Pull request: safesearch cname

Updates #6352.

Squashed commit of the following:

commit 79d24e0e44a19d05750101e2baa4129c9b62e7ac
Merge: 04c2759bf c908eec5d
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Tue Dec 12 12:26:57 2023 +0200

    Merge remote-tracking branch 'origin/master' into 6352-safesearch-cname

    # Conflicts:
    #	CHANGELOG.md

commit 04c2759bf779d124673c9b3d5c6d95a1dc11a7d0
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Tue Dec 12 11:14:13 2023 +0200

    all: fix changelog

commit 78d726e912d2066e8137f10e4057fd9179227884
Merge: 2d2c17436 79d7a1ef4
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Tue Dec 12 11:12:58 2023 +0200

    Merge remote-tracking branch 'origin/master' into 6352-safesearch-cname

commit 2d2c17436266a82b6fadd436df33ffc0bf55e26f
Merge: 2b1c1eabb 7b5cce517
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Mon Dec 11 11:08:08 2023 +0200

    Merge remote-tracking branch 'origin/master' into 6352-safesearch-cname

    # Conflicts:
    #	CHANGELOG.md

commit 2b1c1eabb274351cbaffaeb1c92eb62aeccb384e
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Fri Dec 8 15:24:02 2023 +0200

    all: changelog

commit 38afdbab686d2ec3c322c34ede032f313ba85ddc
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Fri Dec 8 15:21:23 2023 +0200

    safesearch: imp docs

commit e941f5e76efcf1872f7e24bb2378f33e56f06db9
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Fri Dec 8 14:43:39 2023 +0200

    dnsforward: imp code

commit 8dedb4a01db8d3f9005c602bd4c6e54637667101
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Fri Dec 8 14:26:51 2023 +0200

    dnsforward: imp tests

commit 8f23adeae9d10d7b2ffc30dd76d3e18192cc774e
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Fri Dec 8 13:33:50 2023 +0200

    all: safesearch cnames

commit 061a6deeacf801a71d1a027355d67f3fc6455eac
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Fri Dec 8 13:09:32 2023 +0200

    all: changelog

commit 6f7ff7f9e61f492c7ded9c79fb2499cfeeaa5883
Author: Dimitry Kolyshev <dkolyshev@adguard.com>
Date:   Fri Dec 8 13:07:36 2023 +0200

    all: safesearch cnames

CHANGELOG.md

@@ -28,6 +28,13 @@ NOTE: Add new changes BELOW THIS COMMENT.
 - Ability to disable plain-DNS serving via UI if an encrypted protocol is
   already used ([#1660]).
 
+### Fixed
+
+- Omitted CNAME records in safe search results, which can cause YouTube to not
+  work on iOS ([#6352]).
+
+[#6352]: https://github.com/AdguardTeam/AdGuardHome/issues/6352
+
 <!--
 NOTE: Add new changes ABOVE THIS COMMENT.
 -->

internal/dnsforward/dnsforward_test.go

@@ -549,30 +549,39 @@ func TestSafeSearch(t *testing.T) {
 	testCases := []struct {
 		host      string
 		want      netip.Addr
+		wantCNAME string
 	}{{
 		host:      "yandex.com.",
 		want:      yandexIP,
+		wantCNAME: "",
 	}, {
 		host:      "yandex.by.",
 		want:      yandexIP,
+		wantCNAME: "",
 	}, {
 		host:      "yandex.kz.",
 		want:      yandexIP,
+		wantCNAME: "",
 	}, {
 		host:      "yandex.ru.",
 		want:      yandexIP,
+		wantCNAME: "",
 	}, {
 		host:      "www.google.com.",
 		want:      googleIP,
+		wantCNAME: "forcesafesearch.google.com.",
 	}, {
 		host:      "www.google.com.af.",
 		want:      googleIP,
+		wantCNAME: "forcesafesearch.google.com.",
 	}, {
 		host:      "www.google.be.",
 		want:      googleIP,
+		wantCNAME: "forcesafesearch.google.com.",
 	}, {
 		host:      "www.google.by.",
 		want:      googleIP,
+		wantCNAME: "forcesafesearch.google.com.",
 	}}
 
 	for _, tc := range testCases {
@@ -582,7 +591,18 @@ func TestSafeSearch(t *testing.T) {
 			var reply *dns.Msg
 			reply, _, err = client.Exchange(req, addr)
 			require.NoErrorf(t, err, "couldn't talk to server %s: %s", addr, err)
-			assertResponse(t, reply, tc.want)
+
+			if tc.wantCNAME != "" {
+				require.Len(t, reply.Answer, 2)
+
+				cname := testutil.RequireTypeAssert[*dns.CNAME](t, reply.Answer[0])
+				assert.Equal(t, tc.wantCNAME, cname.Target)
+			} else {
+				require.Len(t, reply.Answer, 1)
+			}
+
+			a := testutil.RequireTypeAssert[*dns.A](t, reply.Answer[len(reply.Answer)-1])
+			assert.Equal(t, net.IP(tc.want.AsSlice()), a.A)
 		})
 	}
 }

