Merge bitcoin/bitcoin#21795: fuzz: Terminate immediately if a fuzzing harness tries to perform a DNS lookup (belt and suspenders)

3737d35 fuzz: Terminate immediately if a fuzzing harness ever tries to perform a DNS lookup (belts and suspenders) (practicalswift)

Pull request description:

  Terminate immediately if a fuzzing harness tries to perform a DNS lookup (belt and suspenders).

  Obviously this _should_ never happen, but if it _does_ happen we want immediate termination instead of a DNS lookup :)

ACKs for top commit:
  MarcoFalke:
    review ACK 3737d35

Tree-SHA512: 51cd2d32def7f9f052e02f99c354656af1f807cc9fdf592ab765e620bfe660f1ed26e0484763f94aba650424b44959eafaf352bfd0f81aa273e350510e97356e

Author: MarcoFalke

src/test/fuzz/fuzz.cpp

@@ -13,6 +13,7 @@
 #include <cstdint>
 #include <exception>
 #include <memory>
+#include <string>
 #include <unistd.h>
 #include <vector>
 
@@ -37,6 +38,14 @@ void initialize()
     // Terminate immediately if a fuzzing harness ever tries to create a TCP socket.
     CreateSock = [](const CService&) -> std::unique_ptr<Sock> { std::terminate(); };
 
+    // Terminate immediately if a fuzzing harness ever tries to perform a DNS lookup.
+    g_dns_lookup = [](const std::string& name, bool allow_lookup) {
+        if (allow_lookup) {
+            std::terminate();
+        }
+        return WrappedGetAddrInfo(name, false);
+    };
+
     bool should_abort{false};
     if (std::getenv("PRINT_ALL_FUZZ_TARGETS_AND_ABORT")) {
         for (const auto& t : FuzzTargets()) {