// SPDX-License-Identifier: GPL-2.0-or-later
/* SCTP kernel implementation
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001-2003 International Business Machines, Corp.
 * Copyright (c) 2001 Intel Corp.
 * Copyright (c) 2001 Nokia, Inc.
 * Copyright (c) 2001 La Monte H.P. Yarroll
 *
 * This file is part of the SCTP kernel implementation
 *
 * These functions handle all input from the IP layer into SCTP.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <linux-sctp@vger.kernel.org>
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <piggy@acm.org>
 *    Karl Knutson <karl@athena.chicago.il.us>
 *    Xingang Guo <xingang.guo@intel.com>
 *    Jon Grimm <jgrimm@us.ibm.com>
 *    Hui Huang <hui.huang@nokia.com>
 *    Daisy Chang <daisyc@us.ibm.com>
 *    Sridhar Samudrala <sri@us.ibm.com>
 *    Ardelle Fan <ardelle.fan@intel.com>
 */

#include <linux/types.h>
#include <linux/list.h> /* For struct list_head */
#include <linux/socket.h>
#include <linux/ip.h>
#include <linux/time.h> /* For struct timeval */
#include <linux/slab.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/snmp.h>
#include <net/sock.h>
#include <net/xfrm.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>
#include <net/sctp/checksum.h>
#include <net/net_namespace.h>
#include <linux/rhashtable.h>
#include <net/sock_reuseport.h>

/* Forward declarations for internal helpers. */
static int sctp_rcv_ootb(struct sk_buff *);
static struct sctp_association *__sctp_rcv_lookup(struct net *net,
                                      struct sk_buff *skb,
                                      const union sctp_addr *paddr,
                                      const union sctp_addr *laddr,
                                      struct sctp_transport **transportp);
static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(
                                        struct net *net, struct sk_buff *skb,
                                        const union sctp_addr *laddr,
                                        const union sctp_addr *daddr);
static struct sctp_association *__sctp_lookup_association(
                                        struct net *net,
                                        const union sctp_addr *local,
                                        const union sctp_addr *peer,
                                        struct sctp_transport **pt);

static int sctp_add_backlog(struct sock *sk, struct sk_buff *skb);


/* Calculate the SCTP checksum of an SCTP packet.  */
static inline int sctp_rcv_checksum(struct net *net, struct sk_buff *skb)
{
        struct sctphdr *sh = sctp_hdr(skb);
        __le32 cmp = sh->checksum;
        __le32 val = sctp_compute_cksum(skb, 0);

        if (val != cmp) {
                /* CRC failure, dump it. */
                __SCTP_INC_STATS(net, SCTP_MIB_CHECKSUMERRORS);
                return -1;
        }
        return 0;
}

/*
 * This is the routine which IP calls when receiving an SCTP packet.
 */
int sctp_rcv(struct sk_buff *skb)
{
        struct sock *sk;
        struct sctp_association *asoc;
        struct sctp_endpoint *ep = NULL;
        struct sctp_ep_common *rcvr;
        struct sctp_transport *transport = NULL;
        struct sctp_chunk *chunk;
        union sctp_addr src;
        union sctp_addr dest;
        int family;
        struct sctp_af *af;
        struct net *net = dev_net(skb->dev);
        bool is_gso = skb_is_gso(skb) && skb_is_gso_sctp(skb);

        if (skb->pkt_type != PACKET_HOST)
                goto discard_it;

        __SCTP_INC_STATS(net, SCTP_MIB_INSCTPPACKS);

        /* If packet is too small to contain a single chunk, let's not
         * waste time on it anymore.
         */
        if (skb->len < sizeof(struct sctphdr) + sizeof(struct sctp_chunkhdr) +
                       skb_transport_offset(skb))
                goto discard_it;

        /* If the packet is fragmented and we need to do crc checking,
         * it's better to just linearize it otherwise crc computing
         * takes longer.
         */
        if ((!is_gso && skb_linearize(skb)) ||
            !pskb_may_pull(skb, sizeof(struct sctphdr)))
                goto discard_it;

        /* Pull up the IP header. */
        __skb_pull(skb, skb_transport_offset(skb));

        skb->csum_valid = 0; /* Previous value not applicable */
        if (skb_csum_unnecessary(skb))
                __skb_decr_checksum_unnecessary(skb);
        else if (!sctp_checksum_disable &&
                 !is_gso &&
                 sctp_rcv_checksum(net, skb) < 0)
                goto discard_it;
        skb->csum_valid = 1;

        __skb_pull(skb, sizeof(struct sctphdr));

        family = ipver2af(ip_hdr(skb)->version);
        af = sctp_get_af_specific(family);
        if (unlikely(!af))
                goto discard_it;
        SCTP_INPUT_CB(skb)->af = af;

        /* Initialize local addresses for lookups. */
        af->from_skb(&src, skb, 1);
        af->from_skb(&dest, skb, 0);

        /* If the packet is to or from a non-unicast address,
         * silently discard the packet.
         *
         * This is not clearly defined in the RFC except in section
         * 8.4 - OOTB handling.  However, based on the book "Stream Control
         * Transmission Protocol" 2.1, "It is important to note that the
         * IP address of an SCTP transport address must be a routable
         * unicast address.  In other words, IP multicast addresses and
         * IP broadcast addresses cannot be used in an SCTP transport
         * address."
         */
        if (!af->addr_valid(&src, NULL, skb) ||
            !af->addr_valid(&dest, NULL, skb))
                goto discard_it;

        asoc = __sctp_rcv_lookup(net, skb, &src, &dest, &transport);

        if (!asoc)
                ep = __sctp_rcv_lookup_endpoint(net, skb, &dest, &src);

