af_packet: move strict addr_len check right before dev_[mc/unicast]_[add/del]

My previous patch 914c8ad2d18b62ad1420f518c0cab0b0b90ab308 incorrectly changed
the length check in packet_mc_add to be more strict. The problem is that
userspace is not filling this field (and it stays zeroed) in case of setting
PACKET_MR_PROMISC or PACKET_MR_ALLMULTI. So move the strict check to the point
in path where the addr_len must be set correctly.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Reported-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -1688,6 +1688,8 @@ static int packet_dev_mc(struct net_device *dev, struct packet_mclist *i,
 {
 	switch (i->type) {
 	case PACKET_MR_MULTICAST:
+		if (i->alen != dev->addr_len)
+			return -EINVAL;
 		if (what > 0)
 			return dev_mc_add(dev, i->addr, i->alen, 0);
 		else
@@ -1700,6 +1702,8 @@ static int packet_dev_mc(struct net_device *dev, struct packet_mclist *i,
 		return dev_set_allmulti(dev, what);
 		break;
 	case PACKET_MR_UNICAST:
+		if (i->alen != dev->addr_len)
+			return -EINVAL;
 		if (what > 0)
 			return dev_unicast_add(dev, i->addr);
 		else
@@ -1734,7 +1738,7 @@ static int packet_mc_add(struct sock *sk, struct packet_mreq_max *mreq)
 		goto done;
 
 	err = -EINVAL;
-	if (mreq->mr_alen != dev->addr_len)
+	if (mreq->mr_alen > dev->addr_len)
 		goto done;
 
 	err = -ENOBUFS;