inet: drop prev pointer handling in request sock

[mirror_ubuntu-jammy-kernel.git] / net / dccp / ipv4.c

/*
 *  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/dccp.h>
#include <linux/icmp.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/random.h>

#include <net/icmp.h>
#include <net/inet_common.h>
#include <net/inet_hashtables.h>
#include <net/inet_sock.h>
#include <net/protocol.h>
#include <net/sock.h>
#include <net/timewait_sock.h>
#include <net/tcp_states.h>
#include <net/xfrm.h>
#include <net/secure_seq.h>

#include "ackvec.h"
#include "ccid.h"
#include "dccp.h"
#include "feat.h"

/*
 * The per-net dccp.v4_ctl_sk socket is used for responding to
 * the Out-of-the-blue (OOTB) packets. A control sock will be created
 * for this socket at the initialization time.
 */

int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
        const struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
        struct inet_sock *inet = inet_sk(sk);
        struct dccp_sock *dp = dccp_sk(sk);
        __be16 orig_sport, orig_dport;
        __be32 daddr, nexthop;
        struct flowi4 *fl4;
        struct rtable *rt;
        int err;
        struct ip_options_rcu *inet_opt;

        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;

        inet_opt = rcu_dereference_protected(inet->inet_opt,
                                             sock_owned_by_user(sk));
        if (inet_opt != NULL && inet_opt->opt.srr) {
                if (daddr == 0)
                        return -EINVAL;
                nexthop = inet_opt->opt.faddr;
        }

        orig_sport = inet->inet_sport;
        orig_dport = usin->sin_port;
        fl4 = &inet->cork.fl.u.ip4;
        rt = ip_route_connect(fl4, nexthop, inet->inet_saddr,
                              RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
                              IPPROTO_DCCP,
                              orig_sport, orig_dport, sk);
        if (IS_ERR(rt))
                return PTR_ERR(rt);

        if (rt->rt_flags & (RTCF_MULTICAST | RTCF_BROADCAST)) {
                ip_rt_put(rt);
                return -ENETUNREACH;
        }

        if (inet_opt == NULL || !inet_opt->opt.srr)
                daddr = fl4->daddr;

        if (inet->inet_saddr == 0)
                inet->inet_saddr = fl4->saddr;
        sk_rcv_saddr_set(sk, inet->inet_saddr);
        inet->inet_dport = usin->sin_port;
        sk_daddr_set(sk, daddr);

        inet_csk(sk)->icsk_ext_hdr_len = 0;
        if (inet_opt)
                inet_csk(sk)->icsk_ext_hdr_len = inet_opt->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 = inet_hash_connect(&dccp_death_row, sk);
        if (err != 0)
                goto failure;

        rt = ip_route_newports(fl4, rt, orig_sport, orig_dport,
                               inet->inet_sport, inet->inet_dport, sk);
        if (IS_ERR(rt)) {
                err = PTR_ERR(rt);
                rt = NULL;
                goto failure;
        }
        /* OK, now commit destination to socket.  */
        sk_setup_caps(sk, &rt->dst);

        dp->dccps_iss = secure_dccp_sequence_number(inet->inet_saddr,
                                                    inet->inet_daddr,
                                                    inet->inet_sport,
                                                    inet->inet_dport);
        inet->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->inet_dport = 0;
        goto out;
}
EXPORT_SYMBOL_GPL(dccp_v4_connect);

/*
 * 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;

        dst = inet_csk_update_pmtu(sk, mtu);
        if (!dst)
                return;

        /* 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 &&
            ip_sk_accept_pmtu(sk) &&
            inet_csk(sk)->icsk_pmtu_cookie > mtu) {
                dccp_sync_mss(sk, mtu);

