Fix a couple of problems with random hex string generation

get_random_string uses random.random(), which generates only 53bits
of randomness, but it then calculates 224bits wide hash of the value.
Simply use random.getrandbits() instead.  Convert get_rand_name's
hex string generation logic to use get_random_string, too.

Also remove a call of random.seed with microsecond as its argument,
which degrades random number quality.  The RNG has been initialized
with os.urandom() with enough bits of randomness.

Change-Id: I9302c501b19aa7bf448d95b8f4bdc724c23ed0fb

neutron/common/utils.py

@@ -19,11 +19,9 @@
 """Utilities and helper functions."""
 
 import collections
-import datetime
 import decimal
 import errno
 import functools
-import hashlib
 import math
 import multiprocessing
 import os
@@ -249,17 +247,9 @@ def get_random_mac(base_mac):
 
 def get_random_string(length):
     """Get a random hex string of the specified length.
-
-    based on Cinder library
-      cinder/transfer/api.py
     """
-    rndstr = ""
-    random.seed(datetime.datetime.now().microsecond)
-    while len(rndstr) < length:
-        base_str = str(random.random()).encode('utf-8')
-        rndstr += hashlib.sha224(base_str).hexdigest()
 
-    return rndstr[0:length]
+    return "{0:0{1}x}".format(random.getrandbits(length * 4), length)
 
 
 def get_dhcp_agent_device_id(network_id, host):

neutron/tests/base.py

@@ -20,7 +20,6 @@ import contextlib
 import gc
 import os
 import os.path
-import random
 import weakref
 
 import eventlet.timeout
@@ -43,6 +42,7 @@ from neutron.callbacks import registry
 from neutron.common import config
 from neutron.common import constants
 from neutron.common import rpc as n_rpc
+from neutron.common import utils
 from neutron.db import agentschedulers_db
 from neutron import manager
 from neutron import policy
@@ -84,10 +84,10 @@ def get_rand_name(max_length=None, prefix='test'):
         if length <= 0:
             raise ValueError("'max_length' must be bigger than 'len(prefix)'.")
 
-        suffix = ''.join(str(random.randint(0, 9)) for i in range(length))
     else:
-        suffix = hex(random.randint(0x10000000, 0x7fffffff))[2:]
+        length = 8
-    return prefix + suffix
+
+    return prefix + utils.get_random_string(length)
 
 
 def get_rand_device_name(prefix='test'):