/*
 * 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 <laforge@gnumonks.org>
 *
 * 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>

#define GRE_TIMEOUT             (30 * HZ)
#define GRE_STREAM_TIMEOUT      (180 * HZ)

static int proto_gre_net_id __read_mostly;
struct netns_proto_gre {
        rwlock_t                keymap_lock;
        struct list_head        keymap_list;
};

void nf_ct_gre_keymap_flush(struct net *net)
{
        struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
        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 = net_generic(net, proto_gre_net_id);
        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 = net_generic(net, proto_gre_net_id);
        struct nf_conn_help *help = nfct_help(ct);
        struct nf_ct_gre_keymap **kmp, *km;

        kmp = &help->help.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 = net_generic(net, proto_gre_net_id);
        struct nf_conn_help *help = nfct_help(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 (help->help.ct_pptp_info.keymap[dir]) {
                        pr_debug("removing %p from list\n",
                                 help->help.ct_pptp_info.keymap[dir]);
                        list_del(&help->help.ct_pptp_info.keymap[dir]->list);
                        kfree(help->help.ct_pptp_info.keymap[dir]);
                        help->help.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));
}

/* 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)
{
        /* 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)
{
        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 = GRE_STREAM_TIMEOUT;
        ct->proto.gre.timeout = GRE_TIMEOUT;

        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);
}

/* 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,
        .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
};

static int proto_gre_net_init(struct net *net)
{
        struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);

        rwlock_init(&net_gre->keymap_lock);
        INIT_LIST_HEAD(&net_gre->keymap_list);

        return 0;
}

static void proto_gre_net_exit(struct net *net)
{
        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)
{
        int rv;

        rv = nf_conntrack_l4proto_register(&nf_conntrack_l4proto_gre4);
        if (rv < 0)
                return rv;
        rv = register_pernet_subsys(&proto_gre_net_ops);
        if (rv < 0)
                nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
        return rv;
}

static void __exit nf_ct_proto_gre_fini(void)
{
        nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
        unregister_pernet_subsys(&proto_gre_net_ops);
}

module_init(nf_ct_proto_gre_init);
module_exit(nf_ct_proto_gre_fini);

MODULE_LICENSE("GPL");