        /* Retrieve the common input handling substructure. */
        rcvr = asoc ? &asoc->base : &ep->base;
        sk = rcvr->sk;

        /*
         * If a frame arrives on an interface and the receiving socket is
         * bound to another interface, via SO_BINDTODEVICE, treat it as OOTB
         */
        if (sk->sk_bound_dev_if && (sk->sk_bound_dev_if != af->skb_iif(skb))) {
                if (transport) {
                        sctp_transport_put(transport);
                        asoc = NULL;
                        transport = NULL;
                } else {
                        sctp_endpoint_put(ep);
                        ep = NULL;
                }
                sk = net->sctp.ctl_sock;
                ep = sctp_sk(sk)->ep;
                sctp_endpoint_hold(ep);
                rcvr = &ep->base;
        }

        /*
         * RFC 2960, 8.4 - Handle "Out of the blue" Packets.
         * An SCTP packet is called an "out of the blue" (OOTB)
         * packet if it is correctly formed, i.e., passed the
         * receiver's checksum check, but the receiver is not
         * able to identify the association to which this
         * packet belongs.
         */
        if (!asoc) {
                if (sctp_rcv_ootb(skb)) {
                        __SCTP_INC_STATS(net, SCTP_MIB_OUTOFBLUES);
                        goto discard_release;
                }
        }

        if (!xfrm_policy_check(sk, XFRM_POLICY_IN, skb, family))
                goto discard_release;
        nf_reset_ct(skb);

        if (sk_filter(sk, skb))
                goto discard_release;

        /* Create an SCTP packet structure. */
        chunk = sctp_chunkify(skb, asoc, sk, GFP_ATOMIC);
        if (!chunk)
                goto discard_release;
        SCTP_INPUT_CB(skb)->chunk = chunk;

        /* Remember what endpoint is to handle this packet. */
        chunk->rcvr = rcvr;

        /* Remember the SCTP header. */
        chunk->sctp_hdr = sctp_hdr(skb);

        /* Set the source and destination addresses of the incoming chunk.  */
        sctp_init_addrs(chunk, &src, &dest);

        /* Remember where we came from.  */
        chunk->transport = transport;

        /* Acquire access to the sock lock. Note: We are safe from other
         * bottom halves on this lock, but a user may be in the lock too,
         * so check if it is busy.
         */
        bh_lock_sock(sk);

        if (sk != rcvr->sk) {
                /* Our cached sk is different from the rcvr->sk.  This is
                 * because migrate()/accept() may have moved the association
                 * to a new socket and released all the sockets.  So now we
                 * are holding a lock on the old socket while the user may
                 * be doing something with the new socket.  Switch our veiw
                 * of the current sk.
                 */
                bh_unlock_sock(sk);
                sk = rcvr->sk;
                bh_lock_sock(sk);
        }

        if (sock_owned_by_user(sk) || !sctp_newsk_ready(sk)) {
                if (sctp_add_backlog(sk, skb)) {
                        bh_unlock_sock(sk);
                        sctp_chunk_free(chunk);
                        skb = NULL; /* sctp_chunk_free already freed the skb */
                        goto discard_release;
                }
                __SCTP_INC_STATS(net, SCTP_MIB_IN_PKT_BACKLOG);
        } else {
                __SCTP_INC_STATS(net, SCTP_MIB_IN_PKT_SOFTIRQ);
                sctp_inq_push(&chunk->rcvr->inqueue, chunk);
        }

        bh_unlock_sock(sk);

        /* Release the asoc/ep ref we took in the lookup calls. */
        if (transport)
                sctp_transport_put(transport);
        else
                sctp_endpoint_put(ep);

        return 0;

discard_it:
        __SCTP_INC_STATS(net, SCTP_MIB_IN_PKT_DISCARDS);
        kfree_skb(skb);
        return 0;

discard_release:
        /* Release the asoc/ep ref we took in the lookup calls. */
        if (transport)
                sctp_transport_put(transport);
        else
                sctp_endpoint_put(ep);

        goto discard_it;
}

/* Process the backlog queue of the socket.  Every skb on
 * the backlog holds a ref on an association or endpoint.
 * We hold this ref throughout the state machine to make
 * sure that the structure we need is still around.
 */
int sctp_backlog_rcv(struct sock *sk, struct sk_buff *skb)
{
        struct sctp_chunk *chunk = SCTP_INPUT_CB(skb)->chunk;
        struct sctp_inq *inqueue = &chunk->rcvr->inqueue;
        struct sctp_transport *t = chunk->transport;
        struct sctp_ep_common *rcvr = NULL;
        int backloged = 0;

        rcvr = chunk->rcvr;

        /* If the rcvr is dead then the association or endpoint
         * has been deleted and we can safely drop the chunk
         * and refs that we are holding.
         */
        if (rcvr->dead) {
                sctp_chunk_free(chunk);
                goto done;
        }

        if (unlikely(rcvr->sk != sk)) {
                /* In this case, the association moved from one socket to
                 * another.  We are currently sitting on the backlog of the
                 * old socket, so we need to move.
                 * However, since we are here in the process context we
                 * need to take make sure that the user doesn't own
                 * the new socket when we process the packet.
                 * If the new socket is user-owned, queue the chunk to the
                 * backlog of the new socket without dropping any refs.
                 * Otherwise, we can safely push the chunk on the inqueue.
                 */

                sk = rcvr->sk;
                local_bh_disable();
                bh_lock_sock(sk);

                if (sock_owned_by_user(sk) || !sctp_newsk_ready(sk)) {
                        if (sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf)))
                                sctp_chunk_free(chunk);
                        else
                                backloged = 1;
                } else
                        sctp_inq_push(inqueue, chunk);

                bh_unlock_sock(sk);
                local_bh_enable();