                /*
                 * From RFC 4340, sec. 14.1:
                 *
                 *      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, DCCP_PKT_SYNC);
        } /* else let the usual retransmit timer handle it */
}

static void dccp_do_redirect(struct sk_buff *skb, struct sock *sk)
{
        struct dst_entry *dst = __sk_dst_check(sk, 0);

        if (dst)
                dst->ops->redirect(dst, sk, skb);
}

/*
 * 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.
 */
static void dccp_v4_err(struct sk_buff *skb, u32 info)
{
        const struct iphdr *iph = (struct iphdr *)skb->data;
        const u8 offset = iph->ihl << 2;
        const struct dccp_hdr *dh = (struct dccp_hdr *)(skb->data + offset);
        struct dccp_sock *dp;
        struct inet_sock *inet;
        const int type = icmp_hdr(skb)->type;
        const int code = icmp_hdr(skb)->code;
        struct sock *sk;
        __u64 seq;
        int err;
        struct net *net = dev_net(skb->dev);

        if (skb->len < offset + sizeof(*dh) ||
            skb->len < offset + __dccp_basic_hdr_len(dh)) {
                ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);
                return;
        }

        sk = inet_lookup(net, &dccp_hashinfo,
                        iph->daddr, dh->dccph_dport,
                        iph->saddr, dh->dccph_sport, inet_iif(skb));
        if (sk == NULL) {
                ICMP_INC_STATS_BH(net, ICMP_MIB_INERRORS);
                return;
        }

        if (sk->sk_state == DCCP_TIME_WAIT) {
                inet_twsk_put(inet_twsk(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(net, LINUX_MIB_LOCKDROPPEDICMPS);

        if (sk->sk_state == DCCP_CLOSED)
                goto out;

        dp = dccp_sk(sk);
        seq = dccp_hdr_seq(dh);
        if ((1 << sk->sk_state) & ~(DCCPF_REQUESTING | DCCPF_LISTEN) &&
            !between48(seq, dp->dccps_awl, dp->dccps_awh)) {
                NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);
                goto out;
        }

        switch (type) {
        case ICMP_REDIRECT:
                dccp_do_redirect(skb, sk);
                goto out;
        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;
        case DCCP_LISTEN:
                if (sock_owned_by_user(sk))
                        goto out;
                req = inet_csk_search_req(sk, dh->dccph_dport,
                                          iph->daddr, iph->saddr);
                if (!req)
                        goto out;

                /*
                 * ICMPs are not backlogged, hence we cannot get an established
                 * socket here.
                 */
                WARN_ON(req->sk);

                if (!between48(seq, dccp_rsk(req)->dreq_iss,
                                    dccp_rsk(req)->dreq_gss)) {
                        NET_INC_STATS_BH(net, 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);
                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);
}

static inline __sum16 dccp_v4_csum_finish(struct sk_buff *skb,
                                      __be32 src, __be32 dst)
{
        return csum_tcpudp_magic(src, dst, skb->len, IPPROTO_DCCP, skb->csum);
}

void dccp_v4_send_check(struct sock *sk, struct sk_buff *skb)
{
        const struct inet_sock *inet = inet_sk(sk);
        struct dccp_hdr *dh = dccp_hdr(skb);

        dccp_csum_outgoing(skb);
        dh->dccph_checksum = dccp_v4_csum_finish(skb,
                                                 inet->inet_saddr,
                                                 inet->inet_daddr);
}
EXPORT_SYMBOL_GPL(dccp_v4_send_check);

static inline u64 dccp_v4_init_sequence(const struct sk_buff *skb)
{
        return secure_dccp_sequence_number(ip_hdr(skb)->daddr,
                                           ip_hdr(skb)->saddr,
                                           dccp_hdr(skb)->dccph_dport,
                                           dccp_hdr(skb)->dccph_sport);
}

