nf_conntrack_proto_gre.c

Go to the documentation of this file.

/*
 * ip_conntrack_proto_gre.c - Version 3.0
 *
 * Connection tracking protocol helper module for GRE.
 *
 * GRE is a generic encapsulation protocol, which is generally not very
 * suited for NAT, as it has no protocol-specific part as port numbers.
 *
 * It has an optional key field, which may help us distinguishing two
 * connections between the same two hosts.
 *
 * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
 *
 * PPTP is built on top of a modified version of GRE, and has a mandatory
 * field called "CallID", which serves us for the same purpose as the key
 * field in plain GRE.
 *
 * Documentation about PPTP can be found in RFC 2637
 *
 * (C) 2000-2005 by Harald Welte <[email protected]>
 *
 * Development of this code funded by Astaro AG (http://www.astaro.com/)
 *
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/timer.h>
#include <linux/list.h>
#include <linux/seq_file.h>
#include <linux/in.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <net/dst.h>
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/netfilter/nf_conntrack_l4proto.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <linux/netfilter/nf_conntrack_proto_gre.h>
#include <linux/netfilter/nf_conntrack_pptp.h>

enum grep_conntrack {
    GRE_CT_UNREPLIED,
    GRE_CT_REPLIED,
    GRE_CT_MAX
};

static unsigned int gre_timeouts[GRE_CT_MAX] = {
    [GRE_CT_UNREPLIED]  = 30*HZ,
    [GRE_CT_REPLIED]    = 180*HZ,
};

static int proto_gre_net_id __read_mostly;
struct netns_proto_gre {
    struct nf_proto_net nf;
    rwlock_t        keymap_lock;
    struct list_head    keymap_list;
    unsigned int        gre_timeouts[GRE_CT_MAX];
};

static inline struct netns_proto_gre *gre_pernet(struct net *net)
{
    return net_generic(net, proto_gre_net_id);
}

void nf_ct_gre_keymap_flush(struct net *net)
{
    struct netns_proto_gre *net_gre = gre_pernet(net);
    struct nf_ct_gre_keymap *km, *tmp;

    write_lock_bh(&net_gre->keymap_lock);
    list_for_each_entry_safe(km, tmp, &net_gre->keymap_list, list) {
        list_del(&km->list);
        kfree(km);
    }
    write_unlock_bh(&net_gre->keymap_lock);
}
EXPORT_SYMBOL(nf_ct_gre_keymap_flush);

static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
                const struct nf_conntrack_tuple *t)
{
    return km->tuple.src.l3num == t->src.l3num &&
           !memcmp(&km->tuple.src.u3, &t->src.u3, sizeof(t->src.u3)) &&
           !memcmp(&km->tuple.dst.u3, &t->dst.u3, sizeof(t->dst.u3)) &&
           km->tuple.dst.protonum == t->dst.protonum &&
           km->tuple.dst.u.all == t->dst.u.all;
}

/* look up the source key for a given tuple */
static __be16 gre_keymap_lookup(struct net *net, struct nf_conntrack_tuple *t)
{
    struct netns_proto_gre *net_gre = gre_pernet(net);
    struct nf_ct_gre_keymap *km;
    __be16 key = 0;

    read_lock_bh(&net_gre->keymap_lock);
    list_for_each_entry(km, &net_gre->keymap_list, list) {
        if (gre_key_cmpfn(km, t)) {
            key = km->tuple.src.u.gre.key;
            break;
        }
    }
    read_unlock_bh(&net_gre->keymap_lock);

    pr_debug("lookup src key 0x%x for ", key);
    nf_ct_dump_tuple(t);

    return key;
}

/* add a single keymap entry, associate with specified master ct */
int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
             struct nf_conntrack_tuple *t)
{
    struct net *net = nf_ct_net(ct);
    struct netns_proto_gre *net_gre = gre_pernet(net);
    struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
    struct nf_ct_gre_keymap **kmp, *km;