                /* If the chunk was backloged again, don't drop refs */
                if (backloged)
                        return 0;
        } else {
                if (!sctp_newsk_ready(sk)) {
                        if (!sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf)))
                                return 0;
                        sctp_chunk_free(chunk);
                } else {
                        sctp_inq_push(inqueue, chunk);
                }
        }

done:
        /* Release the refs we took in sctp_add_backlog */
        if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)
                sctp_transport_put(t);
        else if (SCTP_EP_TYPE_SOCKET == rcvr->type)
                sctp_endpoint_put(sctp_ep(rcvr));
        else
                BUG();

        return 0;
}

static int sctp_add_backlog(struct sock *sk, struct sk_buff *skb)
{
        struct sctp_chunk *chunk = SCTP_INPUT_CB(skb)->chunk;
        struct sctp_transport *t = chunk->transport;
        struct sctp_ep_common *rcvr = chunk->rcvr;
        int ret;

        ret = sk_add_backlog(sk, skb, READ_ONCE(sk->sk_rcvbuf));
        if (!ret) {
                /* Hold the assoc/ep while hanging on the backlog queue.
                 * This way, we know structures we need will not disappear
                 * from us
                 */
                if (SCTP_EP_TYPE_ASSOCIATION == rcvr->type)
                        sctp_transport_hold(t);
                else if (SCTP_EP_TYPE_SOCKET == rcvr->type)
                        sctp_endpoint_hold(sctp_ep(rcvr));
                else
                        BUG();
        }
        return ret;

}

/* Handle icmp frag needed error. */
void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
                           struct sctp_transport *t, __u32 pmtu)
{
        if (!t ||
            (t->pathmtu <= pmtu &&
             t->pl.probe_size + sctp_transport_pl_hlen(t) <= pmtu))
                return;

        if (sock_owned_by_user(sk)) {
                atomic_set(&t->mtu_info, pmtu);
                asoc->pmtu_pending = 1;
                t->pmtu_pending = 1;
                return;
        }

        if (!(t->param_flags & SPP_PMTUD_ENABLE))
                /* We can't allow retransmitting in such case, as the
                 * retransmission would be sized just as before, and thus we
                 * would get another icmp, and retransmit again.
                 */
                return;

        /* Update transports view of the MTU. Return if no update was needed.
         * If an update wasn't needed/possible, it also doesn't make sense to
         * try to retransmit now.
         */
        if (!sctp_transport_update_pmtu(t, pmtu))
                return;

        /* Update association pmtu. */
        sctp_assoc_sync_pmtu(asoc);

        /* Retransmit with the new pmtu setting. */
        sctp_retransmit(&asoc->outqueue, t, SCTP_RTXR_PMTUD);
}

void sctp_icmp_redirect(struct sock *sk, struct sctp_transport *t,
                        struct sk_buff *skb)
{
        struct dst_entry *dst;

        if (sock_owned_by_user(sk) || !t)
                return;
        dst = sctp_transport_dst_check(t);
        if (dst)
                dst->ops->redirect(dst, sk, skb);
}

/*
 * SCTP Implementer's Guide, 2.37 ICMP handling procedures
 *
 * ICMP8) If the ICMP code is a "Unrecognized next header type encountered"
 *        or a "Protocol Unreachable" treat this message as an abort
 *        with the T bit set.
 *
 * This function sends an event to the state machine, which will abort the
 * association.
 *
 */
void sctp_icmp_proto_unreachable(struct sock *sk,
                           struct sctp_association *asoc,
                           struct sctp_transport *t)
{
        if (sock_owned_by_user(sk)) {
                if (timer_pending(&t->proto_unreach_timer))
                        return;
                else {
                        if (!mod_timer(&t->proto_unreach_timer,
                                                jiffies + (HZ/20)))
                                sctp_transport_hold(t);
                }
        } else {
                struct net *net = sock_net(sk);

                pr_debug("%s: unrecognized next header type "
                         "encountered!\n", __func__);

                if (del_timer(&t->proto_unreach_timer))
                        sctp_transport_put(t);

                sctp_do_sm(net, SCTP_EVENT_T_OTHER,
                           SCTP_ST_OTHER(SCTP_EVENT_ICMP_PROTO_UNREACH),
                           asoc->state, asoc->ep, asoc, t,
                           GFP_ATOMIC);
        }
}

/* Common lookup code for icmp/icmpv6 error handler. */
struct sock *sctp_err_lookup(struct net *net, int family, struct sk_buff *skb,
                             struct sctphdr *sctphdr,
                             struct sctp_association **app,
                             struct sctp_transport **tpp)
{
        struct sctp_init_chunk *chunkhdr, _chunkhdr;
        union sctp_addr saddr;
        union sctp_addr daddr;
        struct sctp_af *af;
        struct sock *sk = NULL;
        struct sctp_association *asoc;
        struct sctp_transport *transport = NULL;
        __u32 vtag = ntohl(sctphdr->vtag);

        *app = NULL; *tpp = NULL;

        af = sctp_get_af_specific(family);
        if (unlikely(!af)) {
                return NULL;
        }

