linux-kernel - Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and introduce getrandom2()

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Message-ID: <20190920181623.GB1889@1wt.eu>
Date:   Fri, 20 Sep 2019 20:16:23 +0200
From:   Willy Tarreau <w@....eu>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>
Subject: Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and
 introduce getrandom2()

On Fri, Sep 20, 2019 at 11:09:53AM -0700, Linus Torvalds wrote:
(...)
> So:
> 
>  - GRND_INSECURE is (GRND_EXPLICIT | GRND_NONBLOCK)
> 
>    As in "I explicitly ask you not to just not ever block": urandom
> 
>  - GRND_SECURE_BLOCKING is (GRND_EXPLICIT | GRND_RANDOM)
> 
>    As in "I explicitly ask you for those secure random numbers"
> 
>  - GRND_SECURE_NONBLOCKING is (GRND_EXPLICIT | GRND_RANDOM | GRND_NONBLOCK)
> 
>    As in "I want explicitly secure random numbers, but return -EAGAIN
> if that would block".
> 
> Which are the three sane behaviors (that last one is useful for the "I
> can try to generate entropy if you don't have any" case. I'm not sure
> anybody will do it, but it definitely conceptually makes sense).
> 
> And I agree that your naming is better.
> 
> I had it as just "GRND_SECURE" for the blocking version, and
> "GRND_SECURE | GRND_NONBLOCK" for the "secure but return EAGAIN if you
> would need to block for entropy" version.
> 
> But explicitly stating the blockingness in the name makes it clearer
> to the people who just want GRND_INSECURE, and makes them realize that
> they don't want the blocking version.

I really like it this way. Explicit and full control for the application
plus reasonable backwards compatibility, it sounds pretty good.

Willy