[PATCH] landlock: Use bit-fields for storing handled layer access masks

[Günther Noack]

On Thu, Jun 13, 2024 at 11:20:38PM +0200, Mickaël Salaün wrote:
> Great!  Looking at the generated data structures with pahole, it doesn't
> increase the whole size, and it should be fine with other (small) fields
> too.
> 
> With this new struct, we don't need the landlock_get_* helpers anymore.
> We might want to keep the landlock_add_*() helpers as safeguards
> (because of the WARN_ON_ONCE) though.

I am unsure about removing these helper functions, due to the following reasons:

 * landlock_get_fs_access_mask is the place where we transparently add the
   "refer" access right.  If we remove landlock_get_net_access_mask, it would be
   assymetric with keeping the same function for the file system restrictions.

 * landlock_init_layer_masks() is using landlock_get_fs_access_mask and
   landlock_get_net_access_mask through a function pointer.  When these
   functions are gone, we would have to redefine them locally anyway.

   Options to refactor this function include:
    * split it in two separate functions landlock_init_fs_layer_masks and
      landlock_init_net_layer_masks.  It would end up duplicating some of the
      bit manipulation code.
    * add another #if further down in the function

   Both variants seem not nice.

Do you think this is worth doing?

—Günther