[DCCP]: Initial implementation

Development to this point was done on a subversion repository at:

http://oops.ghostprotocols.net:81/cgi-bin/viewcvs.cgi/dccp-2.6/

This repository will be kept at this site for the foreseable future,
so that interested parties can see the history of this code,
attributions, etc.

If I ever decide to take this offline I'll provide the full history at
some other suitable place.

Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1289 insertions, 0 deletions

diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
new file mode 100644
index 000000000000..083bacaecb3b
--- /dev/null
+++ b/net/dccp/ipv4.c
@@ -0,0 +1,1289 @@
+/*
+ *  net/dccp/ipv4.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; either version
+ *      2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/config.h>
+#include <linux/dccp.h>
+#include <linux/icmp.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/random.h>
+
+#include <net/icmp.h>
+#include <net/inet_hashtables.h>
+#include <net/sock.h>
+#include <net/tcp_states.h>
+#include <net/xfrm.h>
+
+#include "ccid.h"
+#include "dccp.h"
+
+struct inet_hashinfo __cacheline_aligned dccp_hashinfo = {
+        .lhash_lock     = RW_LOCK_UNLOCKED,
+        .lhash_users    = ATOMIC_INIT(0),
+        .lhash_wait     = __WAIT_QUEUE_HEAD_INITIALIZER(dccp_hashinfo.lhash_wait),
+        .portalloc_lock = SPIN_LOCK_UNLOCKED,
+        .port_rover     = 1024 - 1,
+};
+
+static int dccp_v4_get_port(struct sock *sk, const unsigned short snum)
+{
+        return inet_csk_get_port(&dccp_hashinfo, sk, snum);
+}
+
+static void dccp_v4_hash(struct sock *sk)
+{
+        inet_hash(&dccp_hashinfo, sk);
+}
+
+static void dccp_v4_unhash(struct sock *sk)
+{
+        inet_unhash(&dccp_hashinfo, sk);
+}
+
+/* called with local bh disabled */
+static int __dccp_v4_check_established(struct sock *sk, const __u16 lport,
+                                      struct inet_timewait_sock **twp)
+{
+        struct inet_sock *inet = inet_sk(sk);
+        const u32 daddr = inet->rcv_saddr;
+        const u32 saddr = inet->daddr;
+        const int dif = sk->sk_bound_dev_if;
+        INET_ADDR_COOKIE(acookie, saddr, daddr)
+        const __u32 ports = INET_COMBINED_PORTS(inet->dport, lport);
+        const int hash = inet_ehashfn(daddr, lport, saddr, inet->dport, dccp_hashinfo.ehash_size);
+        struct inet_ehash_bucket *head = &dccp_hashinfo.ehash[hash];
+        const struct sock *sk2;
+        const struct hlist_node *node;
+        struct inet_timewait_sock *tw;
+
+        write_lock(&head->lock);
+
+        /* Check TIME-WAIT sockets first. */
+        sk_for_each(sk2, node, &(head + dccp_hashinfo.ehash_size)->chain) {
+                tw = inet_twsk(sk2);
+
+                if (INET_TW_MATCH(sk2, acookie, saddr, daddr, ports, dif))
+                        goto not_unique;
+        }
+        tw = NULL;
+
+        /* And established part... */
+        sk_for_each(sk2, node, &head->chain) {
+                if (INET_MATCH(sk2, acookie, saddr, daddr, ports, dif))
+                        goto not_unique;
+        }
+
+        /* Must record num and sport now. Otherwise we will see
+         * in hash table socket with a funny identity. */
+        inet->num = lport;
+        inet->sport = htons(lport);
+        sk->sk_hashent = hash;
+        BUG_TRAP(sk_unhashed(sk));
+        __sk_add_node(sk, &head->chain);
+        sock_prot_inc_use(sk->sk_prot);
+        write_unlock(&head->lock);
+
+        if (twp != NULL) {
+                *twp = tw;
+                NET_INC_STATS_BH(LINUX_MIB_TIMEWAITRECYCLED);
+        } else if (tw != NULL) {
+                /* Silly. Should hash-dance instead... */
+                dccp_tw_deschedule(tw);
+                NET_INC_STATS_BH(LINUX_MIB_TIMEWAITRECYCLED);
+
+                inet_twsk_put(tw);
+        }
+
+        return 0;
+
+not_unique:
+        write_unlock(&head->lock);
+        return -EADDRNOTAVAIL;
+}
+
+/*
+ * Bind a port for a connect operation and hash it.
+ */
+static int dccp_v4_hash_connect(struct sock *sk)
+{
+        const unsigned short snum = inet_sk(sk)->num;
+        struct inet_bind_hashbucket *head;
+        struct inet_bind_bucket *tb;
+        int ret;
+
+        if (snum == 0) {
+                int rover;
+                int low = sysctl_local_port_range[0];
+                int high = sysctl_local_port_range[1];
+                int remaining = (high - low) + 1;
+                struct hlist_node *node;
+                struct inet_timewait_sock *tw = NULL;
+
+                local_bh_disable();
+
+                /* TODO. Actually it is not so bad idea to remove
+                 * dccp_hashinfo.portalloc_lock before next submission to Linus.
+                 * As soon as we touch this place at all it is time to think.
+                 *
+                 * Now it protects single _advisory_ variable dccp_hashinfo.port_rover,
+                 * hence it is mostly useless.
+                 * Code will work nicely if we just delete it, but
+                 * I am afraid in contented case it will work not better or
+                 * even worse: another cpu just will hit the same bucket
+                 * and spin there.
+                 * So some cpu salt could remove both contention and
+                 * memory pingpong. Any ideas how to do this in a nice way?
+                 */
+                spin_lock(&dccp_hashinfo.portalloc_lock);
+                rover = dccp_hashinfo.port_rover;
+
+                do {
+                        rover++;
+                        if ((rover < low) || (rover > high))
+                                rover = low;
+                        head = &dccp_hashinfo.bhash[inet_bhashfn(rover, dccp_hashinfo.bhash_size)];
+                        spin_lock(&head->lock);
+
+                        /* Does not bother with rcv_saddr checks,
+                         * because the established check is already
+                         * unique enough.
