net/handshake: Add API for sending TLS Closure alerts

This helper sends an alert only if a TLS session was established.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/169047936730.5241.618595693821012638.stgit@oracle-102.nfsv4bat.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 61 insertions, 0 deletions

diff --git a/net/handshake/alert.c b/net/handshake/alert.c
new file mode 100644
index 000000000000..2f1a16868ff6
--- /dev/null
+++ b/net/handshake/alert.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Handle the TLS Alert protocol
+ *
+ * Author: Chuck Lever <chuck.lever@oracle.com>
+ *
+ * Copyright (c) 2023, Oracle and/or its affiliates.
+ */
+
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/inet.h>
+
+#include <net/sock.h>
+#include <net/handshake.h>
+#include <net/tls.h>
+#include <net/tls_prot.h>
+
+#include "handshake.h"
+
+/**
+ * tls_alert_send - send a TLS Alert on a kTLS socket
+ * @sock: open kTLS socket to send on
+ * @level: TLS Alert level
+ * @description: TLS Alert description
+ *
+ * Returns zero on success or a negative errno.
+ */
+int tls_alert_send(struct socket *sock, u8 level, u8 description)
+{
+	u8 record_type = TLS_RECORD_TYPE_ALERT;
+	u8 buf[CMSG_SPACE(sizeof(record_type))];
+	struct msghdr msg = { 0 };
+	struct cmsghdr *cmsg;
+	struct kvec iov;
+	u8 alert[2];
+	int ret;
+
+	alert[0] = level;
+	alert[1] = description;
+	iov.iov_base = alert;
+	iov.iov_len = sizeof(alert);
+
+	memset(buf, 0, sizeof(buf));
+	msg.msg_control = buf;
+	msg.msg_controllen = sizeof(buf);
+	msg.msg_flags = MSG_DONTWAIT;
+
+	cmsg = CMSG_FIRSTHDR(&msg);
+	cmsg->cmsg_level = SOL_TLS;
+	cmsg->cmsg_type = TLS_SET_RECORD_TYPE;
+	cmsg->cmsg_len = CMSG_LEN(sizeof(record_type));
+	memcpy(CMSG_DATA(cmsg), &record_type, sizeof(record_type));
+
+	iov_iter_kvec(&msg.msg_iter, ITER_SOURCE, &iov, 1, iov.iov_len);
+	ret = sock_sendmsg(sock, &msg);
+	return ret < 0 ? ret : 0;
+}