[issue27778] PEP 524: Add os.getrandom()

[Donald Stufft]

Changes by Donald Stufft :


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pull_requests: +848

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[issue27778] PEP 524: Add os.getrandom()

[STINNER Victor]

STINNER Victor added the comment:

Because of the lack of interest for getrandom_errno.patch, and Christian saying 
that it's not good to document specific errors, I now close the bug.

Thank you all for your help on this nice security enhancement in Python 3.6!

--
resolution:  -> fixed
status: open -> closed

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[issue27778] PEP 524: Add os.getrandom()

[Christian Heimes]

Christian Heimes added the comment:

I think the documentation is too specific. We typically don't document all 
possible error numbers. Something along the lines "fails with OSError when 
getrandom is not supported" is sufficient.

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assignee:  -> docs@python
components: +Documentation
nosy: +docs@python
priority: normal -> low
type: security -> enhancement

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[issue27778] PEP 524: Add os.getrandom()

[STINNER Victor]

STINNER Victor added the comment:

I pushed the fix for the issue #27955, os.urandom() now handles getrandom() 
failing with EPERM.

@Christian: Thanks for your review, I pushed a change fixing the two issues 
that you reported (memory leak and inefficient temporarily buffer).

I attached getrandom_errno.patch: a change proposing to document ENOSYS and 
EPERM. What do you think?

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Added file: http://bugs.python.org/file44760/getrandom_errno.patch

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[issue27778] PEP 524: Add os.getrandom()

[Roundup Robot]

Roundup Robot added the comment:

New changeset d31b4de433b7 by Victor Stinner in branch '3.6':
Fix memleak in os.getrandom()
https://hg.python.org/cpython/rev/d31b4de433b7

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[issue27778] PEP 524: Add os.getrandom()

[Christian Heimes]

Christian Heimes added the comment:

Oh sorry, I looked in the wrong location and missed it.

* if (PyErr_CheckSignals() < 0) {return NULL;} does not free buffer with 
PyMem_Free(buffer);

* The function allocates memory once with PyMem_Malloc() and later a second 
time with PyBytes_FromStringAndSize(buffer, n). You can avoid the first 
allocation and a memcpy() with PyBytes_FromStringAndSize(NULL, n) and 
PyBytes_AS_STRING().

* The syscall can also raise EPERM as reported by a user on QNAP. IIRC a 
seccomp policy caused EPERM.

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versions: +Python 3.6

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[issue27778] PEP 524: Add os.getrandom()

[Nick Coghlan]

Nick Coghlan added the comment:

Right, the only missing piece now is documentation of the ENOSYS case, which 
end users may encounter if a Python 3.6 binary that supports os.getrandom() is 
run against an older kernel.

That's pretty easy to trigger via containers, as getrandom() was added in Linux 
3.17 and hasn't generally been backported to LTS distribution kernels.

Debian 8: based on 3.16
Ubuntu 14.04: 3.13 default, 4.4 (from 16.04) available as of 14.04.5
RHEL/CentOS 7: based on 3.10
RHEL/CentOS 6: based on 2.6

So of those potential LTS container hosts, a recent Ubuntu or Fedora container 
running Python 3.6 will currently get ENOSYS for everything except a fresh 
Ubuntu 14.04 install that uses the Ubuntu 16.04 kernel.

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[issue27778] PEP 524: Add os.getrandom()

[Martin Panter]

Martin Panter added the comment:

I understand it’s already implemented, and Victor just reopened it for more 
documentation.

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[issue27778] PEP 524: Add os.getrandom()

[Christian Heimes]

Christian Heimes added the comment:

3.6 is in beta phase. Are you interested to add the feature to 3.7?

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nosy: +christian.heimes
versions: +Python 3.7 -Python 3.6

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[issue27778] PEP 524: Add os.getrandom()

[Martin Panter]

Martin Panter added the comment:

I run Arch Linux, but only update packages when I have to. As a result, I am 
running Linux 3.15 installed and running, but the linux-api-headers has more 
recently been updated to 4.7 (i.e. matching Linux 4.7).

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[issue27778] PEP 524: Add os.getrandom()

[Nick Coghlan]

Nick Coghlan added the comment:

Ah, I'd missed that Martin was talking about the other way around from #27990.

