Add asmap_direct fuzzer that tests Interpreter directly

src/Makefile.test.include

@@ -9,6 +9,7 @@ FUZZ_TARGETS = \
   test/fuzz/address_deserialize \
   test/fuzz/addrman_deserialize \
   test/fuzz/asmap \
+  test/fuzz/asmap_direct \
   test/fuzz/banentry_deserialize \
   test/fuzz/base_encode_decode \
   test/fuzz/bech32 \
@@ -322,6 +323,12 @@ test_fuzz_asmap_LDADD = $(FUZZ_SUITE_LD_COMMON)
 test_fuzz_asmap_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
 test_fuzz_asmap_SOURCES = test/fuzz/asmap.cpp
 
+test_fuzz_asmap_direct_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
+test_fuzz_asmap_direct_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
+test_fuzz_asmap_direct_LDADD = $(FUZZ_SUITE_LD_COMMON)
+test_fuzz_asmap_direct_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS)
+test_fuzz_asmap_direct_SOURCES = test/fuzz/asmap_direct.cpp
+
 test_fuzz_banentry_deserialize_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) -DBANENTRY_DESERIALIZE=1
 test_fuzz_banentry_deserialize_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_banentry_deserialize_LDADD = $(FUZZ_SUITE_LD_COMMON)

src/test/fuzz/asmap_direct.cpp

@@ -0,0 +1,46 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <util/asmap.h>
+#include <test/fuzz/fuzz.h>
+
+#include <cstdint>
+#include <vector>
+
+#include <assert.h>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    // Encoding: [asmap using 1 bit / byte] 0xFF [addr using 1 bit / byte]
+    bool have_sep = false;
+    size_t sep_pos;
+    for (size_t pos = 0; pos < buffer.size(); ++pos) {
+        uint8_t x = buffer[pos];
+        if ((x & 0xFE) == 0) continue;
+        if (x == 0xFF) {
+            if (have_sep) return;
+            have_sep = true;
+            sep_pos = pos;
+        } else {
+            return;
+        }
+    }
+    if (!have_sep) return; // Needs exactly 1 separator
+    if (buffer.size() - sep_pos - 1 > 128) return; // At most 128 bits in IP address
+
+    // Checks on asmap
+    std::vector<bool> asmap(buffer.begin(), buffer.begin() + sep_pos);
+    if (SanityCheckASMap(asmap, buffer.size() - 1 - sep_pos)) {
+        // Verify that for valid asmaps, no prefix (except up to 7 zero padding bits) is valid.
+        std::vector<bool> asmap_prefix = asmap;
+        while (!asmap_prefix.empty() && asmap_prefix.size() + 7 > asmap.size() && asmap_prefix.back() == false) asmap_prefix.pop_back();
+        while (!asmap_prefix.empty()) {
+            asmap_prefix.pop_back();
+            assert(!SanityCheckASMap(asmap_prefix, buffer.size() - 1 - sep_pos));
+        }
+        // No address input should trigger assertions in interpreter
+        std::vector<bool> addr(buffer.begin() + sep_pos + 1, buffer.end());
+        (void)Interpret(asmap, addr);
+    }
+}