+                         */
+                        inet_bind_bucket_for_each(tb, node, &head->chain) {
+                                if (tb->port == rover) {
+                                        BUG_TRAP(!hlist_empty(&tb->owners));
+                                        if (tb->fastreuse >= 0)
+                                                goto next_port;
+                                        if (!__dccp_v4_check_established(sk,
+                                                                         rover,
+                                                                         &tw))
+                                                goto ok;
+                                        goto next_port;
+                                }
+                        }
+
+                        tb = inet_bind_bucket_create(dccp_hashinfo.bind_bucket_cachep, head, rover);
+                        if (tb == NULL) {
+                                spin_unlock(&head->lock);
+                                break;
+                        }
+                        tb->fastreuse = -1;
+                        goto ok;
+
+                next_port:
+                        spin_unlock(&head->lock);
+                } while (--remaining > 0);
+                dccp_hashinfo.port_rover = rover;
+                spin_unlock(&dccp_hashinfo.portalloc_lock);
+
+                local_bh_enable();
+
+                return -EADDRNOTAVAIL;
+
+ok:
+                /* All locks still held and bhs disabled */
+                dccp_hashinfo.port_rover = rover;
+                spin_unlock(&dccp_hashinfo.portalloc_lock);
+
+                inet_bind_hash(sk, tb, rover);
+                if (sk_unhashed(sk)) {
+                        inet_sk(sk)->sport = htons(rover);
+                        __inet_hash(&dccp_hashinfo, sk, 0);
+                }
+                spin_unlock(&head->lock);
+
+                if (tw != NULL) {
+                        dccp_tw_deschedule(tw);
+                        inet_twsk_put(tw);
+                }
+
+                ret = 0;
+                goto out;
+        }
+
+        head = &dccp_hashinfo.bhash[inet_bhashfn(snum, dccp_hashinfo.bhash_size)];
+        tb   = inet_csk(sk)->icsk_bind_hash;
+        spin_lock_bh(&head->lock);
+        if (sk_head(&tb->owners) == sk && sk->sk_bind_node.next == NULL) {
+                __inet_hash(&dccp_hashinfo, sk, 0);
+                spin_unlock_bh(&head->lock);
+                return 0;
+        } else {
+                spin_unlock(&head->lock);
+                /* No definite answer... Walk to established hash table */
+                ret = __dccp_v4_check_established(sk, snum, NULL);
+out:
+                local_bh_enable();
+                return ret;
+        }
+}
+
+static int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr,
+                           int addr_len)
+{
+        struct inet_sock *inet = inet_sk(sk);
+        struct dccp_sock *dp = dccp_sk(sk);
+        const struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
+        struct rtable *rt;
+        u32 daddr, nexthop;
+        int tmp;
+        int err;
+
+        dp->dccps_role = DCCP_ROLE_CLIENT;
+
+        if (addr_len < sizeof(struct sockaddr_in))
+                return -EINVAL;
+
+        if (usin->sin_family != AF_INET)
+                return -EAFNOSUPPORT;
+
+        nexthop = daddr = usin->sin_addr.s_addr;
+        if (inet->opt != NULL && inet->opt->srr) {
+                if (daddr == 0)
+                        return -EINVAL;
+                nexthop = inet->opt->faddr;
+        }
+
+        tmp = ip_route_connect(&rt, nexthop, inet->saddr,
+                               RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
+                               IPPROTO_DCCP,
+                               inet->sport, usin->sin_port, sk);
+        if (tmp < 0)
+                return tmp;
+
+        if (rt->rt_flags & (RTCF_MULTICAST | RTCF_BROADCAST)) {
+                ip_rt_put(rt);
+                return -ENETUNREACH;
+        }
+
+        if (inet->opt == NULL || !inet->opt->srr)
+                daddr = rt->rt_dst;
+
+        if (inet->saddr == 0)
+                inet->saddr = rt->rt_src;
+        inet->rcv_saddr = inet->saddr;
+
+        inet->dport = usin->sin_port;
+        inet->daddr = daddr;
+
+        dp->dccps_ext_header_len = 0;
+        if (inet->opt != NULL)
+                dp->dccps_ext_header_len = inet->opt->optlen;
+        /*
+         * Socket identity is still unknown (sport may be zero).
+         * However we set state to DCCP_REQUESTING and not releasing socket
+         * lock select source port, enter ourselves into the hash tables and
+         * complete initialization after this.
+         */
+        dccp_set_state(sk, DCCP_REQUESTING);
+        err = dccp_v4_hash_connect(sk);
+        if (err != 0)
+                goto failure;
+
+        err = ip_route_newports(&rt, inet->sport, inet->dport, sk);
+        if (err != 0)
+                goto failure;
+
+        /* OK, now commit destination to socket.  */
+        sk_setup_caps(sk, &rt->u.dst);
+
+        dp->dccps_gar =
+                dp->dccps_iss = secure_dccp_sequence_number(inet->saddr,
+                                                            inet->daddr,
+                                                            inet->sport,
+                                                            usin->sin_port);
+        dccp_update_gss(sk, dp->dccps_iss);
+
+        inet->id = dp->dccps_iss ^ jiffies;
+
+        err = dccp_connect(sk);
+        rt = NULL;
+        if (err != 0)
+                goto failure;
+out:
+        return err;
+failure:
+        /* This unhashes the socket and releases the local port, if necessary. */
+        dccp_set_state(sk, DCCP_CLOSED);
+        ip_rt_put(rt);
+        sk->sk_route_caps = 0;
+        inet->dport = 0;
+        goto out;
+}
+
+/*
+ * This routine does path mtu discovery as defined in RFC1191.
+ */
+static inline void dccp_do_pmtu_discovery(struct sock *sk,
+                                          const struct iphdr *iph,
+                                          u32 mtu)
+{
+        struct dst_entry *dst;
+        const struct inet_sock *inet = inet_sk(sk);
+        const struct dccp_sock *dp = dccp_sk(sk);
+
+        /* We are not interested in DCCP_LISTEN and request_socks (RESPONSEs
+         * send out by Linux are always < 576bytes so they should go through
+         * unfragmented).
