sctp: Hold sock lock while iterating over address list

Move address list traversal in inet_assoc_attr_size() under the sock
lock to avoid holding the RCU read lock.

Suggested-by: Xin Long <[e-mail]>
Fixes: 8f840e47f190 ("sctp: add the sctp_diag.c file")
Signed-off-by: Stefan Wiehler <[e-mail]>
Acked-by: Xin Long <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/sctp/diag.c

···
 	bool net_admin;
 };
 
-static size_t inet_assoc_attr_size(struct sctp_association *asoc)
+static size_t inet_assoc_attr_size(struct sock *sk,
+				   struct sctp_association *asoc)
 {
 	int addrlen = sizeof(struct sockaddr_storage);
 	int addrcnt = 0;
 	struct sctp_sockaddr_entry *laddr;
 
 	list_for_each_entry_rcu(laddr, &asoc->base.bind_addr.address_list,
-				list)
+				list, lockdep_sock_is_held(sk))
 		addrcnt++;
 
 	return	  nla_total_size(sizeof(struct sctp_info))
···
 	if (err)
 		return err;
 
-	rep = nlmsg_new(inet_assoc_attr_size(assoc), GFP_KERNEL);
-	if (!rep)
-		return -ENOMEM;
-
 	lock_sock(sk);
+
+	rep = nlmsg_new(inet_assoc_attr_size(sk, assoc), GFP_KERNEL);
+	if (!rep) {
+		release_sock(sk);
+		return -ENOMEM;
+	}
+
 	if (ep != assoc->ep) {
 		err = -EAGAIN;
 		goto out;