From: <rsbecker@nexbridge.com>
To: "'brian m. carlson'" <sandals@crustytoothpaste.net>
Cc: "'Jeff King'" <peff@peff.net>, <git@vger.kernel.org>
Subject: RE: [PATCH 1/2] wrapper: add a helper to generate numbers from a CSPRNG
Date: Tue, 16 Nov 2021 18:20:45 -0500 [thread overview]
Message-ID: <00e001d7db40$985c61a0$c91524e0$@nexbridge.com> (raw)
In-Reply-To: <YZQzqjWMzaWVkkfP@camp.crustytoothpaste.net>
On November 16, 2021 5:42 PM, brian m. carlson
> On 2021-11-16 at 16:01:20, rsbecker@nexbridge.com wrote:
> > On November 16, 2021 10:31 AM, Jeff King wrote:
> > > On Tue, Nov 16, 2021 at 03:35:41AM +0000, brian m. carlson wrote:
> > >
> > > > The order of options is also important here. On systems with
> > > > arc4random, which is most of the BSDs, we use that, since, except
> > > > on MirBSD, it uses ChaCha20, which is extremely fast, and sits
> > > > entirely in userspace, avoiding a system call. We then prefer
> > > > getrandom over getentropy, because the former has been available
> > > > longer on Linux, and finally, if none of those are available, we
> > > > use /dev/urandom, because most Unix-like operating systems provide
> > > > that API. We prefer options that don't involve device files when
> > > > possible because those work in some restricted environments where
> device files may not be available.
> > >
> > > I wonder if we'll need a low-quality fallback for older systems
> > > which don't even have /dev/urandom. Because it's going to be used in
> > > such a core part of the system (tempfiles), this basically becomes a
> > > hard requirement for using Git at all.
> > >
> > > I can't say I'm excited in general to be introducing a dependency
> > > like this, just because of the portability headaches. But it may be
> > > the least bad thing (especially if we can fall back to the existing behavior).
> > > One alternative would be to build on top of the system mkstemp(),
> > > which makes it libc's problem. I'm not sure if we'd run into problems
> there, though.
> >
> > None of /dev/urandom, /dev/random, or mkstemp are available on some
> > platforms, including NonStop. This is not a good dependency to add.
> > One variant PRNGD is used in ia64 OpenSSL, while the CPU random
> > generator in hardware is used on x86. I cannot get behind this at all.
> > Libc is also not used in or available to our port. I am very worried
> > about this direction.
>
> I'm really not excited about a fallback here, and I specifically did not include
> one for that reason. I'm happy to add an appropriate dependency on an
> OpenSSL or libgcrypt PRNG if you're linking against that already (e.g., for
> libcurl) or support for libbsd's arc4random or getentropy if that will work on
> your system. For example, how are you dealing with TLS connections over
> HTTPS? That library will almost certainly provide the required primitives in a
> straightforward and portable way.
>
> I do fundamentally believe every operating system and language
> environment need to provide a readily available CSPRNG in 2021, especially
> because in the vast majority of cases, hash tables must be randomized to
> avoid hash DoS attacks on untrusted input. I'm planning to look into our hash
> tables in the future to see if they are vulnerable to that kind of attack, and if
> so, we'll need to have a CSPRNG for basic security reasons, and platforms
> that can't provide one would be subject to a CVE.
>
> If we really can't find a solution, I won't object to a patch on top that adds an
> insecure fallback, but I don't want to put my name or sign-off on such a patch
> because I think it's a mistake. But I think we almost certainly can, though.
We do link with libcurl and use OpenSSL as a DLL to handle TLS. The underlying random source for the nonstop-* configurations as of OpenSSL 3.0 are PNRG supplied by the vendor (HPE) on ia64 and the hardware rdrand* instructions on x86. I know that part of the OpenSSL code rather intimately.
--
Randall Becker
Also from the GTA
next prev parent reply other threads:[~2021-11-16 23:21 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-16 3:35 [PATCH 0/2] Generate temporary files using a CSPRNG brian m. carlson
2021-11-16 3:35 ` [PATCH 1/2] wrapper: add a helper to generate numbers from " brian m. carlson
2021-11-16 15:31 ` Jeff King
2021-11-16 16:01 ` rsbecker
2021-11-16 18:22 ` Taylor Blau
2021-11-16 19:58 ` rsbecker
2021-11-16 22:41 ` brian m. carlson
2021-11-16 23:20 ` rsbecker [this message]
2021-11-17 0:47 ` Carlo Arenas
2021-11-17 3:05 ` rsbecker
2021-11-17 1:03 ` brian m. carlson
2021-11-17 1:50 ` Carlo Arenas
2021-11-17 3:04 ` Jeff King
2021-11-17 3:12 ` rsbecker
2021-11-17 3:36 ` Carlo Arenas
2021-11-17 20:01 ` Jeff King
2021-11-17 20:19 ` rsbecker
2021-11-17 23:30 ` brian m. carlson
2021-11-17 23:34 ` rsbecker
2021-11-17 3:03 ` rsbecker
2021-11-17 7:39 ` Junio C Hamano
2021-11-17 23:01 ` brian m. carlson
2021-11-18 7:19 ` Junio C Hamano
2021-11-18 22:16 ` brian m. carlson
2021-11-22 9:10 ` Junio C Hamano
2021-11-16 3:35 ` [PATCH 2/2] wrapper: use a CSPRNG to generate random file names brian m. carlson
2021-11-16 15:36 ` Jeff King
2021-11-16 18:28 ` Taylor Blau
2021-11-16 18:57 ` Junio C Hamano
2021-11-16 19:21 ` Jeff King
2021-11-16 19:33 ` Taylor Blau
2021-11-16 15:44 ` [PATCH 0/2] Generate temporary files using a CSPRNG Jeff King
2021-11-16 22:17 ` brian m. carlson
2021-11-16 22:29 ` rsbecker
2021-11-16 20:35 ` Ævar Arnfjörð Bjarmason
2021-11-16 21:06 ` Jeff King
2021-11-17 8:36 ` Ævar Arnfjörð Bjarmason
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