+         */
+        if (sk->sk_state == DCCP_LISTEN)
+                return;
+
+        /* We don't check in the destentry if pmtu discovery is forbidden
+         * on this route. We just assume that no packet_to_big packets
+         * are send back when pmtu discovery is not active.
+         * There is a small race when the user changes this flag in the
+         * route, but I think that's acceptable.
+         */
+        if ((dst = __sk_dst_check(sk, 0)) == NULL)
+                return;
+
+        dst->ops->update_pmtu(dst, mtu);
+
+        /* Something is about to be wrong... Remember soft error
+         * for the case, if this connection will not able to recover.
+         */
+        if (mtu < dst_mtu(dst) && ip_dont_fragment(sk, dst))
+                sk->sk_err_soft = EMSGSIZE;
+
+        mtu = dst_mtu(dst);
+
+        if (inet->pmtudisc != IP_PMTUDISC_DONT &&
+            dp->dccps_pmtu_cookie > mtu) {
+                dccp_sync_mss(sk, mtu);
+
+                /*
+                 * From: draft-ietf-dccp-spec-11.txt
+                 *
+                 *      DCCP-Sync packets are the best choice for upward probing,
+                 *      since DCCP-Sync probes do not risk application data loss.
+                 */
+                dccp_send_sync(sk, dp->dccps_gsr);
+        } /* else let the usual retransmit timer handle it */
+}
+
+static void dccp_v4_ctl_send_ack(struct sk_buff *rxskb)
+{
+        int err;
+        struct dccp_hdr *rxdh = dccp_hdr(rxskb), *dh;
+        const int dccp_hdr_ack_len = sizeof(struct dccp_hdr) +
+                                     sizeof(struct dccp_hdr_ext) +
+                                     sizeof(struct dccp_hdr_ack_bits);
+        struct sk_buff *skb;
+
+        if (((struct rtable *)rxskb->dst)->rt_type != RTN_LOCAL)
+                return;
+
+        skb = alloc_skb(MAX_DCCP_HEADER + 15, GFP_ATOMIC);
+        if (skb == NULL)
+                return;
+
+        /* Reserve space for headers. */
+        skb_reserve(skb, MAX_DCCP_HEADER);
+
+        skb->dst = dst_clone(rxskb->dst);
+
+        skb->h.raw = skb_push(skb, dccp_hdr_ack_len);
+        dh = dccp_hdr(skb);
+        memset(dh, 0, dccp_hdr_ack_len);
+
+        /* Build DCCP header and checksum it. */
+        dh->dccph_type     = DCCP_PKT_ACK;
+        dh->dccph_sport    = rxdh->dccph_dport;
+        dh->dccph_dport    = rxdh->dccph_sport;
+        dh->dccph_doff     = dccp_hdr_ack_len / 4;
+        dh->dccph_x        = 1;
+
+        dccp_hdr_set_seq(dh, DCCP_SKB_CB(rxskb)->dccpd_ack_seq);
+        dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), DCCP_SKB_CB(rxskb)->dccpd_seq);
+
+        bh_lock_sock(dccp_ctl_socket->sk);
+        err = ip_build_and_send_pkt(skb, dccp_ctl_socket->sk,
+                                    rxskb->nh.iph->daddr, rxskb->nh.iph->saddr, NULL);
+        bh_unlock_sock(dccp_ctl_socket->sk);
+
+        if (err == NET_XMIT_CN || err == 0) {
+                DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);
+                DCCP_INC_STATS_BH(DCCP_MIB_OUTRSTS);
+        }
+}
+
+static void dccp_v4_reqsk_send_ack(struct sk_buff *skb, struct request_sock *req)
+{
+        dccp_v4_ctl_send_ack(skb);
+}
+
+static int dccp_v4_send_response(struct sock *sk, struct request_sock *req,
+                                 struct dst_entry *dst)
+{
+        int err = -1;
+        struct sk_buff *skb;
+
+        /* First, grab a route. */
+        
+        if (dst == NULL && (dst = inet_csk_route_req(sk, req)) == NULL)
+                goto out;
+
+        skb = dccp_make_response(sk, dst, req);
+        if (skb != NULL) {
+                const struct inet_request_sock *ireq = inet_rsk(req);
+
+                err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
+                                            ireq->rmt_addr,
+                                            ireq->opt);
+                if (err == NET_XMIT_CN)
+                        err = 0;
+        }
+
+out:
+        dst_release(dst);
+        return err;
+}
+
+/*
+ * This routine is called by the ICMP module when it gets some sort of error
+ * condition. If err < 0 then the socket should be closed and the error
+ * returned to the user. If err > 0 it's just the icmp type << 8 | icmp code.
+ * After adjustment header points to the first 8 bytes of the tcp header. We
+ * need to find the appropriate port.
+ *
+ * The locking strategy used here is very "optimistic". When someone else
+ * accesses the socket the ICMP is just dropped and for some paths there is no
+ * check at all. A more general error queue to queue errors for later handling
+ * is probably better.
+ */
+void dccp_v4_err(struct sk_buff *skb, u32 info)
+{
+        const struct iphdr *iph = (struct iphdr *)skb->data;
+        const struct dccp_hdr *dh = (struct dccp_hdr *)(skb->data + (iph->ihl << 2));
+        struct dccp_sock *dp;
+        struct inet_sock *inet;
+        const int type = skb->h.icmph->type;
+        const int code = skb->h.icmph->code;
+        struct sock *sk;
+        __u64 seq;
+        int err;
+
+        if (skb->len < (iph->ihl << 2) + 8) {
+                ICMP_INC_STATS_BH(ICMP_MIB_INERRORS);
+                return;
+        }
+
+        sk = inet_lookup(&dccp_hashinfo, iph->daddr, dh->dccph_dport,
+                         iph->saddr, dh->dccph_sport, inet_iif(skb));
+        if (sk == NULL) {
+                ICMP_INC_STATS_BH(ICMP_MIB_INERRORS);
+                return;
+        }
+
+        if (sk->sk_state == DCCP_TIME_WAIT) {
+                inet_twsk_put((struct inet_timewait_sock *)sk);
+                return;
+        }
+
+        bh_lock_sock(sk);
+        /* If too many ICMPs get dropped on busy
+         * servers this needs to be solved differently.
