1526 lines
43 KiB
C
1526 lines
43 KiB
C
/*-
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* Copyright (c) 2001 McAfee, Inc.
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* Copyright (c) 2006 Andre Oppermann, Internet Business Solutions AG
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* All rights reserved.
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*
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* This software was developed for the FreeBSD Project by Jonathan Lemon
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* and McAfee Research, the Security Research Division of McAfee, Inc. under
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* DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
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* DARPA CHATS research program.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#include "opt_inet.h"
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#include "opt_inet6.h"
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#include "opt_ipsec.h"
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#include "opt_mac.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/kernel.h>
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#include <sys/sysctl.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/malloc.h>
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#include <sys/mac.h>
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#include <sys/mbuf.h>
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#include <sys/md5.h>
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#include <sys/proc.h> /* for proc0 declaration */
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#include <sys/random.h>
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#include <sys/socket.h>
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#include <sys/socketvar.h>
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#include <vm/uma.h>
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#include <net/if.h>
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#include <net/route.h>
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#include <netinet/in.h>
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#include <netinet/in_systm.h>
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#include <netinet/ip.h>
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#include <netinet/in_var.h>
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#include <netinet/in_pcb.h>
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#include <netinet/ip_var.h>
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#include <netinet/ip_options.h>
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#ifdef INET6
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#include <netinet/ip6.h>
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#include <netinet/icmp6.h>
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#include <netinet6/nd6.h>
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#include <netinet6/ip6_var.h>
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#include <netinet6/in6_pcb.h>
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#endif
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#include <netinet/tcp.h>
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#include <netinet/tcp_fsm.h>
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#include <netinet/tcp_seq.h>
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#include <netinet/tcp_timer.h>
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#include <netinet/tcp_var.h>
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#ifdef INET6
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#include <netinet6/tcp6_var.h>
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#endif
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#ifdef IPSEC
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#include <netinet6/ipsec.h>
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#ifdef INET6
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#include <netinet6/ipsec6.h>
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#endif
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#endif /*IPSEC*/
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#ifdef FAST_IPSEC
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#include <netipsec/ipsec.h>
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#ifdef INET6
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#include <netipsec/ipsec6.h>
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#endif
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#include <netipsec/key.h>
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#endif /*FAST_IPSEC*/
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#include <machine/in_cksum.h>
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static int tcp_syncookies = 1;
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SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
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&tcp_syncookies, 0,
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"Use TCP SYN cookies if the syncache overflows");
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static int tcp_syncookiesonly = 0;
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SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
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&tcp_syncookiesonly, 0,
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"Use only TCP SYN cookies");
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#define SYNCOOKIE_SECRET_SIZE 8 /* dwords */
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#define SYNCOOKIE_LIFETIME 16 /* seconds */
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struct syncache {
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TAILQ_ENTRY(syncache) sc_hash;
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struct in_conninfo sc_inc; /* addresses */
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u_long sc_rxttime; /* retransmit time */
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u_int16_t sc_rxmits; /* retransmit counter */
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u_int32_t sc_tsreflect; /* timestamp to reflect */
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u_int32_t sc_ts; /* our timestamp to send */
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u_int32_t sc_tsoff; /* ts offset w/ syncookies */
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u_int32_t sc_flowlabel; /* IPv6 flowlabel */
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tcp_seq sc_irs; /* seq from peer */
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tcp_seq sc_iss; /* our ISS */
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struct mbuf *sc_ipopts; /* source route */
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u_int16_t sc_peer_mss; /* peer's MSS */
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u_int16_t sc_wnd; /* advertised window */
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u_int8_t sc_ip_ttl; /* IPv4 TTL */
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u_int8_t sc_ip_tos; /* IPv4 TOS */
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u_int8_t sc_requested_s_scale:4,
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sc_requested_r_scale:4;
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u_int8_t sc_flags;
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#define SCF_NOOPT 0x01 /* no TCP options */
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#define SCF_WINSCALE 0x02 /* negotiated window scaling */
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#define SCF_TIMESTAMP 0x04 /* negotiated timestamps */
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/* MSS is implicit */
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#define SCF_UNREACH 0x10 /* icmp unreachable received */
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#define SCF_SIGNATURE 0x20 /* send MD5 digests */
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#define SCF_SACK 0x80 /* send SACK option */
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};
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struct syncache_head {
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struct mtx sch_mtx;
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TAILQ_HEAD(sch_head, syncache) sch_bucket;
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struct callout sch_timer;
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int sch_nextc;
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u_int sch_length;
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u_int sch_oddeven;
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u_int32_t sch_secbits_odd[SYNCOOKIE_SECRET_SIZE];
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u_int32_t sch_secbits_even[SYNCOOKIE_SECRET_SIZE];
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u_int sch_reseed; /* time_uptime, seconds */
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};
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static void syncache_drop(struct syncache *, struct syncache_head *);
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static void syncache_free(struct syncache *);
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static void syncache_insert(struct syncache *, struct syncache_head *);
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struct syncache *syncache_lookup(struct in_conninfo *, struct syncache_head **);
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static int syncache_respond(struct syncache *, struct mbuf *);
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static struct socket *syncache_socket(struct syncache *, struct socket *,
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struct mbuf *m);
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static void syncache_timer(void *);
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static void syncookie_generate(struct syncache_head *, struct syncache *,
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u_int32_t *);
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static struct syncache
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*syncookie_lookup(struct in_conninfo *, struct syncache_head *,
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struct syncache *, struct tcpopt *, struct tcphdr *,
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struct socket *);
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/*
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* Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
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* 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
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* the odds are that the user has given up attempting to connect by then.
