1 files changed, 116 insertions, 0 deletions
diff --git a/test/functional/p2p_mutated_blocks.py b/test/functional/p2p_mutated_blocks.py
new file mode 100755
index 0000000000..737edaf5bf
--- /dev/null
+++ b/test/functional/p2p_mutated_blocks.py
@@ -0,0 +1,116 @@
+#!/usr/bin/env python3
+# Copyright (c) The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+"""
+Test that an attacker can't degrade compact block relay by sending unsolicited
+mutated blocks to clear in-flight blocktxn requests from other honest peers.
+"""
+
+from test_framework.p2p import P2PInterface
+from test_framework.messages import (
+    BlockTransactions,
+    msg_cmpctblock,
+    msg_block,
+    msg_blocktxn,
+    HeaderAndShortIDs,
+)
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.blocktools import (
+    COINBASE_MATURITY,
+    create_block,
+    add_witness_commitment,
+    NORMAL_GBT_REQUEST_PARAMS,
+)
+from test_framework.util import assert_equal
+from test_framework.wallet import MiniWallet
+import copy
+
+class MutatedBlocksTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 1
+        self.extra_args = [
+            [
+                "-testactivationheight=segwit@1", # causes unconnected headers/blocks to not have segwit considered deployed
+            ],
+        ]
+
+    def run_test(self):
+        self.wallet = MiniWallet(self.nodes[0])
+        self.generate(self.wallet, COINBASE_MATURITY)
+
+        honest_relayer = self.nodes[0].add_outbound_p2p_connection(P2PInterface(), p2p_idx=0, connection_type="outbound-full-relay")
+        attacker = self.nodes[0].add_p2p_connection(P2PInterface())
+
+        # Create new block with two transactions (coinbase + 1 self-transfer).
+        # The self-transfer transaction is needed to trigger a compact block
+        # `getblocktxn` roundtrip.
+        tx = self.wallet.create_self_transfer()["tx"]
+        block = create_block(tmpl=self.nodes[0].getblocktemplate(NORMAL_GBT_REQUEST_PARAMS), txlist=[tx])
+        add_witness_commitment(block)
+        block.solve()
+
+        # Create mutated version of the block by changing the transaction
+        # version on the self-transfer.
+        mutated_block = copy.deepcopy(block)
+        mutated_block.vtx[1].nVersion = 4
+
+        # Announce the new block via a compact block through the honest relayer
+        cmpctblock = HeaderAndShortIDs()
+        cmpctblock.initialize_from_block(block, use_witness=True)
+        honest_relayer.send_message(msg_cmpctblock(cmpctblock.to_p2p()))
+
+        # Wait for a `getblocktxn` that attempts to fetch the self-transfer
+        def self_transfer_requested():
+            if not honest_relayer.last_message.get('getblocktxn'):
+                return False
+
+            get_block_txn = honest_relayer.last_message['getblocktxn']
+            return get_block_txn.block_txn_request.blockhash == block.sha256 and \
+                   get_block_txn.block_txn_request.indexes == [1]
+        honest_relayer.wait_until(self_transfer_requested, timeout=5)
+
+        # Block at height 101 should be the only one in flight from peer 0
+        peer_info_prior_to_attack = self.nodes[0].getpeerinfo()
+        assert_equal(peer_info_prior_to_attack[0]['id'], 0)
+        assert_equal([101], peer_info_prior_to_attack[0]["inflight"])
+
+        # Attempt to clear the honest relayer's download request by sending the
+        # mutated block (as the attacker).
+        with self.nodes[0].assert_debug_log(expected_msgs=["Block mutated: bad-txnmrklroot, hashMerkleRoot mismatch"]):
+            attacker.send_message(msg_block(mutated_block))
+        # Attacker should get disconnected for sending a mutated block
+        attacker.wait_for_disconnect(timeout=5)
+
+        # Block at height 101 should *still* be the only block in-flight from
+        # peer 0
+        peer_info_after_attack = self.nodes[0].getpeerinfo()
+        assert_equal(peer_info_after_attack[0]['id'], 0)
+        assert_equal([101], peer_info_after_attack[0]["inflight"])
+
+        # The honest relayer should be able to complete relaying the block by
+        # sending the blocktxn that was requested.
+        block_txn = msg_blocktxn()
+        block_txn.block_transactions = BlockTransactions(blockhash=block.sha256, transactions=[tx])
+        honest_relayer.send_and_ping(block_txn)
+        assert_equal(self.nodes[0].getbestblockhash(), block.hash)
+
+        # Check that unexpected-witness mutation check doesn't trigger on a header that doesn't connect to anything
+        assert_equal(len(self.nodes[0].getpeerinfo()), 1)
+        attacker = self.nodes[0].add_p2p_connection(P2PInterface())
+        block_missing_prev = copy.deepcopy(block)
+        block_missing_prev.hashPrevBlock = 123
+        block_missing_prev.solve()
+
+        # Attacker gets a DoS score of 10, not immediately disconnected, so we do it 10 times to get to 100
+        for _ in range(10):
+            assert_equal(len(self.nodes[0].getpeerinfo()), 2)
+            with self.nodes[0].assert_debug_log(expected_msgs=["AcceptBlock FAILED (prev-blk-not-found)"]):
+                attacker.send_message(msg_block(block_missing_prev))
+        attacker.wait_for_disconnect(timeout=5)
+
+
+if __name__ == '__main__':
+    MutatedBlocksTest().main()