Re: [PATCH 1/3] IMA: move read/write counters into struct inode

[Ingo Molnar <mingo@elte.hu>]

* Casey Schaufler <casey@schaufler-ca.com> wrote:

>  On 10/20/2010 8:15 AM, Ingo Molnar wrote:
> > * Eric Paris <eparis@redhat.com> wrote:
> >
> >> On Wed, 2010-10-20 at 16:38 +0200, Ingo Molnar wrote:
> >>> * Eric Paris <eparis@redhat.com> wrote:
> >>>
> >>>> Executive summary of the day's work:
> >>>> Yesterday morning: 944 bytes per inode in core
> >>>> Yesterday night: 24 bytes per inode in core
> >>>> Tonight: 4 bytes per inode in core.
> >>>>
> >>>> That's a x236 time reduction in memory usage.  No I didn't even start looking 
> >>>> at a freezer.  Which could bring that 4 down to 0, but would add a scalability 
> >>>> penalty on all inodes when IMA was enabled.
> >>> Why not use inode->i_security intelligently? That already exists so that way 
> >>> it's 0 bytes.
> >>>
> >>> Thanks,
> >> It still wouldn't be 0 bytes since there would be a 1-1 mapping from inode to 
> >> i_security structs. [...]
> > Only for IMA-affected files, right?
> >
> > My point is to keep it 0 overhead for the _non IMA common case_.
> >
> >> The real reason I don't pursue this route is because of the litany of different 
> >> ways this pointer is used in different LSMs (or not used at all.)  And we all know 
> >> that LSM authors aren't known for seeing the world the same way as each other.  As 
> >> a maintainer of one of those LSMs even I'm scared to try pushing that forward....
> > Ugh. That's a perfect reason to do it exactly like i suggested.
> 
> If you would like to make a proposal on LSM stacking other than the traditional 
> "rip the LSM out" I am sure that everyone in the IMA, SELinux, TOMOYO, AppArmor 
> and Smack communities would be happy to have a look. Short of having a viable 
> mechanism for multiple LSMs to coexist IMA needs its separate space. Yes, people 
> do use both IMA and LSMs on the same machine at the same time.

Yes, that's the essence of what i suggested: if various security concepts can be 
present at once then inode->security should not be a stupid pointer to a single, 
exclusive data structure (because that hardwires a "only a single security subsystem 
active" assumption), but should be a pointer to a linked list of security structures 
- as many as there are security subsystems interested in that inode.
 
Thanks,

	Ingo