+         */
+        if (sock_owned_by_user(sk))
+                NET_INC_STATS_BH(LINUX_MIB_LOCKDROPPEDICMPS);
+
+        if (sk->sk_state == DCCP_CLOSED)
+                goto out;
+
+        dp = dccp_sk(sk);
+        seq = dccp_hdr_seq(skb);
+        if (sk->sk_state != DCCP_LISTEN &&
+            !between48(seq, dp->dccps_swl, dp->dccps_swh)) {
+                NET_INC_STATS(LINUX_MIB_OUTOFWINDOWICMPS);
+                goto out;
+        }
+
+        switch (type) {
+        case ICMP_SOURCE_QUENCH:
+                /* Just silently ignore these. */
+                goto out;
+        case ICMP_PARAMETERPROB:
+                err = EPROTO;
+                break;
+        case ICMP_DEST_UNREACH:
+                if (code > NR_ICMP_UNREACH)
+                        goto out;
+
+                if (code == ICMP_FRAG_NEEDED) { /* PMTU discovery (RFC1191) */
+                        if (!sock_owned_by_user(sk))
+                                dccp_do_pmtu_discovery(sk, iph, info);
+                        goto out;
+                }
+
+                err = icmp_err_convert[code].errno;
+                break;
+        case ICMP_TIME_EXCEEDED:
+                err = EHOSTUNREACH;
+                break;
+        default:
+                goto out;
+        }
+
+        switch (sk->sk_state) {
+                struct request_sock *req , **prev;
+        case DCCP_LISTEN:
+                if (sock_owned_by_user(sk))
+                        goto out;
+                req = inet_csk_search_req(sk, &prev, dh->dccph_dport,
+                                          iph->daddr, iph->saddr);
+                if (!req)
+                        goto out;
+
+                /*
+                 * ICMPs are not backlogged, hence we cannot get an established
+                 * socket here.
+                 */
+                BUG_TRAP(!req->sk);
+
+                if (seq != dccp_rsk(req)->dreq_iss) {
+                        NET_INC_STATS_BH(LINUX_MIB_OUTOFWINDOWICMPS);
+                        goto out;
+                }
+                /*
+                 * Still in RESPOND, just remove it silently.
+                 * There is no good way to pass the error to the newly
+                 * created socket, and POSIX does not want network
+                 * errors returned from accept().
+                 */
+                inet_csk_reqsk_queue_drop(sk, req, prev);
+                goto out;
+
+        case DCCP_REQUESTING:
+        case DCCP_RESPOND:
+                if (!sock_owned_by_user(sk)) {
+                        DCCP_INC_STATS_BH(DCCP_MIB_ATTEMPTFAILS);
+                        sk->sk_err = err;
+
+                        sk->sk_error_report(sk);
+
+                        dccp_done(sk);
+                } else
+                        sk->sk_err_soft = err;
+                goto out;
+        }
+
+        /* If we've already connected we will keep trying
+         * until we time out, or the user gives up.
+         *
+         * rfc1122 4.2.3.9 allows to consider as hard errors
+         * only PROTO_UNREACH and PORT_UNREACH (well, FRAG_FAILED too,
+         * but it is obsoleted by pmtu discovery).
+         *
+         * Note, that in modern internet, where routing is unreliable
+         * and in each dark corner broken firewalls sit, sending random
+         * errors ordered by their masters even this two messages finally lose
+         * their original sense (even Linux sends invalid PORT_UNREACHs)
+         *
+         * Now we are in compliance with RFCs.
+         *                                                      --ANK (980905)
+         */
+
+        inet = inet_sk(sk);
+        if (!sock_owned_by_user(sk) && inet->recverr) {
+                sk->sk_err = err;
+                sk->sk_error_report(sk);
+        } else /* Only an error on timeout */
+                sk->sk_err_soft = err;
+out:
+        bh_unlock_sock(sk);
+        sock_put(sk);
+}
+
+extern struct sk_buff *dccp_make_reset(struct sock *sk, struct dst_entry *dst, enum dccp_reset_codes code);
+
+int dccp_v4_send_reset(struct sock *sk, enum dccp_reset_codes code)
+{
+        struct sk_buff *skb;
+        /*
+         * FIXME: what if rebuild_header fails?
+         * Should we be doing a rebuild_header here?
+         */
+        int err = inet_sk_rebuild_header(sk);
+
+        if (err != 0)
+                return err;
+
+        skb = dccp_make_reset(sk, sk->sk_dst_cache, code);
+        if (skb != NULL) {
+                const struct dccp_sock *dp = dccp_sk(sk);
+                const struct inet_sock *inet = inet_sk(sk);
+
+                err = ip_build_and_send_pkt(skb, sk,
+                                            inet->saddr, inet->daddr, NULL);
+                if (err == NET_XMIT_CN)
+                        err = 0;
+
+                ccid_hc_rx_exit(dp->dccps_hc_rx_ccid, sk);
+                ccid_hc_tx_exit(dp->dccps_hc_tx_ccid, sk);
+        }
+
+        return err;
+}
+
+static inline u64 dccp_v4_init_sequence(const struct sock *sk,
+                                        const struct sk_buff *skb)
+{
+        return secure_dccp_sequence_number(skb->nh.iph->daddr,
+                                           skb->nh.iph->saddr,
+                                           dccp_hdr(skb)->dccph_dport,
+                                           dccp_hdr(skb)->dccph_sport);
+}
+
+int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
+{
+        struct inet_request_sock *ireq;
+        struct dccp_sock dp;
+        struct request_sock *req;
+        struct dccp_request_sock *dreq;
+        const __u32 saddr = skb->nh.iph->saddr;
+        const __u32 daddr = skb->nh.iph->daddr;
+        struct dst_entry *dst = NULL;
+
+        /* Never answer to DCCP_PKT_REQUESTs send to broadcast or multicast */
+        if (((struct rtable *)skb->dst)->rt_flags &
+            (RTCF_BROADCAST | RTCF_MULTICAST))
+                goto drop;
+
+        /*
+         * TW buckets are converted to open requests without
+         * limitations, they conserve resources and peer is
+         * evidently real one.
+         */
+        if (inet_csk_reqsk_queue_is_full(sk))
+                goto drop;
+
+        /*
+         * Accept backlog is full. If we have already queued enough
+         * of warm entries in syn queue, drop request. It is better than
+         * clogging syn queue with openreqs with exponentially increasing
+         * timeout.
+         */
+        if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1)
+                goto drop;
+
+        req = reqsk_alloc(sk->sk_prot->rsk_prot);
+        if (req == NULL)
+                goto drop;
+
+        /* FIXME: process options */
+
+        dccp_openreq_init(req, &dp, skb);
+
+        ireq = inet_rsk(req);
+        ireq->loc_addr = daddr;
+        ireq->rmt_addr = saddr;
+        /* FIXME: Merge Aristeu's option parsing code when ready */
+        req->rcv_wnd    = 100; /* Fake, option parsing will get the right value */
+        ireq->opt       = NULL;
+
+        /* 
+         * Step 3: Process LISTEN state
+         *
+         * Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
+         *
+         * In fact we defer setting S.GSR, S.SWL, S.SWH to
+         * dccp_create_openreq_child.
+         */
+        dreq = dccp_rsk(req);
+        dreq->dreq_isr = DCCP_SKB_CB(skb)->dccpd_seq;
+        dreq->dreq_iss = dccp_v4_init_sequence(sk, skb);
+        dreq->dreq_service = dccp_hdr_request(skb)->dccph_req_service;
+
+        if (dccp_v4_send_response(sk, req, dst))
+                goto drop_and_free;
+
+        inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT);
+        return 0;
+
+drop_and_free:
+        /*
+         * FIXME: should be reqsk_free after implementing req->rsk_ops
+         */
+        __reqsk_free(req);
+drop:
+        DCCP_INC_STATS_BH(DCCP_MIB_ATTEMPTFAILS);
+        return -1;
+}
+
+/*
+ * The three way handshake has completed - we got a valid ACK or DATAACK -
+ * now create the new socket.
+ *
+ * This is the equivalent of TCP's tcp_v4_syn_recv_sock
+ */
+struct sock *dccp_v4_request_recv_sock(struct sock *sk, struct sk_buff *skb,
+                                       struct request_sock *req,
+                                       struct dst_entry *dst)
+{
+        struct inet_request_sock *ireq;
+        struct inet_sock *newinet;
+        struct dccp_sock *newdp;
+        struct sock *newsk;
+
+        if (sk_acceptq_is_full(sk))
+                goto exit_overflow;
+
+        if (dst == NULL && (dst = inet_csk_route_req(sk, req)) == NULL)
+                goto exit;
+
+        newsk = dccp_create_openreq_child(sk, req, skb);
+        if (newsk == NULL)
+                goto exit;
+
+        sk_setup_caps(newsk, dst);
+
+        newdp              = dccp_sk(newsk);
+        newinet            = inet_sk(newsk);
+        ireq               = inet_rsk(req);
+        newinet->daddr     = ireq->rmt_addr;
+        newinet->rcv_saddr = ireq->loc_addr;
+        newinet->saddr     = ireq->loc_addr;
+        newinet->opt       = ireq->opt;
+        ireq->opt          = NULL;
+        newinet->mc_index  = inet_iif(skb);
+        newinet->mc_ttl    = skb->nh.iph->ttl;
+        newinet->id        = jiffies;
+
+        dccp_sync_mss(newsk, dst_mtu(dst));
+
+        __inet_hash(&dccp_hashinfo, newsk, 0);
+        __inet_inherit_port(&dccp_hashinfo, sk, newsk);
+
+        return newsk;
+
+exit_overflow:
+        NET_INC_STATS_BH(LINUX_MIB_LISTENOVERFLOWS);
+exit:
+        NET_INC_STATS_BH(LINUX_MIB_LISTENDROPS);
+        dst_release(dst);
+        return NULL;
+}
+
+static struct sock *dccp_v4_hnd_req(struct sock *sk, struct sk_buff *skb)
+{
+        const struct dccp_hdr *dh = dccp_hdr(skb);
+        const struct iphdr *iph = skb->nh.iph;
+        struct sock *nsk;
+        struct request_sock **prev;
+        /* Find possible connection requests. */
+        struct request_sock *req = inet_csk_search_req(sk, &prev,
+                                                       dh->dccph_sport,
+                                                       iph->saddr, iph->daddr);
+        if (req != NULL)
+                return dccp_check_req(sk, skb, req, prev);
+
+        nsk = __inet_lookup_established(&dccp_hashinfo,
+                                        iph->saddr, dh->dccph_sport,
+                                        iph->daddr, ntohs(dh->dccph_dport),
+                                        inet_iif(skb));
+        if (nsk != NULL) {
+                if (nsk->sk_state != DCCP_TIME_WAIT) {
+                        bh_lock_sock(nsk);
+                        return nsk;
+                }
+                inet_twsk_put((struct inet_timewait_sock *)nsk);
+                return NULL;
+        }
+
+        return sk;
+}
+
+int dccp_v4_checksum(struct sk_buff *skb)
+{
+        struct dccp_hdr* dh = dccp_hdr(skb);
+        int checksum_len;
+        u32 tmp;
+
+        if (dh->dccph_cscov == 0)
+                checksum_len = skb->len;
+        else {
+                checksum_len = (dh->dccph_cscov + dh->dccph_x) * sizeof(u32);
+                checksum_len = checksum_len < skb->len ? checksum_len : skb->len;
+        }
+
+        tmp = csum_partial((unsigned char *)dh, checksum_len, 0);
+        return csum_fold(tmp);
+}
+
+static int dccp_v4_verify_checksum(struct sk_buff *skb)
+{
+        struct dccp_hdr *th = dccp_hdr(skb);
+        const u16 remote_checksum = th->dccph_checksum;
