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On Wed, 2008-07-02 at 19:16 +1000, 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). 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
> > 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.
As discussed elsewhere, the dummy module just needs to die, and capability needs to become the default module. Then we no longer need to deal with keeping them in sync or figuring out to emulate/fake capabilities for userspace from dummy (since userspace expects them to exist in Linux ever since they were first introduced long ago).
BTW, SELinux does not invoke the cap_ or dummy_ inode_setxattr/removexattr hooks as that would cause CAP_SYS_ADMIN to be checked on the security.selinux attribute. But selinux_inode_setotherxattr() has the right logic. -- Stephen Smalley National Security Agency -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html