bpo-32107 - Improve MAC address calculation and fix test_uuid.py (#4600)
``uuid.getnode()`` now preferentially returns universally administered MAC addresses if available, over locally administered MAC addresses. This makes a better guarantee for global uniqueness of UUIDs returned from ``uuid.uuid1()``. If only locally administered MAC addresses are available, the first such one found is returned.
Also improve internal code style by being explicit about ``return None`` rather than falling off the end of the function.
Improve the test robustness.
diff --git a/Lib/uuid.py b/Lib/uuid.py
index 020c6e7..cb2bc09 100644
--- a/Lib/uuid.py
+++ b/Lib/uuid.py
@@ -342,11 +342,30 @@
env=env)
return proc
+# For MAC (a.k.a. IEEE 802, or EUI-48) addresses, the second least significant
+# bit of the first octet signifies whether the MAC address is universally (0)
+# or locally (1) administered. Network cards from hardware manufacturers will
+# always be universally administered to guarantee global uniqueness of the MAC
+# address, but any particular machine may have other interfaces which are
+# locally administered. An example of the latter is the bridge interface to
+# the Touch Bar on MacBook Pros.
+#
+# This bit works out to be the 42nd bit counting from 1 being the least
+# significant, or 1<<41. We'll prefer universally administered MAC addresses
+# over locally administered ones since the former are globally unique, but
+# we'll return the first of the latter found if that's all the machine has.
+#
+# See https://en.wikipedia.org/wiki/MAC_address#Universal_vs._local
+
+def _is_universal(mac):
+ return not (mac & (1 << 41))
+
def _find_mac(command, args, hw_identifiers, get_index):
+ first_local_mac = None
try:
proc = _popen(command, *args.split())
if not proc:
- return
+ return None
with proc:
for line in proc.stdout:
words = line.lower().rstrip().split()
@@ -355,8 +374,9 @@
try:
word = words[get_index(i)]
mac = int(word.replace(b':', b''), 16)
- if mac:
+ if _is_universal(mac):
return mac
+ first_local_mac = first_local_mac or mac
except (ValueError, IndexError):
# Virtual interfaces, such as those provided by
# VPNs, do not have a colon-delimited MAC address
@@ -366,6 +386,7 @@
pass
except OSError:
pass
+ return first_local_mac or None
def _ifconfig_getnode():
"""Get the hardware address on Unix by running ifconfig."""
@@ -375,6 +396,7 @@
mac = _find_mac('ifconfig', args, keywords, lambda i: i+1)
if mac:
return mac
+ return None
def _ip_getnode():
"""Get the hardware address on Unix by running ip."""
@@ -382,6 +404,7 @@
mac = _find_mac('ip', 'link list', [b'link/ether'], lambda i: i+1)
if mac:
return mac
+ return None
def _arp_getnode():
"""Get the hardware address on Unix by running arp."""
@@ -404,8 +427,10 @@
# This works on Linux, FreeBSD and NetBSD
mac = _find_mac('arp', '-an', [os.fsencode('(%s)' % ip_addr)],
lambda i: i+2)
+ # Return None instead of 0.
if mac:
return mac
+ return None
def _lanscan_getnode():
"""Get the hardware address on Unix by running lanscan."""
@@ -415,32 +440,36 @@
def _netstat_getnode():
"""Get the hardware address on Unix by running netstat."""
# This might work on AIX, Tru64 UNIX.
+ first_local_mac = None
try:
proc = _popen('netstat', '-ia')
if not proc:
- return
+ return None
with proc:
words = proc.stdout.readline().rstrip().split()
try:
i = words.index(b'Address')
except ValueError:
- return
+ return None
for line in proc.stdout:
try:
words = line.rstrip().split()
word = words[i]
if len(word) == 17 and word.count(b':') == 5:
mac = int(word.replace(b':', b''), 16)
- if mac:
+ if _is_universal(mac):
return mac
+ first_local_mac = first_local_mac or mac
except (ValueError, IndexError):
pass
except OSError:
pass
+ return first_local_mac or None
def _ipconfig_getnode():
"""Get the hardware address on Windows by running ipconfig.exe."""
import os, re
+ first_local_mac = None
dirs = ['', r'c:\windows\system32', r'c:\winnt\system32']
try:
import ctypes
@@ -458,18 +487,23 @@
for line in pipe:
value = line.split(':')[-1].strip().lower()
if re.match('([0-9a-f][0-9a-f]-){5}[0-9a-f][0-9a-f]', value):
- return int(value.replace('-', ''), 16)
+ mac = int(value.replace('-', ''), 16)
+ if _is_universal(mac):
+ return mac
+ first_local_mac = first_local_mac or mac
+ return first_local_mac or None
def _netbios_getnode():
"""Get the hardware address on Windows using NetBIOS calls.
See http://support.microsoft.com/kb/118623 for details."""
import win32wnet, netbios
+ first_local_mac = None
ncb = netbios.NCB()
ncb.Command = netbios.NCBENUM
ncb.Buffer = adapters = netbios.LANA_ENUM()
adapters._pack()
if win32wnet.Netbios(ncb) != 0:
- return
+ return None
adapters._unpack()
for i in range(adapters.length):
ncb.Reset()
@@ -488,7 +522,11 @@
bytes = status.adapter_address[:6]
if len(bytes) != 6:
continue
- return int.from_bytes(bytes, 'big')
+ mac = int.from_bytes(bytes, 'big')
+ if _is_universal(mac):
+ return mac
+ first_local_mac = first_local_mac or mac
+ return first_local_mac or None
_generate_time_safe = _UuidCreate = None
@@ -601,9 +639,19 @@
return UUID(bytes=bytes_(_buffer.raw)).node
def _random_getnode():
- """Get a random node ID, with eighth bit set as suggested by RFC 4122."""
+ """Get a random node ID."""
+ # RFC 4122, $4.1.6 says "For systems with no IEEE address, a randomly or
+ # pseudo-randomly generated value may be used; see Section 4.5. The
+ # multicast bit must be set in such addresses, in order that they will
+ # never conflict with addresses obtained from network cards."
+ #
+ # The "multicast bit" of a MAC address is defined to be "the least
+ # significant bit of the first octet". This works out to be the 41st bit
+ # counting from 1 being the least significant bit, or 1<<40.
+ #
+ # See https://en.wikipedia.org/wiki/MAC_address#Unicast_vs._multicast
import random
- return random.getrandbits(48) | 0x010000000000
+ return random.getrandbits(48) | (1 << 40)
_node = None
@@ -626,13 +674,14 @@
getters = [_unix_getnode, _ifconfig_getnode, _ip_getnode,
_arp_getnode, _lanscan_getnode, _netstat_getnode]
- for getter in getters + [_random_getnode]:
+ for getter in getters:
try:
_node = getter()
except:
continue
if _node is not None:
return _node
+ return _random_getnode()
_last_timestamp = None