ipcomp.c

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/*
 * IP Payload Compression Protocol (IPComp) - RFC3173.
 *
 * Copyright (c) 2003 James Morris <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * 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 void 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;
    case ICMP_REDIRECT:
        break;
    default:
        return;
    }

    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;

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

/* We always hold one tunnel user reference to indicate a tunnel */
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 == NULL)
        goto out;

    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;
    memcpy(&t->mark, &x->mark, sizeof(t->mark));

    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)
{
    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:
        goto out;
    }

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

    if (x->props.mode == XFRM_MODE_TUNNEL) {
        err = ipcomp_tunnel_attach(x);
        if (err)
            goto out;
    }

    err = 0;
out:
    return err;
}

static const struct xfrm_type ipcomp_type = {
    .description    = "IPCOMP4",
    .owner      = THIS_MODULE,
    .proto          = IPPROTO_COMP,
    .init_state = ipcomp4_init_state,
    .destructor = ipcomp_destroy,
    .input      = ipcomp_input,
    .output     = ipcomp_output
};

static const struct net_protocol ipcomp4_protocol = {
    .handler    =   xfrm4_rcv,
    .err_handler    =   ipcomp4_err,
    .no_policy  =   1,
};

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 (inet_add_protocol(&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 (inet_del_protocol(&ipcomp4_protocol, IPPROTO_COMP) < 0)
        pr_info("%s: can't remove protocol\n", __func__);
    if (xfrm_unregister_type(&ipcomp_type, AF_INET) < 0)
        pr_info("%s: can't remove xfrm type\n", __func__);
}

module_init(ipcomp4_init);
module_exit(ipcomp4_fini);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("IP Payload Compression Protocol (IPComp/IPv4) - RFC3173");
MODULE_AUTHOR("James Morris <[email protected]>");

MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_COMP);