Re: [link@miggy.org: Re: [patch 2/8] personality: fix PER_CLEAR_ON_SETID (CVE-2009-1895)]

[Athanasius <link@miggy.org>]

On Sat, Jul 18, 2009 at 01:48:06PM -0700, Linus Torvalds wrote:
> On Sat, 18 Jul 2009, Greg KH wrote:
> > 
> > and you have the whole idea of personalities being some kind of security
> > mechanism exposed as a joke.
> 
> It's _not_ a "security mechanism". It never was.
...
> In the absense of raised capabilities, the personality flags don't matter: 
> because they aren't security. If you have a personality flag that says "I 
> want to mmap at virtual address zero", you're still going to be limited by 
> the security layer, and if the security layer says "nope, you can't do 
> that", then your personality doesn't matter.
> 
> See?

  I can understand and appreciate that, yes.

  However the content of 'cat /proc/execdomains' is mis-leading for
the default Execution Domain.  The string '0-0' implies either that you
can only set 1 of 3 personalities whilst this Execution Domain is current
OR that this Execution Domain will only be used whilst the set personality
is one of those 3.  But neither is actually true as this default Execution
Domain (being the only one in vanilla kernel tree) is a special case.
  If you don't see a valid reason to change personality(2) behaviour (thus
still allowing setting aribtrary personality values) then surely it would
make more sense for the default domain to set pers_high to PER_MASK ?
I'd suggest it actually be 0xffffffff but the field is only a char.

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