(cc'ed Dave back, sorry for the noise)

On Wed, Sep 14, 2011 at 19:42 +0400, Vasiliy Kulikov wrote:

Hi Dave,

On Wed, Sep 14, 2011 at 08:18 -0700, Dave Hansen wrote:

quoted

On Wed, 2011-09-14 at 17:16 +0400, Vasiliy Kulikov wrote:

quoted

quoted

World readable slabinfo simplifies kernel developers' job of debugging
kernel bugs (e.g. memleaks), but I believe it does more harm than
benefits.  For most users 0444 slabinfo is an unreasonable attack vector.

Please tell if anybody has complains about the restriction - whether it
forces someone besides kernel developers to do "chmod/chgrp".  But if
someone want to debug the kernel, it shouldn't significantly influence
on common users, especially it shouldn't create security issues. 

Ubuntu ships today with a /etc/init/mounted-proc.conf that does:

	chmod 0400 "${MOUNTPOINT}"/slabinfo

After cursing Kees's name a few times, I commented it out and it hasn't
bothered me again.  

Another way is chgrp slabinfo to some "admin" group which are privileged
in this sense and add your user to this group.  But please, sane and
secure defaults!

quoted

I expect that the folks that really care about this (and their distros)
will probably have a similar mechanism.  I guess the sword cuts both
ways in this case: it obviously _works_ to have the distros do it, but
it was a one-time inconvenience for me to override that.

In other words, I dunno.  If we do this in the kernel, can we at least
do something like CONFIG_INSECURE to both track these kinds of things
and make it easy to get them out of a developer's way?

What do you think about adding your user to the slabinfo's group or
chmod it - quite the opposite Ubuntu currently does?  I think it is more
generic (e.g. you may chmod 0444 to allow all users to get debug
information or just 0440 and chgrp admin to allow only trusted users to
do it) and your local policy doesn't touch the kernel.

Thanks,

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments

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