ipv6: report errors for iftoken via netlink extack

Setting iftoken can fail for several different reasons but there
and there was no report to user as to the cause. Add netlink
extended errors to the processing of the request.

This requires adding additional argument through rtnl_af_ops
set_link_af callback.
Reported-by: Hongren Zheng <li@zenithal.me>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/rtnetlink.h

@@ -147,8 +147,8 @@ struct rtnl_af_ops {
 	int			(*validate_link_af)(const struct net_device *dev,
 						    const struct nlattr *attr);
 	int			(*set_link_af)(struct net_device *dev,
-					       const struct nlattr *attr);
-
+					       const struct nlattr *attr,
+					       struct netlink_ext_ack *extack);
 	int			(*fill_stats_af)(struct sk_buff *skb,
 						 const struct net_device *dev);
 	size_t			(*get_stats_af_size)(const struct net_device *dev);

net/core/rtnetlink.c

@@ -2863,7 +2863,7 @@ static int do_setlink(const struct sk_buff *skb,
 
 			BUG_ON(!(af_ops = rtnl_af_lookup(nla_type(af))));
 
-			err = af_ops->set_link_af(dev, af);
+			err = af_ops->set_link_af(dev, af, extack);
 			if (err < 0) {
 				rcu_read_unlock();
 				goto errout;

net/ipv4/devinet.c

@@ -1978,7 +1978,8 @@ static int inet_validate_link_af(const struct net_device *dev,
 	return 0;
 }
 
-static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla)
+static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla,
+			    struct netlink_ext_ack *extack)
 {
 	struct in_device *in_dev = __in_dev_get_rcu(dev);
 	struct nlattr *a, *tb[IFLA_INET_MAX+1];

net/ipv6/addrconf.c

@@ -5669,7 +5669,8 @@ static int inet6_fill_link_af(struct sk_buff *skb, const struct net_device *dev,
 	return 0;
 }
 
-static int inet6_set_iftoken(struct inet6_dev *idev, struct in6_addr *token)
+static int inet6_set_iftoken(struct inet6_dev *idev, struct in6_addr *token,
+			     struct netlink_ext_ack *extack)
 {
 	struct inet6_ifaddr *ifp;
 	struct net_device *dev = idev->dev;
@@ -5680,12 +5681,29 @@ static int inet6_set_iftoken(struct inet6_dev *idev, struct in6_addr *token)
 
 	if (!token)
 		return -EINVAL;
-	if (dev->flags & (IFF_LOOPBACK | IFF_NOARP))
+
+	if (dev->flags & IFF_LOOPBACK) {
+		NL_SET_ERR_MSG_MOD(extack, "Device is loopback");
 		return -EINVAL;
-	if (!ipv6_accept_ra(idev))
+	}
+
+	if (dev->flags & IFF_NOARP) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Device does not do neighbour discovery");
+		return -EINVAL;
+	}
+
+	if (!ipv6_accept_ra(idev)) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Router advertisement is disabled on device");
 		return -EINVAL;
-	if (idev->cnf.rtr_solicits == 0)
+	}
+
+	if (idev->cnf.rtr_solicits == 0) {
+		NL_SET_ERR_MSG(extack,
+			       "Router solicitation is disabled on device");
 		return -EINVAL;
+	}
 
 	write_lock_bh(&idev->lock);
 
@@ -5793,7 +5811,8 @@ static int inet6_validate_link_af(const struct net_device *dev,
 	return 0;
 }
 
-static int inet6_set_link_af(struct net_device *dev, const struct nlattr *nla)
+static int inet6_set_link_af(struct net_device *dev, const struct nlattr *nla,
+			     struct netlink_ext_ack *extack)
 {
 	struct inet6_dev *idev = __in6_dev_get(dev);
 	struct nlattr *tb[IFLA_INET6_MAX + 1];
@@ -5806,7 +5825,8 @@ static int inet6_set_link_af(struct net_device *dev, const struct nlattr *nla)
 		BUG();
 
 	if (tb[IFLA_INET6_TOKEN]) {
-		err = inet6_set_iftoken(idev, nla_data(tb[IFLA_INET6_TOKEN]));
+		err = inet6_set_iftoken(idev, nla_data(tb[IFLA_INET6_TOKEN]),
+					extack);
 		if (err)
 			return err;
 	}