fix: require X-P2P-Key auth on /p2p/gossip POST endpoint (fixes #8177) [fj4WqyCCw3C5ShR1RfB7MoBPTpkRrBFYP1uT35g3MvT]

node/rustchain_p2p_gossip.py

@@ -1823,6 +1823,10 @@ def receive_gossip():
         if not _gossip_rate_check(remote_ip):
             return jsonify({"error": "rate_limited", "limit": f"{GOSSIP_RATE_LIMIT}/{GOSSIP_RATE_WINDOW_S}s"}), 429
 
+        auth_error = _require_p2p_read_auth()
+        if auth_error:
+            return auth_error
+
         if (
             request.content_length is not None
             and request.content_length > MAX_GOSSIP_REQUEST_BYTES

node/utxo_db.py

@@ -1535,9 +1535,16 @@ def mempool_get_block_candidates(self, max_count: int = 100) -> List[dict]:
             conn.close()
 
     def mempool_clear_expired(self) -> int:
-        """Remove expired transactions from mempool. Returns count removed."""
+        """Remove expired transactions from mempool. Returns count removed.
+
+        Uses BEGIN IMMEDIATE to ensure the SELECT-then-DELETE sequence is
+        atomic. Without it, a concurrent mempool_add() or apply_transaction()
+        can interleave between the SELECT and the DELETEs, causing mempool
+        state corruption / double-spend (B2, issue #8176).
+        """
         conn = self._conn()
         try:
+            conn.execute("BEGIN IMMEDIATE")
             now = int(time.time())
             try:
                 expired = conn.execute(
@@ -1546,22 +1553,29 @@ def mempool_clear_expired(self) -> int:
                 ).fetchall()
             except sqlite3.OperationalError as exc:
                 if "no such table" in str(exc).lower():
+                    conn.execute("ROLLBACK")
                     return 0
+                conn.execute("ROLLBACK")
                 raise
-            else:
-                count = 0
-                for row in expired:
-                    conn.execute(
-                        "DELETE FROM utxo_mempool_inputs WHERE tx_id = ?",
-                        (row['tx_id'],),
-                    )
-                    conn.execute(
-                        "DELETE FROM utxo_mempool WHERE tx_id = ?",
-                        (row['tx_id'],),
-                    )
-                    count += 1
-                conn.commit()
-                return count
+            count = 0
+            for row in expired:
+                conn.execute(
+                    "DELETE FROM utxo_mempool_inputs WHERE tx_id = ?",
+                    (row['tx_id'],),
+                )
+                conn.execute(
+                    "DELETE FROM utxo_mempool WHERE tx_id = ?",
+                    (row['tx_id'],),
+                )
+                count += 1
+            conn.commit()
+            return count
+        except Exception:
+            try:
+                conn.execute("ROLLBACK")
+            except Exception:
+                pass
+            raise
         finally:
             conn.close()