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

From: Fan Wu
Date: Tue Mar 12 2024 - 14:14:39 EST




On 3/11/2024 8:07 PM, Eric Biggers wrote:
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@xxxxxxxxxxxxxxx), not fscrypt (linux-fscrypt@xxxxxxxxxxxxxxx).

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

Thanks for the suggestion. I found that using security_inode_setsecurity() causes issues with SMACK's inode_setsecurity() hook. I will crate a dedicated new hook like security_inode_setsig() in the next version.

-Fan