mwifiex: fix memory corruption when unsetting multicast list

When trying to unset a previously-set multicast list (i.e. the new list
has 0 entries), mwifiex_set_multicast_list() was calling down to
mwifiex_request_set_multicast_list() while leaving
mcast_list.num_multicast_addr as an uninitialized value.

We were arriving at mwifiex_cmd_mac_multicast_adr() which would then
proceed to do an often huge memcpy of
mcast_list.num_multicast_addr*ETH_ALEN bytes, causing memory corruption
and hard to debug crashes.

Fix this by setting mcast_list.num_multicast_addr to 0 when no multicast
list is provided. Similarly, fix up the logic in
mwifiex_request_set_multicast_list() to unset the multicast list that
was previously sent to the hardware in such cases.
Signed-off-by: Daniel Drake <dsd@laptop.org>
Acked-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/mwifiex/main.c

@@ -669,7 +669,6 @@ static void mwifiex_set_multicast_list(struct net_device *dev)
 		mcast_list.mode = MWIFIEX_ALL_MULTI_MODE;
 	} else {
 		mcast_list.mode = MWIFIEX_MULTICAST_MODE;
-		if (netdev_mc_count(dev))
 		mcast_list.num_multicast_addr =
 			mwifiex_copy_mcast_addr(&mcast_list, dev);
 	}

drivers/net/wireless/mwifiex/sta_ioctl.c

@@ -104,7 +104,6 @@ int mwifiex_request_set_multicast_list(struct mwifiex_private *priv,
 		} else {
 			priv->curr_pkt_filter &=
 				~HostCmd_ACT_MAC_ALL_MULTICAST_ENABLE;
-			if (mcast_list->num_multicast_addr) {
 			dev_dbg(priv->adapter->dev,
 				"info: Set multicast list=%d\n",
 				mcast_list->num_multicast_addr);
@@ -115,7 +114,6 @@ int mwifiex_request_set_multicast_list(struct mwifiex_private *priv,
 				mcast_list);
 		}
 	}
-	}
 	dev_dbg(priv->adapter->dev,
 		"info: old_pkt_filter=%#x, curr_pkt_filter=%#x\n",
 	       old_pkt_filter, priv->curr_pkt_filter);