to Stefan Hanreich whose advice helped identifying
> many individual puzzle pieces comprising this issue.
>
> References
> ----------
>
> [1]: https://bugzilla.proxmox.com/show_bug.cgi?id=5105
>
> Summary of Changes
> ------------------
>
> Max Carrara (3):
>   rest-server: connection: clean up accept data flow
>   rest-server: connection: log peer address on error
>   fix #5105: rest-server: connection: overhaul TLS handshake check logic
>
>  proxmox-rest-server/src/connection.rs | 165 +++++++++++++-------------
>  1 file changed, 85 insertions(+), 80 deletions(-)



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