extmod/modlwip: Fix crash when calling recv on listening socket.

Add check to prevent calling recv on a socket in the listening state.  This
prevents a crash/hard fault when user code mistakenly tries to recv on the
listening socket instead of on the accepted connection.

Add corresponding test case to demonstrate the bug.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

extmod/modlwip.c

@@ -860,6 +860,12 @@ static mp_uint_t lwip_tcp_receive(lwip_socket_obj_t *socket, byte *buf, mp_uint_
         }
     }
 
+    if (socket->state == STATE_LISTENING) {
+        // original socket in listening state, not the accepted connection.
+        *_errno = MP_ENOTCONN;
+        return -1;
+    }
+
     MICROPY_PY_LWIP_ENTER
 
     assert(socket->pcb.tcp != NULL);

tests/multi_net/tcp_accept_recv.py

@@ -1,30 +1,64 @@
-# Test recv on socket that just accepted a connection
+# Test recv on listening socket after accept(), with various listen() arguments
 
 import socket
 
 PORT = 8000
 
+# Test cases for listen() function
+LISTEN_ARGS = [None, 0, 1, 2]  # None means no argument
+
 
 # Server
 def instance0():
     multitest.globals(IP=multitest.get_network_ip())
-    s = socket.socket()
-    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-    s.bind(socket.getaddrinfo("0.0.0.0", PORT)[0][-1])
-    s.listen(1)
     multitest.next()
-    s.accept()
-    try:
-        print("recv", s.recv(10))  # should raise Errno 107 ENOTCONN
-    except OSError as er:
-        print(er.errno in (107, 128))
-    s.close()
+
+    for i, listen_arg in enumerate(LISTEN_ARGS):
+        s = socket.socket()
+        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        s.bind(socket.getaddrinfo("0.0.0.0", PORT)[0][-1])
+
+        # Call listen with or without argument based on test case
+        if listen_arg is None:
+            print(f"Test case {i + 1}/{len(LISTEN_ARGS)}: listen()")
+            s.listen()
+        else:
+            print(f"Test case {i + 1}/{len(LISTEN_ARGS)}: listen({listen_arg})")
+            s.listen(listen_arg)
+
+        # Signal client that server is ready
+        multitest.broadcast(f"server_ready_{i}")
+
+        # Wait for client connection
+        c, _ = s.accept()
+
+        try:
+            print("recv", s.recv(10))  # should raise Errno 107 ENOTCONN
+        except OSError as er:
+            # Verify the error code is either 107 (ENOTCONN) or 128 (ENOTCONN on Windows)
+            print(er.errno in (107, 128))
+
+        # Cleanup
+        c.close()
+        s.close()
+
+        # Signal client we're done with this test case
+        multitest.broadcast(f"server_done_{i}")
 
 
 # Client
 def instance1():
     multitest.next()
-    s = socket.socket()
-    s.connect(socket.getaddrinfo(IP, PORT)[0][-1])
-    s.send(b"GET / HTTP/1.0\r\n\r\n")
-    s.close()
+
+    for i, _ in enumerate(LISTEN_ARGS):
+        # Wait for server to be ready
+        multitest.wait(f"server_ready_{i}")
+
+        # Connect to server
+        s = socket.socket()
+        s.connect(socket.getaddrinfo(IP, PORT)[0][-1])
+        s.send(b"GET / HTTP/1.0\r\n\r\n")
+        s.close()
+
+        # Wait for server to finish this test case
+        multitest.wait(f"server_done_{i}")