+        u16 local_checksum;
+
+        /* FIXME: don't mess with skb payload */
+        th->dccph_checksum = 0; /* zero it for computation */
+
+        local_checksum = dccp_v4_checksum(skb);
+
+        /* FIXME: don't mess with skb payload */
+        th->dccph_checksum = remote_checksum; /* put it back */
+
+        return remote_checksum == local_checksum ? 0 : -1;
+}
+
+static struct dst_entry* dccp_v4_route_skb(struct sock *sk,
+                                           struct sk_buff *skb)
+{
+        struct rtable *rt;
+        struct flowi fl = { .oif = ((struct rtable *)skb->dst)->rt_iif,
+                            .nl_u = { .ip4_u =
+                                      { .daddr = skb->nh.iph->saddr,
+                                        .saddr = skb->nh.iph->daddr,
+                                        .tos = RT_CONN_FLAGS(sk) } },
+                            .proto = sk->sk_protocol,
+                            .uli_u = { .ports =
+                                       { .sport = dccp_hdr(skb)->dccph_dport,
+                                         .dport = dccp_hdr(skb)->dccph_sport } } };
+
+        if (ip_route_output_flow(&rt, &fl, sk, 0)) {
+                IP_INC_STATS_BH(IPSTATS_MIB_OUTNOROUTES);
+                return NULL;
+        }
+
+        return &rt->u.dst;
+}
+
+void dccp_v4_ctl_send_reset(struct sk_buff *rxskb)
+{
+        int err;
+        struct dccp_hdr *rxdh = dccp_hdr(rxskb), *dh;
+        const int dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
+                                       sizeof(struct dccp_hdr_ext) +
+                                       sizeof(struct dccp_hdr_reset);
+        struct sk_buff *skb;
+        struct dst_entry *dst;
+
+        /* Never send a reset in response to a reset. */
+        if (rxdh->dccph_type == DCCP_PKT_RESET)
+                return;
+
+        if (((struct rtable *)rxskb->dst)->rt_type != RTN_LOCAL)
+                return;
+
+        dst = dccp_v4_route_skb(dccp_ctl_socket->sk, rxskb);
+        if (dst == NULL)
+                return;
+
+        skb = alloc_skb(MAX_DCCP_HEADER + 15, GFP_ATOMIC);
+        if (skb == NULL)
+                goto out;
+
+        /* Reserve space for headers. */
+        skb_reserve(skb, MAX_DCCP_HEADER);
+        skb->dst = dst_clone(dst);
+
+        skb->h.raw = skb_push(skb, dccp_hdr_reset_len);
+        dh = dccp_hdr(skb);
+        memset(dh, 0, dccp_hdr_reset_len);
+
+        /* Build DCCP header and checksum it. */
+        dh->dccph_type     = DCCP_PKT_RESET;
+        dh->dccph_sport    = rxdh->dccph_dport;
+        dh->dccph_dport    = rxdh->dccph_sport;
+        dh->dccph_doff     = dccp_hdr_reset_len / 4;
+        dh->dccph_x        = 1;
+        dccp_hdr_reset(skb)->dccph_reset_code = DCCP_SKB_CB(rxskb)->dccpd_reset_code;
+
+        dccp_hdr_set_seq(dh, DCCP_SKB_CB(rxskb)->dccpd_ack_seq);
+        dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), DCCP_SKB_CB(rxskb)->dccpd_seq);
+
+        dh->dccph_checksum = dccp_v4_checksum(skb);
+
+        bh_lock_sock(dccp_ctl_socket->sk);
+        err = ip_build_and_send_pkt(skb, dccp_ctl_socket->sk,
+                                    rxskb->nh.iph->daddr, rxskb->nh.iph->saddr, NULL);
+        bh_unlock_sock(dccp_ctl_socket->sk);
+
+        if (err == NET_XMIT_CN || err == 0) {
+                DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);
+                DCCP_INC_STATS_BH(DCCP_MIB_OUTRSTS);
+        }
+out:
+         dst_release(dst);
+}
+
+int dccp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
+{
+        struct dccp_hdr *dh = dccp_hdr(skb);
+
+        if (sk->sk_state == DCCP_OPEN) { /* Fast path */
+                if (dccp_rcv_established(sk, skb, dh, skb->len))
+                        goto reset;
+                return 0;
+        }
+
+        /*
+         *  Step 3: Process LISTEN state
+         *     If S.state == LISTEN,
+         *        If P.type == Request or P contains a valid Init Cookie option,
+         *           * Must scan the packet's options to check for an Init
+         *              Cookie.  Only the Init Cookie is processed here,
+         *              however; other options are processed in Step 8.  This
+         *              scan need only be performed if the endpoint uses Init
+         *              Cookies *
+         *           * Generate a new socket and switch to that socket *
+         *           Set S := new socket for this port pair
+         *           S.state = RESPOND
+         *           Choose S.ISS (initial seqno) or set from Init Cookie
+         *           Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
+         *           Continue with S.state == RESPOND
+         *           * A Response packet will be generated in Step 11 *
+         *        Otherwise,
+         *           Generate Reset(No Connection) unless P.type == Reset
+         *           Drop packet and return
+         *
+         * NOTE: the check for the packet types is done in dccp_rcv_state_process
+         */
+        if (sk->sk_state == DCCP_LISTEN) {
+                struct sock *nsk = dccp_v4_hnd_req(sk, skb);
+
+                if (nsk == NULL)
+                        goto discard;
+
+                if (nsk != sk) {
+                        if (dccp_child_process(sk, nsk, skb))
