plugin/loop: avoid panic on invalid server block (#7568)

Ignore invalid ServerBlockKeys in loop plugin that fail
normalization. Retain the default “.” zone instead of
indexing into an empty slice. This prevents an
index-out-of-range panic triggered by malformed
inputs such as "unix://".

Added tests to validate and increase test coverage.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/loop/loop_test.go

@@ -1,6 +1,13 @@
 package loop
 
-import "testing"
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
+)
 
 func TestLoop(t *testing.T) {
 	l := New(".")
@@ -9,3 +16,67 @@ func TestLoop(t *testing.T) {
 		t.Errorf("Failed to inc loop, expected %d, got %d", 1, l.seen())
 	}
 }
+
+func TestLoop_NonHINFO(t *testing.T) {
+	l := New(".")
+	l.Next = test.NextHandler(dns.RcodeSuccess, nil)
+	w := &test.ResponseWriter{}
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeA)
+	if rc, _ := l.ServeDNS(context.Background(), w, m); rc != dns.RcodeSuccess {
+		t.Fatalf("expected %d, got %d", dns.RcodeSuccess, rc)
+	}
+}
+
+func TestLoop_Disabled(t *testing.T) {
+	l := New(".")
+	l.setDisabled()
+	l.Next = test.NextHandler(dns.RcodeSuccess, nil)
+	w := &test.ResponseWriter{}
+	m := new(dns.Msg)
+	m.SetQuestion("example.org.", dns.TypeHINFO)
+	if rc, _ := l.ServeDNS(context.Background(), w, m); rc != dns.RcodeSuccess {
+		t.Fatalf("expected %d, got %d", dns.RcodeSuccess, rc)
+	}
+}
+
+func TestLoop_ZoneMismatch(t *testing.T) {
+	l := New("example.org.")
+	l.Next = test.NextHandler(dns.RcodeSuccess, nil)
+	w := &test.ResponseWriter{}
+	m := new(dns.Msg)
+	m.SetQuestion("a.example.com.", dns.TypeHINFO)
+	if rc, _ := l.ServeDNS(context.Background(), w, m); rc != dns.RcodeSuccess {
+		t.Fatalf("expected %d, got %d", dns.RcodeSuccess, rc)
+	}
+}
+
+func TestLoop_MatchAndInc(t *testing.T) {
+	l := New(".")
+	l.Next = test.NextHandler(dns.RcodeSuccess, nil)
+	l.qname = "1.2.example.org."
+	w := &test.ResponseWriter{}
+	m := new(dns.Msg)
+	m.SetQuestion(l.qname, dns.TypeHINFO)
+
+	if l.seen() != 0 {
+		t.Fatalf("expected initial seen 0, got %d", l.seen())
+	}
+	if _, err := l.ServeDNS(context.Background(), w, m); err != nil {
+		t.Fatalf("ServeDNS returned error: %v", err)
+	}
+	if l.seen() != 1 {
+		t.Fatalf("expected seen to be 1 after matching query, got %d", l.seen())
+	}
+}
+
+func TestLoop_SetAddressAndName(t *testing.T) {
+	l := New(".")
+	l.setAddress("127.0.0.1:1053")
+	if l.address() != "127.0.0.1:1053" {
+		t.Fatalf("expected address to be set")
+	}
+	if l.Name() != "loop" {
+		t.Fatalf("expected Name() to be 'loop', got %q", l.Name())
+	}
+}

plugin/loop/setup.go

@@ -73,7 +73,10 @@ func parse(c *caddy.Controller) (*Loop, error) {
 		}
 
 		if len(c.ServerBlockKeys) > 0 {
-			zones = plugin.Host(c.ServerBlockKeys[0]).NormalizeExact()
+			z := plugin.Host(c.ServerBlockKeys[0]).NormalizeExact()
+			if len(z) > 0 {
+				zones = z
+			}
 		}
 	}
 	return New(zones[0]), nil

plugin/loop/setup_test.go

@@ -17,3 +17,32 @@ func TestSetup(t *testing.T) {
 		t.Fatal("Expected errors, but got none")
 	}
 }
+
+func TestParseServerBlockKeys(t *testing.T) {
+	tests := []struct {
+		name   string
+		key    string
+		want   string
+		wantOk bool
+	}{
+		{name: "valid domain", key: "example.org", want: "example.org.", wantOk: true},
+		{name: "invalid scheme", key: "unix://", want: ".", wantOk: true},
+		{name: "empty", key: "", want: ".", wantOk: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c := caddy.NewTestController("dns", `loop`)
+			if tt.key != "" {
+				c.ServerBlockKeys = []string{tt.key}
+			}
+			l, err := parse(c)
+			if (err == nil) != tt.wantOk {
+				t.Fatalf("parse err=%v, wantOk=%v", err, tt.wantOk)
+			}
+			if l.zone != tt.want {
+				t.Fatalf("zone=%q, want %q", l.zone, tt.want)
+			}
+		})
+	}
+}