Re: [PATCH] Protection for exploiting null dereference using mmap

[Stephen Smalley <sds@tycho.nsa.gov>]

On Tue, 2007-06-05 at 17:28 -0400, Eric Paris wrote:
> On Tue, 2007-06-05 at 17:16 -0400, Alan Cox wrote:
> > On Tue, Jun 05, 2007 at 05:00:51PM -0400, James Morris wrote:
> > > This should be an unsigned long.
> > > 
> > > I wonder if the default should be for this value to be zero (i.e. preserve 
> > > existing behavior).  It could break binaries, albeit potentially insecure 
> > 
> > Agreed - DOSemu type apps and lrmi need to map at zero for vm86
> 
> While I understand, there are a few users who will have problems with
> this default are we really better to not provide this defense in depth
> for the majority of users and let those with problems turn it off rather
> than provide no defense by default?  I could even provide a different
> default for SELinux and non-SELinux if anyone saw value in that?  But if
> others think that off default is  best I'll send another patch shortly
> with the unsigned long fix and the default set to 0.  My hope is then
> that distros will figure out to turn this on.

I'd be ok with having a different default for SELinux vs. non-SELinux,
i.e. no restrictions by default under dummy/capability, but restrict it
by default to 64k if selinux is enabled.  Then we can use policy to
grant it as needed to the specific programs.

-- 
Stephen Smalley
National Security Agency

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