add padding_auth plugin

plugin/enabled_plugins.go

@@ -64,6 +64,7 @@ import (
 
 	// executable and matcher
 	_ "github.com/IrineSistiana/mosdns/v5/plugin/mark"
+	_ "github.com/IrineSistiana/mosdns/v5/plugin/padding_auth"
 
 	// server
 	_ "github.com/IrineSistiana/mosdns/v5/plugin/server/http_server"

plugin/padding_auth/padding_auth.go

@@ -0,0 +1,119 @@
+/*
+ * Copyright (C) 2020-2022, IrineSistiana
+ *
+ * This file is part of mosdns.
+ *
+ * mosdns is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * mosdns is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package padding_auth
+
+import (
+	"bytes"
+	"context"
+	"crypto/md5"
+
+	"github.com/IrineSistiana/mosdns/v5/pkg/dnsutils"
+	"github.com/IrineSistiana/mosdns/v5/pkg/query_context"
+	"github.com/IrineSistiana/mosdns/v5/plugin/executable/sequence"
+	"github.com/miekg/dns"
+)
+
+const PluginType = "padding_auth"
+
+func init() {
+	sequence.MustRegExecQuickSetup(PluginType, func(_ sequence.BQ, args string) (any, error) {
+		return newPaddingAuth(args), nil
+	})
+	sequence.MustRegMatchQuickSetup(PluginType, func(_ sequence.BQ, args string) (sequence.Matcher, error) {
+		return newPaddingAuth(args), nil
+	})
+}
+
+var _ sequence.RecursiveExecutable = (*paddingAuth)(nil)
+var _ sequence.Matcher = (*paddingAuth)(nil)
+
+type paddingAuth struct {
+	key []byte
+}
+
+func (m *paddingAuth) Match(_ context.Context, qCtx *query_context.Context) (bool, error) {
+	q := qCtx.Q()
+
+	opt := q.IsEdns0()
+	if opt == nil {
+		return false, nil
+	}
+	for i, optRR := range opt.Option {
+		if padding, ok := optRR.(*dns.EDNS0_PADDING); ok {
+			if bytes.Equal(padding.Padding, m.key) {
+				opt.Option = append(opt.Option[:i], opt.Option[i+1:]...)
+				return true, nil
+			}
+		}
+	}
+
+	return false, nil
+}
+
+func (m *paddingAuth) Exec(ctx context.Context, qCtx *query_context.Context, next sequence.ChainWalker) error {
+	upgraded := m.addPadding(qCtx.Q())
+	err := next.ExecNext(ctx, qCtx)
+	if err != nil {
+		return err
+	}
+
+	if r := qCtx.R(); r != nil {
+		if upgraded {
+			dnsutils.RemoveEDNS0(r)
+		}
+	}
+	return nil
+}
+
+func (m *paddingAuth) addPadding(q *dns.Msg) (upgraded bool) {
+	padding := &dns.EDNS0_PADDING{
+		Padding: append([]byte(nil), m.key...),
+	}
+
+	opt := q.IsEdns0()
+	if opt == nil {
+		upgraded = true
+		o := new(dns.OPT)
+		o.SetUDPSize(dns.MinMsgSize)
+		o.Hdr.Name = "."
+		o.Hdr.Rrtype = dns.TypeOPT
+		q.Extra = append(q.Extra, o)
+		return
+	}
+
+	var overwritten bool
+	for o := range opt.Option {
+		if opt.Option[o].Option() == dns.EDNS0PADDING {
+			opt.Option[o] = padding
+			overwritten = true
+			break
+		}
+	}
+	if !overwritten {
+		opt.Option = append(opt.Option, padding)
+	}
+	return
+}
+
+// newPaddingAuth format: str_key
+func newPaddingAuth(s string) *paddingAuth {
+	key := md5.Sum([]byte(s))
+	return &paddingAuth{key: key[:]}
+}