xfrm: Provide API to register translator module

Add a skeleton for xfrm_compat module and provide API to register it in
xfrm_state.ko. struct xfrm_translator will have function pointers to
translate messages received from 32-bit userspace or to be sent to it
from 64-bit kernel.
module_get()/module_put() are used instead of rcu_read_lock() as the
module will vmalloc() memory for translation.
The new API is registered with xfrm_state module, not with xfrm_user as
the former needs translator for user_policy set by setsockopt() and
xfrm_user already uses functions from xfrm_state.

Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/net/xfrm/xfrm_compat.c b/net/xfrm/xfrm_compat.c
new file mode 100644
index 000000000000..f01d9af41c55
--- /dev/null
+++ b/net/xfrm/xfrm_compat.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * XFRM compat layer
+ * Author: Dmitry Safonov <dima@arista.com>
+ * Based on code and translator idea by: Florian Westphal <fw@strlen.de>
+ */
+#include <linux/compat.h>
+#include <linux/xfrm.h>
+#include <net/xfrm.h>
+
+static struct xfrm_translator xfrm_translator = {
+	.owner				= THIS_MODULE,
+};
+
+static int __init xfrm_compat_init(void)
+{
+	return xfrm_register_translator(&xfrm_translator);
+}
+
+static void __exit xfrm_compat_exit(void)
+{
+	xfrm_unregister_translator(&xfrm_translator);
+}
+
+module_init(xfrm_compat_init);
+module_exit(xfrm_compat_exit);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Dmitry Safonov");
+MODULE_DESCRIPTION("XFRM 32-bit compatibility layer");