/*
 * 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 sock *newsk;

        if (sk_acceptq_is_full(sk))
                goto exit_overflow;

        newsk = dccp_create_openreq_child(sk, req, skb);
        if (newsk == NULL)
                goto exit_nonewsk;

        newinet            = inet_sk(newsk);
        ireq               = inet_rsk(req);
        sk_daddr_set(newsk, ireq->ir_rmt_addr);
        sk_rcv_saddr_set(newsk, ireq->ir_loc_addr);
        newinet->inet_saddr     = ireq->ir_loc_addr;
        newinet->inet_opt       = ireq->opt;
        ireq->opt          = NULL;
        newinet->mc_index  = inet_iif(skb);
        newinet->mc_ttl    = ip_hdr(skb)->ttl;
        newinet->inet_id   = jiffies;

        if (dst == NULL && (dst = inet_csk_route_child_sock(sk, newsk, req)) == NULL)
                goto put_and_exit;

        sk_setup_caps(newsk, dst);

        dccp_sync_mss(newsk, dst_mtu(dst));

        if (__inet_inherit_port(sk, newsk) < 0)
                goto put_and_exit;
        __inet_hash_nolisten(newsk, NULL);

        return newsk;

exit_overflow:
        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
exit_nonewsk:
        dst_release(dst);
exit:
        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_LISTENDROPS);
        return NULL;
put_and_exit:
        inet_csk_prepare_forced_close(newsk);
        dccp_done(newsk);
        goto exit;
}
EXPORT_SYMBOL_GPL(dccp_v4_request_recv_sock);

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 = ip_hdr(skb);
        struct sock *nsk;
        /* Find possible connection requests. */
        struct request_sock *req = inet_csk_search_req(sk, dh->dccph_sport,
                                                       iph->saddr, iph->daddr);
        if (req)
                return dccp_check_req(sk, skb, req);

        nsk = inet_lookup_established(sock_net(sk), &dccp_hashinfo,
                                      iph->saddr, dh->dccph_sport,
                                      iph->daddr, 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(inet_twsk(nsk));
                return NULL;
        }

        return sk;
}

static struct dst_entry* dccp_v4_route_skb(struct net *net, struct sock *sk,
                                           struct sk_buff *skb)
{
        struct rtable *rt;
        const struct iphdr *iph = ip_hdr(skb);
        struct flowi4 fl4 = {
                .flowi4_oif = inet_iif(skb),
                .daddr = iph->saddr,
                .saddr = iph->daddr,
                .flowi4_tos = RT_CONN_FLAGS(sk),
                .flowi4_proto = sk->sk_protocol,
                .fl4_sport = dccp_hdr(skb)->dccph_dport,
                .fl4_dport = dccp_hdr(skb)->dccph_sport,
        };

        security_skb_classify_flow(skb, flowi4_to_flowi(&fl4));
        rt = ip_route_output_flow(net, &fl4, sk);
        if (IS_ERR(rt)) {
                IP_INC_STATS_BH(net, IPSTATS_MIB_OUTNOROUTES);
                return NULL;
        }

        return &rt->dst;
}

static int dccp_v4_send_response(struct sock *sk, struct request_sock *req)
{
        int err = -1;
        struct sk_buff *skb;
        struct dst_entry *dst;
        struct flowi4 fl4;

        dst = inet_csk_route_req(sk, &fl4, req);
        if (dst == NULL)
                goto out;

        skb = dccp_make_response(sk, dst, req);
        if (skb != NULL) {
                const struct inet_request_sock *ireq = inet_rsk(req);
                struct dccp_hdr *dh = dccp_hdr(skb);

                dh->dccph_checksum = dccp_v4_csum_finish(skb, ireq->ir_loc_addr,
                                                              ireq->ir_rmt_addr);
                err = ip_build_and_send_pkt(skb, sk, ireq->ir_loc_addr,
                                            ireq->ir_rmt_addr,
                                            ireq->opt);
                err = net_xmit_eval(err);
        }

out:
        dst_release(dst);
        return err;
}

static void dccp_v4_ctl_send_reset(struct sock *sk, struct sk_buff *rxskb)
{
        int err;
        const struct iphdr *rxiph;
        struct sk_buff *skb;
        struct dst_entry *dst;
        struct net *net = dev_net(skb_dst(rxskb)->dev);
        struct sock *ctl_sk = net->dccp.v4_ctl_sk;