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*/
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#define SYNCACHE_MAXREXMTS 3
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/* Arbitrary values */
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#define TCP_SYNCACHE_HASHSIZE 512
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#define TCP_SYNCACHE_BUCKETLIMIT 30
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struct tcp_syncache {
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struct syncache_head *hashbase;
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uma_zone_t zone;
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u_int hashsize;
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u_int hashmask;
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u_int bucket_limit;
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u_int cache_count; /* XXX: unprotected */
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u_int cache_limit;
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u_int rexmt_limit;
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u_int hash_secret;
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};
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static struct tcp_syncache tcp_syncache;
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SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0, "TCP SYN cache");
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SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
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&tcp_syncache.bucket_limit, 0, "Per-bucket hash limit for syncache");
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SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
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&tcp_syncache.cache_limit, 0, "Overall entry limit for syncache");
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SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, count, CTLFLAG_RD,
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&tcp_syncache.cache_count, 0, "Current number of entries in syncache");
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SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
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&tcp_syncache.hashsize, 0, "Size of TCP syncache hashtable");
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SYSCTL_INT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
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&tcp_syncache.rexmt_limit, 0, "Limit on SYN/ACK retransmissions");
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static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
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#define SYNCACHE_HASH(inc, mask) \
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((tcp_syncache.hash_secret ^ \
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(inc)->inc_faddr.s_addr ^ \
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((inc)->inc_faddr.s_addr >> 16) ^ \
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(inc)->inc_fport ^ (inc)->inc_lport) & mask)
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#define SYNCACHE_HASH6(inc, mask) \
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((tcp_syncache.hash_secret ^ \
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(inc)->inc6_faddr.s6_addr32[0] ^ \
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(inc)->inc6_faddr.s6_addr32[3] ^ \
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(inc)->inc_fport ^ (inc)->inc_lport) & mask)
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#define ENDPTS_EQ(a, b) ( \
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(a)->ie_fport == (b)->ie_fport && \
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(a)->ie_lport == (b)->ie_lport && \
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(a)->ie_faddr.s_addr == (b)->ie_faddr.s_addr && \
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(a)->ie_laddr.s_addr == (b)->ie_laddr.s_addr \
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)
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#define ENDPTS6_EQ(a, b) (memcmp(a, b, sizeof(*a)) == 0)
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#define SYNCACHE_TIMEOUT(sc, sch, co) do { \
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(sc)->sc_rxmits++; \
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(sc)->sc_rxttime = ticks + \
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TCPTV_RTOBASE * tcp_backoff[(sc)->sc_rxmits - 1]; \
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if ((sch)->sch_nextc > (sc)->sc_rxttime) \
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(sch)->sch_nextc = (sc)->sc_rxttime; \
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if (!TAILQ_EMPTY(&(sch)->sch_bucket) && !(co)) \
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callout_reset(&(sch)->sch_timer, \
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(sch)->sch_nextc - ticks, \
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syncache_timer, (void *)(sch)); \
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} while (0)
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#define SCH_LOCK(sch) mtx_lock(&(sch)->sch_mtx)
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#define SCH_UNLOCK(sch) mtx_unlock(&(sch)->sch_mtx)
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#define SCH_LOCK_ASSERT(sch) mtx_assert(&(sch)->sch_mtx, MA_OWNED)
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/*
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* Requires the syncache entry to be already removed from the bucket list.
