linux-kernel - Re: [PATCH -v4] random: introduce getrandom(2) system call

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Date:	Wed, 30 Jul 2014 14:26:20 +0200
From:	Pavel Machek <pavel@....cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-crypto@...r.kernel.org, beck@...nbsd.org,
	deraadt@....openbsd.org
Subject: Re: [PATCH -v4] random: introduce getrandom(2) system call

Hi!

> The rationale of this system call is to provide resiliance against
> file descriptor exhaustion attacks, where the attacker consumes all
> available file descriptors, forcing the use of the fallback code where
> /dev/[u]random is not available.  Since the fallback code is often not
> well-tested, it is better to eliminate this potential failure mode
> entirely.

I'm not sure I understand the rationale; if someone can eat all your
file descriptors, he can make you stop working. So you can just stop
working when you can't open /dev/urandom, no?

Fallback code is probably very bad idea to use...

> The other feature provided by this new system call is the ability to
> request randomness from the /dev/urandom entropy pool, but to block
> until at least 128 bits of entropy has been accumulated in the
> /dev/urandom entropy pool.  Historically, the emphasis in the
> /dev/urandom development has been to ensure that urandom pool is
> initialized as quickly as possible after system boot, and preferably
> before the init scripts start execution.

Sounds like ioctl() for /dev/urandom for this behaviour would be nice?

									Pavel
-- 
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