        /* Initialize local addresses for lookups. */
        af->from_skb(&saddr, skb, 1);
        af->from_skb(&daddr, skb, 0);

        /* Look for an association that matches the incoming ICMP error
         * packet.
         */
        asoc = __sctp_lookup_association(net, &saddr, &daddr, &transport);
        if (!asoc)
                return NULL;

        sk = asoc->base.sk;

        /* RFC 4960, Appendix C. ICMP Handling
         *
         * ICMP6) An implementation MUST validate that the Verification Tag
         * contained in the ICMP message matches the Verification Tag of
         * the peer.  If the Verification Tag is not 0 and does NOT
         * match, discard the ICMP message.  If it is 0 and the ICMP
         * message contains enough bytes to verify that the chunk type is
         * an INIT chunk and that the Initiate Tag matches the tag of the
         * peer, continue with ICMP7.  If the ICMP message is too short
         * or the chunk type or the Initiate Tag does not match, silently
         * discard the packet.
         */
        if (vtag == 0) {
                /* chunk header + first 4 octects of init header */
                chunkhdr = skb_header_pointer(skb, skb_transport_offset(skb) +
                                              sizeof(struct sctphdr),
                                              sizeof(struct sctp_chunkhdr) +
                                              sizeof(__be32), &_chunkhdr);
                if (!chunkhdr ||
                    chunkhdr->chunk_hdr.type != SCTP_CID_INIT ||
                    ntohl(chunkhdr->init_hdr.init_tag) != asoc->c.my_vtag)
                        goto out;

        } else if (vtag != asoc->c.peer_vtag) {
                goto out;
        }

        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(net, LINUX_MIB_LOCKDROPPEDICMPS);

        *app = asoc;
        *tpp = transport;
        return sk;

out:
        sctp_transport_put(transport);
        return NULL;
}

/* Common cleanup code for icmp/icmpv6 error handler. */
void sctp_err_finish(struct sock *sk, struct sctp_transport *t)
        __releases(&((__sk)->sk_lock.slock))
{
        bh_unlock_sock(sk);
        sctp_transport_put(t);
}

static void sctp_v4_err_handle(struct sctp_transport *t, struct sk_buff *skb,
                               __u8 type, __u8 code, __u32 info)
{
        struct sctp_association *asoc = t->asoc;
        struct sock *sk = asoc->base.sk;
        int err = 0;

        switch (type) {
        case ICMP_PARAMETERPROB:
                err = EPROTO;
                break;
        case ICMP_DEST_UNREACH:
                if (code > NR_ICMP_UNREACH)
                        return;
                if (code == ICMP_FRAG_NEEDED) {
                        sctp_icmp_frag_needed(sk, asoc, t, SCTP_TRUNC4(info));
                        return;
                }
                if (code == ICMP_PROT_UNREACH) {
                        sctp_icmp_proto_unreachable(sk, asoc, t);
                        return;
                }
                err = icmp_err_convert[code].errno;
                break;
        case ICMP_TIME_EXCEEDED:
                if (code == ICMP_EXC_FRAGTIME)
                        return;

                err = EHOSTUNREACH;
                break;
        case ICMP_REDIRECT:
                sctp_icmp_redirect(sk, t, skb);
                return;
        default:
                return;
        }
        if (!sock_owned_by_user(sk) && inet_sk(sk)->recverr) {
                sk->sk_err = err;
                sk_error_report(sk);
        } else {  /* Only an error on timeout */
                sk->sk_err_soft = 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 sctp 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.
 *
 */
int sctp_v4_err(struct sk_buff *skb, __u32 info)
{
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        const int type = icmp_hdr(skb)->type;
        const int code = icmp_hdr(skb)->code;
        struct net *net = dev_net(skb->dev);
        struct sctp_transport *transport;
        struct sctp_association *asoc;
        __u16 saveip, savesctp;
        struct sock *sk;

        /* Fix up skb to look at the embedded net header. */
        saveip = skb->network_header;
        savesctp = skb->transport_header;
        skb_reset_network_header(skb);
        skb_set_transport_header(skb, iph->ihl * 4);
        sk = sctp_err_lookup(net, AF_INET, skb, sctp_hdr(skb), &asoc, &transport);
        /* Put back, the original values. */
        skb->network_header = saveip;
        skb->transport_header = savesctp;
        if (!sk) {
                __ICMP_INC_STATS(net, ICMP_MIB_INERRORS);
                return -ENOENT;
        }

        sctp_v4_err_handle(transport, skb, type, code, info);
        sctp_err_finish(sk, transport);

        return 0;
}

int sctp_udp_v4_err(struct sock *sk, struct sk_buff *skb)
{
        struct net *net = dev_net(skb->dev);
        struct sctp_association *asoc;
        struct sctp_transport *t;
        struct icmphdr *hdr;
        __u32 info = 0;

        skb->transport_header += sizeof(struct udphdr);
        sk = sctp_err_lookup(net, AF_INET, skb, sctp_hdr(skb), &asoc, &t);
        if (!sk) {
                __ICMP_INC_STATS(net, ICMP_MIB_INERRORS);
                return -ENOENT;
        }

        skb->transport_header -= sizeof(struct udphdr);
        hdr = (struct icmphdr *)(skb_network_header(skb) - sizeof(struct icmphdr));
        if (hdr->type == ICMP_REDIRECT) {
                /* can't be handled without outer iphdr known, leave it to udp_err */
                sctp_err_finish(sk, t);
                return 0;
        }
        if (hdr->type == ICMP_DEST_UNREACH && hdr->code == ICMP_FRAG_NEEDED)
                info = ntohs(hdr->un.frag.mtu);
        sctp_v4_err_handle(t, skb, hdr->type, hdr->code, info);

        sctp_err_finish(sk, t);
        return 1;
}

/*
 * RFC 2960, 8.4 - Handle "Out of the blue" Packets.
 *
 * This function scans all the chunks in the OOTB packet to determine if
 * the packet should be discarded right away.  If a response might be needed
 * for this packet, or, if further processing is possible, the packet will
 * be queued to a proper inqueue for the next phase of handling.
 *
 * Output:
 * Return 0 - If further processing is needed.
 * Return 1 - If the packet can be discarded right away.
 */
static int sctp_rcv_ootb(struct sk_buff *skb)
{
        struct sctp_chunkhdr *ch, _ch;
        int ch_end, offset = 0;

