network: treat loopback address as sender address

When learning about nodes in an answer,
we used to drop nodes with loopback address.
Address is now replaced by the packet sender
address and the port is preserved.

src/network_engine.cpp

@@ -307,32 +307,25 @@ NetworkEngine::rateLimit(const SockAddr& addr)
 bool
 NetworkEngine::isMartian(const SockAddr& addr)
 {
-    // Check that sa_family can be accessed safely
-    if (addr.second < sizeof(sockaddr_in))
+    if (addr.getPort() == 0)
         return true;
-
-    switch(addr.first.ss_family) {
+    switch(addr.getFamily()) {
     case AF_INET: {
-        sockaddr_in *sin = (sockaddr_in*)&addr.first;
-        const uint8_t *address = (const uint8_t*)&sin->sin_addr;
-        return sin->sin_port == 0 ||
-            (address[0] == 0) ||
-            (address[0] == 127) ||
-            ((address[0] & 0xE0) == 0xE0);
+        const auto& sin = addr.getIPv4();
+        const uint8_t* address = (const uint8_t*)&sin.sin_addr;
+        return (address[0] == 0) ||
+              ((address[0] & 0xE0) == 0xE0);
     }
     case AF_INET6: {
         if (addr.second < sizeof(sockaddr_in6))
             return true;
-        sockaddr_in6 *sin6 = (sockaddr_in6*)&addr.first;
-        const uint8_t *address = (const uint8_t*)&sin6->sin6_addr;
-        return sin6->sin6_port == 0 ||
-            (address[0] == 0xFF) ||
-            (address[0] == 0xFE && (address[1] & 0xC0) == 0x80) ||
-            (memcmp(address, zeroes.data(), 15) == 0 &&
-             (address[15] == 0 || address[15] == 1)) ||
-            (memcmp(address, v4prefix, 12) == 0);
+        const auto& sin6 = addr.getIPv6();
+        const uint8_t* address = (const uint8_t*)&sin6.sin6_addr;
+        return address[0] == 0xFF ||
+              (address[0] == 0xFE && (address[1] & 0xC0) == 0x80) ||
+               memcmp(address, zeroes.data(), 16) == 0 ||
+               memcmp(address, v4prefix,      12) == 0;
     }
-
     default:
         return true;
     }
@@ -516,11 +509,11 @@ NetworkEngine::process(std::unique_ptr<ParsedMessage>&& msg, const SockAddr& fro
              requests.erase(req_it);
              req->reply_time = scheduler.time();
 
-             deserializeNodes(*msg);
+             deserializeNodes(*msg, from);
              req->setDone(std::move(*msg));
              break;
          } else { /* request socket data */
-             deserializeNodes(*msg);
+             deserializeNodes(*msg, from);
              rsocket->on_receive(rsocket->node, std::move(*msg));
          }
         default:
@@ -784,25 +777,43 @@ NetworkEngine::sendGetValues(Sp<Node> n, const InfoHash& info_hash, const Query&
     return req;
 }
 
+SockAddr deserializeIPv4(const uint8_t* ni) {
+    SockAddr addr;
+    auto& sin = addr.getIPv4();
+    std::fill_n((uint8_t*)&sin, sizeof(sockaddr_in), 0);
+    addr.setFamily(AF_INET);
+    memcpy(&sin.sin_addr, ni, 4);
+    memcpy(&sin.sin_port, ni + 4, 2);
+    return addr;
+}
+SockAddr deserializeIPv6(const uint8_t* ni) {
+    SockAddr addr;
+    auto& sin6 = addr.getIPv6();
+    std::fill_n((uint8_t*)&sin6, sizeof(sockaddr_in6), 0);
+    addr.setFamily(AF_INET6);
+    memcpy(&sin6.sin6_addr, ni, 16);
+    memcpy(&sin6.sin6_port, ni + 16, 2);
+    return addr;
+}
+
 void
-NetworkEngine::deserializeNodes(ParsedMessage& msg) {
+NetworkEngine::deserializeNodes(ParsedMessage& msg, const SockAddr& from) {
     if (msg.nodes4_raw.size() % NODE4_INFO_BUF_LEN != 0 || msg.nodes6_raw.size() % NODE6_INFO_BUF_LEN != 0) {
         throw DhtProtocolException {DhtProtocolException::WRONG_NODE_INFO_BUF_LEN};
     } else {
         // deserialize nodes
         const auto& now = scheduler.time();
-        SockAddr addr;
         for (unsigned i = 0; i < msg.nodes4_raw.size() / NODE4_INFO_BUF_LEN; i++) {
             uint8_t *ni = msg.nodes4_raw.data() + i * NODE4_INFO_BUF_LEN;
             const InfoHash& ni_id = *reinterpret_cast<InfoHash*>(ni);
             if (ni_id == myid)
                 continue;
-            auto sin = (sockaddr_in*)&addr.first;
-            std::fill_n((uint8_t*)sin, sizeof(sockaddr_in), 0);
-            sin->sin_family = AF_INET;
-            memcpy(&sin->sin_addr, ni + ni_id.size(), 4);
-            memcpy(&sin->sin_port, ni + ni_id.size() + 4, 2);
-            addr.second = sizeof(sockaddr_in);
+            SockAddr addr = deserializeIPv4(ni + ni_id.size());
+            if (addr.isLoopback() and from.getFamily() == AF_INET) {
+                auto port = addr.getPort();
+                addr = from;
+                addr.setPort(port);
+            }
             if (isMartian(addr) || isNodeBlacklisted(addr))
                 continue;
             msg.nodes4.emplace_back(cache.getNode(ni_id, addr, now, false));
@@ -813,12 +824,12 @@ NetworkEngine::deserializeNodes(ParsedMessage& msg) {
             const InfoHash& ni_id = *reinterpret_cast<InfoHash*>(ni);
             if (ni_id == myid)
                 continue;
-            auto sin6 = (sockaddr_in6*)&addr.first;
-            std::fill_n((uint8_t*)sin6, sizeof(sockaddr_in6), 0);
-            sin6->sin6_family = AF_INET6;
-            memcpy(&sin6->sin6_addr, ni + HASH_LEN, 16);
-            memcpy(&sin6->sin6_port, ni + HASH_LEN + 16, 2);
-            addr.second = sizeof(sockaddr_in6);
+            SockAddr addr = deserializeIPv6(ni + ni_id.size());
+            if (addr.isLoopback() and from.getFamily() == AF_INET6) {
+                auto port = addr.getPort();
+                addr = from;
+                addr.setPort(port);
+            }
             if (isMartian(addr) || isNodeBlacklisted(addr))
                 continue;
             msg.nodes6.emplace_back(cache.getNode(ni_id, addr, now, false));