Fix DP coordinator ZMQ port TOCTOU

vllm/utils/network_utils.py

@@ -247,7 +247,7 @@ def split_zmq_path(path: str) -> tuple[str, str, str]:
 
     scheme = parsed.scheme
     host = parsed.hostname or ""
-    port = str(parsed.port or "")
+    port = "" if parsed.port is None else str(parsed.port)
     if host.startswith("[") and host.endswith("]"):
         host = host[1:-1]  # Remove brackets for IPv6 address
 

vllm/v1/engine/coordinator.py

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 import copy
 import multiprocessing
+import multiprocessing.connection
 import time
 import weakref
 
@@ -10,7 +11,7 @@
 
 from vllm.config import ParallelConfig
 from vllm.logger import init_logger
-from vllm.utils.network_utils import make_zmq_socket
+from vllm.utils.network_utils import get_tcp_uri, make_zmq_socket
 from vllm.utils.system_utils import get_mp_context, set_process_title
 from vllm.v1.engine import EngineCoreOutputs, EngineCoreRequestType
 from vllm.v1.serial_utils import MsgpackDecoder
@@ -55,6 +56,25 @@ class DPCoordinator:
     request wave / running state changes.
     """
 
+    def _wait_for_zmq_addrs(self, zmq_addr_pipe) -> tuple[str, str, str]:
+        try:
+            ready = multiprocessing.connection.wait(
+                [zmq_addr_pipe, self.proc.sentinel], timeout=30
+            )
+            if not ready:
+                raise RuntimeError(
+                    "DP Coordinator process failed to report ZMQ addresses "
+                    "during startup."
+                )
+            try:
+                return zmq_addr_pipe.recv()
+            except EOFError:
+                raise RuntimeError(
+                    "DP Coordinator process failed during startup."
+                ) from None
+        finally:
+            zmq_addr_pipe.close()
+
     def __init__(
         self, parallel_config: ParallelConfig, enable_wave_coordination: bool = True
     ):
@@ -66,18 +86,24 @@ def __init__(
         # Assume coordinator is colocated with front-end procs when not in
         # either external or hybrid DP LB mode.
         local_only = not parallel_config.local_engines_only
-        front_publish_address = get_engine_client_zmq_addr(
-            local_only=local_only, host=host
-        )
-
         local_only_eng = dp_size == parallel_config.data_parallel_size_local
         # NOTE(yongji): handling scaling from intra-node to inter-node
         if parallel_config.enable_elastic_ep:
             local_only_eng = False
-        back_publish_address = get_engine_client_zmq_addr(local_only_eng, host)
-        back_output_address = get_engine_client_zmq_addr(local_only_eng, host)
+
+        def bind_address(local_only: bool) -> str:
+            return (
+                get_engine_client_zmq_addr(local_only=True, host=host)
+                if local_only
+                else get_tcp_uri(host, 0)
+            )
+
+        front_publish_address = bind_address(local_only)
+        back_publish_address = bind_address(local_only_eng)
+        back_output_address = bind_address(local_only_eng)
 
         context = get_mp_context()
+        parent_zmq_addr_pipe, child_zmq_addr_pipe = context.Pipe(duplex=False)
         self.proc: multiprocessing.Process = context.Process(
             target=DPCoordinatorProc.run_coordinator,
             name="VLLM_DP_Coordinator",
@@ -86,11 +112,18 @@ def __init__(
                 "front_publish_address": front_publish_address,
                 "back_output_address": back_output_address,
                 "back_publish_address": back_publish_address,
+                "zmq_addr_pipe": child_zmq_addr_pipe,
                 "enable_wave_coordination": enable_wave_coordination,
             },
             daemon=True,
         )
         self.proc.start()
+        child_zmq_addr_pipe.close()
+        (
+            front_publish_address,
+            back_output_address,
+            back_publish_address,
+        ) = self._wait_for_zmq_addrs(parent_zmq_addr_pipe)
 
         self.stats_publish_address = front_publish_address
         self.coord_in_address = back_publish_address
@@ -136,6 +169,7 @@ def run_coordinator(
         front_publish_address: str,
         back_output_address: str,
         back_publish_address: str,
+        zmq_addr_pipe=None,
         min_stats_update_interval_ms: int = 100,
         enable_wave_coordination: bool = True,
     ):
@@ -149,15 +183,20 @@ def run_coordinator(
                 front_publish_address,
                 back_output_address,
                 back_publish_address,
+                zmq_addr_pipe,
             )
         except KeyboardInterrupt:
             logger.info("DP Coordinator process exiting")
+        finally:
+            if zmq_addr_pipe is not None:
+                zmq_addr_pipe.close()
 
     def process_input_socket(
         self,
         front_publish_address: str,
         back_output_address: str,
         back_publish_address: str,
+        zmq_addr_pipe=None,
     ):
         decoder = MsgpackDecoder(EngineCoreOutputs)
 
@@ -191,6 +230,17 @@ def process_input_socket(
                 bind=True,
             ) as publish_back,
         ):
+            if zmq_addr_pipe is not None:
+                try:
+                    zmq_addr_pipe.send(
+                        (
+                            publish_front.getsockopt(zmq.LAST_ENDPOINT).decode(),
+                            output_back.getsockopt(zmq.LAST_ENDPOINT).decode(),
+                            publish_back.getsockopt(zmq.LAST_ENDPOINT).decode(),
+                        )
+                    )
+                finally:
+                    zmq_addr_pipe.close()
             # Wait until all engines subscribe.
             for _ in self.engines:
                 if publish_back.recv() != b"\x01":