        /* Scan through all the chunks in the packet.  */
        do {
                /* Make sure we have at least the header there */
                if (offset + sizeof(_ch) > skb->len)
                        break;

                ch = skb_header_pointer(skb, offset, sizeof(*ch), &_ch);

                /* Break out if chunk length is less then minimal. */
                if (ntohs(ch->length) < sizeof(_ch))
                        break;

                ch_end = offset + SCTP_PAD4(ntohs(ch->length));
                if (ch_end > skb->len)
                        break;

                /* RFC 8.4, 2) If the OOTB packet contains an ABORT chunk, the
                 * receiver MUST silently discard the OOTB packet and take no
                 * further action.
                 */
                if (SCTP_CID_ABORT == ch->type)
                        goto discard;

                /* RFC 8.4, 6) If the packet contains a SHUTDOWN COMPLETE
                 * chunk, the receiver should silently discard the packet
                 * and take no further action.
                 */
                if (SCTP_CID_SHUTDOWN_COMPLETE == ch->type)
                        goto discard;

                /* RFC 4460, 2.11.2
                 * This will discard packets with INIT chunk bundled as
                 * subsequent chunks in the packet.  When INIT is first,
                 * the normal INIT processing will discard the chunk.
                 */
                if (SCTP_CID_INIT == ch->type && (void *)ch != skb->data)
                        goto discard;

                offset = ch_end;
        } while (ch_end < skb->len);

        return 0;

discard:
        return 1;
}

/* Insert endpoint into the hash table.  */
static int __sctp_hash_endpoint(struct sctp_endpoint *ep)
{
        struct sock *sk = ep->base.sk;
        struct net *net = sock_net(sk);
        struct sctp_hashbucket *head;
        struct sctp_ep_common *epb;

        epb = &ep->base;
        epb->hashent = sctp_ep_hashfn(net, epb->bind_addr.port);
        head = &sctp_ep_hashtable[epb->hashent];

        if (sk->sk_reuseport) {
                bool any = sctp_is_ep_boundall(sk);
                struct sctp_ep_common *epb2;
                struct list_head *list;
                int cnt = 0, err = 1;

                list_for_each(list, &ep->base.bind_addr.address_list)
                        cnt++;

                sctp_for_each_hentry(epb2, &head->chain) {
                        struct sock *sk2 = epb2->sk;

                        if (!net_eq(sock_net(sk2), net) || sk2 == sk ||
                            !uid_eq(sock_i_uid(sk2), sock_i_uid(sk)) ||
                            !sk2->sk_reuseport)
                                continue;

                        err = sctp_bind_addrs_check(sctp_sk(sk2),
                                                    sctp_sk(sk), cnt);
                        if (!err) {
                                err = reuseport_add_sock(sk, sk2, any);
                                if (err)
                                        return err;
                                break;
                        } else if (err < 0) {
                                return err;
                        }
                }

                if (err) {
                        err = reuseport_alloc(sk, any);
                        if (err)
                                return err;
                }
        }

        write_lock(&head->lock);
        hlist_add_head(&epb->node, &head->chain);
        write_unlock(&head->lock);
        return 0;
}

/* Add an endpoint to the hash. Local BH-safe. */
int sctp_hash_endpoint(struct sctp_endpoint *ep)
{
        int err;

        local_bh_disable();
        err = __sctp_hash_endpoint(ep);
        local_bh_enable();

        return err;
}

/* Remove endpoint from the hash table.  */
static void __sctp_unhash_endpoint(struct sctp_endpoint *ep)
{
        struct sock *sk = ep->base.sk;
        struct sctp_hashbucket *head;
        struct sctp_ep_common *epb;

        epb = &ep->base;

        epb->hashent = sctp_ep_hashfn(sock_net(sk), epb->bind_addr.port);

        head = &sctp_ep_hashtable[epb->hashent];

        if (rcu_access_pointer(sk->sk_reuseport_cb))
                reuseport_detach_sock(sk);

        write_lock(&head->lock);
        hlist_del_init(&epb->node);
        write_unlock(&head->lock);
}

/* Remove endpoint from the hash.  Local BH-safe. */
void sctp_unhash_endpoint(struct sctp_endpoint *ep)
{
        local_bh_disable();
        __sctp_unhash_endpoint(ep);
        local_bh_enable();
}

static inline __u32 sctp_hashfn(const struct net *net, __be16 lport,
                                const union sctp_addr *paddr, __u32 seed)
{
        __u32 addr;

        if (paddr->sa.sa_family == AF_INET6)
                addr = jhash(&paddr->v6.sin6_addr, 16, seed);
        else
                addr = (__force __u32)paddr->v4.sin_addr.s_addr;

        return  jhash_3words(addr, ((__force __u32)paddr->v4.sin_port) << 16 |
                             (__force __u32)lport, net_hash_mix(net), seed);
}

