hsr: add restart routine into hsr_get_node_list()

The hsr_get_node_list() is to send node addresses to the userspace.
If there are so many nodes, it could fail because of buffer size.
In order to avoid this failure, the restart routine is added.

Fixes: f421436a ("net/hsr: Add support for the High-availability Seamless Redundancy protocol (HSRv0)")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/hsr/hsr_netlink.c

@@ -360,16 +360,14 @@ static int hsr_get_node_status(struct sk_buff *skb_in, struct genl_info *info)
  */
 static int hsr_get_node_list(struct sk_buff *skb_in, struct genl_info *info)
 {
-	/* For receiving */
-	struct nlattr *na;
+	unsigned char addr[ETH_ALEN];
 	struct net_device *hsr_dev;
-
-	/* For sending */
 	struct sk_buff *skb_out;
-	void *msg_head;
 	struct hsr_priv *hsr;
-	void *pos;
-	unsigned char addr[ETH_ALEN];
+	bool restart = false;
+	struct nlattr *na;
+	void *pos = NULL;
+	void *msg_head;
 	int res;
 
 	if (!info)
@@ -387,8 +385,9 @@ static int hsr_get_node_list(struct sk_buff *skb_in, struct genl_info *info)
 	if (!is_hsr_master(hsr_dev))
 		goto rcu_unlock;
 
+restart:
 	/* Send reply */
-	skb_out = genlmsg_new(NLMSG_GOODSIZE, GFP_ATOMIC);
+	skb_out = genlmsg_new(GENLMSG_DEFAULT_SIZE, GFP_ATOMIC);
 	if (!skb_out) {
 		res = -ENOMEM;
 		goto fail;
@@ -402,17 +401,28 @@ static int hsr_get_node_list(struct sk_buff *skb_in, struct genl_info *info)
 		goto nla_put_failure;
 	}
 
-	res = nla_put_u32(skb_out, HSR_A_IFINDEX, hsr_dev->ifindex);
-	if (res < 0)
-		goto nla_put_failure;
+	if (!restart) {
+		res = nla_put_u32(skb_out, HSR_A_IFINDEX, hsr_dev->ifindex);
+		if (res < 0)
+			goto nla_put_failure;
+	}
 
 	hsr = netdev_priv(hsr_dev);
 
-	pos = hsr_get_next_node(hsr, NULL, addr);
+	if (!pos)
+		pos = hsr_get_next_node(hsr, NULL, addr);
 	while (pos) {
 		res = nla_put(skb_out, HSR_A_NODE_ADDR, ETH_ALEN, addr);
-		if (res < 0)
+		if (res < 0) {
+			if (res == -EMSGSIZE) {
+				genlmsg_end(skb_out, msg_head);
+				genlmsg_unicast(genl_info_net(info), skb_out,
+						info->snd_portid);
+				restart = true;
+				goto restart;
+			}
 			goto nla_put_failure;
+		}
 		pos = hsr_get_next_node(hsr, pos, addr);
 	}
 	rcu_read_unlock();
@@ -429,7 +439,7 @@ static int hsr_get_node_list(struct sk_buff *skb_in, struct genl_info *info)
 	return 0;
 
 nla_put_failure:
-	kfree_skb(skb_out);
+	nlmsg_free(skb_out);
 	/* Fall through */
 
 fail: