linux-kernel - Re: [PATCH v5] ELF: implement AT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <20081026224659.af213906.akpm@linux-foundation.org>
Date:	Sun, 26 Oct 2008 22:46:59 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	Kees Cook <kees.cook@...onical.com>, jakub@...hat.com,
	arjan@...radead.org, roland@...hat.com,
	linux-kernel@...r.kernel.org, libc-alpha@...rceware.org
Subject: Re: [PATCH v5] ELF: implement AT_RANDOM for glibc PRNG seeding

On Tue, 21 Oct 2008 13:22:18 -0700 Ulrich Drepper <drepper@...hat.com> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Andrew Morton wrote:
> > I read the above changeloglet and read the above-linked page and it's
> > still 87% unclear to me what this feature does.  Something to do with
> > stack randomisation, apparently.  I suppose I could go do further
> > hunting, but from the quality-of-changelog POV I don't think I should
> > need to do so.
> 
> Not stack randomization.  glibc needs right after startup a bit of
> random data for internal protections (stack canary etc).  What is now in
> upstream glibc is that we always unconditionally open /dev/urandom, read
> some data, and use it.  For every process startup.  That's slow.
> 
> In addition Andi mentioned that this use of /dev/urandom might be
> problematic.  I let him explain this.
> 
> The solution is to provide a limited amount of random data to the
> starting process in the aux vector.  I suggested 16 bytes and this is
> what the patch implements.  If we need only 16 bytes or less we use the
> data directly.  If we need more we'll use the 16 bytes to see a PRNG.
> This avoids the costly /dev/urandom use and it allows the kernel to use
> the most adequate source of random data for this purpose.  It might not
> be the same pool as that for /dev/urandom.
> 

Thanks.

> > It's unclear to me that the random-number issue got sorted out?
> 
> I think the last patch used the normal function to get 16 random bytes,
> equivalent to the data used for stack randomization etc.
> 
> If Andi has concrete proposals for a revamp of the use of entropy in the
> kernel this can be easily done as an add-on.  This patch doesn't make
> the situation worse, it doesn't deplete entropy more than it happens now.
> 

True.

As long as glibc doesn't do the /dev/urandom read when the kenrel has
already done that.  I assume that it will do so, until AT_RANDOM-aware
glibc has propagated out?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/