require bsdtar for VMs

diff --git a/init_buildsystem b/init_buildsystem
index 679f189..294215c 100755 (executable)
--- a/init_buildsystem
+++ b/init_buildsystem
@@ -133,6 +133,13 @@ preinstall()
        CPIO="/usr/bin/bsdtar --chroot -o --numeric-owner -x -f-"
        TAR="/usr/bin/bsdtar --chroot -o --numeric-owner -x"
     else
+       # cpio isn't safe so we require bsdtar for VMs. chroot is
+       # unsafe anyways so it's ok for that.
+       if [ -n "$PREPARE_VM" ]; then
+           echo "Error: setting up a VM requires bsdtar for security reasons."
+           echo "Please install bsdtar"
+           cleanup_and_exit 1
+       fi
        CPIO="cpio --extract --unconditional --preserve-modification-time --make-directories --no-absolute-filenames --quiet"
        TAR="tar -x"
     fi