xfrm4_mode_tunnel.c

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/*
 * xfrm4_mode_tunnel.c - Tunnel mode encapsulation for IPv4.
 *
 * Copyright (c) 2004-2006 Herbert Xu <[email protected]>
 */

#include <linux/gfp.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/stringify.h>
#include <net/dst.h>
#include <net/inet_ecn.h>
#include <net/ip.h>
#include <net/xfrm.h>

/* Informational hook. The decap is still done here. */
static struct xfrm_tunnel __rcu *rcv_notify_handlers __read_mostly;
static DEFINE_MUTEX(xfrm4_mode_tunnel_input_mutex);

int xfrm4_mode_tunnel_input_register(struct xfrm_tunnel *handler)
{
    struct xfrm_tunnel __rcu **pprev;
    struct xfrm_tunnel *t;
    int ret = -EEXIST;
    int priority = handler->priority;

    mutex_lock(&xfrm4_mode_tunnel_input_mutex);

    for (pprev = &rcv_notify_handlers;
         (t = rcu_dereference_protected(*pprev,
         lockdep_is_held(&xfrm4_mode_tunnel_input_mutex))) != NULL;
         pprev = &t->next) {
        if (t->priority > priority)
            break;
        if (t->priority == priority)
            goto err;

    }

    handler->next = *pprev;
    rcu_assign_pointer(*pprev, handler);

    ret = 0;

err:
    mutex_unlock(&xfrm4_mode_tunnel_input_mutex);
    return ret;
}
EXPORT_SYMBOL_GPL(xfrm4_mode_tunnel_input_register);

int xfrm4_mode_tunnel_input_deregister(struct xfrm_tunnel *handler)
{
    struct xfrm_tunnel __rcu **pprev;
    struct xfrm_tunnel *t;
    int ret = -ENOENT;

    mutex_lock(&xfrm4_mode_tunnel_input_mutex);
    for (pprev = &rcv_notify_handlers;
         (t = rcu_dereference_protected(*pprev,
         lockdep_is_held(&xfrm4_mode_tunnel_input_mutex))) != NULL;
         pprev = &t->next) {
        if (t == handler) {
            *pprev = handler->next;
            ret = 0;
            break;
        }
    }
    mutex_unlock(&xfrm4_mode_tunnel_input_mutex);
    synchronize_net();

    return ret;
}
EXPORT_SYMBOL_GPL(xfrm4_mode_tunnel_input_deregister);

static inline void ipip_ecn_decapsulate(struct sk_buff *skb)
{
    struct iphdr *inner_iph = ipip_hdr(skb);

    if (INET_ECN_is_ce(XFRM_MODE_SKB_CB(skb)->tos))
        IP_ECN_set_ce(inner_iph);
}

/* Add encapsulation header.
 *
 * The top IP header will be constructed per RFC 2401.
 */
static int xfrm4_mode_tunnel_output(struct xfrm_state *x, struct sk_buff *skb)
{
    struct dst_entry *dst = skb_dst(skb);
    struct iphdr *top_iph;
    int flags;

    skb_set_network_header(skb, -x->props.header_len);
    skb->mac_header = skb->network_header +
              offsetof(struct iphdr, protocol);
    skb->transport_header = skb->network_header + sizeof(*top_iph);
    top_iph = ip_hdr(skb);

    top_iph->ihl = 5;
    top_iph->version = 4;

    top_iph->protocol = xfrm_af2proto(skb_dst(skb)->ops->family);

    /* DS disclosed */
    top_iph->tos = INET_ECN_encapsulate(XFRM_MODE_SKB_CB(skb)->tos,
                        XFRM_MODE_SKB_CB(skb)->tos);

    flags = x->props.flags;
    if (flags & XFRM_STATE_NOECN)
        IP_ECN_clear(top_iph);

    top_iph->frag_off = (flags & XFRM_STATE_NOPMTUDISC) ?
        0 : (XFRM_MODE_SKB_CB(skb)->frag_off & htons(IP_DF));
    ip_select_ident(top_iph, dst->child, NULL);

    top_iph->ttl = ip4_dst_hoplimit(dst->child);

    top_iph->saddr = x->props.saddr.a4;
    top_iph->daddr = x->id.daddr.a4;

    return 0;
}

#define for_each_input_rcu(head, handler)   \
    for (handler = rcu_dereference(head);   \
         handler != NULL;           \
         handler = rcu_dereference(handler->next))

static int xfrm4_mode_tunnel_input(struct xfrm_state *x, struct sk_buff *skb)
{
    struct xfrm_tunnel *handler;
    int err = -EINVAL;

    if (XFRM_MODE_SKB_CB(skb)->protocol != IPPROTO_IPIP)
        goto out;

    if (!pskb_may_pull(skb, sizeof(struct iphdr)))
        goto out;

    for_each_input_rcu(rcv_notify_handlers, handler)
        handler->handler(skb);

    if (skb_cloned(skb) &&
        (err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
        goto out;

    if (x->props.flags & XFRM_STATE_DECAP_DSCP)
        ipv4_copy_dscp(XFRM_MODE_SKB_CB(skb)->tos, ipip_hdr(skb));
    if (!(x->props.flags & XFRM_STATE_NOECN))
        ipip_ecn_decapsulate(skb);

    skb_reset_network_header(skb);
    skb_mac_header_rebuild(skb);

    err = 0;

out:
    return err;
}

static struct xfrm_mode xfrm4_tunnel_mode = {
    .input2 = xfrm4_mode_tunnel_input,
    .input = xfrm_prepare_input,
    .output2 = xfrm4_mode_tunnel_output,
    .output = xfrm4_prepare_output,
    .owner = THIS_MODULE,
    .encap = XFRM_MODE_TUNNEL,
    .flags = XFRM_MODE_FLAG_TUNNEL,
};

static int __init xfrm4_mode_tunnel_init(void)
{
    return xfrm_register_mode(&xfrm4_tunnel_mode, AF_INET);
}

static void __exit xfrm4_mode_tunnel_exit(void)
{
    int err;

    err = xfrm_unregister_mode(&xfrm4_tunnel_mode, AF_INET);
    BUG_ON(err);
}

module_init(xfrm4_mode_tunnel_init);
module_exit(xfrm4_mode_tunnel_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_TUNNEL);