cregit-Linux how code gets into the kernel

Release 4.8 net/dccp/ipv6.c

Directory: net/dccp
 *      DCCP over IPv6
 *      Linux INET6 implementation
 *      Based on net/dccp6/ipv6.c
 *      Arnaldo Carvalho de Melo <>
 *      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/module.h>
#include <linux/random.h>
#include <linux/slab.h>
#include <linux/xfrm.h>

#include <net/addrconf.h>
#include <net/inet_common.h>
#include <net/inet_hashtables.h>
#include <net/inet_sock.h>
#include <net/inet6_connection_sock.h>
#include <net/inet6_hashtables.h>
#include <net/ip6_route.h>
#include <net/ipv6.h>
#include <net/protocol.h>
#include <net/transp_v6.h>
#include <net/ip6_checksum.h>
#include <net/xfrm.h>
#include <net/secure_seq.h>

#include "dccp.h"
#include "ipv6.h"
#include "feat.h"

/* The per-net dccp.v6_ctl_sk is used for sending RSTs and ACKs */

static const struct inet_connection_sock_af_ops dccp_ipv6_mapped;

static const struct inet_connection_sock_af_ops dccp_ipv6_af_ops;

/* add pseudo-header to DCCP checksum stored in skb->csum */

static inline __sum16 dccp_v6_csum_finish(struct sk_buff *skb, const struct in6_addr *saddr, const struct in6_addr *daddr) { return csum_ipv6_magic(saddr, daddr, skb->len, IPPROTO_DCCP, skb->csum); }


arnaldo carvalho de meloarnaldo carvalho de melo3173.81%125.00%
gerrit renkergerrit renker819.05%125.00%
eric dumazeteric dumazet24.76%125.00%
al viroal viro12.38%125.00%

static inline void dccp_v6_send_check(struct sock *sk, struct sk_buff *skb) { struct ipv6_pinfo *np = inet6_sk(sk); struct dccp_hdr *dh = dccp_hdr(skb); dccp_csum_outgoing(skb); dh->dccph_checksum = dccp_v6_csum_finish(skb, &np->saddr, &sk->sk_v6_daddr); }


gerrit renkergerrit renker5996.72%150.00%
eric dumazeteric dumazet23.28%150.00%

static inline __u64 dccp_v6_init_sequence(struct sk_buff *skb) { return secure_dccpv6_sequence_number(ipv6_hdr(skb)->daddr.s6_addr32, ipv6_hdr(skb)->saddr.s6_addr32, dccp_hdr(skb)->dccph_dport, dccp_hdr(skb)->dccph_sport ); }


arnaldo carvalho de meloarnaldo carvalho de melo3981.25%240.00%
gerrit renkergerrit renker816.67%240.00%
david s. millerdavid s. miller12.08%120.00%

static void dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt, u8 type, u8 code, int offset, __be32 info) { const struct ipv6hdr *hdr = (const struct ipv6hdr *)skb->data; const struct dccp_hdr *dh = (struct dccp_hdr *)(skb->data + offset); struct dccp_sock *dp; struct ipv6_pinfo *np; struct sock *sk; int err; __u64 seq; struct net *net = dev_net(skb->dev); if (skb->len < offset + sizeof(*dh) || skb->len < offset + __dccp_basic_hdr_len(dh)) { __ICMP6_INC_STATS(net, __in6_dev_get(skb->dev), ICMP6_MIB_INERRORS); return; } sk = __inet6_lookup_established(net, &dccp_hashinfo, &hdr->daddr, dh->dccph_dport, &hdr->saddr, ntohs(dh->dccph_sport), inet6_iif(skb)); if (!sk) { __ICMP6_INC_STATS(net, __in6_dev_get(skb->dev), ICMP6_MIB_INERRORS); return; } if (sk->sk_state == DCCP_TIME_WAIT) { inet_twsk_put(inet_twsk(sk)); return; } seq = dccp_hdr_seq(dh); if (sk->sk_state == DCCP_NEW_SYN_RECV) return dccp_req_err(sk, seq); bh_lock_sock(sk); if (sock_owned_by_user(sk)) __NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS); if (sk->sk_state == DCCP_CLOSED) goto out; dp = dccp_sk(sk); if ((1 << sk->sk_state) & ~(DCCPF_REQUESTING | DCCPF_LISTEN) && !between48(seq, dp->dccps_awl, dp->dccps_awh)) { __NET_INC_STATS(net, LINUX_MIB_OUTOFWINDOWICMPS); goto out; } np = inet6_sk(sk); if (type == NDISC_REDIRECT) { struct dst_entry *dst = __sk_dst_check(sk, np->dst_cookie); if (dst) dst->ops->redirect(dst, sk, skb); goto out; } if (type == ICMPV6_PKT_TOOBIG) { struct dst_entry *dst = NULL; if (!ip6_sk_accept_pmtu(sk)) goto out; if (sock_owned_by_user(sk)) goto out; if ((1 << sk->sk_state) & (DCCPF_LISTEN | DCCPF_CLOSED)) goto out; dst = inet6_csk_update_pmtu(sk, ntohl(info)); if (!dst) goto out; if (inet_csk(sk)->icsk_pmtu_cookie > dst_mtu(dst)) dccp_sync_mss(sk, dst_mtu(dst)); goto out; } icmpv6_err_convert(type, code, &err); /* Might be for an request_sock */ switch (sk->sk_state) { case DCCP_REQUESTING: case DCCP_RESPOND: /* Cannot happen. It can, it SYNs are crossed. --ANK */ if (!sock_owned_by_user(sk)) { __DCCP_INC_STATS(DCCP_MIB_ATTEMPTFAILS); sk->sk_err = err; /* * Wake people up to see the error * (see connect in sock.c) */ sk->sk_error_report(sk); dccp_done(sk); } else sk->sk_err_soft = err; goto out; } if (!sock_owned_by_user(sk) && np->recverr) { sk->sk_err = err; sk->sk_error_report(sk); } else sk->sk_err_soft = err; out: bh_unlock_sock(sk); sock_put(sk); }


