[PATCH v2 05/10] generate deterministic clear-text password hash

[Felix Moessbauer <felix.moessbauer@siemens.com>]

This patch changes how we derive the hashed password of a user that is
created using the clear-text-password flag. Previously, the clear-text
password was directly input into chpasswd. However, chpasswd internally
creates a 16-character random salt. This breaks the reproducability.

Instead of letting chpasswd create the hashed password string, we now
create it manually by deriving the salt from the SOURCE_DATE_EPOCH
variable. This is technically done using the host openssl tool. As
openssl is a transitive dependency of sbuild, we do not need to add
it explicitly to the host-tools.

In case SOURCE_DATE_EPOCH is not set, chpasswd is used
directly to create the salt.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
---
 meta/classes/image-account-extension.bbclass | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/meta/classes/image-account-extension.bbclass b/meta/classes/image-account-extension.bbclass
index 70950a7..bb173b1 100644
--- a/meta/classes/image-account-extension.bbclass
+++ b/meta/classes/image-account-extension.bbclass
@@ -253,7 +253,15 @@ image_postprocess_accounts() {
         if [ -n "$password" -o "${flags}" != "${flags%*,allow-empty-password,*}" ]; then
             chpasswd_args="-e"
             if [ "${flags}" != "${flags%*,clear-text-password,*}" ]; then
-                chpasswd_args=""
+                # chpasswd adds a random salt when running against a clear-text password.
+                # For reproducible images, we manually generate the password and use the
+                # SOURCE_DATE_EPOCH to generate the salt in a deterministic way.
+                if [ -z "${SOURCE_DATE_EPOCH}"]; then
+                    chpasswd_args=""
+                else
+                    salt="$(echo "${SOURCE_DATE_EPOCH}" | sha256sum -z | cut -c 1-15)"
+                    password="$(openssl passwd -6 -salt $salt "$password")"
+                fi
             fi
             printf '%s:%s' "$name" "$password" | sudo chroot '${ROOTFSDIR}' \
                 /usr/sbin/chpasswd $chpasswd_args
-- 
2.34.1