[PATCH v2 18/25] LSM: Use lsmcontext in security_dentry_init_security

[Kees Cook]

On Wed, Jun 19, 2019 at 10:31:45AM -0700, Casey Schaufler wrote:
> On 6/18/2019 10:41 PM, Kees Cook wrote:
> > I think this is wrong: for NUL-terminated strings, "context.len" isn't
> > currently including the NUL byte (it's set to strlen()).
> >
> > So, if kmemdup() is used here, it means strlen() isn't correct in the
> > context init helper, it should be using the "size" argument, etc.
> 
> Would all be true if the context where being set by lsmcontext_init,
> but it's not. It's coming from the dentry_init_security hook, and
> the one instance of that, selinux_dentry_init_security() sets the
> size to strlen() + 1. The kmemdup() will include the terminating NUL.

Ah-ha! Okay, thanks, yes. I see now. Carry on! :)

> I too wish that the hooks and their use where more consistent.
> My sincere hope is that this revision of the infrastructure will
> help that to some extent.

Once these changes land it should be much much easier to find ways to
refactor for greater sanity. :)

> > Should label be set to NULL here and len reduced to 0?
> 
> It wasn't before, and I'd hate to make too many assumptions
> about what might be fragile in the NFS code.

Gotcha.

-- 
Kees Cook