mac80211: check channel context methods

Verify that the channel context methods are
all assigned by the driver or not used.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/main.c

@@ -549,6 +549,13 @@ struct ieee80211_hw *ieee80211_alloc_hw(size_t priv_data_len,
 	if (WARN_ON(ops->sta_state && (ops->sta_add || ops->sta_remove)))
 		return NULL;
 
+	/* check all or no channel context operations exist */
+	i = !!ops->add_chanctx + !!ops->remove_chanctx +
+	    !!ops->change_chanctx + !!ops->assign_vif_chanctx +
+	    !!ops->unassign_vif_chanctx;
+	if (WARN_ON(i != 0 && i != 5))
+		return NULL;
+
 	/* Ensure 32-byte alignment of our private data and hw private data.
 	 * We use the wiphy priv data for both our ieee80211_local and for
 	 * the driver's private data