gerrit renkergerrit renker23039.32%14.35%
arnaldo carvalho de meloarnaldo carvalho de melo14224.27%313.04%
wei yongjunwei yongjun9315.90%28.70%
david s. millerdavid s. miller457.69%417.39%
eric dumazeteric dumazet355.98%521.74%
pavel emelianovpavel emelianov203.42%417.39%
hannes frederic sowahannes frederic sowa111.88%14.35%
denis v. lunevdenis v. lunev40.68%14.35%
duan jiongduan jiong30.51%14.35%
brian haleybrian haley20.34%14.35%

static int dccp_v6_send_response(const struct sock *sk, struct request_sock *req) { struct inet_request_sock *ireq = inet_rsk(req); struct ipv6_pinfo *np = inet6_sk(sk); struct sk_buff *skb; struct in6_addr *final_p, final; struct flowi6 fl6; int err = -1; struct dst_entry *dst; memset(&fl6, 0, sizeof(fl6)); fl6.flowi6_proto = IPPROTO_DCCP; fl6.daddr = ireq->ir_v6_rmt_addr; fl6.saddr = ireq->ir_v6_loc_addr; fl6.flowlabel = 0; fl6.flowi6_oif = ireq->ir_iif; fl6.fl6_dport = ireq->ir_rmt_port; fl6.fl6_sport = htons(ireq->ir_num); security_req_classify_flow(req, flowi6_to_flowi(&fl6)); rcu_read_lock(); final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final); rcu_read_unlock(); dst = ip6_dst_lookup_flow(sk, &fl6, final_p); if (IS_ERR(dst)) { err = PTR_ERR(dst); dst = NULL; goto done; } skb = dccp_make_response(sk, dst, req); if (skb != NULL) { struct dccp_hdr *dh = dccp_hdr(skb); struct ipv6_txoptions *opt; dh->dccph_checksum = dccp_v6_csum_finish(skb, &ireq->ir_v6_loc_addr, &ireq->ir_v6_rmt_addr); fl6.daddr = ireq->ir_v6_rmt_addr; rcu_read_lock(); opt = ireq->ipv6_opt; if (!opt) opt = rcu_dereference(np->opt); err = ip6_xmit(sk, skb, &fl6, opt, np->tclass); rcu_read_unlock(); err = net_xmit_eval(err); } done: dst_release(dst); return err; }


gerrit renkergerrit renker10030.86%315.00%
arnaldo carvalho de meloarnaldo carvalho de melo9529.32%210.00%
david s. millerdavid s. miller4313.27%315.00%
eric dumazeteric dumazet4212.96%525.00%
huw davieshuw davies257.72%15.00%
arnaud ebalardarnaud ebalard61.85%15.00%
denis v. lunevdenis v. lunev51.54%15.00%
alexey dobriyanalexey dobriyan30.93%15.00%
li rongqingli rongqing20.62%15.00%
hideaki yoshifujihideaki yoshifuji20.62%15.00%
venkat yekkiralavenkat yekkirala10.31%15.00%