/* Look up an endpoint. */
static struct sctp_endpoint *__sctp_rcv_lookup_endpoint(
                                        struct net *net, struct sk_buff *skb,
                                        const union sctp_addr *laddr,
                                        const union sctp_addr *paddr)
{
        struct sctp_hashbucket *head;
        struct sctp_ep_common *epb;
        struct sctp_endpoint *ep;
        struct sock *sk;
        __be16 lport;
        int hash;

        lport = laddr->v4.sin_port;
        hash = sctp_ep_hashfn(net, ntohs(lport));
        head = &sctp_ep_hashtable[hash];
        read_lock(&head->lock);
        sctp_for_each_hentry(epb, &head->chain) {
                ep = sctp_ep(epb);
                if (sctp_endpoint_is_match(ep, net, laddr))
                        goto hit;
        }

        ep = sctp_sk(net->sctp.ctl_sock)->ep;

hit:
        sk = ep->base.sk;
        if (sk->sk_reuseport) {
                __u32 phash = sctp_hashfn(net, lport, paddr, 0);

                sk = reuseport_select_sock(sk, phash, skb,
                                           sizeof(struct sctphdr));
                if (sk)
                        ep = sctp_sk(sk)->ep;
        }
        sctp_endpoint_hold(ep);
        read_unlock(&head->lock);
        return ep;
}

/* rhashtable for transport */
struct sctp_hash_cmp_arg {
        const union sctp_addr   *paddr;
        const struct net        *net;
        __be16                  lport;
};

static inline int sctp_hash_cmp(struct rhashtable_compare_arg *arg,
                                const void *ptr)
{
        struct sctp_transport *t = (struct sctp_transport *)ptr;
        const struct sctp_hash_cmp_arg *x = arg->key;
        int err = 1;

        if (!sctp_cmp_addr_exact(&t->ipaddr, x->paddr))
                return err;
        if (!sctp_transport_hold(t))
                return err;

        if (!net_eq(t->asoc->base.net, x->net))
                goto out;
        if (x->lport != htons(t->asoc->base.bind_addr.port))
                goto out;

        err = 0;
out:
        sctp_transport_put(t);
        return err;
}

static inline __u32 sctp_hash_obj(const void *data, u32 len, u32 seed)
{
        const struct sctp_transport *t = data;

        return sctp_hashfn(t->asoc->base.net,
                           htons(t->asoc->base.bind_addr.port),
                           &t->ipaddr, seed);
}

static inline __u32 sctp_hash_key(const void *data, u32 len, u32 seed)
{
        const struct sctp_hash_cmp_arg *x = data;

        return sctp_hashfn(x->net, x->lport, x->paddr, seed);
}

static const struct rhashtable_params sctp_hash_params = {
        .head_offset            = offsetof(struct sctp_transport, node),
        .hashfn                 = sctp_hash_key,
        .obj_hashfn             = sctp_hash_obj,
        .obj_cmpfn              = sctp_hash_cmp,
        .automatic_shrinking    = true,
};

int sctp_transport_hashtable_init(void)
{
        return rhltable_init(&sctp_transport_hashtable, &sctp_hash_params);
}

void sctp_transport_hashtable_destroy(void)
{
        rhltable_destroy(&sctp_transport_hashtable);
}

int sctp_hash_transport(struct sctp_transport *t)
{
        struct sctp_transport *transport;
        struct rhlist_head *tmp, *list;
        struct sctp_hash_cmp_arg arg;
        int err;

        if (t->asoc->temp)
                return 0;

        arg.net   = t->asoc->base.net;
        arg.paddr = &t->ipaddr;
        arg.lport = htons(t->asoc->base.bind_addr.port);

        rcu_read_lock();
        list = rhltable_lookup(&sctp_transport_hashtable, &arg,
                               sctp_hash_params);

        rhl_for_each_entry_rcu(transport, tmp, list, node)
                if (transport->asoc->ep == t->asoc->ep) {
                        rcu_read_unlock();
                        return -EEXIST;
                }
        rcu_read_unlock();

        err = rhltable_insert_key(&sctp_transport_hashtable, &arg,
                                  &t->node, sctp_hash_params);
        if (err)
                pr_err_once("insert transport fail, errno %d\n", err);

        return err;
}

void sctp_unhash_transport(struct sctp_transport *t)
{
        if (t->asoc->temp)
                return;

        rhltable_remove(&sctp_transport_hashtable, &t->node,
                        sctp_hash_params);
}

/* return a transport with holding it */
struct sctp_transport *sctp_addrs_lookup_transport(
                                struct net *net,

