// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * IP Payload Compression Protocol (IPComp) - RFC3173.
 *
 * Copyright (c) 2003 James Morris <jmorris@intercode.com.au>
 *
 * Todo:
 *   - Tunable compression parameters.
 *   - Compression stats.
 *   - Adaptive compression.
 */
#include <linux/module.h>
#include <linux/err.h>
#include <linux/rtnetlink.h>
#include <net/ip.h>
#include <net/xfrm.h>
#include <net/icmp.h>
#include <net/ipcomp.h>
#include <net/protocol.h>
#include <net/sock.h>

static int ipcomp4_err(struct sk_buff *skb, u32 info)
{
        struct net *net = dev_net(skb->dev);
        __be32 spi;
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct ip_comp_hdr *ipch = (struct ip_comp_hdr *)(skb->data+(iph->ihl<<2));
        struct xfrm_state *x;

        switch (icmp_hdr(skb)->type) {
        case ICMP_DEST_UNREACH:
                if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
                        return 0;
                break;
        case ICMP_REDIRECT:
                break;
        default:
                return 0;
        }

        spi = htonl(ntohs(ipch->cpi));
        x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,
                              spi, IPPROTO_COMP, AF_INET);
        if (!x)
                return 0;

        if (icmp_hdr(skb)->type == ICMP_DEST_UNREACH)
                ipv4_update_pmtu(skb, net, info, 0, IPPROTO_COMP);
        else
                ipv4_redirect(skb, net, 0, IPPROTO_COMP);
        xfrm_state_put(x);

        return 0;
}

/* We always hold one tunnel user reference to indicate a tunnel */
static struct lock_class_key xfrm_state_lock_key;
static struct xfrm_state *ipcomp_tunnel_create(struct xfrm_state *x)
{
        struct net *net = xs_net(x);
        struct xfrm_state *t;

        t = xfrm_state_alloc(net);
        if (!t)
                goto out;
        lockdep_set_class(&t->lock, &xfrm_state_lock_key);

        t->id.proto = IPPROTO_IPIP;
        t->id.spi = x->props.saddr.a4;
        t->id.daddr.a4 = x->id.daddr.a4;
        memcpy(&t->sel, &x->sel, sizeof(t->sel));
        t->props.family = AF_INET;
        t->props.mode = x->props.mode;
        t->props.saddr.a4 = x->props.saddr.a4;
        t->props.flags = x->props.flags;
        t->props.extra_flags = x->props.extra_flags;
        memcpy(&t->mark, &x->mark, sizeof(t->mark));
        t->if_id = x->if_id;

        if (xfrm_init_state(t))
                goto error;

        atomic_set(&t->tunnel_users, 1);
out:
        return t;

error:
        t->km.state = XFRM_STATE_DEAD;
        xfrm_state_put(t);
        t = NULL;
        goto out;
}

/*
 * Must be protected by xfrm_cfg_mutex.  State and tunnel user references are
 * always incremented on success.
 */
static int ipcomp_tunnel_attach(struct xfrm_state *x)
{
        struct net *net = xs_net(x);
        int err = 0;
        struct xfrm_state *t;
        u32 mark = x->mark.v & x->mark.m;

        t = xfrm_state_lookup(net, mark, (xfrm_address_t *)&x->id.daddr.a4,
                              x->props.saddr.a4, IPPROTO_IPIP, AF_INET);
        if (!t) {
                t = ipcomp_tunnel_create(x);
                if (!t) {
                        err = -EINVAL;
                        goto out;
                }
                xfrm_state_insert(t);
                xfrm_state_hold(t);
        }
        x->tunnel = t;
        atomic_inc(&t->tunnel_users);
out:
        return err;
}

static int ipcomp4_init_state(struct xfrm_state *x,
                              struct netlink_ext_ack *extack)
{
        int err = -EINVAL;

        x->props.header_len = 0;
        switch (x->props.mode) {
        case XFRM_MODE_TRANSPORT:
                break;
        case XFRM_MODE_TUNNEL:
                x->props.header_len += sizeof(struct iphdr);
                break;
        default:
                NL_SET_ERR_MSG(extack, "Unsupported XFRM mode for IPcomp");
                goto out;
        }

        err = ipcomp_init_state(x, extack);
        if (err)
                goto out;

        if (x->props.mode == XFRM_MODE_TUNNEL) {
                err = ipcomp_tunnel_attach(x);
                if (err) {
                        NL_SET_ERR_MSG(extack, "Kernel error: failed to initialize the associated state");
                        goto out;
                }
        }

        err = 0;
out:
        return err;
}

static int ipcomp4_rcv_cb(struct sk_buff *skb, int err)
{
        return 0;
}

static const struct xfrm_type ipcomp_type = {
        .owner          = THIS_MODULE,
        .proto          = IPPROTO_COMP,
        .init_state     = ipcomp4_init_state,
        .destructor     = ipcomp_destroy,
        .input          = ipcomp_input,
        .output         = ipcomp_output
};

static struct xfrm4_protocol ipcomp4_protocol = {
        .handler        =       xfrm4_rcv,
        .input_handler  =       xfrm_input,
        .cb_handler     =       ipcomp4_rcv_cb,
        .err_handler    =       ipcomp4_err,
        .priority       =       0,
};

static int __init ipcomp4_init(void)
{
        if (xfrm_register_type(&ipcomp_type, AF_INET) < 0) {
                pr_info("%s: can't add xfrm type\n", __func__);
                return -EAGAIN;
        }
        if (xfrm4_protocol_register(&ipcomp4_protocol, IPPROTO_COMP) < 0) {
                pr_info("%s: can't add protocol\n", __func__);
                xfrm_unregister_type(&ipcomp_type, AF_INET);
                return -EAGAIN;
        }
        return 0;
}

static void __exit ipcomp4_fini(void)
{
        if (xfrm4_protocol_deregister(&ipcomp4_protocol, IPPROTO_COMP) < 0)
                pr_info("%s: can't remove protocol\n", __func__);
        xfrm_unregister_type(&ipcomp_type, AF_INET);
}

module_init(ipcomp4_init);
module_exit(ipcomp4_fini);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("IP Payload Compression Protocol (IPComp/IPv4) - RFC3173");
MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");

MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_COMP);