mptcp: more detailed error reporting on endpoint creation

Endpoint creation can fail for a number of reasons; in case of failure
append the error number to the extended ack message, using a newly
introduced generic helper.

Additionally let mptcp_pm_nl_append_new_local_addr() report different
error reasons.
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/genetlink.h

@@ -125,6 +125,9 @@ static inline void genl_info_net_set(struct genl_info *info, struct net *net)
 
 #define GENL_SET_ERR_MSG(info, msg) NL_SET_ERR_MSG((info)->extack, msg)
 
+#define GENL_SET_ERR_MSG_FMT(info, msg, args...) \
+	NL_SET_ERR_MSG_FMT((info)->extack, msg, ##args)
+
 /* Report that a root attribute is missing */
 #define GENL_REQ_ATTR_CHECK(info, attr) ({				\
 	struct genl_info *__info = (info);				\

net/mptcp/pm_netlink.c

@@ -912,10 +912,14 @@ static int mptcp_pm_nl_append_new_local_addr(struct pm_nl_pernet *pernet,
 	 */
 	if (pernet->next_id == MPTCP_PM_MAX_ADDR_ID)
 		pernet->next_id = 1;
-	if (pernet->addrs >= MPTCP_PM_ADDR_MAX)
+	if (pernet->addrs >= MPTCP_PM_ADDR_MAX) {
+		ret = -ERANGE;
 		goto out;
-	if (test_bit(entry->addr.id, pernet->id_bitmap))
+	}
+	if (test_bit(entry->addr.id, pernet->id_bitmap)) {
+		ret = -EBUSY;
 		goto out;
+	}
 
 	/* do not insert duplicate address, differentiate on port only
 	 * singled addresses
@@ -929,8 +933,10 @@ static int mptcp_pm_nl_append_new_local_addr(struct pm_nl_pernet *pernet,
 			 * endpoint is an implicit one and the user-space
 			 * did not provide an endpoint id
 			 */
-			if (!(cur->flags & MPTCP_PM_ADDR_FLAG_IMPLICIT))
+			if (!(cur->flags & MPTCP_PM_ADDR_FLAG_IMPLICIT)) {
+				ret = -EEXIST;
 				goto out;
+			}
 			if (entry->addr.id)
 				goto out;
 
@@ -1016,16 +1022,12 @@ static int mptcp_pm_nl_create_listen_socket(struct sock *sk,
 		addrlen = sizeof(struct sockaddr_in6);
 #endif
 	err = kernel_bind(ssock, (struct sockaddr *)&addr, addrlen);
-	if (err) {
-		pr_warn("kernel_bind error, err=%d", err);
+	if (err)
 		return err;
-	}
 
 	err = kernel_listen(ssock, backlog);
-	if (err) {
-		pr_warn("kernel_listen error, err=%d", err);
+	if (err)
 		return err;
-	}
 
 	return 0;
 }
@@ -1329,13 +1331,13 @@ static int mptcp_nl_cmd_add_addr(struct sk_buff *skb, struct genl_info *info)
 	if (entry->addr.port) {
 		ret = mptcp_pm_nl_create_listen_socket(skb->sk, entry);
 		if (ret) {
-			GENL_SET_ERR_MSG(info, "create listen socket error");
+			GENL_SET_ERR_MSG_FMT(info, "create listen socket error: %d", ret);
 			goto out_free;
 		}
 	}
 	ret = mptcp_pm_nl_append_new_local_addr(pernet, entry);
 	if (ret < 0) {
-		GENL_SET_ERR_MSG(info, "too many addresses or duplicate one");
+		GENL_SET_ERR_MSG_FMT(info, "too many addresses or duplicate one: %d", ret);
 		goto out_free;
 	}