/*
 * 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/)
 *
 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
 */

#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 <net/netfilter/nf_conntrack_timeout.h>
#include <linux/netfilter/nf_conntrack_proto_gre.h>
#include <linux/netfilter/nf_conntrack_pptp.h>

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

/* used when expectation is added */
static DEFINE_SPINLOCK(keymap_lock);

static inline struct nf_gre_net *gre_pernet(struct net *net)
{
        return &net->nf_ct_gre;
}

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

        spin_lock_bh(&keymap_lock);
        list_for_each_entry_safe(km, tmp, &net_gre->keymap_list, list) {
                list_del_rcu(&km->list);
                kfree_rcu(km, rcu);
        }
        spin_unlock_bh(&keymap_lock);
}

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 nf_gre_net *net_gre = gre_pernet(net);
        struct nf_ct_gre_keymap *km;
        __be16 key = 0;

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

        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 nf_gre_net *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 */
                list_for_each_entry_rcu(km, &net_gre->keymap_list, list) {
                        if (gre_key_cmpfn(km, t) && km == *kmp)
                                return 0;
                }
                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);

        spin_lock_bh(&keymap_lock);
        list_add_tail(&km->list, &net_gre->keymap_list);
        spin_unlock_bh(&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 nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
        enum ip_conntrack_dir dir;

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

        spin_lock_bh(&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_rcu(&ct_pptp_info->keymap[dir]->list);
                        kfree_rcu(ct_pptp_info->keymap[dir], rcu);
                        ct_pptp_info->keymap[dir] = NULL;
                }
        }
        spin_unlock_bh(&keymap_lock);
}
EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);

/* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */

/* gre hdr info to tuple */
bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
                      struct net *net, struct nf_conntrack_tuple *tuple)
{
        const struct pptp_gre_header *pgrehdr;
        struct pptp_gre_header _pgrehdr;
        __be16 srckey;
        const struct gre_base_hdr *grehdr;
        struct gre_base_hdr _grehdr;

        /* first only delinearize old RFC1701 GRE header */
        grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
        if (!grehdr || (grehdr->flags & GRE_VERSION) != GRE_VERSION_1) {
                /* 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 (grehdr->protocol != GRE_PROTO_PPP) {
                pr_debug("Unsupported GRE proto(0x%x)\n", ntohs(grehdr->protocol));
                return false;
        }

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

        return true;
}

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

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

/* Returns verdict for packet, and may modify conntrack */
int nf_conntrack_gre_packet(struct nf_conn *ct,
                            struct sk_buff *skb,
                            unsigned int dataoff,
                            enum ip_conntrack_info ctinfo,
                            const struct nf_hook_state *state)
{
        if (state->pf != NFPROTO_IPV4)
                return -NF_ACCEPT;

        if (!nf_ct_is_confirmed(ct)) {
                unsigned int *timeouts = nf_ct_timeout_lookup(ct);

                if (!timeouts)
                        timeouts = gre_get_timeouts(nf_ct_net(ct));

                /* 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];
        }

        /* 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 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);
}

#ifdef CONFIG_NF_CONNTRACK_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 nf_gre_net *net_gre = gre_pernet(net);

        if (!timeouts)
                timeouts = gre_get_timeouts(net);
        /* set default timeouts for GRE. */
        timeouts[GRE_CT_UNREPLIED] = net_gre->timeouts[GRE_CT_UNREPLIED];
        timeouts[GRE_CT_REPLIED] = net_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_CONNTRACK_TIMEOUT */

static int gre_init_net(struct net *net)
{
        struct nf_gre_net *net_gre = gre_pernet(net);
        int i;

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

        return 0;
}

/* protocol helper struct */
const struct nf_conntrack_l4proto nf_conntrack_l4proto_gre = {
        .l4proto         = IPPROTO_GRE,
#ifdef CONFIG_NF_CONNTRACK_PROCFS
        .print_conntrack = gre_print_conntrack,
#endif
        .destroy         = gre_destroy,
#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
#ifdef CONFIG_NF_CONNTRACK_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_CONNTRACK_TIMEOUT */
        .init_net       = gre_init_net,
};