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Commit 80f76aa1 authored by Mike Yu's avatar Mike Yu
Browse files

DoT quick fallback 

If a DNS query that was sent to a DoT server times out, instead
of trying the next DoT server, let the query fall back to UDP.

This will be helpful when firewall blocks TCP/853 traffic, for
example captive portal re-login.

DoT quick fallback is enabled by default. It's configurable by
the flag `dot_quick_fallback`.

Bug: 228594312
Test: cd packages/modules/DnsResolver && atest
Test: On a wifi network with 2 validated DoT servers, blocked TCP/853
      traffic. DNS queries took 1x time w/ the flag enabled, and
      took 2x time w/o the flag enabled.
Change-Id: I27992baf4dd450391ab6241a5bf46b71ae656766
parent 84f5fa8b

DnsTlsDispatcher.cpp

+5 −1
Original line number Diff line number Diff line
@@ -107,7 +107,8 @@ std::list<DnsTlsServer> DnsTlsDispatcher::getOrderedAndUsableServerList( 


DnsTlsTransport::Response DnsTlsDispatcher::query(const std::list<DnsTlsServer>& tlsServers,

                                                  ResState* statp, const Slice query,

                                                  const Slice ans, int* resplen) {

                                                  const Slice ans, int* resplen,

                                                  bool dotQuickFallback) {

    const std::list<DnsTlsServer> servers(

            getOrderedAndUsableServerList(tlsServers, statp->netid, statp->mark));
@@ -150,6 +151,9 @@ DnsTlsTransport::Response DnsTlsDispatcher::query(const std::list<DnsTlsServer>& 
                // Sync from res_tls_send in res_send.cpp

                dnsQueryEvent->set_rcode(NS_R_TIMEOUT);

                resolv_stats_add(statp->netid, IPSockAddr::toIPSockAddr(server.ss), dnsQueryEvent);

                if (dotQuickFallback) {

                    return code;

                }

                break;

            case DnsTlsTransport::Response::internal_error:

                dnsQueryEvent->set_rcode(NS_R_INTERNAL_ERROR);

DnsTlsDispatcher.h

+2 −1
Original line number Diff line number Diff line
@@ -52,7 +52,8 @@ class DnsTlsDispatcher : public PrivateDnsValidationObserver { 
    // order passed in by the caller.

    DnsTlsTransport::Response query(const std::list<DnsTlsServer>& tlsServers,

                                    ResState* _Nonnull statp, const netdutils::Slice query,

                                    const netdutils::Slice ans, int* _Nonnull resplen);

                                    const netdutils::Slice ans, int* _Nonnull resplen,

                                    bool dotQuickFallback);



    // Given a |query|, sends it to the server on the network indicated by |mark|,

    // and writes the response into |ans|, and indicates the number of bytes written in |resplen|.

Experiments.h

+1 −0
Original line number Diff line number Diff line
@@ -59,6 +59,7 @@ class Experiments { 
            "dot_revalidation_threshold",

            "dot_xport_unusable_threshold",

            "dot_query_timeout_ms",

            "dot_quick_fallback",

            "dot_validation_latency_factor",

            "dot_validation_latency_offset_ms",

            "doh",

res_send.cpp

+6 −2
Original line number Diff line number Diff line
@@ -1436,9 +1436,13 @@ int res_tls_send(const std::list<DnsTlsServer>& tlsServers, ResState* statp, con 
                 const Slice answer, int* rcode, PrivateDnsMode mode) {

    if (tlsServers.empty()) return -1;

    LOG(INFO) << __func__ << ": performing query over TLS";

    const bool dotQuickFallback =

            (mode == PrivateDnsMode::STRICT)

                    ? 0

                    : Experiments::getInstance()->getFlag("dot_quick_fallback", 1);

    int resplen = 0;

    const auto response =

            DnsTlsDispatcher::getInstance().query(tlsServers, statp, query, answer, &resplen);

    const auto response = DnsTlsDispatcher::getInstance().query(tlsServers, statp, query, answer,

                                                                &resplen, dotQuickFallback);



    LOG(INFO) << __func__ << ": TLS query result: " << static_cast<int>(response);

    if (mode == PrivateDnsMode::OPPORTUNISTIC) {

tests/dns_responder/dns_tls_frontend.h

+1 −0
Original line number Diff line number Diff line
@@ -58,6 +58,7 @@ class DnsTlsFrontend { 
    void clearQueries() { queries_ = 0; }

    bool waitForQueries(int expected_count) const;

    int acceptConnectionsCount() const { return accept_connection_count_; }

    void clearConnectionsCount() { accept_connection_count_ = 0; }



    void set_chain_length(int length) { chain_length_ = length; }

    void setHangOnHandshakeForTesting(bool hangOnHandshake) { hangOnHandshake_ = hangOnHandshake; }