Yes, I think it's worth documenting that os.getrandom() may raise OSError if 
the running kernel doesn't provide the syscall - that's going to be pretty easy 
to trigger by running a container with Python 3.6 on a container host running 
an older Linux kernel.

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[issue27778] PEP 524: Add os.getrandom()

[STINNER Victor]

STINNER Victor added the comment:

> HAVE_GETRANDOM_SYSCALL seems to be a compile-time library check, not a 
> runtime check. I compiled and run on Linux 3.15.5, and os.getrandom() exists 
> but raises ENOSYS:

Oh, I'm surprised the configure sees getrandom() as available. But well ok, the 
error can occur if you compile Python on a more recent kernel than the running 
kernel.

I fixed the unit test: skip getrandom() tests if getrandom() fails with ENOSYS.

Do you think that it's worth to document this case?

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resolution: fixed -> 
status: closed -> open

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[issue27778] PEP 524: Add os.getrandom()

[Roundup Robot]

Roundup Robot added the comment:

New changeset 7a243a40b421 by Victor Stinner in branch 'default':
Fix test_os.GetRandomTests()
https://hg.python.org/cpython/rev/7a243a40b421

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[issue27778] PEP 524: Add os.getrandom()

[Nick Coghlan]

Nick Coghlan added the comment:

Huh, I thought I'd already filed an issue for that, but it looks like it was 
only a security-sig thread: 
https://mail.python.org/pipermail/security-sig/2016-June/60.html

I've now remedied that omission and filed http://bugs.python.org/issue27990 to 
cover it explicitly.

Since that was a pre-existing problem that also happens to affect this API, 
rather than something new introduced by Victor's patch, closing this again.

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stage:  -> resolved
status: open -> closed

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[issue27778] PEP 524: Add os.getrandom()

[Martin Panter]

Martin Panter added the comment:

HAVE_GETRANDOM_SYSCALL seems to be a compile-time library check, not a runtime 
check. I compiled and run on Linux 3.15.5, and os.getrandom() exists but raises 
ENOSYS:

==
ERROR: test_getrandom0 (test.test_os.GetRandomTests)
--
Traceback (most recent call last):
  File "/media/disk/home/proj/python/cpython/Lib/test/test_os.py", line 1280, 
in test_getrandom0
empty = os.getrandom(0)
OSError: [Errno 38] Function not implemented

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status: closed -> open

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[issue27778] PEP 524: Add os.getrandom()

[STINNER Victor]

Changes by STINNER Victor :


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resolution:  -> fixed
status: open -> closed

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[issue27778] PEP 524: Add os.getrandom()

[Roundup Robot]

Roundup Robot added the comment:

New changeset 27267d2fb091 by Victor Stinner in branch 'default':
Add os.getrandom()
https://hg.python.org/cpython/rev/27267d2fb091

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[issue27778] PEP 524: Add os.getrandom()

[Nick Coghlan]

Nick Coghlan added the comment:

Given docs (with the Linux-only platform support disclaimer), +1 for this as an 
initial implementation.

Providing it on Solaris as well can be a separate patch, but it's less 
important there (since /dev/urandom and os.urandom() are already blocking APIs)

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nosy: +ncoghlan

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[issue27778] PEP 524: Add os.getrandom()

[STINNER Victor]

New submission from STINNER Victor:

Attached patch adds os.getrandom(): thin wrapper on the Linux getrandom() 
syscall.

os.getrandom() can return less bytes than requested.

The patch is incomplete: it doesn't include documentation.

I chose to not implement a loop to not loose entropy if a following call fails 
(ex: fail with EINTR). Rationale:
https://mail.python.org/pipermail/security-sig/2016-July/72.html

We should also add Solaris support later.

See also #27776: "PEP 524: Make os.urandom() blocking on Linux".

--
components: Library (Lib)
files: getrandom.patch
keywords: patch
messages: 272867
nosy: haypo
priority: normal
severity: normal
status: open
title: PEP 524: Add os.getrandom()
type: security
versions: Python 3.6
Added file: http://bugs.python.org/file44127/getrandom.patch

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