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SubjectRe: [patch] security: fix dummy xattr functions
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On Wed, 2 Jul 2008, James Morris wrote:
> On Wed, 2 Jul 2008, Miklos Szeredi wrote:
>
> > So where do the dummy_ functions figure into this? As I understand,
> > they are called whenever LSM is disabled, but the LSM doesn't define a
> > particular hook, so there's a default implementation. Is that correct?
>
> If LSM is disabled, nothing is called (the security hooks are optimized
> away).

Right. I meant to say "enabled", instead of "disabled" above :)

> It's for when LSM is enabled, but there is either no LSM module
> selected, or as fallbacks for hooks which are not implemented by an LSM
> module.

Yes, we were thinking of the fallback case. When falling back to the
default, that should be equivalent to the "no LSM" case, no?

Currently it's not.

> > If so, then in theory it is still theoretically possible that with
> > LSM+capabilities, the LSM doesn't explicitly stack inode_setxattr and
> > inode_removexattr, and so the dummy implementation should do that
> > instead. What am I missing?
>
> The LSM is responsible for performing this stacking (or not), depending on
> which particular security models are desired. It may, for example, not
> want filesystem capabilities.
>
> I guess it might be safer to force the LSM to override fs capabilities if
> it doesn't want them, but I'd like to see what others think.

No, this patch is _not_ forcing anything is LSM defines its own
inode_{set,remove}xattr methods. I agree, that should be decided by
the LSM.

The patch is just fixing the fallback dummy functions to be in sync
with the the disabled LSM case.

Miklos


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