// SPDX-License-Identifier: GPL-2.0-only
/* xfrm4_tunnel.c: Generic IP tunnel transformer.
 *
 * Copyright (C) 2003 David S. Miller (davem@redhat.com)
 */

#define pr_fmt(fmt) "IPsec: " fmt

#include <linux/skbuff.h>
#include <linux/module.h>
#include <net/xfrm.h>
#include <net/protocol.h>

static int ipip_output(struct xfrm_state *x, struct sk_buff *skb)
{
        skb_push(skb, -skb_network_offset(skb));
        return 0;
}

static int ipip_xfrm_rcv(struct xfrm_state *x, struct sk_buff *skb)
{
        return ip_hdr(skb)->protocol;
}

static int ipip_init_state(struct xfrm_state *x, struct netlink_ext_ack *extack)
{
        if (x->props.mode != XFRM_MODE_TUNNEL) {
                NL_SET_ERR_MSG(extack, "IPv4 tunnel can only be used with tunnel mode");
                return -EINVAL;
        }

        if (x->encap) {
                NL_SET_ERR_MSG(extack, "IPv4 tunnel is not compatible with encapsulation");
                return -EINVAL;
        }

        x->props.header_len = sizeof(struct iphdr);

        return 0;
}

static void ipip_destroy(struct xfrm_state *x)
{
}

static const struct xfrm_type ipip_type = {
        .owner          = THIS_MODULE,
        .proto          = IPPROTO_IPIP,
        .init_state     = ipip_init_state,
        .destructor     = ipip_destroy,
        .input          = ipip_xfrm_rcv,
        .output         = ipip_output
};

static int xfrm_tunnel_rcv(struct sk_buff *skb)
{
        return xfrm4_rcv_spi(skb, IPPROTO_IPIP, ip_hdr(skb)->saddr);
}

static int xfrm_tunnel_err(struct sk_buff *skb, u32 info)
{
        return -ENOENT;
}

static struct xfrm_tunnel xfrm_tunnel_handler __read_mostly = {
        .handler        =       xfrm_tunnel_rcv,
        .err_handler    =       xfrm_tunnel_err,
        .priority       =       4,
};

#if IS_ENABLED(CONFIG_IPV6)
static struct xfrm_tunnel xfrm64_tunnel_handler __read_mostly = {
        .handler        =       xfrm_tunnel_rcv,
        .err_handler    =       xfrm_tunnel_err,
        .priority       =       3,
};
#endif

static int __init ipip_init(void)
{
        if (xfrm_register_type(&ipip_type, AF_INET) < 0) {
                pr_info("%s: can't add xfrm type\n", __func__);
                return -EAGAIN;
        }

        if (xfrm4_tunnel_register(&xfrm_tunnel_handler, AF_INET)) {
                pr_info("%s: can't add xfrm handler for AF_INET\n", __func__);
                xfrm_unregister_type(&ipip_type, AF_INET);
                return -EAGAIN;
        }
#if IS_ENABLED(CONFIG_IPV6)
        if (xfrm4_tunnel_register(&xfrm64_tunnel_handler, AF_INET6)) {
                pr_info("%s: can't add xfrm handler for AF_INET6\n", __func__);
                xfrm4_tunnel_deregister(&xfrm_tunnel_handler, AF_INET);
                xfrm_unregister_type(&ipip_type, AF_INET);
                return -EAGAIN;
        }
#endif
        return 0;
}

static void __exit ipip_fini(void)
{
#if IS_ENABLED(CONFIG_IPV6)
        if (xfrm4_tunnel_deregister(&xfrm64_tunnel_handler, AF_INET6))
                pr_info("%s: can't remove xfrm handler for AF_INET6\n",
                        __func__);
#endif
        if (xfrm4_tunnel_deregister(&xfrm_tunnel_handler, AF_INET))
                pr_info("%s: can't remove xfrm handler for AF_INET\n",
                        __func__);
        xfrm_unregister_type(&ipip_type, AF_INET);
}

module_init(ipip_init);
module_exit(ipip_fini);
MODULE_DESCRIPTION("IPv4 XFRM tunnel driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_IPIP);