[RTNL]: Validate hardware and broadcast address attribute for RTM_NEWLINK

RTM_NEWLINK allows for already existing links to be modified. For this
purpose do_setlink() is called which expects address attributes with a
payload length of at least dev->addr_len. This patch adds the necessary
validation for the RTM_NEWLINK case.

The address length for links to be created is not checked for now as the
actual attribute length is used when copying the address to the netdevice
structure. It might make sense to report an error if less than addr_len
bytes are provided but enforcing this might break drivers trying to be
smart with not transmitting all zero addresses.

Signed-off-by: Thomas Graf <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/rtnetlink.c

···
 	return net;
 }
 
+static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[])
+{
+	if (dev) {
+		if (tb[IFLA_ADDRESS] &&
+		    nla_len(tb[IFLA_ADDRESS]) < dev->addr_len)
+			return -EINVAL;
+
+		if (tb[IFLA_BROADCAST] &&
+		    nla_len(tb[IFLA_BROADCAST]) < dev->addr_len)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int do_setlink(struct net_device *dev, struct ifinfomsg *ifm,
 		      struct nlattr **tb, char *ifname, int modified)
 {
···
 		goto errout;
 	}
 
-	if (tb[IFLA_ADDRESS] &&
-	    nla_len(tb[IFLA_ADDRESS]) < dev->addr_len)
-		goto errout_dev;
-
-	if (tb[IFLA_BROADCAST] &&
-	    nla_len(tb[IFLA_BROADCAST]) < dev->addr_len)
+	if ((err = validate_linkmsg(dev, tb)) < 0)
 		goto errout_dev;
 
 	err = do_setlink(dev, ifm, tb, ifname, 0);
···
 		dev = __dev_get_by_name(net, ifname);
 	else
 		dev = NULL;
+
+	if ((err = validate_linkmsg(dev, tb)) < 0)
+		return err;
 
 	if (tb[IFLA_LINKINFO]) {
 		err = nla_parse_nested(linkinfo, IFLA_INFO_MAX,