Bound wakeword payload length to prevent DoS

Added a 10MB limit and lower bound to `payload_length` read from network payloads in `wakeword.py` and `wakeword_bench.py` to prevent unbounded memory allocation and infinite waiting for malicious/corrupt frames.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

.jules/sentinel.md

@@ -0,0 +1,3 @@
+## 2025-02-14 — Bound wakeword payload length
+**Learning:** `payload_length` read from network JSON payloads in `wakeword.py` and `wakeword_bench.py` lacked bounds checks, allowing a malicious Wyoming server (or MITM) to cause a DoS by providing a huge length and freezing the read loop or consuming all memory.
+**Action:** Added `if not (0 <= payload_len <= 10 * 1024 * 1024):` bounds check to safely drop oversized or negative `payload_length` frames.

linux/blitztext/wakeword.py

@@ -112,6 +112,9 @@ class WakewordListener:
                                 self._handle_detection()
                                 
                             payload_len = msg.get("payload_length", 0)
+                            if not (0 <= payload_len <= 10 * 1024 * 1024):
+                                logbuffer.log(f"[wakeword] Disconnecting: payload length {payload_len} out of bounds", level="WARNING")
+                                break
                             if payload_len > 0:
                                 # Consume payload
                                 remaining = payload_len
@@ -258,6 +261,9 @@ class WakewordActionListener:
                                     self._stop_event.set()   # one-shot: stop after first fire
                                     cb()
                             payload_len = msg.get("payload_length", 0)
+                            if not (0 <= payload_len <= 10 * 1024 * 1024):
+                                logbuffer.log(f"[wakeword-action] Disconnecting: payload length {payload_len} out of bounds", level="WARNING")
+                                break
                             if payload_len > 0:
                                 remaining = payload_len
                                 while remaining > 0:

linux/blitztext/wakeword_bench.py

@@ -322,6 +322,9 @@ def _drain_detections(buf: bytes) -> tuple[bytes, int]:
         except (ValueError, UnicodeDecodeError):
             return rest, found
         plen = msg.get("payload_length", 0) or 0
+        if not (0 <= plen <= 10 * 1024 * 1024):
+            # Abort this buffer completely if framing is corrupt or size is unreasonable
+            return b"", found
         if len(rest) < plen:
             return buf, found  # payload not fully arrived yet; wait for more
         rest = rest[plen:]