IPv4: add extack info for IPv4 address add/delete

Add extack info for IPv4 address add/delete, which would be useful for
users to understand the problem without having to read kernel code.

No extack message for the ifa_local checking in __inet_insert_ifa() as
it has been checked in find_matching_ifa().
Suggested-by: Ido Schimmel <idosch@idosch.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/devinet.c

@@ -509,6 +509,7 @@ static int __inet_insert_ifa(struct in_ifaddr *ifa, struct nlmsghdr *nlh,
 				return -EEXIST;
 			}
 			if (ifa1->ifa_scope != ifa->ifa_scope) {
+				NL_SET_ERR_MSG(extack, "ipv4: Invalid scope value");
 				inet_free_ifa(ifa);
 				return -EINVAL;
 			}
@@ -664,6 +665,7 @@ static int inet_rtm_deladdr(struct sk_buff *skb, struct nlmsghdr *nlh,
 	ifm = nlmsg_data(nlh);
 	in_dev = inetdev_by_index(net, ifm->ifa_index);
 	if (!in_dev) {
+		NL_SET_ERR_MSG(extack, "ipv4: Device not found");
 		err = -ENODEV;
 		goto errout;
 	}
@@ -688,6 +690,7 @@ static int inet_rtm_deladdr(struct sk_buff *skb, struct nlmsghdr *nlh,
 		return 0;
 	}
 
+	NL_SET_ERR_MSG(extack, "ipv4: Address not found");
 	err = -EADDRNOTAVAIL;
 errout:
 	return err;
@@ -839,13 +842,23 @@ static struct in_ifaddr *rtm_to_ifaddr(struct net *net, struct nlmsghdr *nlh,
 
 	ifm = nlmsg_data(nlh);
 	err = -EINVAL;
-	if (ifm->ifa_prefixlen > 32 || !tb[IFA_LOCAL])
+
+	if (ifm->ifa_prefixlen > 32) {
+		NL_SET_ERR_MSG(extack, "ipv4: Invalid prefix length");
+		goto errout;
+	}
+
+	if (!tb[IFA_LOCAL]) {
+		NL_SET_ERR_MSG(extack, "ipv4: Local address is not supplied");
 		goto errout;
+	}
 
 	dev = __dev_get_by_index(net, ifm->ifa_index);
 	err = -ENODEV;
-	if (!dev)
+	if (!dev) {
+		NL_SET_ERR_MSG(extack, "ipv4: Device not found");
 		goto errout;
+	}
 
 	in_dev = __in_dev_get_rtnl(dev);
 	err = -ENOBUFS;
@@ -897,6 +910,7 @@ static struct in_ifaddr *rtm_to_ifaddr(struct net *net, struct nlmsghdr *nlh,
 
 		ci = nla_data(tb[IFA_CACHEINFO]);
 		if (!ci->ifa_valid || ci->ifa_prefered > ci->ifa_valid) {
+			NL_SET_ERR_MSG(extack, "ipv4: address lifetime invalid");
 			err = -EINVAL;
 			goto errout_free;
 		}
@@ -954,6 +968,7 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 			int ret = ip_mc_autojoin_config(net, true, ifa);
 
 			if (ret < 0) {
+				NL_SET_ERR_MSG(extack, "ipv4: Multicast auto join failed");
 				inet_free_ifa(ifa);
 				return ret;
 			}
@@ -967,8 +982,10 @@ static int inet_rtm_newaddr(struct sk_buff *skb, struct nlmsghdr *nlh,
 		inet_free_ifa(ifa);
 
 		if (nlh->nlmsg_flags & NLM_F_EXCL ||
-		    !(nlh->nlmsg_flags & NLM_F_REPLACE))
+		    !(nlh->nlmsg_flags & NLM_F_REPLACE)) {
+			NL_SET_ERR_MSG(extack, "ipv4: Address already assigned");
 			return -EEXIST;
+		}
 		ifa = ifa_existing;
 
 		if (ifa->ifa_rt_priority != new_metric) {