os.urandom() should use Linux 3.17 getrandom() syscall #66377

vstinner · 2014-08-10T23:32:43Z

BPO	22181
Nosy	@pitrou, @vstinner, @tiran, @jwilk, @alex, @MojoVampire
Files	random.patch random-2.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2015-03-30.11:42:45.852>
created_at = <Date 2014-08-10.23:32:43.376>
labels = ['type-security']
title = 'os.urandom() should use Linux 3.17 getrandom() syscall'
updated_at = <Date 2015-03-30.11:42:45.851>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2015-03-30.11:42:45.851>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2015-03-30.11:42:45.852>
closer = 'vstinner'
components = []
creation = <Date 2014-08-10.23:32:43.376>
creator = 'vstinner'
dependencies = []
files = ['38310', '38330']
hgrepos = []
issue_num = 22181
keywords = ['patch']
message_count = 23.0
messages = ['225171', '225363', '228250', '228639', '228645', '228655', '228785', '228790', '228791', '228792', '228794', '228795', '228847', '228850', '237102', '237190', '238440', '238504', '238559', '238568', '238676', '238688', '239585']
nosy_count = 11.0
nosy_names = ['pitrou', 'vstinner', 'christian.heimes', 'jwilk', 'Arfrever', 'alex', 'neologix', 'python-dev', 'anand.jeyahar', 'josh.r', '700eb415']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'security'
url = 'https://bugs.python.org/issue22181'
versions = ['Python 3.5']

vstinner · 2014-08-10T23:32:43Z

The future Linux kernel 3.17 will have a new getrandom() syscall which avoids the need of a file descriptor:
http://lwn.net/Articles/606141/

The file descriptor of os.urandom() causes perfomance issues and surprising bugs: bpo-18756, bpo-21207.

I don't know when the function will land in the libc.

OpenBSD 5.6 (not released yet) will also have a new getentropy() syscall.

For Python 2.7, see also the PEP-466 and the issue bpo-21305.

vstinner · 2014-08-15T20:13:55Z

Manual page of the OpenBSD getentropy() function:
http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2

LibreSSL didn't wait for the libc, search for getentropy_getrandom():
http://openbsd.cs.toronto.edu/cgi-bin/cvsweb/src/lib/libcrypto/crypto/getentropy_linux.c?rev=1.32&content-type=text/x-cvsweb-markup

The code is currently disabled with "#if 0". The syscall is directly used, the function doesn't handle the ENOSYS error.

See also this issue of the cryptography project, "Use getentropy(2) and getrandom(2) syscalls when available 1299":
pyca/cryptography#1299

700eb415 · 2014-10-02T18:03:18Z

It's worth noting that LibreSSL has now enabled the blocked code. If anyone is interested, I would be willing to help port it.

anandjeyahar · 2014-10-06T05:02:37Z

Hi,
This will need latest kernel to develop, fix and test. I (on Debian 7) couldn't find the latest kernel, but picked up ubuntu kernel from here http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.17-rc7-utopic/. I picked up the latest i.e: linux-image-3.17.0-031700rc7-generic_3.17.0-031700rc7.201409281835_amd64.deb and installed manually, but couldn't find the getrandom() function call either in stdlib.h or linux/random.h.

Can anyone confirm it's availability in a kernel image (from some other distribution?).

neologix · 2014-10-06T07:22:33Z

Note that I'm not fussed about it: far from simplifying the code, it
will make it more complex, thus more error-prone.

vstinner · 2014-10-06T10:24:01Z

The Linux kernel 3.17 has been released with the new getrandom() syscall.

glibc request to implement the function in the C library:
https://sourceware.org/bugzilla/show_bug.cgi?id=17252
"Bug 17252 - getrandom and getentropy syscall"

It looks like nobody asks for it on the libc-alpha mailing list yet.

tiran · 2014-10-08T10:51:20Z

Let's not be early adopters here. I suggest we wait until glibc has a proper interface.

700eb415 · 2014-10-08T13:59:57Z

OpenBSD already provides high quality pseudorandom numbers from arc4random(). I don't think this would make us "early adopters" since it has been around for some time on this platform.

It's also worth mentioning that getentropy() is not recommended in use for normal code as per stated in the man page. arc4random() is recommended, but there may be a reason the first poster has recommended getentropy()

pitrou · 2014-10-08T14:06:55Z

This issue is about Linux support. Does the glibc have arc4random? I can't find it on my Ubuntu 13.10 system.

alex · 2014-10-08T14:20:22Z

As I said on the other ticket, using arc4random() indiscriminately would be a very poor idea, on some platforms (such as OS X) arc4random() really does use ARC4, which means there are serious security concerns with it.

700eb415 · 2014-10-08T14:29:56Z

While I agree it may not be wise to use arc4random() globally, OpenBSD is unlikely to create a duplicate interface since it's already available.

Python is currently unusable in chroots on that platform without reducing the security of the host partition by removing the nodev mount flag.

I feel like there must be a good solution to this.

pitrou · 2014-10-08T14:30:55Z

Since this is a Linux-specific issue (see the title), you should create a separate issue for OpenBSD support. Bonus points if you want to submit a patch as well :-)

vstinner · 2014-10-09T09:27:58Z

This issue is specific to Linux: it depends on the Linux kernel version and we are waiting until the new syscall is available in the C library (especially the glibc). For these reasons, I prefer to open a new specific issue for OpenBSD, since they release the kernel and C library at the same time (different release process): issue bpo-22585. OpenBSD 5.6 scheduled in one month will get the new getentropy() syscall and a new getentropy() function at the same time.

vstinner · 2014-10-09T09:45:14Z

Since this is a Linux-specific issue (see the title), you should create a separate issue for OpenBSD support.

