Q: Given the following code slice:
```
1 void rtm_phonet_notify(int event, struct net_device *dev, u8 dst)
3 	struct sk_buff *skb;
6 	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +```
which has a CWE-787 vulnerability at line:
```
6 	skb = nlmsg_new(NLMSG_ALIGN(sizeof(struct ifaddrmsg)) +
```
Please analyze the root cause of the vulnerability.