[pbs-devel] [PATCH proxmox] rest-server: connection: fix busy waiting on closed connections pre tls

[Dominik Csapak]

when a connection is closed before we have enough data to determine
if it's tls or not, the socket stays in a readable state.

Sadly, the tokio timeout we use here gets starved by the async_io
callback.

To fix this, save the amount of bytes peek returned and if they did not
change between invocations of the callback, we assume that the
connection was closed and exit with an error.

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
---
 proxmox-rest-server/src/connection.rs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/proxmox-rest-server/src/connection.rs b/proxmox-rest-server/src/connection.rs
index 3815a8f4..4fed84b1 100644
--- a/proxmox-rest-server/src/connection.rs
+++ b/proxmox-rest-server/src/connection.rs
@@ -477,6 +477,7 @@ impl AcceptBuilder {
         const HANDSHAKE_BYTES_LEN: usize = 5;
 
         let future = async {
+            let mut old_peek_len = 0;
             incoming_stream
                 .async_io(tokio::io::Interest::READABLE, || {
                     let mut buf = [0; HANDSHAKE_BYTES_LEN];
@@ -491,6 +492,8 @@ impl AcceptBuilder {
 
                     let peek_res = std_stream.peek(&mut buf);
 
+                    std_stream.read(buf)
+
                     match peek_res {
                         // If we didn't get enough bytes, raise an EAGAIN / EWOULDBLOCK which tells
                         // tokio to await the readiness of the socket again. This should normally
@@ -500,7 +503,14 @@ impl AcceptBuilder {
                         // This means we will peek into the stream's queue until we got
                         // HANDSHAKE_BYTE_LEN bytes or an error.
                         Ok(peek_len) if peek_len < HANDSHAKE_BYTES_LEN => {
-                            Err(io::ErrorKind::WouldBlock.into())
+                            // if we detect the same peek len again but still got a readable
+                            // stream, the connection was probably closed, so abort here
+                            if peek_len == old_peek_len {
+                                Err(io::ErrorKind::UnexpectedEof.into())
+                            } else {
+                                old_peek_len = peek_len;
+                                Err(io::ErrorKind::WouldBlock.into())
+                            }
                         }
                         // Either we got Ok(HANDSHAKE_BYTES_LEN) or some error.
                         res => res.map(|_| contains_tls_handshake_fragment(&buf)),
-- 
2.39.5