Chain on ECS matching, and consider a mismatch in returned ECS as a spoof attempt

diff --git a/pdns/recursordist/lwres.cc b/pdns/recursordist/lwres.cc
index 14e42e5dadd1b077a91de767aa007737d6ef444f..7dcc6ad45a1a08ed7ad23be506f22870cb49b9a4 100644 (file)
--- a/pdns/recursordist/lwres.cc
+++ b/pdns/recursordist/lwres.cc
@@ -422,7 +422,6 @@ static LWResult::Result asyncresolve(const ComboAddress& address, const DNSName&
   pw.getHeader()->cd = (sendRDQuery && g_dnssecmode != DNSSECMode::Off);
 
   string ping;
-  bool weWantEDNSSubnet = false;
   std::optional<EDNSSubnetOpts> subnetOpts = std::nullopt;
   if (EDNS0Level > 0) {
     DNSPacketWriter::optvect_t opts;
@@ -430,7 +429,6 @@ static LWResult::Result asyncresolve(const ComboAddress& address, const DNSName&
       subnetOpts = EDNSSubnetOpts{};
       subnetOpts->source = *srcmask;
       opts.emplace_back(EDNSOptionCode::ECS, makeEDNSSubnetOptsString(*subnetOpts));
-      weWantEDNSSubnet = true;
     }
 
     if (dnsOverTLS && g_paddingOutgoing) {
@@ -499,7 +497,7 @@ static LWResult::Result asyncresolve(const ComboAddress& address, const DNSName&
 #endif /* HAVE_FSTRM */
 
     // sleep until we see an answer to this, interface to mtasker
-    ret = arecvfrom(buf, 0, address, len, qid, domain, type, queryfd, *now);
+    ret = arecvfrom(buf, 0, address, len, qid, domain, type, queryfd, subnetOpts, *now);
   }
   else {
     bool isNew;
@@ -600,11 +598,22 @@ static LWResult::Result asyncresolve(const ComboAddress& address, const DNSName&
     if (EDNS0Level > 0 && getEDNSOpts(mdp, &edo)) {
       lwr->d_haveEDNS = true;
 
-      if (weWantEDNSSubnet) {
+      // If we sent out ECS, we can also expect to see a return with or without ECS, the absent case is
+      // not handled explicitly. If we do see a ECS in the reply, the source part *must* match with
+      // what we sent out See https://www.rfc-editor.org/rfc/rfc7871#section-7.3
+      if (subnetOpts) {
         for (const auto& opt : edo.d_options) {
           if (opt.first == EDNSOptionCode::ECS) {
             EDNSSubnetOpts reso;
             if (getEDNSSubnetOptsFromString(opt.second, &reso)) {
+              if (!(reso.source == subnetOpts->source)) {
+                g_slogout->info(Logr::Notice, "Incoming ECS does not match outgoing",
+                                "server", Logging::Loggable(address),
+                                "qname", Logging::Loggable(domain),
+                                "outgoing", Logging::Loggable(subnetOpts->source),
+                                "incoming", Logging::Loggable(reso.source));
+                return LWResult::Result::Spoofed; // XXXXX OK?
+              }
               /* rfc7871 states that 0 "indicate[s] that the answer is suitable for all addresses in FAMILY",
                  so we might want to still pass the information along to be able to differentiate between
                  IPv4 and IPv6. Still I'm pretty sure it doesn't matter in real life, so let's not duplicate

diff --git a/pdns/recursordist/lwres.hh b/pdns/recursordist/lwres.hh
index 807157309f3ab099b793a62e839dbb3e4e4452e1..49976c9ef8123745cfdf06518af63c12218fcf46 100644 (file)
--- a/pdns/recursordist/lwres.hh
+++ b/pdns/recursordist/lwres.hh
@@ -91,6 +91,6 @@ struct EDNSSubnetOpts;
 LWResult::Result asendto(const void* data, size_t len, int flags, const ComboAddress& toAddress, uint16_t qid,
                          const DNSName& domain, uint16_t qtype, const std::optional<EDNSSubnetOpts>& ecs, int* fileDesc, timeval& now);
 LWResult::Result arecvfrom(PacketBuffer& packet, int flags, const ComboAddress& fromAddr, size_t& len, uint16_t qid,
-                           const DNSName& domain, uint16_t qtype, int fileDesc, const struct timeval& now);
+                           const DNSName& domain, uint16_t qtype, int fileDesc, const std::optional<EDNSSubnetOpts>& ecs, const struct timeval& now);
 
