Function lomac_vnode_check_relabel

freebsd/security/mac_lomac/mac_lomac.c:2483–2557

}

static int
lomac_vnode_check_relabel(struct ucred *cred, struct vnode *vp,
    struct label *vplabel, struct label *newlabel)
{
	struct mac_lomac *old, *new, *subj;
	int error;

	old = SLOT(vplabel);
	new = SLOT(newlabel);
	subj = SLOT(cred->cr_label);

	/*
	 * If there is a LOMAC label update for the vnode, it must be a
	 * single label, with an optional explicit auxiliary single.
	 */
	error = lomac_atmostflags(new,
	    MAC_LOMAC_FLAG_SINGLE | MAC_LOMAC_FLAG_AUX);
	if (error)
		return (error);

	/*
	 * To perform a relabel of the vnode (LOMAC label or not), LOMAC must
	 * authorize the relabel.
	 */
	if (!lomac_single_in_range(old, subj))
		return (EPERM);

	/*
	 * If the LOMAC label is to be changed, authorize as appropriate.
	 */
	if (new->ml_flags & MAC_LOMAC_FLAG_SINGLE) {
		/*
		 * To change the LOMAC label on a vnode, the new vnode label
		 * must be in the subject range.
		 */
		if (!lomac_single_in_range(new, subj))
			return (EPERM);

		/*
		 * To change the LOMAC label on the vnode to be EQUAL, the
		 * subject must have appropriate privilege.
		 */
		if (lomac_contains_equal(new)) {
			error = lomac_subject_privileged(subj);
			if (error)
				return (error);
		}
	}
	if (new->ml_flags & MAC_LOMAC_FLAG_AUX) {
		/*
		 * Fill in the missing parts from the previous label.
		 */
		if ((new->ml_flags & MAC_LOMAC_FLAG_SINGLE) == 0)
			lomac_copy_single(subj, new);

		/*
		 * To change the auxiliary LOMAC label on a vnode, the new
		 * vnode label must be in the subject range.