On Mon, 2023-11-27 at 12:12 -0500, Violet Purcell wrote:
> Currently, using a custom path for MODULES_SIGN_KEY requires the key to
> be readable by portage:portage. This is not ideal for security, since
> the file has to be either owned by portage:portage or readable by all
> users in this case. Instead, export the contents of MODULES_SIGN_KEY to
> a variable in pkg_setup, and then create a temporary file with it in
> src_configure to ensure that the temporary key is readable by the user
> that the kernel is being built as. The variable is then unset so it does
> not end up in the final environment file.
> 
> Signed-off-by: Violet Purcell <vimproved@inventati.org>
> ---
>  eclass/kernel-build.eclass | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/eclass/kernel-build.eclass b/eclass/kernel-build.eclass
> index 4f7e4d047739..cf958c86ff29 100644
> --- a/eclass/kernel-build.eclass
> +++ b/eclass/kernel-build.eclass
> @@ -114,6 +114,13 @@ kernel-build_pkg_setup() {
>  	python-any-r1_pkg_setup
>  	if [[ ${KERNEL_IUSE_MODULES_SIGN} ]]; then
>  		secureboot_pkg_setup
> +		if [[ -e ${MODULES_SIGN_KEY} && ${MODULES_SIGN_KEY} != pkcs11:* ]]; then
> +			if [[ -e ${MODULES_SIGN_CERT} && ${MODULES_SIGN_CERT} != ${MODULES_SIGN_KEY} ]]; then
> +				export MODULES_SIGN_KEY_CONTENTS="$(cat "${MODULES_SIGN_CERT}" "${MODULES_SIGN_KEY}")"
> +			else
> +				export MODULES_SIGN_KEY_CONTENTS="$(< "${MODULES_SIGN_KEY}")"

You don't need to export it.  Unexported variables are also preserved.

> +			fi
> +		fi
>  	fi
>  }
>  
> @@ -427,12 +434,12 @@ kernel-build_merge_configs() {
>  				CONFIG_MODULE_SIG_FORCE=y
>  				CONFIG_MODULE_SIG_${MODULES_SIGN_HASH^^}=y
>  			EOF
> -			if [[ -e ${MODULES_SIGN_KEY} && -e ${MODULES_SIGN_CERT} &&
> -				${MODULES_SIGN_KEY} != ${MODULES_SIGN_CERT} &&
> -				${MODULES_SIGN_KEY} != pkcs11:* ]]
> -			then
> -				cat "${MODULES_SIGN_CERT}" "${MODULES_SIGN_KEY}" > "${T}/kernel_key.pem" || die
> -				MODULES_SIGN_KEY="${T}/kernel_key.pem"
> +			if [[ -n "${MODULES_SIGN_KEY_CONTENTS}" ]]; then
> +				touch "${T}/kernel_key.pem" || die
> +				chmod 0600 "${T}/kernel_key.pem" || die

This creates a race condition whereupon the file can be opened between
the call to touch and chmod.  It's better to use a subshell and set
umask.

> +				echo "${MODULES_SIGN_KEY_CONTENTS}" > "${T}/kernel_key.pem" || die
> +				unset MODULES_SIGN_KEY_CONTENTS
> +				export MODULES_SIGN_KEY="${T}/kernel_key.pem"
>  			fi
>  			if [[ ${MODULES_SIGN_KEY} == pkcs11:* || -r ${MODULES_SIGN_KEY} ]]; then
>  				echo "CONFIG_MODULE_SIG_KEY=\"${MODULES_SIGN_KEY}\"" \

-- 
Best regards,
Michał Górny