tests: add tests for invalid P2P messages

E.g., ensure that we can't DoS a node by sending it a bunch of large,
unrecognized messages.

test/functional/p2p_invalid_messages.py

@@ -0,0 +1,175 @@
+#!/usr/bin/env python3
+# Copyright (c) 2015-2018 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 node responses to invalid network messages."""
+import struct
+
+from test_framework import messages
+from test_framework.mininode import P2PDataStore
+from test_framework.test_framework import BitcoinTestFramework
+
+
+class msg_unrecognized:
+    """Nonsensical message. Modeled after similar types in test_framework.messages."""
+
+    command = b'badmsg'
+
+    def __init__(self, str_data):
+        self.str_data = str_data.encode() if not isinstance(str_data, bytes) else str_data
+
+    def serialize(self):
+        return messages.ser_string(self.str_data)
+
+    def __repr__(self):
+        return "{}(data={})".format(self.command, self.str_data)
+
+
+class msg_nametoolong(msg_unrecognized):
+
+    command = b'thisnameiswayyyyyyyyytoolong'
+
+
+class InvalidMessagesTest(BitcoinTestFramework):
+
+    def set_test_params(self):
+        self.num_nodes = 1
+        self.setup_clean_chain = True
+
+    def run_test(self):
+        """
+        0. Send a bunch of large (4MB) messages of an unrecognized type. Check to see
+           that it isn't an effective DoS against the node.
+
+        1. Send an oversized (4MB+) message and check that we're disconnected.
+
+        2. Send a few messages with an incorrect data size in the header, ensure the
+           messages are ignored.
+
+        3. Send an unrecognized message with a command name longer than 12 characters.
+
+        """
+        node = self.nodes[0]
+        self.node = node
+        node.add_p2p_connection(P2PDataStore())
+        conn2 = node.add_p2p_connection(P2PDataStore())
+
+        msg_limit = 4 * 1000 * 1000  # 4MB, per MAX_PROTOCOL_MESSAGE_LENGTH
+        valid_data_limit = msg_limit - 5  # Account for the 4-byte length prefix
+
+        #
+        # 0.
+        #
+        # Send as large a message as is valid, ensure we aren't disconnected but
+        # also can't exhaust resources.
+        #
+        msg_at_size = msg_unrecognized("b" * valid_data_limit)
+        assert len(msg_at_size.serialize()) == msg_limit
+
+        with node.assert_memory_usage_stable(perc_increase_allowed=0.03):
+            self.log.info(
+                "Sending a bunch of large, junk messages to test "
+                "memory exhaustion. May take a bit...")
+
+            # Run a bunch of times to test for memory exhaustion.
+            for _ in range(200):
+                node.p2p.send_message(msg_at_size)
+
+            # Check that, even though the node is being hammered by nonsense from one
+            # connection, it can still service other peers in a timely way.
+            for _ in range(20):
+                conn2.sync_with_ping(timeout=2)
+
+            # Peer 1, despite serving up a bunch of nonsense, should still be connected.
+            self.log.info("Waiting for node to drop junk messages.")
+            node.p2p.sync_with_ping(timeout=8)
+            assert node.p2p.is_connected
+
+        #
+        # 1.
+        #
+        # Send an oversized message, ensure we're disconnected.
+        #
+        msg_over_size = msg_unrecognized("b" * (valid_data_limit + 1))
+        assert len(msg_over_size.serialize()) == (msg_limit + 1)
+
+        with node.assert_debug_log(["Oversized message from peer=0, disconnecting"]):
+            # An unknown message type (or *any* message type) over
+            # MAX_PROTOCOL_MESSAGE_LENGTH should result in a disconnect.
+            node.p2p.send_message(msg_over_size)
+            node.p2p.wait_for_disconnect(timeout=4)
+
+        node.disconnect_p2ps()
+        conn = node.add_p2p_connection(P2PDataStore())
+        conn.wait_for_verack()
+
+        #
+        # 2.
+        #
+        # Send messages with an incorrect data size in the header.
+        #
+        actual_size = 100
+        msg = msg_unrecognized("b" * actual_size)
+
+        # TODO: handle larger-than cases. I haven't been able to pin down what behavior to expect.
+        for wrong_size in (2, 77, 78, 79):
+            self.log.info("Sending a message with incorrect size of {}".format(wrong_size))
+
+            # Unmodified message should submit okay.
+            node.p2p.send_and_ping(msg)
+
+            # A message lying about its data size results in a disconnect when the incorrect
+            # data size is less than the actual size.
+            #
+            # TODO: why does behavior change at 78 bytes?
+            #
+            node.p2p.send_raw_message(self._tweak_msg_data_size(msg, wrong_size))
+
+            # For some reason unknown to me, we sometimes have to push additional data to the
+            # peer in order for it to realize a disconnect.
+            try:
+                node.p2p.send_message(messages.msg_ping(nonce=123123))
+            except IOError:
+                pass
+
+            node.p2p.wait_for_disconnect(timeout=10)
+            node.disconnect_p2ps()
+            node.add_p2p_connection(P2PDataStore())
+
+        #
+        # 3.
+        #
+        # Send a message with a too-long command name.
+        #
+        node.p2p.send_message(msg_nametoolong("foobar"))
+        node.p2p.wait_for_disconnect(timeout=4)
+
+        # Node is still up.
+        conn = node.add_p2p_connection(P2PDataStore())
+        conn.sync_with_ping()
+
+
+    def _tweak_msg_data_size(self, message, wrong_size):
+        """
+        Return a raw message based on another message but with an incorrect data size in
+        the message header.
+        """
+        raw_msg = self.node.p2p.build_message(message)
+
+        bad_size_bytes = struct.pack("<I", wrong_size)
+        num_header_bytes_before_size = 4 + 12
+
+        # Replace the correct data size in the message with an incorrect one.
+        raw_msg_with_wrong_size = (
+            raw_msg[:num_header_bytes_before_size] +
+            bad_size_bytes +
+            raw_msg[(num_header_bytes_before_size + len(bad_size_bytes)):]
+        )
+        assert len(raw_msg) == len(raw_msg_with_wrong_size)
+
+        return raw_msg_with_wrong_size
+
+
+
+if __name__ == '__main__':
+    InvalidMessagesTest().main()

test/functional/test_runner.py

@@ -139,6 +139,7 @@
     'mining_prioritisetransaction.py',
     'p2p_invalid_locator.py',
     'p2p_invalid_block.py',
+    'p2p_invalid_messages.py',
     'p2p_invalid_tx.py',
     'feature_assumevalid.py',
     'example_test.py',