    kmp = &ct_pptp_info->keymap[dir];
    if (*kmp) {
        /* check whether it's a retransmission */
        read_lock_bh(&net_gre->keymap_lock);
        list_for_each_entry(km, &net_gre->keymap_list, list) {
            if (gre_key_cmpfn(km, t) && km == *kmp) {
                read_unlock_bh(&net_gre->keymap_lock);
                return 0;
            }
        }
        read_unlock_bh(&net_gre->keymap_lock);
        pr_debug("trying to override keymap_%s for ct %p\n",
             dir == IP_CT_DIR_REPLY ? "reply" : "orig", ct);
        return -EEXIST;
    }

    km = kmalloc(sizeof(*km), GFP_ATOMIC);
    if (!km)
        return -ENOMEM;
    memcpy(&km->tuple, t, sizeof(*t));
    *kmp = km;

    pr_debug("adding new entry %p: ", km);
    nf_ct_dump_tuple(&km->tuple);

    write_lock_bh(&net_gre->keymap_lock);
    list_add_tail(&km->list, &net_gre->keymap_list);
    write_unlock_bh(&net_gre->keymap_lock);

    return 0;
}
EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);

/* destroy the keymap entries associated with specified master ct */
void nf_ct_gre_keymap_destroy(struct nf_conn *ct)
{
    struct net *net = nf_ct_net(ct);
    struct netns_proto_gre *net_gre = gre_pernet(net);
    struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
    enum ip_conntrack_dir dir;

    pr_debug("entering for ct %p\n", ct);

    write_lock_bh(&net_gre->keymap_lock);
    for (dir = IP_CT_DIR_ORIGINAL; dir < IP_CT_DIR_MAX; dir++) {
        if (ct_pptp_info->keymap[dir]) {
            pr_debug("removing %p from list\n",
                 ct_pptp_info->keymap[dir]);
            list_del(&ct_pptp_info->keymap[dir]->list);
            kfree(ct_pptp_info->keymap[dir]);
            ct_pptp_info->keymap[dir] = NULL;
        }
    }
    write_unlock_bh(&net_gre->keymap_lock);
}
EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);

/* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */

/* invert gre part of tuple */
static bool gre_invert_tuple(struct nf_conntrack_tuple *tuple,
                 const struct nf_conntrack_tuple *orig)
{
    tuple->dst.u.gre.key = orig->src.u.gre.key;
    tuple->src.u.gre.key = orig->dst.u.gre.key;
    return true;
}

/* gre hdr info to tuple */
static bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
                 struct nf_conntrack_tuple *tuple)
{
    struct net *net = dev_net(skb->dev ? skb->dev : skb_dst(skb)->dev);
    const struct gre_hdr_pptp *pgrehdr;
    struct gre_hdr_pptp _pgrehdr;
    __be16 srckey;
    const struct gre_hdr *grehdr;
    struct gre_hdr _grehdr;

    /* first only delinearize old RFC1701 GRE header */
    grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
    if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
        /* try to behave like "nf_conntrack_proto_generic" */
        tuple->src.u.all = 0;
        tuple->dst.u.all = 0;
        return true;
    }

    /* PPTP header is variable length, only need up to the call_id field */
    pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
    if (!pgrehdr)
        return true;

    if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
        pr_debug("GRE_VERSION_PPTP but unknown proto\n");
        return false;
    }

    tuple->dst.u.gre.key = pgrehdr->call_id;
    srckey = gre_keymap_lookup(net, tuple);
    tuple->src.u.gre.key = srckey;

    return true;
}

/* print gre part of tuple */
static int gre_print_tuple(struct seq_file *s,
               const struct nf_conntrack_tuple *tuple)
{
    return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
              ntohs(tuple->src.u.gre.key),
              ntohs(tuple->dst.u.gre.key));
}

