[gentoo-dev] [PATCH] kernel-build.eclass: work around permissions issue with module signing

[Violet Purcell <vimproved@inventati.org>]

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}")"
+			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
+				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}\"" \
-- 
2.43.0