 LWResult::Result asyncresolve(const ComboAddress& address, const DNSName& domain, int type, bool doTCP, bool sendRDQuery, int EDNS0Level, struct timeval* now, boost::optional<Netmask>& srcmask, const ResolveContext& context, const std::shared_ptr<std::vector<std::unique_ptr<RemoteLogger>>>& outgoingLoggers, const std::shared_ptr<std::vector<std::unique_ptr<FrameStreamLogger>>>& fstrmLoggers, const std::set<uint16_t>& exportTypes, LWResult* lwr, bool* chained);

diff --git a/pdns/recursordist/pdns_recursor.cc b/pdns/recursordist/pdns_recursor.cc
index 98a1579d0a8c39c90d02214aacc2ea6100e21353..fb74135980be54614f7bfafc03d3aae7f3c12de6 100644 (file)
--- a/pdns/recursordist/pdns_recursor.cc
+++ b/pdns/recursordist/pdns_recursor.cc
@@ -284,11 +284,13 @@ LWResult::Result asendto(const void* data, size_t len, int /* flags */,
   pident->domain = domain;
   pident->remote = toAddress;
   pident->type = qtype;
-
+  if (ecs) {
+    pident->ecsSubnet = ecs->source;
+  }
   // We cannot merge ECS-enabled queries based on the ECS source only, as the scope
   // of the response might be narrower, so instead we do not chain ECS-enabled queries
   // at all.
-  if (!ecs) {
+  if (true || !ecs) {
     // See if there is an existing outstanding request we can chain on to, using partial equivalence
     // function looking for the same query (qname and qtype) to the same host, but with a different
     // message ID.
@@ -342,7 +344,7 @@ LWResult::Result asendto(const void* data, size_t len, int /* flags */,
 }
 
 LWResult::Result arecvfrom(PacketBuffer& packet, int /* flags */, const ComboAddress& fromAddr, size_t& len,
-                           uint16_t qid, const DNSName& domain, uint16_t qtype, int fileDesc, const struct timeval& now)
+                           uint16_t qid, const DNSName& domain, uint16_t qtype, int fileDesc, const std::optional<EDNSSubnetOpts>& ecs, const struct timeval& now)
 {
   static const unsigned int nearMissLimit = ::arg().asNum("spoof-nearmiss-max");
 
@@ -353,7 +355,13 @@ LWResult::Result arecvfrom(PacketBuffer& packet, int /* flags */, const ComboAdd
   pident->type = qtype;
   pident->remote = fromAddr;
   pident->creationTime = now;
-
+  if (ecs) {
+    // We sent out the query using ecs
+    // We expect incoming source ECS to match, see https://www.rfc-editor.org/rfc/rfc7871#section-7.3
+    // But there's also section 11-2, which says we should treat absent incoming ecs as scope zero
+    // We fill in the search key with the ecs we sent out, so both cases are covered and accepted here.
+    pident->ecsSubnet = ecs->source;
+  }
   int ret = g_multiTasker->waitEvent(pident, &packet, authWaitTimeMSec(g_multiTasker), &now);
   len = 0;
 

diff --git a/pdns/recursordist/syncres.hh b/pdns/recursordist/syncres.hh
index 4e149008561ceffea3ce594ab60c04353902b857..c02228f2433a222b533edccb25beaf1288173629 100644 (file)
--- a/pdns/recursordist/syncres.hh
+++ b/pdns/recursordist/syncres.hh
@@ -781,6 +781,7 @@ struct PacketID
   mutable chain_t authReqChain;
   shared_ptr<TCPIOHandler> tcphandler{nullptr};
   timeval creationTime{};
+  std::optional<Netmask> ecsSubnet;
   string::size_type inPos{0}; // how far are we along in the inMSG
   size_t inWanted{0}; // if this is set, we'll read until inWanted bytes are read
   string::size_type outPos{0}; // how far we are along in the outMSG
@@ -820,10 +821,10 @@ struct PacketIDCompare
 {
   bool operator()(const std::shared_ptr<PacketID>& lhs, const std::shared_ptr<PacketID>& rhs) const
   {
-    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type) < std::tie(rhs->remote, rhs->tcpsock, rhs->type)) {
+    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type, lhs->ecsSubnet) < std::tie(rhs->remote, rhs->tcpsock, rhs->type, rhs->ecsSubnet)) {
       return true;
     }
-    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type) > std::tie(rhs->remote, rhs->tcpsock, rhs->type)) {
+    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type, lhs->ecsSubnet) > std::tie(rhs->remote, rhs->tcpsock, rhs->type, rhs->ecsSubnet)) {
       return false;
     }
 
@@ -835,10 +836,10 @@ struct PacketIDBirthdayCompare
 {
   bool operator()(const std::shared_ptr<PacketID>& lhs, const std::shared_ptr<PacketID>& rhs) const
   {
-    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type) < std::tie(rhs->remote, rhs->tcpsock, rhs->type)) {
+    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type, lhs->ecsSubnet) < std::tie(rhs->remote, rhs->tcpsock, rhs->type, rhs->ecsSubnet)) {
       return true;
     }
-    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type) > std::tie(rhs->remote, rhs->tcpsock, rhs->type)) {
+    if (std::tie(lhs->remote, lhs->tcpsock, lhs->type, lhs->ecsSubnet) > std::tie(rhs->remote, rhs->tcpsock, rhs->type, rhs->ecsSubnet)) {
       return false;
     }
     return lhs->domain < rhs->domain;