[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[STINNER Victor]

STINNER Victor added the comment:

Oh, sorry, I introduced the bug in Python 3.6 with the PEP 524 (os.urandom() 
now blocks on Linux). Too bad that there is no simple way to write an unit test 
for that.

> ... but only on Windows on Python 3.6

With the bug, or when the fix when _PyOS_URandomNonblock() fails, Random.seed() 
uses:

* Reading system entropy failed, fall back on the worst entropy:
  use the current time and process identifier. */
random_seed_time_pid(self);

It's just that on Windows, the system clock has a resolution around 15 ms, 
whereas it has a resolution better than 1 us on Linux. So it's just that 
calling Random.seed() usually takes longer than the resolution of the system 
clock on Linux :-) Not really that the bug is specific to Windows.

Thanks for the fix Benjamin!

--
nosy: +haypo

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Roundup Robot]

Roundup Robot added the comment:

New changeset 0a55e039d25f by Benjamin Peterson in branch '3.6':
fix error check, so that Random.seed actually uses OS randomness (closes #29085)
https://hg.python.org/cpython/rev/0a55e039d25f

New changeset fc3eab44765f by Benjamin Peterson in branch 'default':
merge 3.6 (#29085)
https://hg.python.org/cpython/rev/fc3eab44765f

--
nosy: +python-dev
resolution:  -> fixed
stage:  -> resolved
status: open -> closed

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Eryk Sun]

Eryk Sun added the comment:

The secrets module uses SystemRandom, which overrides random() and 
getrandbits() to use os.urandom, so it's not affected.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Brett Cannon]

Changes by Brett Cannon :


--
nosy: +paul.moore, steve.dower, tim.golden, zach.ware

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Brett Cannon]

Brett Cannon added the comment:

Does this affect the secrets module at all?

--
nosy: +brett.cannon

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


--
assignee:  -> rhettinger
nosy: +rhettinger

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Eryk Sun]

Eryk Sun added the comment:

> It's presumably failing to read nonblocking random from CrpytGen 
> and falling back to seeding using time and pid.

Yes and no. CryptGenRandom is not failing, but it is nonetheless calling 
random_seed_time_pid:

>>> r = random.Random()
Breakpoint 0 hit
python36_d!random_seed:
`5e7277c0 4889542410  mov qword ptr [rsp+10h],rdx
ss:0095`053ef0e8=
0:000> g
Breakpoint 1 hit
python36_d!random_seed_time_pid:
`5e728910 48894c2408  mov qword ptr [rsp+8],rcx
ss:0095`053ef040=02319b6f3b88
0:000> kc 3
Call Site
python36_d!random_seed_time_pid
python36_d!random_seed
python36_d!random_new

It looks like there's a bug in the new implementation of random_seed():

 if (arg == NULL || arg == Py_None) {
if (random_seed_urandom(self) >= 0) {
PyErr_Clear();

/* Reading system entropy failed, fall back on the worst entropy:
   use the current time and process identifier. */
random_seed_time_pid(self);
}
Py_RETURN_NONE;
}

If random_seed_urandom fails, it returns -1, so this should be testing if the 
result is less than 0.

--
nosy: +eryksun

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Kyle Altendorf]

Kyle Altendorf added the comment:

time.sleep(0) and time.sleep(0.0) acted the same for me and both exhibited 
matching 'random' values in some cases.  (win10, python3.6)  I also printed 
time.time() with each 'random' value and it wasn't a perfect match but matching 
times tended to go with matching 'random' values.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Ammar Askar]

Ammar Askar added the comment:

Can recreate under

Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 08:06:12) [MSC v.1900 64 bit 
(AMD64)] on win32

and on latest master.

--
nosy: +ammar2
versions: +Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Donald Stufft]

Donald Stufft added the comment:

It's presumably failing to read nonblocking random from CrpytGen and falling 
back to seeding using time and pid.

--
nosy: +dstufft

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Ned Batchelder]

Ned Batchelder added the comment:

Adding a time.sleep(0.001) (or maybe even just 0) between the calls prevents 
the problem.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Kyle Altendorf]

Changes by Kyle Altendorf :


--
nosy: +altendky

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Ned Batchelder]

Changes by Ned Batchelder :


--
versions: +Python 3.6

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue29085] Python 3.6 on Windows doesn't seed Random() well enough

[Ned Batchelder]

New submission from Ned Batchelder:

Creating two Random() instances in quick succession produces the same sequence, 
but only on Windows on Python 3.6.  On 3.5 or earlier, or on Mac/Linux, the 
randomization is good.

Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 07:18:10) [MSC v.1900 32 bit 
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import random; print(random.Random().randint(1, 99), 
>>> random.Random().randint(1, 99))
903885 903885
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(2)])
996947 56476
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(2)])
793282 793282
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(2)])
519702 519702
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(2)])
230678 230678
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(3)])
474701 474701 474701
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(3)])
890942 890942 890942
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(3)])
997495 997495 997495
>>> import random; print(*[random.Random().randint(1, 99) for _ in 
>>> range(5)])
27803 27803 27803 27803 919401
>>>

I would expect each of these runs to produce unique numbers, with no duplicates.

--
keywords: 3.6regression
messages: 284118
nosy: nedbat
priority: normal
severity: normal
status: open
title: Python 3.6 on Windows doesn't seed Random() well enough

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com