From d1ea70d6884696ca4ff23e791ece3a05ede996a3 Mon Sep 17 00:00:00 2001
From: Cuong Manh Le <cuong@windscribe.com>
Date: Mon, 20 Apr 2026 14:28:27 +0700
Subject: [PATCH] fix: prevent panic on network change during SetSelfIP

SetSelfIP unconditionally accessed t.dhcp, but t.dhcp is only
initialized when DHCP discovery is enabled. A network change event
can fire SetSelfIP regardless of the discovery configuration,
causing a nil pointer dereference.

Guard the t.dhcp access with a nil check so the self IP is still
updated on the Table even when DHCP discovery is disabled.
---
 internal/clientinfo/client_info.go      |  6 ++-
 internal/clientinfo/client_info_test.go | 55 +++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/internal/clientinfo/client_info.go b/internal/clientinfo/client_info.go
index f69b670..acae754 100644
--- a/internal/clientinfo/client_info.go
+++ b/internal/clientinfo/client_info.go
@@ -173,8 +173,10 @@ func (t *Table) SetSelfIP(ip string) {
 	t.selfIPLock.Lock()
 	defer t.selfIPLock.Unlock()
 	t.selfIP = ip
-	t.dhcp.selfIP = t.selfIP
-	t.dhcp.addSelf()
+	if t.dhcp != nil {
+		t.dhcp.selfIP = t.selfIP
+		t.dhcp.addSelf()
+	}
 }
 
 // initSelfDiscover initializes necessary client metadata for self query.
diff --git a/internal/clientinfo/client_info_test.go b/internal/clientinfo/client_info_test.go
index b5bdfa5..a1e22a6 100644
--- a/internal/clientinfo/client_info_test.go
+++ b/internal/clientinfo/client_info_test.go
@@ -1,9 +1,64 @@
 package clientinfo
 
 import (
+	"sync"
 	"testing"
 )
 
+// TestTable_SetSelfIP_NilDHCP ensures SetSelfIP does not panic when t.dhcp is
+// nil, which happens when DHCP discovery is disabled and the network-change
+// callback fires before or without initialisation.
+func TestTable_SetSelfIP_NilDHCP(t *testing.T) {
+	table := &Table{} // dhcp is nil
+	// Must not panic.
+	table.SetSelfIP("192.168.1.1")
+	if got := table.SelfIP(); got != "192.168.1.1" {
+		t.Fatalf("SelfIP() = %q, want %q", got, "192.168.1.1")
+	}
+}
+
+// TestTable_SetSelfIP_UpdatesDHCP ensures SetSelfIP propagates the new IP to
+// the dhcp discover and calls addSelf when dhcp is initialised.
+func TestTable_SetSelfIP_UpdatesDHCP(t *testing.T) {
+	table := &Table{
+		dhcp: &dhcp{selfIP: "10.0.0.1"},
+	}
+	table.SetSelfIP("10.0.0.2")
+	if got := table.SelfIP(); got != "10.0.0.2" {
+		t.Fatalf("SelfIP() = %q, want %q", got, "10.0.0.2")
+	}
+	if table.dhcp.selfIP != "10.0.0.2" {
+		t.Fatalf("dhcp.selfIP = %q, want %q", table.dhcp.selfIP, "10.0.0.2")
+	}
+}
+
+// TestTable_SetSelfIP_Concurrent ensures concurrent calls to SetSelfIP do not
+// race, regardless of whether dhcp is nil or not.
+func TestTable_SetSelfIP_Concurrent(t *testing.T) {
+	for _, tc := range []struct {
+		name  string
+		table *Table
+	}{
+		{"nil dhcp", &Table{}},
+		{"with dhcp", &Table{dhcp: &dhcp{}}},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			var wg sync.WaitGroup
+			for range 10 {
+				wg.Add(1)
+				go func() {
+					defer wg.Done()
+					tc.table.SetSelfIP("192.168.1.1")
+					_ = tc.table.SelfIP()
+				}()
+			}
+			wg.Wait()
+		})
+	}
+}
+
 func Test_normalizeIP(t *testing.T) {
 	tests := []struct {
 		name string