[RFC PATCH v14 15/19] fsverity: consume builtin signature via LSM hook

[Eric Biggers]

On Mon, Mar 11, 2024 at 07:57:12PM -0700, Eric Biggers wrote:
> 
> As I've said before, this commit message needs some work.  It currently doesn't
> say anything about what the patch actually does.
> 
> BTW, please make sure you're Cc'ing the fsverity mailing list
> (fsverity at lists.linux.dev), not fscrypt (linux-fscrypt at vger.kernel.org).

Also, I thought this patch was using a new LSM hook, but I now see that you're
actually abusing the existing security_inode_setsecurity() LSM hook.  Currently
that hook is called when an xattr is set.  I don't see any precedent for
overloading it for other purposes.  This seems problematic, as it means that a
request to set an xattr with the name you chose ("fsverity.builtin-sig") will be
interpreted by LSMs as the fsverity builtin signature.  A dedicated LSM hook may
be necessary to avoid issues with overloading the existing xattr hook like this.

- Eric