From 6204fc33f022318845e3c090a73f064c908b92c3 Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Thu, 30 Apr 2020 12:24:04 +0200
Subject: [PATCH] p2p: add low port check in dialer

We already have a check like this for UDP ports, add a similar one in
the dialer. This prevents dials to port zero and it's also an extra
layer of protection against spamming HTTP servers.
---
 p2p/dial.go | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/p2p/dial.go b/p2p/dial.go
index d190e866af..c3c4cace9c 100644
--- a/p2p/dial.go
+++ b/p2p/dial.go
@@ -78,6 +78,7 @@ var (
 	errAlreadyConnected = errors.New("already connected")
 	errRecentlyDialed   = errors.New("recently dialed")
 	errNotWhitelisted   = errors.New("not contained in netrestrict whitelist")
+	errLowPort          = errors.New("TCP port too low")
 )
 
 // dialer creates outbound connections and submits them into Server.
@@ -388,6 +389,9 @@ func (d *dialScheduler) checkDial(n *enode.Node) error {
 	if n.ID() == d.self {
 		return errSelf
 	}
+	if n.IP() != nil && n.TCP() < 1024 {
+		return errLowPort
+	}
 	if _, ok := d.dialing[n.ID()]; ok {
 		return errAlreadyDialing
 	}
@@ -474,15 +478,13 @@ type dialError struct {
 }
 
 func (t *dialTask) run(d *dialScheduler) {
-	if t.dest.Incomplete() {
-		if !t.resolve(d) {
-			return
-		}
+	if t.needResolve() && !t.resolve(d) {
+		return
 	}
 
 	err := t.dial(d, t.dest)
 	if err != nil {
-		// Try resolving the ID of static nodes if dialing failed.
+		// For static nodes, resolve one more time if dialing fails.
 		if _, ok := err.(*dialError); ok && t.flags&staticDialedConn != 0 {
 			if t.resolve(d) {
 				t.dial(d, t.dest)
@@ -491,6 +493,10 @@ func (t *dialTask) run(d *dialScheduler) {
 	}
 }
 
+func (t *dialTask) needResolve() bool {
+	return t.flags&staticDialedConn != 0 && t.dest.IP() == nil
+}
+
 // resolve attempts to find the current endpoint for the destination
 // using discovery.
 //