From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: "Zack Weinberg" <zack@owlfolio.org>,
"Cristian Rodríguez" <cristian@rodriguez.im>,
"Florian Weimer" <fweimer@redhat.com>
Cc: Wilco Dijkstra <Wilco.Dijkstra@arm.com>,
GNU libc development <libc-alpha@sourceware.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
"Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: Re: [PATCH 2/2] Add single-threaded fast path to rand()
Date: Fri, 22 Mar 2024 15:05:32 -0300 [thread overview]
Message-ID: <50b42519-4557-4e8c-8a58-0077168aa25d@linaro.org> (raw)
In-Reply-To: <667f5ebb-13e5-4110-a002-3b2b0dfc2bdb@app.fastmail.com>
On 22/03/24 12:30, Zack Weinberg wrote:
> On Fri, Mar 22, 2024, at 10:46 AM, Adhemerval Zanella Netto wrote:
>> On 22/03/24 11:27, Zack Weinberg wrote:
>>> On Thu, Mar 21, 2024, at 11:53 AM, Adhemerval Zanella Netto wrote:
>>>> And even if arc4random is explicit a non CPRNG, there were some worries that
>>>> users might misuse the interface and thus add some security issues.
>>>
>>> No opinion about anything else in this thread, but if we add arc4random at all
>>> it MUST be a CSPRNG. That's a documented guarantee on all the systems that
>>> do have it, and applications rely on it.
>>
>> Yeah, this is another point of contention where one might consider that a
>> userland CPRNG that has no feedback from kernel to where/how to properly
>> reseed might not be considered a CPRNG.
>
> I would describe that as a "CSPRNG with a known bug that makes it unsuitable
> for use under some conditions", but not as "not a CSPRNG". I would only
> call it "not a CSPRNG" if the cryptographic primitives were no good
> (e.g. RC4 or Xorshift or something even more predictable) or if there was
> a way to leak or clone the state *in a single-threaded program that does
> not fork*.
I tend to agree, but the contention point was really 'that makes it unsuitable
for use under some conditions' was a deal breaker in face that kernel provides
an API with better guarantees.
>
> On a related note, why is MADV_WIPEONFORK not adequate "feedback from the
> kernel"?
If I recall correctly, the problem was not only state wipe on fork (with
MADV_WIPEONFORK should take care), but rather when the state needs to be
reseed due various situations outside of the userland knowledge (on the
arc4random thread Jason gave us some examples, I don't really recall all
of them by hearth). That's why the idea of providing the arc4random through
a vDSO primitive (where kernel can reseed any time it likes).
next prev parent reply other threads:[~2024-03-22 18:05 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-18 15:20 Wilco Dijkstra
2024-03-18 19:24 ` Cristian Rodríguez
2024-03-19 15:44 ` Wilco Dijkstra
2024-03-20 12:31 ` Adhemerval Zanella Netto
2024-03-20 14:18 ` Cristian Rodríguez
2024-03-20 14:27 ` Adhemerval Zanella Netto
2024-03-21 7:39 ` Florian Weimer
2024-03-21 13:33 ` Cristian Rodríguez
2024-03-21 14:35 ` Mathieu Desnoyers
2024-03-21 15:07 ` Szabolcs Nagy
2024-03-21 15:18 ` Wilco Dijkstra
2024-03-21 15:53 ` Adhemerval Zanella Netto
2024-03-22 14:27 ` Zack Weinberg
2024-03-22 14:46 ` Adhemerval Zanella Netto
2024-03-22 15:30 ` Zack Weinberg
2024-03-22 18:05 ` Adhemerval Zanella Netto [this message]
2024-03-22 19:47 ` Mathieu Desnoyers
2024-03-22 22:54 ` Cristian Rodríguez
2024-03-23 14:01 ` Zack Weinberg
2024-03-23 15:23 ` Mathieu Desnoyers
2024-03-25 14:09 ` Mathieu Desnoyers
2024-03-25 17:52 ` Adhemerval Zanella Netto
2024-03-24 0:59 ` Cristian Rodríguez
2024-03-25 6:44 ` Florian Weimer
2024-03-20 14:28 ` Wilco Dijkstra
2024-03-20 14:40 ` Xi Ruoyao
-- strict thread matches above, loose matches on Subject: below --
2023-11-28 17:37 Wilco Dijkstra
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