inet_diag: fix possible overflow in inet_diag_dump_one_icsk()

inet_diag_dump_one_icsk() allocates too small skb.

Add inet_sk_attr_size() helper right before inet_sk_diag_fill()
so that it can be updated if/when new attributes are added.

iproute2/ss currently does not use this dump_one() interface,
this might explain nobody noticed this problem yet.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/inet_diag.c

@@ -71,6 +71,20 @@ static inline void inet_diag_unlock_handler(
 	mutex_unlock(&inet_diag_table_mutex);
 }
 
+static size_t inet_sk_attr_size(void)
+{
+	return	  nla_total_size(sizeof(struct tcp_info))
+		+ nla_total_size(1) /* INET_DIAG_SHUTDOWN */
+		+ nla_total_size(1) /* INET_DIAG_TOS */
+		+ nla_total_size(1) /* INET_DIAG_TCLASS */
+		+ nla_total_size(sizeof(struct inet_diag_meminfo))
+		+ nla_total_size(sizeof(struct inet_diag_msg))
+		+ nla_total_size(SK_MEMINFO_VARS * sizeof(u32))
+		+ nla_total_size(TCP_CA_NAME_MAX)
+		+ nla_total_size(sizeof(struct tcpvegas_info))
+		+ 64;
+}
+
 int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 			      struct sk_buff *skb, struct inet_diag_req_v2 *req,
 			      struct user_namespace *user_ns,		      	
@@ -326,9 +340,7 @@ int inet_diag_dump_one_icsk(struct inet_hashinfo *hashinfo, struct sk_buff *in_s
 	if (err)
 		goto out;
 
-	rep = nlmsg_new(sizeof(struct inet_diag_msg) +
-			sizeof(struct inet_diag_meminfo) +
-			sizeof(struct tcp_info) + 64, GFP_KERNEL);
+	rep = nlmsg_new(inet_sk_attr_size(), GFP_KERNEL);
 	if (!rep) {
 		err = -ENOMEM;
 		goto out;