        /* Never send a reset in response to a reset. */
        if (dccp_hdr(rxskb)->dccph_type == DCCP_PKT_RESET)
                return;

        if (skb_rtable(rxskb)->rt_type != RTN_LOCAL)
                return;

        dst = dccp_v4_route_skb(net, ctl_sk, rxskb);
        if (dst == NULL)
                return;

        skb = dccp_ctl_make_reset(ctl_sk, rxskb);
        if (skb == NULL)
                goto out;

        rxiph = ip_hdr(rxskb);
        dccp_hdr(skb)->dccph_checksum = dccp_v4_csum_finish(skb, rxiph->saddr,
                                                                 rxiph->daddr);
        skb_dst_set(skb, dst_clone(dst));

        bh_lock_sock(ctl_sk);
        err = ip_build_and_send_pkt(skb, ctl_sk,
                                    rxiph->daddr, rxiph->saddr, NULL);
        bh_unlock_sock(ctl_sk);

        if (net_xmit_eval(err) == 0) {
                DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);
                DCCP_INC_STATS_BH(DCCP_MIB_OUTRSTS);
        }
out:
         dst_release(dst);
}

static void dccp_v4_reqsk_destructor(struct request_sock *req)
{
        dccp_feat_list_purge(&dccp_rsk(req)->dreq_featneg);
        kfree(inet_rsk(req)->opt);
}

void dccp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
{
}
EXPORT_SYMBOL(dccp_syn_ack_timeout);

static struct request_sock_ops dccp_request_sock_ops __read_mostly = {
        .family         = PF_INET,
        .obj_size       = sizeof(struct dccp_request_sock),
        .rtx_syn_ack    = dccp_v4_send_response,
        .send_ack       = dccp_reqsk_send_ack,
        .destructor     = dccp_v4_reqsk_destructor,
        .send_reset     = dccp_v4_ctl_send_reset,
        .syn_ack_timeout = dccp_syn_ack_timeout,
};

int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
{
        struct inet_request_sock *ireq;
        struct request_sock *req;
        struct dccp_request_sock *dreq;
        const __be32 service = dccp_hdr_request(skb)->dccph_req_service;
        struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);

        /* Never answer to DCCP_PKT_REQUESTs send to broadcast or multicast */
        if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
                return 0;       /* discard, don't send a reset here */

        if (dccp_bad_service_code(sk, service)) {
                dcb->dccpd_reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
                goto drop;
        }
        /*
         * TW buckets are converted to open requests without
         * limitations, they conserve resources and peer is
         * evidently real one.
         */
        dcb->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
        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 = inet_reqsk_alloc(&dccp_request_sock_ops, sk);
        if (req == NULL)
                goto drop;

        if (dccp_reqsk_init(req, dccp_sk(sk), skb))
                goto drop_and_free;

        dreq = dccp_rsk(req);
        if (dccp_parse_options(sk, dreq, skb))
                goto drop_and_free;

        if (security_inet_conn_request(sk, skb, req))
                goto drop_and_free;

        ireq = inet_rsk(req);
        sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
        sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
        ireq->ireq_family = AF_INET;
        ireq->ir_iif = sk->sk_bound_dev_if;

        /*
         * Step 3: Process LISTEN state
         *
         * Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
         *
         * Setting S.SWL/S.SWH to is deferred to dccp_create_openreq_child().
         */
        dreq->dreq_isr     = dcb->dccpd_seq;
        dreq->dreq_gsr     = dreq->dreq_isr;
        dreq->dreq_iss     = dccp_v4_init_sequence(skb);
        dreq->dreq_gss     = dreq->dreq_iss;
        dreq->dreq_service = service;

        if (dccp_v4_send_response(sk, req))
                goto drop_and_free;

        inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT);
        return 0;

drop_and_free:
        reqsk_free(req);
drop:
        DCCP_INC_STATS_BH(DCCP_MIB_ATTEMPTFAILS);
        return -1;
}
EXPORT_SYMBOL_GPL(dccp_v4_conn_request);

