[PATCH v3 08/10] evm: Enforce signatures on unsupported filesystem for EVM_INIT_X509

[Mimi Zohar]

On Fri, 2024-02-23 at 12:25 -0500, Stefan Berger wrote:
> Unsupported filesystems currently do not enforce any signatures. Add
> support for signature enforcement of the "original" and "portable &
> immutable" signatures when EVM_INIT_X509 is enabled.
> 
> The "original" signature type contains filesystem specific metadata.
> Thus it cannot be copied up and verified. However with EVM_INIT_X509
> and EVM_ALLOW_METADATA_WRITES enabled, the "original" file signature
> may be written.
> 
> When EVM_ALLOW_METADATA_WRITES is not set or once it is removed from
> /sys/kernel/security/evm by setting EVM_INIT_HMAC for example, it is not
> possible to write or remove xattrs on the overlay filesystem.

This paragraph is currently correct, but at some point EVM_ALLOW_METADATA_WRITES
will be deprecated.  Refer to commit 1434c6a1d32a ("evm: Deprecate
EVM_ALLOW_METADATA_WRITES").

Mimi

> 
> This change still prevents EVM from writing HMAC signatures on
> unsupported filesystem when EVM_INIT_HMAC is enabled.
> 
> Co-developed-by: Mimi Zohar <zohar at linux.ibm.com>
> Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>

Signed-off-by: Mimi Zohar <zohar at linux.ibm.com>