From: Jeff King <peff@peff.net>
To: Carlo Arenas <carenas@gmail.com>
Cc: "brian m. carlson" <sandals@crustytoothpaste.net>,
rsbecker@nexbridge.com, git@vger.kernel.org
Subject: Re: [PATCH 1/2] wrapper: add a helper to generate numbers from a CSPRNG
Date: Wed, 17 Nov 2021 15:01:50 -0500 [thread overview]
Message-ID: <YZVfrhos+lZas7hk@coredump.intra.peff.net> (raw)
In-Reply-To: <CAPUEsphh-enSYS66mi7_XaS0n1bmUvGXRcgVp6iqhg94xSHVog@mail.gmail.com>
On Tue, Nov 16, 2021 at 07:36:51PM -0800, Carlo Arenas wrote:
> > > for the little amount of random data we need, it might be wiser to
> > > fallback to something POSIX like lrand48 which is most likely to be
> > > available, but of course your tests that consume lots of random data
> > > will need to change.
> >
> > Unfortunately that won't help. You have to seed lrand48 with something,
> > which usually means pid and/or timestamp. Which are predictable to an
> > attacker, which was the start of the whole conversation. You really need
> > _some_ source of entropy, and only the OS can provide that.
>
> again, showing my ignorance here; but that "something" doesn't need to
> be guessable externally; ex: git add could use as seed contents from
> the file that is adding, or even better mix it up with the other
> sources as a poor man's /dev/urandom
Those contents are still predictable. So you've made the attacker's job
a little harder (now they have to block tempfiles for, say, each tag
you're going to verify), but haven't changed the fundamental problem.
It definitely would help in _some_ threat models, but I think we should
strive for a solution that can be explained clearly as "nobody can DoS
your tempfiles" without complicated qualifications.
-Peff
next prev parent reply other threads:[~2021-11-17 20:02 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
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 [this message]
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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