static void dccp_v6_reqsk_destructor(struct request_sock *req) { dccp_feat_list_purge(&dccp_rsk(req)->dreq_featneg); kfree(inet_rsk(req)->ipv6_opt); kfree_skb(inet_rsk(req)->pktopts); }


gerrit renkergerrit renker2559.52%240.00%
huw davieshuw davies1023.81%120.00%
arnaldo carvalho de meloarnaldo carvalho de melo614.29%120.00%
eric dumazeteric dumazet12.38%120.00%

static void dccp_v6_ctl_send_reset(const struct sock *sk, struct sk_buff *rxskb) { const struct ipv6hdr *rxip6h; struct sk_buff *skb; struct flowi6 fl6; struct net *net = dev_net(skb_dst(rxskb)->dev); struct sock *ctl_sk = net->dccp.v6_ctl_sk; struct dst_entry *dst; if (dccp_hdr(rxskb)->dccph_type == DCCP_PKT_RESET) return; if (!ipv6_unicast_destination(rxskb)) return; skb = dccp_ctl_make_reset(ctl_sk, rxskb); if (skb == NULL) return; rxip6h = ipv6_hdr(rxskb); dccp_hdr(skb)->dccph_checksum = dccp_v6_csum_finish(skb, &rxip6h->saddr, &rxip6h->daddr); memset(&fl6, 0, sizeof(fl6)); fl6.daddr = rxip6h->saddr; fl6.saddr = rxip6h->daddr; fl6.flowi6_proto = IPPROTO_DCCP; fl6.flowi6_oif = inet6_iif(rxskb); fl6.fl6_dport = dccp_hdr(skb)->dccph_dport; fl6.fl6_sport = dccp_hdr(skb)->dccph_sport; security_skb_classify_flow(rxskb, flowi6_to_flowi(&fl6)); /* sk = NULL, but it is safe for now. RST socket required. */ dst = ip6_dst_lookup_flow(ctl_sk, &fl6, NULL); if (!IS_ERR(dst)) { skb_dst_set(skb, dst); ip6_xmit(ctl_sk, skb, &fl6, NULL, 0); DCCP_INC_STATS(DCCP_MIB_OUTSEGS); DCCP_INC_STATS(DCCP_MIB_OUTRSTS); return; } kfree_skb(skb); }


gerrit renkergerrit renker11543.23%421.05%
arnaldo carvalho de meloarnaldo carvalho de melo6022.56%210.53%
david s. millerdavid s. miller3212.03%315.79%
pavel emelianovpavel emelianov269.77%210.53%
eric dumazeteric dumazet217.89%526.32%
hideaki yoshifujihideaki yoshifuji51.88%15.26%
venkat yekkiralavenkat yekkirala51.88%15.26%
alexey dobriyanalexey dobriyan20.75%15.26%

static struct request_sock_ops dccp6_request_sock_ops = { .family = AF_INET6, .obj_size = sizeof(struct dccp6_request_sock), .rtx_syn_ack = dccp_v6_send_response, .send_ack = dccp_reqsk_send_ack, .destructor = dccp_v6_reqsk_destructor, .send_reset = dccp_v6_ctl_send_reset, .syn_ack_timeout = dccp_syn_ack_timeout, };
static int dccp_v6_conn_request(struct sock *sk, struct sk_buff *skb) { struct request_sock *req; struct dccp_request_sock *dreq; struct inet_request_sock *ireq; struct ipv6_pinfo *np = inet6_sk(sk); const __be32 service = dccp_hdr_request(skb)->dccph_req_service; struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb); if (skb->protocol == htons(ETH_P_IP)) return dccp_v4_conn_request(sk, skb); if (!ipv6_unicast_destination(skb)) 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; } /* * There are no SYN attacks on IPv6, yet... */ dcb->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY; if (inet_csk_reqsk_queue_is_full(sk)) goto drop; if (sk_acceptq_is_full(sk) && inet_csk_reqsk_queue_young(sk) > 1) goto drop; req = inet_reqsk_alloc(&dccp6_request_sock_ops, sk, true); 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); ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; ireq->ireq_family = AF_INET6; if (ipv6_opt_accepted(sk, skb, IP6CB(skb)) || np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { atomic_inc(&skb->users); ireq->pktopts = skb; } ireq->ir_iif = sk->sk_bound_dev_if; /* So that link locals have meaning */ if (!sk->sk_bound_dev_if && ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) ireq->ir_iif = inet6_iif(skb); /* * 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_v6_init_sequence(skb); dreq->dreq_gss = dreq->dreq_iss; dreq->dreq_service = service; if (dccp_v6_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(DCCP_MIB_ATTEMPTFAILS); return -1; }