                                const union sctp_addr *laddr,
                                const union sctp_addr *paddr)
{
        struct rhlist_head *tmp, *list;
        struct sctp_transport *t;
        struct sctp_hash_cmp_arg arg = {
                .paddr = paddr,
                .net   = net,
                .lport = laddr->v4.sin_port,
        };

        list = rhltable_lookup(&sctp_transport_hashtable, &arg,
                               sctp_hash_params);

        rhl_for_each_entry_rcu(t, tmp, list, node) {
                if (!sctp_transport_hold(t))
                        continue;

                if (sctp_bind_addr_match(&t->asoc->base.bind_addr,
                                         laddr, sctp_sk(t->asoc->base.sk)))
                        return t;
                sctp_transport_put(t);
        }

        return NULL;
}

/* return a transport without holding it, as it's only used under sock lock */
struct sctp_transport *sctp_epaddr_lookup_transport(
                                const struct sctp_endpoint *ep,
                                const union sctp_addr *paddr)
{
        struct rhlist_head *tmp, *list;
        struct sctp_transport *t;
        struct sctp_hash_cmp_arg arg = {
                .paddr = paddr,
                .net   = ep->base.net,
                .lport = htons(ep->base.bind_addr.port),
        };

        list = rhltable_lookup(&sctp_transport_hashtable, &arg,
                               sctp_hash_params);

        rhl_for_each_entry_rcu(t, tmp, list, node)
                if (ep == t->asoc->ep)
                        return t;

        return NULL;
}

/* Look up an association. */
static struct sctp_association *__sctp_lookup_association(
                                        struct net *net,
                                        const union sctp_addr *local,
                                        const union sctp_addr *peer,
                                        struct sctp_transport **pt)
{
        struct sctp_transport *t;
        struct sctp_association *asoc = NULL;

        t = sctp_addrs_lookup_transport(net, local, peer);
        if (!t)
                goto out;

        asoc = t->asoc;
        *pt = t;

out:
        return asoc;
}

/* Look up an association. protected by RCU read lock */
static
struct sctp_association *sctp_lookup_association(struct net *net,
                                                 const union sctp_addr *laddr,
                                                 const union sctp_addr *paddr,
                                                 struct sctp_transport **transportp)
{
        struct sctp_association *asoc;

        rcu_read_lock();
        asoc = __sctp_lookup_association(net, laddr, paddr, transportp);
        rcu_read_unlock();

        return asoc;
}

/* Is there an association matching the given local and peer addresses? */
bool sctp_has_association(struct net *net,
                          const union sctp_addr *laddr,
                          const union sctp_addr *paddr)
{
        struct sctp_transport *transport;

        if (sctp_lookup_association(net, laddr, paddr, &transport)) {
                sctp_transport_put(transport);
                return true;
        }

        return false;
}

/*
 * SCTP Implementors Guide, 2.18 Handling of address
 * parameters within the INIT or INIT-ACK.
 *
 * D) When searching for a matching TCB upon reception of an INIT
 *    or INIT-ACK chunk the receiver SHOULD use not only the
 *    source address of the packet (containing the INIT or
 *    INIT-ACK) but the receiver SHOULD also use all valid
 *    address parameters contained within the chunk.
 *
 * 2.18.3 Solution description
 *
 * This new text clearly specifies to an implementor the need
 * to look within the INIT or INIT-ACK. Any implementation that
 * does not do this, may not be able to establish associations
 * in certain circumstances.
 *
 */
static struct sctp_association *__sctp_rcv_init_lookup(struct net *net,
        struct sk_buff *skb,
        const union sctp_addr *laddr, struct sctp_transport **transportp)
{
        struct sctp_association *asoc;
        union sctp_addr addr;
        union sctp_addr *paddr = &addr;
        struct sctphdr *sh = sctp_hdr(skb);
        union sctp_params params;
        struct sctp_init_chunk *init;
        struct sctp_af *af;

        /*
         * This code will NOT touch anything inside the chunk--it is
         * strictly READ-ONLY.
         *
         * RFC 2960 3  SCTP packet Format
         *
         * Multiple chunks can be bundled into one SCTP packet up to
         * the MTU size, except for the INIT, INIT ACK, and SHUTDOWN
         * COMPLETE chunks.  These chunks MUST NOT be bundled with any
         * other chunk in a packet.  See Section 6.10 for more details
         * on chunk bundling.
         */

        /* Find the start of the TLVs and the end of the chunk.  This is
         * the region we search for address parameters.
         */
        init = (struct sctp_init_chunk *)skb->data;

        /* Walk the parameters looking for embedded addresses. */
        sctp_walk_params(params, init, init_hdr.params) {

                /* Note: Ignoring hostname addresses. */
                af = sctp_get_af_specific(param_type2af(params.p->type));
                if (!af)
                        continue;

                if (!af->from_addr_param(paddr, params.addr, sh->source, 0))
                        continue;

                asoc = __sctp_lookup_association(net, laddr, paddr, transportp);
                if (asoc)
                        return asoc;
        }

        return NULL;
}

/* ADD-IP, Section 5.2
 * When an endpoint receives an ASCONF Chunk from the remote peer
 * special procedures may be needed to identify the association the
 * ASCONF Chunk is associated with. To properly find the association
 * the following procedures SHOULD be followed:
 *
 * D2) If the association is not found, use the address found in the
 * Address Parameter TLV combined with the port number found in the
 * SCTP common header. If found proceed to rule D4.
 *
 * D2-ext) If more than one ASCONF Chunks are packed together, use the
 * address found in the ASCONF Address Parameter TLV of each of the
 * subsequent ASCONF Chunks. If found, proceed to rule D4.
 */
static struct sctp_association *__sctp_rcv_asconf_lookup(
                                        struct net *net,
                                        struct sctp_chunkhdr *ch,
                                        const union sctp_addr *laddr,
                                        __be16 peer_port,
                                        struct sctp_transport **transportp)
{
        struct sctp_addip_chunk *asconf = (struct sctp_addip_chunk *)ch;
        struct sctp_af *af;
        union sctp_addr_param *param;
        union sctp_addr paddr;

        if (ntohs(ch->length) < sizeof(*asconf) + sizeof(struct sctp_paramhdr))
                return NULL;

