linux-kernel - Re: [PATCH 6/7] Add /sys/kernel/notes

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Message-Id: <20070711220423.98F324D0555@magilla.localdomain>
Date:	Wed, 11 Jul 2007 15:04:23 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] Add /sys/kernel/notes

> Yeah, we've made that mistake before, and I'm not saying we are perfect 
> here, but if we make this world-readable, I think it needs to guarantee it 
> doesn't really give any rootkit people any new information.

It will give them at least as reliable an identification of the kernel
binary as the "uname -rv" info if they have access to a set of candidate
known binaries to select from.  It's of no direct help at all in getting
anything like kernel addresses.  In practice, it is probably no easier for
a rootkit to use than "uname -rv" to pick an exploit for a particular known
distro kernel binary, just easier for legitimate debugging tools.  I think
it's not only more harmless than what you might call "past mistakes", but
is actually just plain harmless.  But I'm not really one to talk a man out
of his paranoia.

> And yes, I do think normal people shouldn't be able to read the vmlinuz 
> binary, the same way they are generally not allowed to read /etc/grub.conf 
> etc.

I have no special opinions about that, but I haven't seen an install where
the /boot files were not readable anyway.  But certainly in a chroot or
such, you won't have /boot at all but might have /proc and /sys.

All in all, this seems like a question of local policy.  Ideally the modes
would be flexibly chosen by admins, or else constrained more precisely by
SELinux policy or suchlike.  But I have no axe to grind on the subject with
this particular change.  I care more that the feature gets in and at least
root can use it, than about the permissions question.

Thanks,
Roland
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