fix: geoip wrong matching logic in fallback-filter

#1478

config/config.go

@@ -1473,7 +1473,7 @@ func parseDNS(rawCfg *RawConfig, hosts *trie.DomainTrie[resolver.HostValue], rul
 			if err != nil {
 				return nil, fmt.Errorf("load GeoIP dns fallback filter error, %w", err)
 			}
-			dnsCfg.FallbackIPFilter = append(dnsCfg.FallbackIPFilter, matcher)
+			dnsCfg.FallbackIPFilter = append(dnsCfg.FallbackIPFilter, matcher.DnsFallbackFilter())
 		}
 		if len(cfg.FallbackFilter.IPCIDR) > 0 {
 			cidrSet := cidr.NewIpCidrSet()

rules/common/geoip.go

@@ -22,7 +22,6 @@ type GEOIP struct {
 	adapter     string
 	noResolveIP bool
 	isSourceIP  bool
-	geodata     bool
 }
 
 var _ C.Rule = (*GEOIP)(nil)
@@ -115,6 +114,36 @@ func (g *GEOIP) MatchIp(ip netip.Addr) bool {
 	return slices.Contains(codes, g.country)
 }
 
+// MatchIp implements C.IpMatcher
+func (g dnsFallbackFilter) MatchIp(ip netip.Addr) bool {
+	if !ip.IsValid() {
+		return false
+	}
+
+	if g.isLan(ip) { // compatible with original behavior
+		return false
+	}
+
+	if C.GeodataMode {
+		matcher, err := g.getIPMatcher()
+		if err != nil {
+			return false
+		}
+		return !matcher.Match(ip)
+	}
+
+	codes := mmdb.IPInstance().LookupCode(ip.AsSlice())
+	return !slices.Contains(codes, g.country)
+}
+
+type dnsFallbackFilter struct {
+	*GEOIP
+}
+
+func (g *GEOIP) DnsFallbackFilter() C.IpMatcher { // for dns.fallback-filter.geoip
+	return dnsFallbackFilter{GEOIP: g}
+}
+
 func (g *GEOIP) isLan(ip netip.Addr) bool {
 	return ip.IsPrivate() ||
 		ip.IsUnspecified() ||