internal/dnsforward/filter.go

@@ -95,7 +95,7 @@ func (s *Server) filterDNSRequest(dctx *dnsContext) (res *filtering.Result, err
 		dctx.origQuestion = q
 		req.Question[0].Name = dns.Fqdn(res.CanonName)
 	case res.Reason == filtering.Rewritten:
-		pctx.Res = s.filterRewritten(req, host, res, q.Qtype)
+		pctx.Res = s.getCNAMEWithIPs(req, res.IPList, res.CanonName)
 	case res.Reason.In(filtering.RewrittenRule, filtering.RewrittenAutoHosts):
 		if err = s.filterDNSRewrite(req, res, pctx); err != nil {
 			return nil, err
@@ -105,37 +105,6 @@ func (s *Server) filterDNSRequest(dctx *dnsContext) (res *filtering.Result, err
 	return res, err
 }
 
-// filterRewritten handles DNS rewrite filters.  It returns a DNS response with
-// the data from the filtering result.  All parameters must not be nil.
-func (s *Server) filterRewritten(
-	req *dns.Msg,
-	host string,
-	res *filtering.Result,
-	qt uint16,
-) (resp *dns.Msg) {
-	resp = s.makeResponse(req)
-	name := host
-	if len(res.CanonName) != 0 {
-		resp.Answer = append(resp.Answer, s.genAnswerCNAME(req, res.CanonName))
-		name = res.CanonName
-	}
-
-	for _, ip := range res.IPList {
-		switch qt {
-		case dns.TypeA:
-			a := s.genAnswerA(req, ip)
-			a.Hdr.Name = dns.Fqdn(name)
-			resp.Answer = append(resp.Answer, a)
-		case dns.TypeAAAA:
-			a := s.genAnswerAAAA(req, ip)
-			a.Hdr.Name = dns.Fqdn(name)
-			resp.Answer = append(resp.Answer, a)
-		}
-	}
-
-	return resp
-}
-
 // checkHostRules checks the host against filters.  It is safe for concurrent
 // use.
 func (s *Server) checkHostRules(

internal/dnsforward/msg.go

@@ -66,12 +66,46 @@ func (s *Server) genDNSFilterMessage(
 		// If Safe Search generated the necessary IP addresses, use them.
 		// Otherwise, if there were no errors, there are no addresses for the
 		// requested IP version, so produce a NODATA response.
-		return s.genResponseWithIPs(req, ipsFromRules(res.Rules))
+		return s.getCNAMEWithIPs(req, ipsFromRules(res.Rules), res.CanonName)
 	default:
 		return s.genForBlockingMode(req, ipsFromRules(res.Rules))
 	}
 }
 
+// getCNAMEWithIPs generates a filtered response to req for with CNAME record
+// and provided ips.
+func (s *Server) getCNAMEWithIPs(req *dns.Msg, ips []netip.Addr, cname string) (resp *dns.Msg) {
+	resp = s.makeResponse(req)
+
+	originalName := req.Question[0].Name
+
+	var ans []dns.RR
+	if cname != "" {
+		ans = append(ans, s.genAnswerCNAME(req, cname))
+
+		// The given IPs actually are resolved for this cname.
+		req.Question[0].Name = dns.Fqdn(cname)
+		defer func() { req.Question[0].Name = originalName }()
+	}
+
+	switch req.Question[0].Qtype {
+	case dns.TypeA:
+		ans = append(ans, s.genAnswersWithIPv4s(req, ips)...)
+	case dns.TypeAAAA:
+		for _, ip := range ips {
+			if ip.Is6() {
+				ans = append(ans, s.genAnswerAAAA(req, ip))
+			}
+		}
+	default:
+		// Go on and return an empty response.
+	}
+
+	resp.Answer = ans
+
+	return resp
+}
+
 // genForBlockingMode generates a filtered response to req based on the server's
 // blocking mode.
 func (s *Server) genForBlockingMode(req *dns.Msg, ips []netip.Addr) (resp *dns.Msg) {

internal/filtering/safesearch/safesearch.go

@@ -226,7 +226,8 @@ func (ss *Default) searchHost(host string, qtype rules.RRType) (res *rules.DNSRe
 // empty result is converted into a NODATA response.
 //
 // TODO(a.garipov): Use the main rewrite result mechanism used in
-// [dnsforward.Server.filterDNSRequest].
+// [dnsforward.Server.filterDNSRequest].  Now we resolve IPs for CNAME to save
+// them in the safe search cache.
 func (ss *Default) newResult(
 	rewrite *rules.DNSRewrite,
 	qtype rules.RRType,
@@ -255,6 +256,8 @@ func (ss *Default) newResult(
 		return res, nil
 	}
 
+	res.CanonName = host
+
 	ss.log(log.DEBUG, "resolving %q", host)
 
 	ips, err := ss.resolver.LookupIP(context.Background(), qtypeToProto(qtype), host)