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TCP Proxy: Fix TLS passthrough for fragmented ClientHello. #11843

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TCP Proxy: Fix TLS passthrough for fragmented ClientHello. #11843

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35 changes: 31 additions & 4 deletions pkg/tcpproxy/tcp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,11 @@ type TCPProxy struct {
Default *TCPServer
}

var (
tlsHeaderLength = 5
tlsMaxMessageLength = 16384
)

// Get returns the TCPServer to use for a given host.
func (p *TCPProxy) Get(host string) *TCPServer {
if p.ServerList == nil {
Expand All @@ -59,15 +64,37 @@ func (p *TCPProxy) Get(host string) *TCPServer {
// and open a connection to the passthrough server.
func (p *TCPProxy) Handle(conn net.Conn) {
defer conn.Close()
// See: https://www.ibm.com/docs/en/ztpf/1.1.0.15?topic=sessions-ssl-record-format
data := make([]byte, 16384)

length, err := conn.Read(data)
// It appears that the ClientHello must fit into *one* TLSPlaintext message:
// When a client first connects to a server, it is REQUIRED to send the ClientHello as its first TLS message.
// Source: https://datatracker.ietf.org/doc/html/rfc8446#section-4.1.2

// length: The length (in bytes) of the following TLSPlaintext.fragment. The length MUST NOT exceed 2^14 bytes.
// An endpoint that receives a record that exceeds this length MUST terminate the connection with a "record_overflow" alert.
// Source: https://datatracker.ietf.org/doc/html/rfc8446#section-5.1
// bytes 0 : content type
// bytes 1-2: legacy version
// bytes 3-4: length
// bytes 5+ : message
// https://en.wikipedia.org/wiki/Transport_Layer_Security#TLS_record
// Thus, we need to allocate 5 + 16384 bytes
data := make([]byte, tlsHeaderLength+tlsMaxMessageLength)

length, err := io.ReadAtLeast(conn, data, tlsHeaderLength)
if err != nil {
klog.V(4).ErrorS(err, "Error reading data from the connection")
return
}

// otherwise, ReadAtLeast may produce an index out of bounds
clientHelloLength := min(int(data[3])<<8+int(data[4]), tlsMaxMessageLength)

bLength, err := io.ReadAtLeast(conn, data[length:], tlsHeaderLength+clientHelloLength-length)
if err != nil {
klog.V(4).ErrorS(err, fmt.Sprintf("Error reading ClientHello of length %d from the connection", clientHelloLength))
return
}
length += bLength

proxy := p.Default
hostname, err := parser.GetHostname(data)
if err == nil {
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