enforce claiming maximum coinbase amount

Claiming a slightly lesser amount does not yield the size gains
that were seen pre rct, so this closes a fingerprinting vector

src/cryptonote_config.h

@@ -173,6 +173,7 @@
 #define HF_VERSION_REJECT_SIGS_IN_COINBASE      12
 #define HF_VERSION_ENFORCE_MIN_AGE              12
 #define HF_VERSION_EFFECTIVE_SHORT_TERM_MEDIAN_IN_PENALTY 12
+#define HF_VERSION_EXACT_COINBASE               13
 
 #define PER_KB_FEE_QUANTIZATION_DECIMALS        8
 

src/cryptonote_core/blockchain.cpp

@@ -1392,8 +1392,8 @@ bool Blockchain::validate_miner_transaction(const block& b, size_t cumulative_bl
     MERROR_VER("coinbase transaction spend too much money (" << print_money(money_in_use) << "). Block reward is " << print_money(base_reward + fee) << "(" << print_money(base_reward) << "+" << print_money(fee) << "), cumulative_block_weight " << cumulative_block_weight);
     return false;
   }
-  // From hard fork 2, we allow a miner to claim less block reward than is allowed, in case a miner wants less dust
-  if (version < 2)
+  // From hard fork 2 till 12, we allow a miner to claim less block reward than is allowed, in case a miner wants less dust
+  if (version < 2 || version >= HF_VERSION_EXACT_COINBASE)
   {
     if(base_reward + fee != money_in_use)
     {

tests/core_tests/block_validation.cpp

@@ -655,3 +655,19 @@ bool gen_block_late_v1_coinbase_tx::generate(std::vector<test_event_entry>& even
 
   return true;
 }
+
+bool gen_block_low_coinbase::generate(std::vector<test_event_entry>& events) const
+{
+  BLOCK_VALIDATION_INIT_GENERATE();
+
+  block blk_1;
+  std::vector<size_t> block_weights;
+  generator.construct_block(blk_1, cryptonote::get_block_height(blk_0) + 1, cryptonote::get_block_hash(blk_0),
+    miner_account, blk_0.timestamp + DIFFICULTY_TARGET_V2, COIN + generator.get_already_generated_coins(cryptonote::get_block_hash(blk_0)),
+    block_weights, {}, HF_VERSION_EXACT_COINBASE);
+  events.push_back(blk_1);
+
+  DO_CALLBACK(events, "check_block_purged");
+
+  return true;
+}

tests/core_tests/block_validation.h

@@ -218,3 +218,15 @@ struct get_test_options<gen_block_late_v1_coinbase_tx> {
     hard_forks, 0
   };
 };
+
+struct gen_block_low_coinbase : public gen_block_verification_base<1>
+{
+  bool generate(std::vector<test_event_entry>& events) const;
+};
+template<>
+struct get_test_options<gen_block_low_coinbase> {
+  const std::pair<uint8_t, uint64_t> hard_forks[3] = {std::make_pair(1, 0), std::make_pair(HF_VERSION_EXACT_COINBASE, 1), std::make_pair(0, 0)};
+  const cryptonote::test_options test_options = {
+    hard_forks, 0
+  };
+};

tests/core_tests/chaingen_main.cpp

@@ -264,6 +264,8 @@ int main(int argc, char* argv[])
     GENERATE_AND_PLAY(gen_bp_tx_invalid_wrong_amount);
     GENERATE_AND_PLAY(gen_bp_tx_invalid_borromean_type);
 
+    GENERATE_AND_PLAY(gen_block_low_coinbase);
+
     el::Level level = (failed_tests.empty() ? el::Level::Info : el::Level::Error);
     if (!list_tests)
     {