Force "fork" method for RADIUS daemon in OTP test

The RADIUS daemon used in the OTP test relies on
multiprocessing.Process. Since Python 3.14, multiprocessing changed its
start method from "fork" to "forkserver". This method is not compatible
with the t_otp.py test.

This commit explicitly sets multiprocessing's start method to "fork" for
test t_otp.py, using multiprocessing.set_start_method() (available since
Python 3.4).

Pull-request: krb5/krb5#1483

Author: jrisc

src/tests/t_otp.py

@@ -38,10 +38,14 @@
 except ImportError:
     skip_rest('OTP tests', 'Python pyrad module not found')
 try:
-    from multiprocessing import Process, Queue
+    import multiprocessing
 except ImportError:
     skip_rest('OTP tests', 'Python version 2.6 required')
 
+# Since Python 3.14, "forkserver" replaces "fork" as default method on POSIX.
+# "forkserver" is not compatible with this test, so force the "fork" method.
+multiprocessing.set_start_method('fork', force=True)
+
 # We could use a dictionary file, but since we need so few attributes,
 # we'll just include them here.
 radius_attributes = '''
@@ -52,7 +56,7 @@
 ATTRIBUTE    Message-Authenticator 80 octets
 '''
 
-class RadiusDaemon(Process):
+class RadiusDaemon(multiprocessing.Process):
     MAX_PACKET_SIZE = 4096
     DICTIONARY = dictionary.Dictionary(io.StringIO(radius_attributes))
 
@@ -186,7 +190,7 @@ def otpconfig(toktype, username=None, indicators=None):
                 'unix': {'server': socket_file,
                          'strip_realm': 'false'}}}
 
-queue = Queue()
+queue = multiprocessing.Queue()
 
 realm = K5Realm(kdc_conf=conf)
 realm.run([kadminl, 'modprinc', '+requires_preauth', realm.user_princ])
@@ -259,7 +263,7 @@ def otpconfig(toktype, username=None, indicators=None):
 ## tokens configured, with the first rejecting and the second
 ## accepting.  With the bug, the KDC incorrectly rejects the request
 ## and then performs invalid memory accesses, most likely crashing.
-queue2 = Queue()
+queue2 = multiprocessing.Queue()
 daemon1 = UDPRadiusDaemon(args=(server_addr, secret_file, 'accept1', queue))
 daemon2 = UnixRadiusDaemon(args=(socket_file, None, 'accept2', queue2))
 daemon1.start()