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 <lucien.xin@gmail.com>
Fixes: 8f840e4 ("sctp: add the sctp_diag.c file")
Signed-off-by: Stefan Wiehler <stefan.wiehler@nokia.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/20251028161506.3294376-4-stefan.wiehler@nokia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: sephalon

net/sctp/diag.c

@@ -230,14 +230,15 @@ struct sctp_comm_param {
 	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))
@@ -263,11 +264,14 @@ static int sctp_sock_dump_one(struct sctp_endpoint *ep, struct sctp_transport *t
 	if (err)
 		return err;
 
-	rep = nlmsg_new(inet_assoc_attr_size(assoc), GFP_KERNEL);
-	if (!rep)
+	lock_sock(sk);
+
+	rep = nlmsg_new(inet_assoc_attr_size(sk, assoc), GFP_KERNEL);
+	if (!rep) {
+		release_sock(sk);
 		return -ENOMEM;
+	}
 
-	lock_sock(sk);
 	if (ep != assoc->ep) {
 		err = -EAGAIN;
 		goto out;