/* print private data for conntrack */
static int gre_print_conntrack(struct seq_file *s, struct nf_conn *ct)
{
    return seq_printf(s, "timeout=%u, stream_timeout=%u ",
              (ct->proto.gre.timeout / HZ),
              (ct->proto.gre.stream_timeout / HZ));
}

static unsigned int *gre_get_timeouts(struct net *net)
{
    return gre_pernet(net)->gre_timeouts;
}

/* Returns verdict for packet, and may modify conntrack */
static int gre_packet(struct nf_conn *ct,
              const struct sk_buff *skb,
              unsigned int dataoff,
              enum ip_conntrack_info ctinfo,
              u_int8_t pf,
              unsigned int hooknum,
              unsigned int *timeouts)
{
    /* If we've seen traffic both ways, this is a GRE connection.
     * Extend timeout. */
    if (ct->status & IPS_SEEN_REPLY) {
        nf_ct_refresh_acct(ct, ctinfo, skb,
                   ct->proto.gre.stream_timeout);
        /* Also, more likely to be important, and not a probe. */
        if (!test_and_set_bit(IPS_ASSURED_BIT, &ct->status))
            nf_conntrack_event_cache(IPCT_ASSURED, ct);
    } else
        nf_ct_refresh_acct(ct, ctinfo, skb,
                   ct->proto.gre.timeout);

    return NF_ACCEPT;
}

/* Called when a new connection for this protocol found. */
static bool gre_new(struct nf_conn *ct, const struct sk_buff *skb,
            unsigned int dataoff, unsigned int *timeouts)
{
    pr_debug(": ");
    nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);

    /* initialize to sane value.  Ideally a conntrack helper
     * (e.g. in case of pptp) is increasing them */
    ct->proto.gre.stream_timeout = timeouts[GRE_CT_REPLIED];
    ct->proto.gre.timeout = timeouts[GRE_CT_UNREPLIED];

    return true;
}

/* Called when a conntrack entry has already been removed from the hashes
 * and is about to be deleted from memory */
static void gre_destroy(struct nf_conn *ct)
{
    struct nf_conn *master = ct->master;
    pr_debug(" entering\n");

    if (!master)
        pr_debug("no master !?!\n");
    else
        nf_ct_gre_keymap_destroy(master);
}

#if IS_ENABLED(CONFIG_NF_CT_NETLINK_TIMEOUT)

#include <linux/netfilter/nfnetlink.h>
#include <linux/netfilter/nfnetlink_cttimeout.h>

static int gre_timeout_nlattr_to_obj(struct nlattr *tb[],
                     struct net *net, void *data)
{
    unsigned int *timeouts = data;
    struct netns_proto_gre *net_gre = gre_pernet(net);

    /* set default timeouts for GRE. */
    timeouts[GRE_CT_UNREPLIED] = net_gre->gre_timeouts[GRE_CT_UNREPLIED];
    timeouts[GRE_CT_REPLIED] = net_gre->gre_timeouts[GRE_CT_REPLIED];

    if (tb[CTA_TIMEOUT_GRE_UNREPLIED]) {
        timeouts[GRE_CT_UNREPLIED] =
            ntohl(nla_get_be32(tb[CTA_TIMEOUT_GRE_UNREPLIED])) * HZ;
    }
    if (tb[CTA_TIMEOUT_GRE_REPLIED]) {
        timeouts[GRE_CT_REPLIED] =
            ntohl(nla_get_be32(tb[CTA_TIMEOUT_GRE_REPLIED])) * HZ;
    }
    return 0;
}

static int
gre_timeout_obj_to_nlattr(struct sk_buff *skb, const void *data)
{
    const unsigned int *timeouts = data;

    if (nla_put_be32(skb, CTA_TIMEOUT_GRE_UNREPLIED,
             htonl(timeouts[GRE_CT_UNREPLIED] / HZ)) ||
        nla_put_be32(skb, CTA_TIMEOUT_GRE_REPLIED,
             htonl(timeouts[GRE_CT_REPLIED] / HZ)))
        goto nla_put_failure;
    return 0;

