rtnetlink: move validate_linkmsg out of do_setlink

This patch moves validate_linkmsg() out of do_setlink() to its callers
and deletes the early validate_linkmsg() call in __rtnl_newlink(), so
that it will not call validate_linkmsg() twice in either of the paths:

  - __rtnl_newlink() -> do_setlink()
  - __rtnl_newlink() -> rtnl_newlink_create() -> rtnl_create_link()

Additionally, as validate_linkmsg() is now only called with a real
dev, we can remove the NULL check for dev in validate_linkmsg().

Note that we moved validate_linkmsg() check to the places where it has
not done any changes to the dev, as Jakub suggested.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/cf2ef061e08251faf9e8be25ff0d61150c030475.1686585334.git.lucien.xin@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/rtnetlink.c

@@ -2383,7 +2383,6 @@ static	int rtnl_set_vf_rate(struct net_device *dev, int vf, int min_tx_rate,
 static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[],
 			    struct netlink_ext_ack *extack)
 {
-	if (dev) {
 	if (tb[IFLA_ADDRESS] &&
 	    nla_len(tb[IFLA_ADDRESS]) < dev->addr_len)
 		return -EINVAL;
@@ -2422,7 +2421,6 @@ static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[],
 		NL_SET_ERR_MSG(extack, "too big gro_ipv4_max_size");
 		return -EINVAL;
 	}
-	}
 
 	if (tb[IFLA_AF_SPEC]) {
 		struct nlattr *af;
@@ -2742,10 +2740,6 @@ static int do_setlink(const struct sk_buff *skb,
 	char ifname[IFNAMSIZ];
 	int err;
 
-	err = validate_linkmsg(dev, tb, extack);
-	if (err < 0)
-		return err;
-
 	if (tb[IFLA_IFNAME])
 		nla_strscpy(ifname, tb[IFLA_IFNAME], IFNAMSIZ);
 	else
@@ -3162,6 +3156,10 @@ static int rtnl_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 		goto errout;
 	}
 
+	err = validate_linkmsg(dev, tb, extack);
+	if (err < 0)
+		goto errout;
+
 	err = do_setlink(skb, dev, ifm, extack, tb, 0);
 errout:
 	return err;
@@ -3405,6 +3403,9 @@ static int rtnl_group_changelink(const struct sk_buff *skb,
 
 	for_each_netdev_safe(net, dev, aux) {
 		if (dev->group == group) {
+			err = validate_linkmsg(dev, tb, extack);
+			if (err < 0)
+				return err;
 			err = do_setlink(skb, dev, ifm, extack, tb, 0);
 			if (err < 0)
 				return err;
@@ -3562,10 +3563,6 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 			m_ops = master_dev->rtnl_link_ops;
 	}
 
-	err = validate_linkmsg(dev, tb, extack);
-	if (err < 0)
-		return err;
-
 	if (tb[IFLA_LINKINFO]) {
 		err = nla_parse_nested_deprecated(linkinfo, IFLA_INFO_MAX,
 						  tb[IFLA_LINKINFO],
@@ -3629,6 +3626,10 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 		if (nlh->nlmsg_flags & NLM_F_REPLACE)
 			return -EOPNOTSUPP;
 
+		err = validate_linkmsg(dev, tb, extack);
+		if (err < 0)
+			return err;
+
 		if (linkinfo[IFLA_INFO_DATA]) {
 			if (!ops || ops != dev->rtnl_link_ops ||
 			    !ops->changelink)