+                                goto reset;
+                        return 0;
+                }
+        }
+
+        if (dccp_rcv_state_process(sk, skb, dh, skb->len))
+                goto reset;
+        return 0;
+
+reset:
+        DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION;
+        dccp_v4_ctl_send_reset(skb);
+discard:
+        kfree_skb(skb);
+        return 0;
+}
+
+static inline int dccp_invalid_packet(struct sk_buff *skb)
+{
+        const struct dccp_hdr *dh;
+
+        if (skb->pkt_type != PACKET_HOST)
+                return 1;
+
+        if (!pskb_may_pull(skb, sizeof(struct dccp_hdr))) {
+                dccp_pr_debug("pskb_may_pull failed\n");
+                return 1;
+        }
+
+        dh = dccp_hdr(skb);
+
+        /* If the packet type is not understood, drop packet and return */
+        if (dh->dccph_type >= DCCP_PKT_INVALID) {
+                dccp_pr_debug("invalid packet type\n");
+                return 1;
+        }
+
+        /*
+         * If P.Data Offset is too small for packet type, or too large for
+         * packet, drop packet and return
+         */
+        if (dh->dccph_doff < dccp_hdr_len(skb) / sizeof(u32)) {
+                dccp_pr_debug("Offset(%u) too small 1\n", dh->dccph_doff);
+                return 1;
+        }
+
+        if (!pskb_may_pull(skb, dh->dccph_doff * sizeof(u32))) {
+                dccp_pr_debug("P.Data Offset(%u) too small 2\n", dh->dccph_doff);
+                return 1;
+        }
+
+        dh = dccp_hdr(skb);
+
+        /*
+         * If P.type is not Data, Ack, or DataAck and P.X == 0 (the packet
+         * has short sequence numbers), drop packet and return
+         */
+        if (dh->dccph_x == 0 &&
+            dh->dccph_type != DCCP_PKT_DATA &&
+            dh->dccph_type != DCCP_PKT_ACK &&
+            dh->dccph_type != DCCP_PKT_DATAACK) {
+                dccp_pr_debug("P.type (%s) not Data, Ack nor DataAck and P.X == 0\n",
+                              dccp_packet_name(dh->dccph_type));
+                return 1;
+        }
+
+        /* If the header checksum is incorrect, drop packet and return */
+        if (dccp_v4_verify_checksum(skb) < 0) {
+                dccp_pr_debug("header checksum is incorrect\n");
+                return 1;
+        }
+
+        return 0;
+}
+
+/* this is called when real data arrives */
+int dccp_v4_rcv(struct sk_buff *skb)
+{
+        const struct dccp_hdr *dh;
+        struct sock *sk;
+        int rc;
+
+        /* Step 1: Check header basics: */
+
+        if (dccp_invalid_packet(skb))
+                goto discard_it;
+
+        dh = dccp_hdr(skb);
+#if 0
+        /*
+         * Use something like this to simulate some DATA/DATAACK loss to test
+         * dccp_ackpkts_add, you'll get something like this on a session that
+         * sends 10 DATA/DATAACK packets:
+         *
+         * dccp_ackpkts_print: 281473596467422 |0,0|3,0|0,0|3,0|0,0|3,0|0,0|3,0|0,1|
+         *
+         * 0, 0 means: DCCP_ACKPKTS_STATE_RECEIVED, RLE == just this packet
+         * 0, 1 means: DCCP_ACKPKTS_STATE_RECEIVED, RLE == two adjacent packets with the same state
+         * 3, 0 means: DCCP_ACKPKTS_STATE_NOT_RECEIVED, RLE == just this packet
+         *
+         * So...
+         *
+         * 281473596467422 was received
+         * 281473596467421 was not received
+         * 281473596467420 was received
+         * 281473596467419 was not received
+         * 281473596467418 was received
+         * 281473596467417 was not received
+         * 281473596467416 was received
+         * 281473596467415 was not received
+         * 281473596467414 was received
+         * 281473596467413 was received (this one was the 3way handshake RESPONSE)
+         *
+         */
+        if (dh->dccph_type == DCCP_PKT_DATA || dh->dccph_type == DCCP_PKT_DATAACK) {
+                static int discard = 0;
+
+                if (discard) {
+                        discard = 0;
+                        goto discard_it;
+                }
+                discard = 1;
+        }
+#endif
+        DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(skb);
+        DCCP_SKB_CB(skb)->dccpd_type = dh->dccph_type;
+
+        dccp_pr_debug("%8.8s "
+                      "src=%u.%u.%u.%u@%-5d "
+                      "dst=%u.%u.%u.%u@%-5d seq=%llu",
+                      dccp_packet_name(dh->dccph_type),
+                      NIPQUAD(skb->nh.iph->saddr), ntohs(dh->dccph_sport),
+                      NIPQUAD(skb->nh.iph->daddr), ntohs(dh->dccph_dport),
+                      DCCP_SKB_CB(skb)->dccpd_seq);
+
+        if (dccp_packet_without_ack(skb)) {
+                DCCP_SKB_CB(skb)->dccpd_ack_seq = DCCP_PKT_WITHOUT_ACK_SEQ;
+                dccp_pr_debug_cat("\n");
+        } else {
+                DCCP_SKB_CB(skb)->dccpd_ack_seq = dccp_hdr_ack_seq(skb);
+                dccp_pr_debug_cat(", ack=%llu\n", DCCP_SKB_CB(skb)->dccpd_ack_seq);
+        }
+
+        /* Step 2:
+         *      Look up flow ID in table and get corresponding socket */
+        sk = __inet_lookup(&dccp_hashinfo,
+                           skb->nh.iph->saddr, dh->dccph_sport,
+                           skb->nh.iph->daddr, ntohs(dh->dccph_dport),
+                           inet_iif(skb));
+
+        /* 
+         * Step 2:
+         *      If no socket ...
