tipc: check return value of nlmsg_new

Function nlmsg_new() will return a NULL pointer if there is no enough
memory, and its return value should be checked before it is used.
However, in function tipc_nl_node_get_monitor(), the validation of the
return value of function nlmsg_new() is missed. This patch fixes the
bug.
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/node.c

@@ -2098,6 +2098,8 @@ int tipc_nl_node_get_monitor(struct sk_buff *skb, struct genl_info *info)
 	int err;
 
 	msg.skb = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
+	if (!msg.skb)
+		return -ENOMEM;
 	msg.portid = info->snd_portid;
 	msg.seq = info->snd_seq;