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 P.type == Request or P contains a valid Init Cookie option,
         *            (* Must scan the packet's options to check for Init
         *               Cookies.  Only Init Cookies are 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 Cookies
         *            Initialize S.GAR := S.ISS
         *            Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookies
         *            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_v4_ctl_send_reset(sk, skb);
discard:
        kfree_skb(skb);
        return 0;
}
EXPORT_SYMBOL_GPL(dccp_v4_do_rcv);

/**
 *      dccp_invalid_packet  -  check for malformed packets
 *      Implements RFC 4340, 8.5:  Step 1: Check header basics
 *      Packets that fail these checks are ignored and do not receive Resets.
 */
int dccp_invalid_packet(struct sk_buff *skb)
{
        const struct dccp_hdr *dh;
        unsigned int cscov;

        if (skb->pkt_type != PACKET_HOST)
                return 1;

        /* If the packet is shorter than 12 bytes, drop packet and return */
        if (!pskb_may_pull(skb, sizeof(struct dccp_hdr))) {
                DCCP_WARN("pskb_may_pull failed\n");
                return 1;
        }

        dh = dccp_hdr(skb);

        /* If P.type is not understood, drop packet and return */
        if (dh->dccph_type >= DCCP_PKT_INVALID) {
                DCCP_WARN("invalid packet type\n");
                return 1;
        }

        /*
         * If P.Data Offset is too small for packet type, drop packet and return
         */
        if (dh->dccph_doff < dccp_hdr_len(skb) / sizeof(u32)) {
                DCCP_WARN("P.Data Offset(%u) too small\n", dh->dccph_doff);
                return 1;
        }
        /*
         * If P.Data Offset is too too large for packet, drop packet and return
         */
        if (!pskb_may_pull(skb, dh->dccph_doff * sizeof(u32))) {
                DCCP_WARN("P.Data Offset(%u) too large\n", dh->dccph_doff);
                return 1;
        }

        /*
         * 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_type < DCCP_PKT_DATA    ||
            dh->dccph_type > DCCP_PKT_DATAACK) && dh->dccph_x == 0)  {
                DCCP_WARN("P.type (%s) not Data || [Data]Ack, while P.X == 0\n",
                          dccp_packet_name(dh->dccph_type));
                return 1;
        }

        /*
         * If P.CsCov is too large for the packet size, drop packet and return.
         * This must come _before_ checksumming (not as RFC 4340 suggests).
         */
        cscov = dccp_csum_coverage(skb);
        if (cscov > skb->len) {
                DCCP_WARN("P.CsCov %u exceeds packet length %d\n",
                          dh->dccph_cscov, skb->len);
                return 1;
        }

        /* If header checksum is incorrect, drop packet and return.
         * (This step is completed in the AF-dependent functions.) */
        skb->csum = skb_checksum(skb, 0, cscov, 0);

        return 0;
}
EXPORT_SYMBOL_GPL(dccp_invalid_packet);

/* this is called when real data arrives */
static int dccp_v4_rcv(struct sk_buff *skb)
{
        const struct dccp_hdr *dh;
        const struct iphdr *iph;
        struct sock *sk;
        int min_cov;

        /* Step 1: Check header basics */

        if (dccp_invalid_packet(skb))
                goto discard_it;

        iph = ip_hdr(skb);
        /* Step 1: If header checksum is incorrect, drop packet and return */
        if (dccp_v4_csum_finish(skb, iph->saddr, iph->daddr)) {
                DCCP_WARN("dropped packet with invalid checksum\n");
                goto discard_it;
        }

        dh = dccp_hdr(skb);

        DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(dh);
        DCCP_SKB_CB(skb)->dccpd_type = dh->dccph_type;

        dccp_pr_debug("%8.8s src=%pI4@%-5d dst=%pI4@%-5d seq=%llu",
                      dccp_packet_name(dh->dccph_type),
                      &iph->saddr, ntohs(dh->dccph_sport),
                      &iph->daddr, ntohs(dh->dccph_dport),
                      (unsigned long long) 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", (unsigned long long)
                                  DCCP_SKB_CB(skb)->dccpd_ack_seq);
        }

        /* Step 2:
         *      Look up flow ID in table and get corresponding socket */
        sk = __inet_lookup_skb(&dccp_hashinfo, skb,
                               dh->dccph_sport, dh->dccph_dport);
        /*
         * Step 2:
         *      If no socket ...
         */
        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: do_time_wait\n");
                inet_twsk_put(inet_twsk(sk));
                goto no_dccp_socket;
        }

        /*
         * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
         *      o if MinCsCov = 0, only packets with CsCov = 0 are accepted
         *      o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
         */
        min_cov = dccp_sk(sk)->dccps_pcrlen;
        if (dh->dccph_cscov && (min_cov == 0 || dh->dccph_cscov < min_cov))  {
                dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
                              dh->dccph_cscov, min_cov);
                /* FIXME: "Such packets SHOULD be reported using Data Dropped
                 *         options (Section 11.7) with Drop Code 0, Protocol
                 *         Constraints."                                     */
                goto discard_and_relse;
        }

        if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
                goto discard_and_relse;
        nf_reset(skb);

        return sk_receive_skb(sk, skb, 1);

no_dccp_socket:
        if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
                goto discard_it;
        /*
         * Step 2:
         *      If no socket ...
         *              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(sk, skb);
        }

discard_it:
        kfree_skb(skb);
        return 0;

discard_and_relse:
        sock_put(sk);
        goto discard_it;
}

static const struct inet_connection_sock_af_ops dccp_ipv4_af_ops = {
        .queue_xmit        = ip_queue_xmit,
        .send_check        = dccp_v4_send_check,
        .rebuild_header    = inet_sk_rebuild_header,
        .conn_request      = dccp_v4_conn_request,
        .syn_recv_sock     = dccp_v4_request_recv_sock,
        .net_header_len    = sizeof(struct iphdr),
        .setsockopt        = ip_setsockopt,
        .getsockopt        = ip_getsockopt,
        .addr2sockaddr     = inet_csk_addr2sockaddr,
        .sockaddr_len      = sizeof(struct sockaddr_in),
        .bind_conflict     = inet_csk_bind_conflict,
#ifdef CONFIG_COMPAT
        .compat_setsockopt = compat_ip_setsockopt,
        .compat_getsockopt = compat_ip_getsockopt,
#endif
};

static int dccp_v4_init_sock(struct sock *sk)
{
        static __u8 dccp_v4_ctl_sock_initialized;
        int err = dccp_init_sock(sk, dccp_v4_ctl_sock_initialized);

        if (err == 0) {
                if (unlikely(!dccp_v4_ctl_sock_initialized))
                        dccp_v4_ctl_sock_initialized = 1;
                inet_csk(sk)->icsk_af_ops = &dccp_ipv4_af_ops;
        }

        return err;
}

static struct timewait_sock_ops dccp_timewait_sock_ops = {
        .twsk_obj_size  = sizeof(struct inet_timewait_sock),
};

static 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                   = inet_hash,
        .unhash                 = inet_unhash,
        .accept                 = inet_csk_accept,
        .get_port               = inet_csk_get_port,
        .shutdown               = dccp_shutdown,
        .destroy                = dccp_destroy_sock,
        .orphan_count           = &dccp_orphan_count,
        .max_header             = MAX_DCCP_HEADER,
        .obj_size               = sizeof(struct dccp_sock),
        .slab_flags             = SLAB_DESTROY_BY_RCU,
        .rsk_prot               = &dccp_request_sock_ops,
        .twsk_prot              = &dccp_timewait_sock_ops,
        .h.hashinfo             = &dccp_hashinfo,
#ifdef CONFIG_COMPAT
        .compat_setsockopt      = compat_dccp_setsockopt,
        .compat_getsockopt      = compat_dccp_getsockopt,
#endif
};