        /* Skip over the ADDIP header and find the Address parameter */
        param = (union sctp_addr_param *)(asconf + 1);

        af = sctp_get_af_specific(param_type2af(param->p.type));
        if (unlikely(!af))
                return NULL;

        if (!af->from_addr_param(&paddr, param, peer_port, 0))
                return NULL;

        return __sctp_lookup_association(net, laddr, &paddr, transportp);
}


/* SCTP-AUTH, Section 6.3:
*    If the receiver does not find a STCB for a packet containing an AUTH
*    chunk as the first chunk and not a COOKIE-ECHO chunk as the second
*    chunk, it MUST use the chunks after the AUTH chunk to look up an existing
*    association.
*
* This means that any chunks that can help us identify the association need
* to be looked at to find this association.
*/
static struct sctp_association *__sctp_rcv_walk_lookup(struct net *net,
                                      struct sk_buff *skb,
                                      const union sctp_addr *laddr,
                                      struct sctp_transport **transportp)
{
        struct sctp_association *asoc = NULL;
        struct sctp_chunkhdr *ch;
        int have_auth = 0;
        unsigned int chunk_num = 1;
        __u8 *ch_end;

        /* Walk through the chunks looking for AUTH or ASCONF chunks
         * to help us find the association.
         */
        ch = (struct sctp_chunkhdr *)skb->data;
        do {
                /* Break out if chunk length is less then minimal. */
                if (ntohs(ch->length) < sizeof(*ch))
                        break;

                ch_end = ((__u8 *)ch) + SCTP_PAD4(ntohs(ch->length));
                if (ch_end > skb_tail_pointer(skb))
                        break;

                switch (ch->type) {
                case SCTP_CID_AUTH:
                        have_auth = chunk_num;
                        break;

                case SCTP_CID_COOKIE_ECHO:
                        /* If a packet arrives containing an AUTH chunk as
                         * a first chunk, a COOKIE-ECHO chunk as the second
                         * chunk, and possibly more chunks after them, and
                         * the receiver does not have an STCB for that
                         * packet, then authentication is based on
                         * the contents of the COOKIE- ECHO chunk.
                         */
                        if (have_auth == 1 && chunk_num == 2)
                                return NULL;
                        break;

                case SCTP_CID_ASCONF:
                        if (have_auth || net->sctp.addip_noauth)
                                asoc = __sctp_rcv_asconf_lookup(
                                                net, ch, laddr,
                                                sctp_hdr(skb)->source,
                                                transportp);
                        break;
                default:
                        break;
                }

                if (asoc)
                        break;

                ch = (struct sctp_chunkhdr *)ch_end;
                chunk_num++;
        } while (ch_end + sizeof(*ch) < skb_tail_pointer(skb));

        return asoc;
}

/*
 * There are circumstances when we need to look inside the SCTP packet
 * for information to help us find the association.   Examples
 * include looking inside of INIT/INIT-ACK chunks or after the AUTH
 * chunks.
 */
static struct sctp_association *__sctp_rcv_lookup_harder(struct net *net,
                                      struct sk_buff *skb,
                                      const union sctp_addr *laddr,
                                      struct sctp_transport **transportp)
{
        struct sctp_chunkhdr *ch;

        /* We do not allow GSO frames here as we need to linearize and
         * then cannot guarantee frame boundaries. This shouldn't be an
         * issue as packets hitting this are mostly INIT or INIT-ACK and
         * those cannot be on GSO-style anyway.
         */
        if (skb_is_gso(skb) && skb_is_gso_sctp(skb))
                return NULL;

        ch = (struct sctp_chunkhdr *)skb->data;

        /* The code below will attempt to walk the chunk and extract
         * parameter information.  Before we do that, we need to verify
         * that the chunk length doesn't cause overflow.  Otherwise, we'll
         * walk off the end.
         */
        if (SCTP_PAD4(ntohs(ch->length)) > skb->len)
                return NULL;

        /* If this is INIT/INIT-ACK look inside the chunk too. */
        if (ch->type == SCTP_CID_INIT || ch->type == SCTP_CID_INIT_ACK)
                return __sctp_rcv_init_lookup(net, skb, laddr, transportp);

        return __sctp_rcv_walk_lookup(net, skb, laddr, transportp);
}

/* Lookup an association for an inbound skb. */
static struct sctp_association *__sctp_rcv_lookup(struct net *net,
                                      struct sk_buff *skb,
                                      const union sctp_addr *paddr,
                                      const union sctp_addr *laddr,
                                      struct sctp_transport **transportp)
{
        struct sctp_association *asoc;

        asoc = __sctp_lookup_association(net, laddr, paddr, transportp);
        if (asoc)
                goto out;

        /* Further lookup for INIT/INIT-ACK packets.
         * SCTP Implementors Guide, 2.18 Handling of address
         * parameters within the INIT or INIT-ACK.
         */
        asoc = __sctp_rcv_lookup_harder(net, skb, laddr, transportp);
        if (asoc)
                goto out;

        if (paddr->sa.sa_family == AF_INET)
                pr_debug("sctp: asoc not found for src:%pI4:%d dst:%pI4:%d\n",
                         &laddr->v4.sin_addr, ntohs(laddr->v4.sin_port),
                         &paddr->v4.sin_addr, ntohs(paddr->v4.sin_port));
        else
                pr_debug("sctp: asoc not found for src:%pI6:%d dst:%pI6:%d\n",
                         &laddr->v6.sin6_addr, ntohs(laddr->v6.sin6_port),
                         &paddr->v6.sin6_addr, ntohs(paddr->v6.sin6_port));

out:
        return asoc;
}