gerrit renkergerrit renker28565.67%525.00%
arnaldo carvalho de meloarnaldo carvalho de melo9321.43%420.00%
eric dumazeteric dumazet327.37%735.00%
samuel jerosamuel jero173.92%15.00%
venkat yekkiralavenkat yekkirala40.92%15.00%
alexey dobriyanalexey dobriyan20.46%15.00%
octavian purdilaoctavian purdila10.23%15.00%

static struct sock *dccp_v6_request_recv_sock(const struct sock *sk, struct sk_buff *skb, struct request_sock *req, struct dst_entry *dst, struct request_sock *req_unhash, bool *own_req) { struct inet_request_sock *ireq = inet_rsk(req); struct ipv6_pinfo *newnp; const struct ipv6_pinfo *np = inet6_sk(sk); struct ipv6_txoptions *opt; struct inet_sock *newinet; struct dccp6_sock *newdp6; struct sock *newsk; if (skb->protocol == htons(ETH_P_IP)) { /* * v6 mapped */ newsk = dccp_v4_request_recv_sock(sk, skb, req, dst, req_unhash, own_req); if (newsk == NULL) return NULL; newdp6 = (struct dccp6_sock *)newsk; newinet = inet_sk(newsk); newinet->pinet6 = &newdp6->inet6; newnp = inet6_sk(newsk); memcpy(newnp, np, sizeof(struct ipv6_pinfo)); newnp->saddr = newsk->sk_v6_rcv_saddr; inet_csk(newsk)->icsk_af_ops = &dccp_ipv6_mapped; newsk->sk_backlog_rcv = dccp_v4_do_rcv; newnp->pktoptions = NULL; newnp->opt = NULL; newnp->mcast_oif = inet6_iif(skb); newnp->mcast_hops = ipv6_hdr(skb)->hop_limit; /* * No need to charge this sock to the relevant IPv6 refcnt debug socks count * here, dccp_create_openreq_child now does this for us, see the comment in * that function for the gory details. -acme */ /* It is tricky place. Until this moment IPv4 tcp worked with IPv6 icsk.icsk_af_ops. Sync it now. */ dccp_sync_mss(newsk, inet_csk(newsk)->icsk_pmtu_cookie); return newsk; } if (sk_acceptq_is_full(sk)) goto out_overflow; if (!dst) { struct flowi6 fl6; dst = inet6_csk_route_req(sk, &fl6, req, IPPROTO_DCCP); if (!dst) goto out; } newsk = dccp_create_openreq_child(sk, req, skb); if (newsk == NULL) goto out_nonewsk; /* * No need to charge this sock to the relevant IPv6 refcnt debug socks * count here, dccp_create_openreq_child now does this for us, see the * comment in that function for the gory details. -acme */ ip6_dst_store(newsk, dst, NULL, NULL); newsk->sk_route_caps = dst->dev->features & ~(NETIF_F_IP_CSUM | NETIF_F_TSO); newdp6 = (struct dccp6_sock *)newsk; newinet = inet_sk(newsk); newinet->pinet6 = &newdp6->inet6; newnp = inet6_sk(newsk); memcpy(newnp, np, sizeof(struct ipv6_pinfo)); newsk->sk_v6_daddr = ireq->ir_v6_rmt_addr; newnp->saddr = ireq->ir_v6_loc_addr; newsk->sk_v6_rcv_saddr = ireq->ir_v6_loc_addr; newsk->sk_bound_dev_if = ireq->ir_iif; /* Now IPv6 options... First: no IPv4 options. */ newinet->inet_opt = NULL; /* Clone RX bits */ newnp->rxopt.all = np->rxopt.all; newnp->pktoptions = NULL; newnp->opt = NULL; newnp->mcast_oif = inet6_iif(skb); newnp->mcast_hops = ipv6_hdr(skb)->hop_limit; /* * Clone native IPv6 options from listening socket (if any) * * Yes, keeping reference count would be much more clever, but we make * one more one thing there: reattach optmem to newsk. */ opt = ireq->ipv6_opt; if (!opt) opt = rcu_dereference(np->opt); if (opt) { opt = ipv6_dup_options(newsk, opt); RCU_INIT_POINTER(newnp->opt, opt); } inet_csk(newsk)->icsk_ext_hdr_len = 0; if (opt) inet_csk(newsk)->icsk_ext_hdr_len = opt->opt_nflen + opt->opt_flen; dccp_sync_mss(newsk, dst_mtu(dst)); newinet->inet_daddr = newinet->inet_saddr = LOOPBACK4_IPV6; newinet->inet_rcv_saddr = LOOPBACK4_IPV6; if (__inet_inherit_port(sk, newsk) < 0) { inet_csk_prepare_forced_close(newsk); dccp_done(newsk); goto out; } *own_req = inet_ehash_nolisten(newsk, req_to_sk(req_unhash)); /* Clone pktoptions received with SYN, if we own the req */ if (*own_req && ireq->pktopts) { newnp->pktoptions = skb_clone(ireq->pktopts, GFP_ATOMIC); consume_skb(ireq->pktopts); ireq->pktopts = NULL; if (newnp->pktoptions) skb_set_owner_r(newnp->pktoptions, newsk); } return newsk; out_overflow: __NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); out_nonewsk: dst_release(dst); out: __NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENDROPS); return NULL; }