nla_put_failure:
    return -ENOSPC;
}

static const struct nla_policy
gre_timeout_nla_policy[CTA_TIMEOUT_GRE_MAX+1] = {
    [CTA_TIMEOUT_GRE_UNREPLIED] = { .type = NLA_U32 },
    [CTA_TIMEOUT_GRE_REPLIED]   = { .type = NLA_U32 },
};
#endif /* CONFIG_NF_CT_NETLINK_TIMEOUT */

static int gre_init_net(struct net *net, u_int16_t proto)
{
    struct netns_proto_gre *net_gre = gre_pernet(net);
    int i;

    rwlock_init(&net_gre->keymap_lock);
    INIT_LIST_HEAD(&net_gre->keymap_list);
    for (i = 0; i < GRE_CT_MAX; i++)
        net_gre->gre_timeouts[i] = gre_timeouts[i];

    return 0;
}

/* protocol helper struct */
static struct nf_conntrack_l4proto nf_conntrack_l4proto_gre4 __read_mostly = {
    .l3proto     = AF_INET,
    .l4proto     = IPPROTO_GRE,
    .name        = "gre",
    .pkt_to_tuple    = gre_pkt_to_tuple,
    .invert_tuple    = gre_invert_tuple,
    .print_tuple     = gre_print_tuple,
    .print_conntrack = gre_print_conntrack,
    .get_timeouts    = gre_get_timeouts,
    .packet      = gre_packet,
    .new         = gre_new,
    .destroy     = gre_destroy,
    .me          = THIS_MODULE,
#if IS_ENABLED(CONFIG_NF_CT_NETLINK)
    .tuple_to_nlattr = nf_ct_port_tuple_to_nlattr,
    .nlattr_tuple_size = nf_ct_port_nlattr_tuple_size,
    .nlattr_to_tuple = nf_ct_port_nlattr_to_tuple,
    .nla_policy  = nf_ct_port_nla_policy,
#endif
#if IS_ENABLED(CONFIG_NF_CT_NETLINK_TIMEOUT)
    .ctnl_timeout    = {
        .nlattr_to_obj  = gre_timeout_nlattr_to_obj,
        .obj_to_nlattr  = gre_timeout_obj_to_nlattr,
        .nlattr_max = CTA_TIMEOUT_GRE_MAX,
        .obj_size   = sizeof(unsigned int) * GRE_CT_MAX,
        .nla_policy = gre_timeout_nla_policy,
    },
#endif /* CONFIG_NF_CT_NETLINK_TIMEOUT */
    .net_id     = &proto_gre_net_id,
    .init_net   = gre_init_net,
};

static int proto_gre_net_init(struct net *net)
{
    int ret = 0;
    ret = nf_conntrack_l4proto_register(net, &nf_conntrack_l4proto_gre4);
    if (ret < 0)
        pr_err("nf_conntrack_l4proto_gre4 :protocol register failed.\n");
    return ret;
}

static void proto_gre_net_exit(struct net *net)
{
    nf_conntrack_l4proto_unregister(net, &nf_conntrack_l4proto_gre4);
    nf_ct_gre_keymap_flush(net);
}

static struct pernet_operations proto_gre_net_ops = {
    .init = proto_gre_net_init,
    .exit = proto_gre_net_exit,
    .id   = &proto_gre_net_id,
    .size = sizeof(struct netns_proto_gre),
};

static int __init nf_ct_proto_gre_init(void)
{
    return register_pernet_subsys(&proto_gre_net_ops);
}

static void __exit nf_ct_proto_gre_fini(void)
{
    unregister_pernet_subsys(&proto_gre_net_ops);
}

module_init(nf_ct_proto_gre_init);
module_exit(nf_ct_proto_gre_fini);

MODULE_LICENSE("GPL");