libselinux: flush the class/perm string mapping cache on policy reload
This improves the robustness of programs using selinux_check_access()
in the face of policy updates that alter the values of the class or
permissions that they are checking. Otherwise, a policy update can
trigger false permission denials, as in
https://bugzilla.redhat.com/show_bug.cgi?id=1264051
Changes to the userspace class/permission definitions should still be
handled with care, as not all userspace object managers have been converted
to use selinux_check_access() and even those that do use it are still not
entirely safe against an interleaving of a policy reload and a call to
selinux_check_access(). The change does however address the issue in
the above bug and avoids the need to restart systemd.
This change restores the flush_class_cache() function that was removed in
commit 435fae64a931 ("libselinux: Remove unused flush_class_cache method")
because it had no users at the time, but makes it hidden to avoid exposing
it as part of the libselinux ABI.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
3 files changed