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 463f99644e07eadfbd0bb26ccf407d4e3200394a..acf6d01cb9d45bad017bda2d28df5d9abc0bc882 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;
@@ -599,11 +597,22 @@ 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 c5dd5cc90819612ba0e3ca620def7a393d8cebe8..3c17c159dd8482e0a253d5a9d4fec7ace26c2958 100644 (file)
--- a/pdns/recursordist/pdns_recursor.cc
+++ b/pdns/recursordist/pdns_recursor.cc
@@ -290,11 +290,13 @@ 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.
@@ -348,7 +350,7 @@ 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");
 
@@ -359,7 +361,13 @@ 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 eb33f9e07de4a3a7bfee989f8ad45b0b652168ac..9ab3d0c56e86ea0f41f4e1e1cb84e2b527201a6a 100644 (file)
--- a/pdns/recursordist/syncres.hh
+++ b/pdns/recursordist/syncres.hh
@@ -767,6 +767,7 @@ 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
@@ -806,10 +807,10 @@ 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;
     }
 
@@ -821,10 +822,10 @@ 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;