static const struct net_protocol dccp_v4_protocol = {
        .handler        = dccp_v4_rcv,
        .err_handler    = dccp_v4_err,
        .no_policy      = 1,
        .netns_ok       = 1,
        .icmp_strict_tag_validation = 1,
};

static const struct proto_ops inet_dccp_ops = {
        .family            = PF_INET,
        .owner             = THIS_MODULE,
        .release           = inet_release,
        .bind              = inet_bind,
        .connect           = inet_stream_connect,
        .socketpair        = sock_no_socketpair,
        .accept            = inet_accept,
        .getname           = inet_getname,
        /* FIXME: work on tcp_poll to rename it to inet_csk_poll */
        .poll              = dccp_poll,
        .ioctl             = inet_ioctl,
        /* FIXME: work on inet_listen to rename it to sock_common_listen */
        .listen            = inet_dccp_listen,
        .shutdown          = inet_shutdown,
        .setsockopt        = sock_common_setsockopt,
        .getsockopt        = sock_common_getsockopt,
        .sendmsg           = inet_sendmsg,
        .recvmsg           = sock_common_recvmsg,
        .mmap              = sock_no_mmap,
        .sendpage          = sock_no_sendpage,
#ifdef CONFIG_COMPAT
        .compat_setsockopt = compat_sock_common_setsockopt,
        .compat_getsockopt = compat_sock_common_getsockopt,
#endif
};

static struct inet_protosw dccp_v4_protosw = {
        .type           = SOCK_DCCP,
        .protocol       = IPPROTO_DCCP,
        .prot           = &dccp_v4_prot,
        .ops            = &inet_dccp_ops,
        .flags          = INET_PROTOSW_ICSK,
};

static int __net_init dccp_v4_init_net(struct net *net)
{
        if (dccp_hashinfo.bhash == NULL)
                return -ESOCKTNOSUPPORT;

        return inet_ctl_sock_create(&net->dccp.v4_ctl_sk, PF_INET,
                                    SOCK_DCCP, IPPROTO_DCCP, net);
}

static void __net_exit dccp_v4_exit_net(struct net *net)
{
        inet_ctl_sock_destroy(net->dccp.v4_ctl_sk);
}

static struct pernet_operations dccp_v4_ops = {
        .init   = dccp_v4_init_net,
        .exit   = dccp_v4_exit_net,
};

static int __init dccp_v4_init(void)
{
        int err = proto_register(&dccp_v4_prot, 1);

        if (err != 0)
                goto out;

        err = inet_add_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
        if (err != 0)
                goto out_proto_unregister;

        inet_register_protosw(&dccp_v4_protosw);

        err = register_pernet_subsys(&dccp_v4_ops);
        if (err)
                goto out_destroy_ctl_sock;
out:
        return err;
out_destroy_ctl_sock:
        inet_unregister_protosw(&dccp_v4_protosw);
        inet_del_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
out_proto_unregister:
        proto_unregister(&dccp_v4_prot);
        goto out;
}

static void __exit dccp_v4_exit(void)
{
        unregister_pernet_subsys(&dccp_v4_ops);
        inet_unregister_protosw(&dccp_v4_protosw);
        inet_del_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
        proto_unregister(&dccp_v4_prot);
}

module_init(dccp_v4_init);
module_exit(dccp_v4_exit);

/*
 * __stringify doesn't likes enums, so use SOCK_DCCP (6) and IPPROTO_DCCP (33)
 * values directly, Also cover the case where the protocol is not specified,
 * i.e. net-pf-PF_INET-proto-0-type-SOCK_DCCP
 */
MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 33, 6);
MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 0, 6);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@mandriva.com>");
MODULE_DESCRIPTION("DCCP - Datagram Congestion Controlled Protocol");