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

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Date:	Sun, 3 Aug 2014 13:38:59 +0200
From:	Pavel Machek <pavel@....cz>
To:	Bernd Petrovitsch <bernd@...rovitsch.priv.at>
Cc:	Bob Beck <beck@...nbsd.org>, Theodore Ts'o <tytso@....edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org,
	linux-crypto <linux-crypto@...r.kernel.org>,
	Theo de Raadt <deraadt@....openbsd.org>
Subject: Re: [PATCH -v4] random: introduce getrandom(2) system call

On Thu 2014-07-31 10:06:37, Bernd Petrovitsch wrote:
> On Don, 2014-07-31 at 00:18 +0200, Pavel Machek wrote:
> > On Wed 2014-07-30 16:40:52, Bernd Petrovitsch wrote:
> > > On Mit, 2014-07-30 at 07:56 -0600, Bob Beck wrote:
> > > > Pavel. I have bit 'ol enterprise daemon running with established file
> > > > descriptors serving thousands of connections
> > > > which periodically require entropy.  Now I run out of descriptors. I
> > > > can't establish new connections. but I should
> > > > now halt all the other ones that require entropy?  I should raise
> > > > SIGKILL on my process serving these thousands
> > > > of connetions?  I don't think so.
> > > 
> > > If that long-running daemon periodically needs something from a device,
> > > one would better keep the fd for that open the whole time. Saves some
> > > CPU cycles and latency too BTW.
> > 
> > Agreed.
> > 
> > On the other hand, keeping a fd open is quite tricky for a
> > library. But better solution might be to make that easier.
> 
> Yes, in a (full-fledged, standalone) library seems at least tricky (also
> referring to some off-list mails here: think about fork() - which could
> be inside system() or popen() or similar). 
> 
> But as part of the *application* (where one has control over fork()
> etc.), this should be somewhat less risky. Yes, that doesn't really help
> libssl;-)

...

> Hehe, we (Unix!) have (had) gettimeofday(), time() and similar sys-calls
> since ages and no one proposed to make devices for them and get rid of
> the system-calls.

Well, but we do open(/dev/sda), read(1); not read_from_sda(...). And
cat /dev/urandom > file is useful operation. So it is not like
getentropy() can replace /dev/*random.

> > open( , O_IM_A_LIBRARY_GIVE_ME_ONE_OF_THREE_RESERVED_FDS) might be one
> > solution. Actually, one reserved fd should be enough.
> 
> Well, this can also be DoSed and the proposal aims to make that
> impossible (and where does this reserved count against? process-limits,
> kernel-wide limit?).

Process limit. DoS should not be an issue here. Remember, we are doing
this to help libraries.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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