brontide: set read deadlines on socket during initial handshake

This commit fixes a lingering issue within lnd, which can cause a
server to freeze up, and not handle any incoming connections properly,
or cause clients to freeze and not return in a timely manner from a
failed connection attempt.

To avoid this, each time we need to read from the socket during the
initial brontide handshake, we add a 15 second read deadline. If we
don’t successfully read from the buffer during that time frame, then
the Read method will return a timeout error.

With this in place, we ensure that the main listener goroutine will
never be blocked waiting on a remote party to write ActOne.

brontide/conn.go

@@ -55,6 +55,11 @@ func Dial(localPriv *btcec.PrivateKey, netAddr *lnwire.NetAddress) (*Conn, error
 		return nil, err
 	}
 
+	// We'll ensure that we get ActTwo from the remote peer in a timely
+	// manner. If they don't respond within 15 seconds, then we'll kill the
+	// connection.
+	conn.SetReadDeadline(time.Now().Add(time.Second * 15))
+
 	// If the first act was successful (we know that address is actually
 	// remotePub), then read the second act after which we'll be able to
 	// send our static public key to the remote peer with strong forward
@@ -81,6 +86,10 @@ func Dial(localPriv *btcec.PrivateKey, netAddr *lnwire.NetAddress) (*Conn, error
 		return nil, err
 	}
 
+	// We'll reset the deadline as it's no longer critical beyond the
+	// initial handshake.
+	conn.SetReadDeadline(time.Time{})
+
 	return b, nil
 }
 

brontide/listener.go

@@ -3,6 +3,7 @@ package brontide
 import (
 	"io"
 	"net"
+	"time"
 
 	"github.com/roasbeef/btcd/btcec"
 )
@@ -59,6 +60,11 @@ func (l *Listener) Accept() (net.Conn, error) {
 		noise: NewBrontideMachine(false, l.localStatic, nil),
 	}
 
+	// We'll ensure that we get ActOne from the remote peer in a timely
+	// manner. If they don't respond within 15 seconds, then we'll kill the
+	// connection.
+	conn.SetReadDeadline(time.Now().Add(time.Second * 15))
+
 	// Attempt to carry out the first act of the handshake protocol. If the
 	// connecting node doesn't know our long-term static public key, then
 	// this portion will fail with a non-nil error.
@@ -84,6 +90,11 @@ func (l *Listener) Accept() (net.Conn, error) {
 		return nil, err
 	}
 
+	// We'll ensure that we get ActTwo from the remote peer in a timely
+	// manner. If they don't respond within 15 seconds, then we'll kill the
+	// connection.
+	conn.SetReadDeadline(time.Now().Add(time.Second * 15))
+
 	// Finally, finish the handshake processes by reading and decrypting
 	// the connection peer's static public key. If this succeeds then both
 	// sides have mutually authenticated each other.
@@ -97,6 +108,10 @@ func (l *Listener) Accept() (net.Conn, error) {
 		return nil, err
 	}
 
+	// We'll reset the deadline as it's no longer critical beyond the
+	// initial handshake.
+	conn.SetReadDeadline(time.Time{})
+
 	return brontideConn, nil
 }