Fix a time-of-check/time-of-use error when mounting type=bind and
type=cache directories that use a "src" flag. A hostile writer could
use a concurrently-running stage or build to replace that "src" location
between the point when we had resolved possible symbolic links and when
runc/crun/whatever actually went to create the bind mount
(CVE-2024-11218).
Stop ignoring the "src" option for cache mounts when there's no "from"
option.
Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>
9ddac02a51