+         *              Generate Reset(No Connection) unless P.type == Reset
+         *              Drop packet and return
+         */
+        if (sk == NULL) {
+                dccp_pr_debug("failed to look up flow ID in table and "
+                              "get corresponding socket\n");
+                goto no_dccp_socket;
+        }
+
+        /* 
+         * Step 2:
+         *      ... or S.state == TIMEWAIT,
+         *              Generate Reset(No Connection) unless P.type == Reset
+         *              Drop packet and return
+         */
+               
+        if (sk->sk_state == DCCP_TIME_WAIT) {
+                dccp_pr_debug("sk->sk_state == DCCP_TIME_WAIT: discard_and_relse\n");
+                goto discard_and_relse;
+        }
+
+        if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb)) {
+                dccp_pr_debug("xfrm4_policy_check failed\n");
+                goto discard_and_relse;
+        }
+
+        if (sk_filter(sk, skb, 0)) {
+                dccp_pr_debug("sk_filter failed\n");
+                goto discard_and_relse;
+        }
+
+        skb->dev = NULL;
+
+        bh_lock_sock(sk);
+        rc = 0;
+        if (!sock_owned_by_user(sk))
+                rc = dccp_v4_do_rcv(sk, skb);
+        else
+                sk_add_backlog(sk, skb);
+        bh_unlock_sock(sk);
+
+        sock_put(sk);
+        return rc;
+
+no_dccp_socket:
+        if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
+                goto discard_it;
+        /*
+         * Step 2:
+         *              Generate Reset(No Connection) unless P.type == Reset
+         *              Drop packet and return
+         */
+        if (dh->dccph_type != DCCP_PKT_RESET) {
+                DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION;
+                dccp_v4_ctl_send_reset(skb);
+        }
+
+discard_it:
+        /* Discard frame. */
+        kfree_skb(skb);
+        return 0;
+
+discard_and_relse:
+        sock_put(sk);
+        goto discard_it;
+}
+
+static int dccp_v4_init_sock(struct sock *sk)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+        static int dccp_ctl_socket_init = 1;
+
+        dccp_options_init(&dp->dccps_options);
+
+        if (dp->dccps_options.dccpo_send_ack_vector) {
+                dp->dccps_hc_rx_ackpkts = dccp_ackpkts_alloc(DCCP_MAX_ACK_VECTOR_LEN,
+                                                             GFP_KERNEL);
+
+                if (dp->dccps_hc_rx_ackpkts == NULL)
+                        return -ENOMEM;
+        }
+
+        /*
+         * FIXME: We're hardcoding the CCID, and doing this at this point makes
+         * the listening (master) sock get CCID control blocks, which is not
+         * necessary, but for now, to not mess with the test userspace apps,
+         * lets leave it here, later the real solution is to do this in a
+         * setsockopt(CCIDs-I-want/accept). -acme
+         */
+        if (likely(!dccp_ctl_socket_init)) {
+                dp->dccps_hc_rx_ccid = ccid_init(dp->dccps_options.dccpo_ccid, sk);
+                dp->dccps_hc_tx_ccid = ccid_init(dp->dccps_options.dccpo_ccid, sk);
+                if (dp->dccps_hc_rx_ccid == NULL ||
+                    dp->dccps_hc_tx_ccid == NULL) {
+                        ccid_exit(dp->dccps_hc_rx_ccid, sk);
+                        ccid_exit(dp->dccps_hc_tx_ccid, sk);
+                        dccp_ackpkts_free(dp->dccps_hc_rx_ackpkts);
+                        dp->dccps_hc_rx_ackpkts = NULL;
+                        dp->dccps_hc_rx_ccid = dp->dccps_hc_tx_ccid = NULL;
+                        return -ENOMEM;
+                }
+        } else
+                dccp_ctl_socket_init = 0;
+
+        dccp_init_xmit_timers(sk);
+        sk->sk_state = DCCP_CLOSED;
+        dp->dccps_mss_cache = 536;
+        dp->dccps_role = DCCP_ROLE_UNDEFINED;
+
+        return 0;
+}
+
+int dccp_v4_destroy_sock(struct sock *sk)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+
+        /*
+         * DCCP doesn't use sk_qrite_queue, just sk_send_head
+         * for retransmissions
+         */
+        if (sk->sk_send_head != NULL) {
+                kfree_skb(sk->sk_send_head);
+                sk->sk_send_head = NULL;
+        }
+
+        /* Clean up a referenced DCCP bind bucket. */
+        if (inet_csk(sk)->icsk_bind_hash != NULL)
+                inet_put_port(&dccp_hashinfo, sk);
+
+        dccp_ackpkts_free(dp->dccps_hc_rx_ackpkts);
+        dp->dccps_hc_rx_ackpkts = NULL;
+        ccid_exit(dp->dccps_hc_rx_ccid, sk);
+        ccid_exit(dp->dccps_hc_tx_ccid, sk);
+        dp->dccps_hc_rx_ccid = dp->dccps_hc_tx_ccid = NULL;
+
+        return 0;
+}
+
+static void dccp_v4_reqsk_destructor(struct request_sock *req)
+{
+        kfree(inet_rsk(req)->opt);
+}
+
+static struct request_sock_ops dccp_request_sock_ops = {
+        .family         = PF_INET,
+        .obj_size       = sizeof(struct dccp_request_sock),
+        .rtx_syn_ack    = dccp_v4_send_response,
+        .send_ack       = dccp_v4_reqsk_send_ack,
+        .destructor     = dccp_v4_reqsk_destructor,
+        .send_reset     = dccp_v4_ctl_send_reset,
+};
+
+struct proto dccp_v4_prot = {
+        .name                   = "DCCP",
+        .owner                  = THIS_MODULE,
+        .close                  = dccp_close,
+        .connect                = dccp_v4_connect,
+        .disconnect             = dccp_disconnect,
+        .ioctl                  = dccp_ioctl,
+        .init                   = dccp_v4_init_sock,
+        .setsockopt             = dccp_setsockopt,
+        .getsockopt             = dccp_getsockopt,
+        .sendmsg                = dccp_sendmsg,
+        .recvmsg                = dccp_recvmsg,
+        .backlog_rcv            = dccp_v4_do_rcv,
+        .hash                   = dccp_v4_hash,
+        .unhash                 = dccp_v4_unhash,
+        .accept                 = inet_csk_accept,
+        .get_port               = dccp_v4_get_port,
+        .shutdown               = dccp_shutdown,
+        .destroy                = dccp_v4_destroy_sock,
+        .orphan_count           = &dccp_orphan_count,
+        .max_header             = MAX_DCCP_HEADER,
+        .obj_size               = sizeof(struct dccp_sock),
+        .rsk_prot               = &dccp_request_sock_ops,
+        .twsk_obj_size          = sizeof(struct inet_timewait_sock), /* FIXME! create dccp_timewait_sock */
+};