700eb415 opened the issue bpo-22542 for arc4random().

vstinner · 2015-03-03T02:04:16Z

Commit in the Linux kernel:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c6e9d6f38894798696f23c8084ca7edbf16ee895

--

Here is a patch to use the new getrandom() syscall of Linux 3.17 in the Python function os.urandom().

The function falls back to reading /dev/urandom if getrandom() is not supported (returns ENOSYS at runtime).

On my Linux 3.18, the EINTR path is never taken. But I was able to test it manually by setting flags to GRND_RANDOM (2) and injecting many signals using signal.setitimer(): see my http://bugs.python.org/issue23285#msg237100

vstinner · 2015-03-04T16:38:32Z

random-2.patch: updated patch (I don't understand why random.patch doesn't apply cleanly).

python-dev · 2015-03-18T13:42:38Z

New changeset 1fc32bf069ff by Victor Stinner in branch 'default':
Issue bpo-22181: On Linux, os.urandom() now uses the new getrandom() syscall if
https://hg.python.org/cpython/rev/1fc32bf069ff

vstinner · 2015-03-19T12:43:17Z

Oh, test_os now fails on Linux because os.urandom() doesn't use a file descriptor anymore. The test should be skipped when getrandom() is used. The test is already skipped when getentropy() is used.

python-dev · 2015-03-19T21:23:02Z

New changeset 4491bdb6527b by Victor Stinner in branch 'default':
Issue bpo-22181: The availability of the getrandom() is now checked in configure,
https://hg.python.org/cpython/rev/4491bdb6527b

python-dev · 2015-03-19T22:30:21Z

New changeset 8c73af0b3cd9 by Victor Stinner in branch 'default':
Issue bpo-22181: Fix dev_urandom_noraise(), try calling py_getrandom() before
https://hg.python.org/cpython/rev/8c73af0b3cd9

Arfrever · 2015-03-20T14:07:43Z

New changeset 4491bdb6527b by Victor Stinner in branch 'default':
Issue bpo-22181: The availability of the getrandom() is now checked in configure,
https://hg.python.org/cpython/rev/4491bdb6527b

You forgot to run aclocal, which resulted in PKG_PROG_PKG_CONFIG not being expanded in configure.

python-dev · 2015-03-20T15:03:33Z

New changeset b8ceb071159f by Victor Stinner in branch 'default':
Issue bpo-22181: Run "aclocal; autoconf; autoheader" to regenerate configure
https://hg.python.org/cpython/rev/b8ceb071159f

python-dev · 2015-03-30T09:20:16Z

New changeset 28b465d8c519 by Victor Stinner in branch 'default':
Issue bpo-22181: os.urandom() now releases the GIL when the getrandom()
https://hg.python.org/cpython/rev/28b465d8c519

pitrou added the type-feature A feature request or enhancement label Aug 10, 2014

vstinner added type-security A security issue and removed type-feature A feature request or enhancement labels Oct 9, 2014

vstinner closed this as completed Mar 18, 2015

vstinner reopened this Mar 19, 2015

vstinner closed this as completed Mar 30, 2015

ezio-melotti transferred this issue from another repository Apr 10, 2022

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os.urandom() should use Linux 3.17 getrandom() syscall #66377

os.urandom() should use Linux 3.17 getrandom() syscall #66377

vstinner commented Aug 10, 2014

vstinner commented Aug 10, 2014

vstinner commented Aug 15, 2014

700eb415 mannequin commented Oct 2, 2014

anandjeyahar mannequin commented Oct 6, 2014

neologix mannequin commented Oct 6, 2014

vstinner commented Oct 6, 2014

tiran commented Oct 8, 2014

700eb415 mannequin commented Oct 8, 2014

pitrou commented Oct 8, 2014

alex commented Oct 8, 2014

700eb415 mannequin commented Oct 8, 2014

pitrou commented Oct 8, 2014

vstinner commented Oct 9, 2014

vstinner commented Oct 9, 2014

vstinner commented Mar 3, 2015

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python-dev mannequin commented Mar 18, 2015

vstinner commented Mar 19, 2015

python-dev mannequin commented Mar 19, 2015

python-dev mannequin commented Mar 19, 2015

Arfrever mannequin commented Mar 20, 2015

python-dev mannequin commented Mar 20, 2015

python-dev mannequin commented Mar 30, 2015

os.urandom() should use Linux 3.17 getrandom() syscall #66377

os.urandom() should use Linux 3.17 getrandom() syscall #66377

Comments

vstinner commented Aug 10, 2014

vstinner commented Aug 10, 2014

vstinner commented Aug 15, 2014

700eb415 mannequin commented Oct 2, 2014

anandjeyahar mannequin commented Oct 6, 2014

neologix mannequin commented Oct 6, 2014

vstinner commented Oct 6, 2014

tiran commented Oct 8, 2014

700eb415 mannequin commented Oct 8, 2014

pitrou commented Oct 8, 2014

alex commented Oct 8, 2014

700eb415 mannequin commented Oct 8, 2014

pitrou commented Oct 8, 2014

vstinner commented Oct 9, 2014

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python-dev mannequin commented Mar 18, 2015

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Arfrever mannequin commented Mar 20, 2015

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python-dev mannequin commented Mar 30, 2015