netfilter.c

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#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/ipv6.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv6.h>
#include <linux/export.h>
#include <net/dst.h>
#include <net/ipv6.h>
#include <net/ip6_route.h>
#include <net/xfrm.h>
#include <net/ip6_checksum.h>
#include <net/netfilter/nf_queue.h>

int ip6_route_me_harder(struct sk_buff *skb)
{
    struct net *net = dev_net(skb_dst(skb)->dev);
    const struct ipv6hdr *iph = ipv6_hdr(skb);
    unsigned int hh_len;
    struct dst_entry *dst;
    struct flowi6 fl6 = {
        .flowi6_oif = skb->sk ? skb->sk->sk_bound_dev_if : 0,
        .flowi6_mark = skb->mark,
        .daddr = iph->daddr,
        .saddr = iph->saddr,
    };

    dst = ip6_route_output(net, skb->sk, &fl6);
    if (dst->error) {
        IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
        LIMIT_NETDEBUG(KERN_DEBUG "ip6_route_me_harder: No more route.\n");
        dst_release(dst);
        return -EINVAL;
    }

    /* Drop old route. */
    skb_dst_drop(skb);

    skb_dst_set(skb, dst);

#ifdef CONFIG_XFRM
    if (!(IP6CB(skb)->flags & IP6SKB_XFRM_TRANSFORMED) &&
        xfrm_decode_session(skb, flowi6_to_flowi(&fl6), AF_INET6) == 0) {
        skb_dst_set(skb, NULL);
        dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), skb->sk, 0);
        if (IS_ERR(dst))
            return -1;
        skb_dst_set(skb, dst);
    }
#endif

    /* Change in oif may mean change in hh_len. */
    hh_len = skb_dst(skb)->dev->hard_header_len;
    if (skb_headroom(skb) < hh_len &&
        pskb_expand_head(skb, HH_DATA_ALIGN(hh_len - skb_headroom(skb)),
                 0, GFP_ATOMIC))
        return -1;

    return 0;
}
EXPORT_SYMBOL(ip6_route_me_harder);

/*
 * Extra routing may needed on local out, as the QUEUE target never
 * returns control to the table.
 */

struct ip6_rt_info {
    struct in6_addr daddr;
    struct in6_addr saddr;
    u_int32_t mark;
};

static void nf_ip6_saveroute(const struct sk_buff *skb,
                 struct nf_queue_entry *entry)
{
    struct ip6_rt_info *rt_info = nf_queue_entry_reroute(entry);

    if (entry->hook == NF_INET_LOCAL_OUT) {
        const struct ipv6hdr *iph = ipv6_hdr(skb);

        rt_info->daddr = iph->daddr;
        rt_info->saddr = iph->saddr;
        rt_info->mark = skb->mark;
    }
}

static int nf_ip6_reroute(struct sk_buff *skb,
              const struct nf_queue_entry *entry)
{
    struct ip6_rt_info *rt_info = nf_queue_entry_reroute(entry);

    if (entry->hook == NF_INET_LOCAL_OUT) {
        const struct ipv6hdr *iph = ipv6_hdr(skb);
        if (!ipv6_addr_equal(&iph->daddr, &rt_info->daddr) ||
            !ipv6_addr_equal(&iph->saddr, &rt_info->saddr) ||
            skb->mark != rt_info->mark)
            return ip6_route_me_harder(skb);
    }
    return 0;
}

static int nf_ip6_route(struct net *net, struct dst_entry **dst,
            struct flowi *fl, bool strict)
{
    static const struct ipv6_pinfo fake_pinfo;
    static const struct inet_sock fake_sk = {
        /* makes ip6_route_output set RT6_LOOKUP_F_IFACE: */
        .sk.sk_bound_dev_if = 1,
        .pinet6 = (struct ipv6_pinfo *) &fake_pinfo,
    };
    const void *sk = strict ? &fake_sk : NULL;
    struct dst_entry *result;
    int err;

    result = ip6_route_output(net, sk, &fl->u.ip6);
    err = result->error;
    if (err)
        dst_release(result);
    else
        *dst = result;
    return err;
}

__sum16 nf_ip6_checksum(struct sk_buff *skb, unsigned int hook,
                 unsigned int dataoff, u_int8_t protocol)
{
    const struct ipv6hdr *ip6h = ipv6_hdr(skb);
    __sum16 csum = 0;

    switch (skb->ip_summed) {
    case CHECKSUM_COMPLETE:
        if (hook != NF_INET_PRE_ROUTING && hook != NF_INET_LOCAL_IN)
            break;
        if (!csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr,
                     skb->len - dataoff, protocol,
                     csum_sub(skb->csum,
                          skb_checksum(skb, 0,
                               dataoff, 0)))) {
            skb->ip_summed = CHECKSUM_UNNECESSARY;
            break;
        }
        /* fall through */
    case CHECKSUM_NONE:
        skb->csum = ~csum_unfold(
                csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr,
                         skb->len - dataoff,
                         protocol,
                         csum_sub(0,
                              skb_checksum(skb, 0,
                                   dataoff, 0))));
        csum = __skb_checksum_complete(skb);
    }
    return csum;
}
EXPORT_SYMBOL(nf_ip6_checksum);

static __sum16 nf_ip6_checksum_partial(struct sk_buff *skb, unsigned int hook,
                       unsigned int dataoff, unsigned int len,
                       u_int8_t protocol)
{
    const struct ipv6hdr *ip6h = ipv6_hdr(skb);
    __wsum hsum;
    __sum16 csum = 0;

    switch (skb->ip_summed) {
    case CHECKSUM_COMPLETE:
        if (len == skb->len - dataoff)
            return nf_ip6_checksum(skb, hook, dataoff, protocol);
        /* fall through */
    case CHECKSUM_NONE:
        hsum = skb_checksum(skb, 0, dataoff, 0);
        skb->csum = ~csum_unfold(csum_ipv6_magic(&ip6h->saddr,
                             &ip6h->daddr,
                             skb->len - dataoff,
                             protocol,
                             csum_sub(0, hsum)));
        skb->ip_summed = CHECKSUM_NONE;
        return __skb_checksum_complete_head(skb, dataoff + len);
    }
    return csum;
};

static const struct nf_afinfo nf_ip6_afinfo = {
    .family         = AF_INET6,
    .checksum       = nf_ip6_checksum,
    .checksum_partial   = nf_ip6_checksum_partial,
    .route          = nf_ip6_route,
    .saveroute      = nf_ip6_saveroute,
    .reroute        = nf_ip6_reroute,
    .route_key_size     = sizeof(struct ip6_rt_info),
};

int __init ipv6_netfilter_init(void)
{
    return nf_register_afinfo(&nf_ip6_afinfo);
}

/* This can be called from inet6_init() on errors, so it cannot
 * be marked __exit. -DaveM
 */
void ipv6_netfilter_fini(void)
{
    nf_unregister_afinfo(&nf_ip6_afinfo);
}