gerrit renkergerrit renker27139.22%13.85%
arnaldo carvalho de meloarnaldo carvalho de melo21931.69%27.69%
eric dumazeteric dumazet13719.83%1350.00%
balazs scheidlerbalazs scheidler253.62%13.85%
huw davieshuw davies111.59%13.85%
pavel emelianovpavel emelianov101.45%13.85%
christoph paaschchristoph paasch60.87%13.85%
david s. millerdavid s. miller50.72%27.69%
alexey dobriyanalexey dobriyan30.43%13.85%
li rongqingli rongqing20.29%13.85%
brian haleybrian haley10.14%13.85%
hideaki yoshifujihideaki yoshifuji10.14%13.85%

/* The socket must have it's spinlock held when we get * here. * * We have a potential double-lock case here, so even when * doing backlog processing we use the BH locking scheme. * This is because we cannot sleep with the original spinlock * held. */
static int dccp_v6_do_rcv(struct sock *sk, struct sk_buff *skb) { struct ipv6_pinfo *np = inet6_sk(sk); struct sk_buff *opt_skb = NULL; /* Imagine: socket is IPv6. IPv4 packet arrives, goes to IPv4 receive handler and backlogged. From backlog it always goes here. Kerboom... Fortunately, dccp_rcv_established and rcv_established handle them correctly, but it is not case with dccp_v6_hnd_req and dccp_v6_ctl_send_reset(). --ANK */ if (skb->protocol == htons(ETH_P_IP)) return dccp_v4_do_rcv(sk, skb); if (sk_filter(sk, skb)) goto discard; /* * socket locking is here for SMP purposes as backlog rcv is currently * called with bh processing disabled. */ /* Do Stevens' IPV6_PKTOPTIONS. Yes, guys, it is the only place in our code, where we may make it not affecting IPv4. The rest of code is protocol independent, and I do not like idea to uglify IPv4. Actually, all the idea behind IPV6_PKTOPTIONS looks not very well thought. For now we latch options, received in the last packet, enqueued by tcp. Feel free to propose better solution. --ANK (980728) */ if (np->rxopt.all) /* * FIXME: Add handling of IPV6_PKTOPTIONS skb. See the comments below * (wrt ipv6_pktopions) and net/ipv6/tcp_ipv6.c for an example. */ opt_skb = skb_clone(skb, GFP_ATOMIC); if (sk->sk_state == DCCP_OPEN) { /* Fast path */ if (dccp_rcv_established(sk, skb, dccp_hdr(skb), skb->len)) goto reset; if (opt_skb) { /* XXX This is where we would goto ipv6_pktoptions. */ __kfree_skb(opt_skb); } 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 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 (dccp_rcv_state_process(sk, skb, dccp_hdr(skb), skb->len)) goto reset; if (opt_skb) { /* XXX This is where we would goto ipv6_pktoptions. */ __kfree_skb(opt_skb); } return 0; reset: dccp_v6_ctl_send_reset(sk, skb); discard: if (opt_skb != NULL) __kfree_skb(opt_skb); kfree_skb(skb); return 0; }


gerrit renkergerrit renker15577.89%240.00%
arnaldo carvalho de meloarnaldo carvalho de melo4120.60%120.00%
hideaki yoshifujihideaki yoshifuji31.51%240.00%

static int dccp_v6_rcv(struct sk_buff *skb) { const struct dccp_hdr *dh; bool refcounted; struct sock *sk; int min_cov; /* Step 1: Check header basics */ if (dccp_invalid_packet(skb)) goto discard_it; /* Step 1: If header checksum is incorrect, drop packet and return. */ if (dccp_v6_csum_finish(skb, &ipv6_hdr(skb)->saddr, &ipv6_hdr(skb)->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; if (dccp_packet_without_ack(skb)) DCCP_SKB_CB(skb)->dccpd_ack_seq