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References: <20240130214620.3155380-1-stefanb@linux.ibm.com> <20240130214620.3155380-6-stefanb@linux.ibm.com>
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From: Amir Goldstein <amir73il@gmail.com>
Date: Wed, 31 Jan 2024 16:06:05 +0200
Message-ID: <CAOQ4uxikngPf5t9zmJqV3SKkdmMm6ZwF095uoa6HLN-yAkdnSQ@mail.gmail.com>
Subject: Re: [PATCH 5/5] evm: Enforce signatures on unsupported filesystem for EVM_INIT_X509
To: Stefan Berger <stefanb@linux.ibm.com>
Cc: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, 
	linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, 
	paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com, 
	roberto.sassu@huawei.com, miklos@szeredi.hu, 
	Christian Brauner <brauner@kernel.org>
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On Tue, Jan 30, 2024 at 11:46=E2=80=AFPM Stefan Berger <stefanb@linux.ibm.c=
om> 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 change still prevents EVM from writing HMAC signatures on
> unsupported filesystem when EVM_INIT_HMAC is enabled.
>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>  security/integrity/evm/evm_main.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/e=
vm_main.c
> index e96d127b48a2..f49609dfcbc7 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -192,7 +192,11 @@ static enum integrity_status evm_verify_hmac(struct =
dentry *dentry,
>                      iint->evm_status =3D=3D INTEGRITY_PASS_IMMUTABLE))
>                 return iint->evm_status;
>
> -       if (is_unsupported_fs(dentry))
> +       /*
> +        * On unsupported filesystems with EVM_INIT_X509 not enabled, ski=
p
> +        * signature verification.
> +        */
> +       if (!(evm_initialized & EVM_INIT_X509) && is_unsupported_fs(dentr=
y))
>                 return INTEGRITY_UNKNOWN;
>

Are the names is_unsupported_fs() and SB_I_EVM_UNSUPPORTED still
a good description of what overlayfs is after this change?
Is EVM really not supported on overlayfs after this change?

Would you consider a better descriptive name, for the helper and flag,
at least as descriptive as SB_I_IMA_UNVERIFIABLE_SIGNATURE?

Thanks,
Amir.