net: Sanitize message type for logging

- Use `SanitizeString` when logging message errors to make sure that the
message type is sanitized.

- For the `MESSAGESTART` error don't inspect and log header details at
all: receiving invalid start bytes makes it likely that the packet isn't
even formatted as valid P2P message. Logging the four unexpected start
bytes should be enough.

- Update `p2p_invalid_messages.py` test to check this.

Issue reported by gmaxwell.

src/net.cpp

@@ -687,13 +687,13 @@ int V1TransportDeserializer::readHeader(Span<const uint8_t> msg_bytes)
 
     // Check start string, network magic
     if (memcmp(hdr.pchMessageStart, m_chain_params.MessageStart(), CMessageHeader::MESSAGE_START_SIZE) != 0) {
-        LogPrint(BCLog::NET, "HEADER ERROR - MESSAGESTART (%s, %u bytes), received %s, peer=%d\n", hdr.GetCommand(), hdr.nMessageSize, HexStr(hdr.pchMessageStart), m_node_id);
+        LogPrint(BCLog::NET, "HEADER ERROR - MESSAGESTART received %s, peer=%d\n", HexStr(hdr.pchMessageStart), m_node_id);
         return -1;
     }
 
     // reject messages larger than MAX_SIZE or MAX_PROTOCOL_MESSAGE_LENGTH
     if (hdr.nMessageSize > MAX_SIZE || hdr.nMessageSize > MAX_PROTOCOL_MESSAGE_LENGTH) {
-        LogPrint(BCLog::NET, "HEADER ERROR - SIZE (%s, %u bytes), peer=%d\n", hdr.GetCommand(), hdr.nMessageSize, m_node_id);
+        LogPrint(BCLog::NET, "HEADER ERROR - SIZE (%s, %u bytes), peer=%d\n", SanitizeString(hdr.GetCommand()), hdr.nMessageSize, m_node_id);
         return -1;
     }
 
@@ -755,7 +755,7 @@ std::optional<CNetMessage> V1TransportDeserializer::GetMessage(const std::chrono
         msg = std::nullopt;
     } else if (!hdr.IsCommandValid()) {
         LogPrint(BCLog::NET, "HEADER ERROR - COMMAND (%s, %u bytes), peer=%d\n",
-                 hdr.GetCommand(), msg->m_message_size, m_node_id);
+                 SanitizeString(hdr.GetCommand()), msg->m_message_size, m_node_id);
         out_err_raw_size = msg->m_raw_message_size;
         msg.reset();
     }

test/functional/p2p_invalid_messages.py

@@ -37,7 +37,7 @@ VALID_DATA_LIMIT = MAX_PROTOCOL_MESSAGE_LENGTH - 5  # Account for the 5-byte len
 class msg_unrecognized:
     """Nonsensical message. Modeled after similar types in test_framework.messages."""
 
-    msgtype = b'badmsg'
+    msgtype = b'badmsg\x01'
 
     def __init__(self, *, str_data):
         self.str_data = str_data.encode() if not isinstance(str_data, bytes) else str_data
@@ -104,7 +104,7 @@ class InvalidMessagesTest(BitcoinTestFramework):
     def test_magic_bytes(self):
         self.log.info("Test message with invalid magic bytes disconnects peer")
         conn = self.nodes[0].add_p2p_connection(P2PDataStore())
-        with self.nodes[0].assert_debug_log(['HEADER ERROR - MESSAGESTART (badmsg, 2 bytes), received ffffffff']):
+        with self.nodes[0].assert_debug_log(['HEADER ERROR - MESSAGESTART received ffffffff']):
             msg = conn.build_message(msg_unrecognized(str_data="d"))
             # modify magic bytes
             msg = b'\xff' * 4 + msg[4:]