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*/
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static void
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syncache_free(struct syncache *sc)
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{
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if (sc->sc_ipopts)
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(void) m_free(sc->sc_ipopts);
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uma_zfree(tcp_syncache.zone, sc);
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}
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void
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syncache_init(void)
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{
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int i;
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tcp_syncache.cache_count = 0;
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tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
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tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
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tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
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tcp_syncache.hash_secret = arc4random();
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TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
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&tcp_syncache.hashsize);
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TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
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&tcp_syncache.bucket_limit);
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if (!powerof2(tcp_syncache.hashsize) || tcp_syncache.hashsize == 0) {
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printf("WARNING: syncache hash size is not a power of 2.\n");
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tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
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}
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tcp_syncache.hashmask = tcp_syncache.hashsize - 1;
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/* Set limits. */
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tcp_syncache.cache_limit =
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tcp_syncache.hashsize * tcp_syncache.bucket_limit;
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TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
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&tcp_syncache.cache_limit);
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/* Allocate the hash table. */
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MALLOC(tcp_syncache.hashbase, struct syncache_head *,
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tcp_syncache.hashsize * sizeof(struct syncache_head),
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M_SYNCACHE, M_WAITOK | M_ZERO);
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/* Initialize the hash buckets. */
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for (i = 0; i < tcp_syncache.hashsize; i++) {
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TAILQ_INIT(&tcp_syncache.hashbase[i].sch_bucket);
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mtx_init(&tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
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NULL, MTX_DEF);
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callout_init_mtx(&tcp_syncache.hashbase[i].sch_timer,
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&tcp_syncache.hashbase[i].sch_mtx, 0);
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tcp_syncache.hashbase[i].sch_length = 0;
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}
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/* Create the syncache entry zone. */
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tcp_syncache.zone = uma_zcreate("syncache", sizeof(struct syncache),
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NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
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uma_zone_set_max(tcp_syncache.zone, tcp_syncache.cache_limit);
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}
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/*
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* Inserts a syncache entry into the specified bucket row.
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* Locks and unlocks the syncache_head autonomously.
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*/
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static void
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syncache_insert(struct syncache *sc, struct syncache_head *sch)
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{
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struct syncache *sc2;
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SCH_LOCK(sch);
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/*
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* Make sure that we don't overflow the per-bucket limit.
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* If the bucket is full, toss the oldest element.
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*/
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if (sch->sch_length >= tcp_syncache.bucket_limit) {
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KASSERT(!TAILQ_EMPTY(&sch->sch_bucket),
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("sch->sch_length incorrect"));
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sc2 = TAILQ_LAST(&sch->sch_bucket, sch_head);
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syncache_drop(sc2, sch);
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tcpstat.tcps_sc_bucketoverflow++;
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}
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/* Put it into the bucket. */
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TAILQ_INSERT_HEAD(&sch->sch_bucket, sc, sc_hash);
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sch->sch_length++;
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/* Reinitialize the bucket row's timer. */
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SYNCACHE_TIMEOUT(sc, sch, 1);
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SCH_UNLOCK(sch);
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tcp_syncache.cache_count++;
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tcpstat.tcps_sc_added++;
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}
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/*
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* Remove and free entry from syncache bucket row.
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* Expects locked syncache head.
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*/
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static void
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syncache_drop(struct syncache *sc, struct syncache_head *sch)
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{
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SCH_LOCK_ASSERT(sch);
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TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
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sch->sch_length--;
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syncache_free(sc);
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tcp_syncache.cache_count--;
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}
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/*
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* Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
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* If we have retransmitted an entry the maximum number of times, expire it.
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* One separate timer for each bucket row.
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*/
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static void
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syncache_timer(void *xsch)
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{
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struct syncache_head *sch = (struct syncache_head *)xsch;
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struct syncache *sc, *nsc;
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int tick = ticks;
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/* NB: syncache_head has already been locked by the callout. */
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SCH_LOCK_ASSERT(sch);
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TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
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/*
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* We do not check if the listen socket still exists
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* and accept the case where the listen socket may be
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* gone by the time we resend the SYN/ACK. We do
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* not expect this to happens often. If it does,
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* then the RST will be sent by the time the remote
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* host does the SYN/ACK->ACK.
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*/
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if (sc->sc_rxttime >= tick) {
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if (sc->sc_rxttime < sch->sch_nextc)
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sch->sch_nextc = sc->sc_rxttime;
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continue;
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}
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if (sc->sc_rxmits > tcp_syncache.rexmt_limit) {
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syncache_drop(sc, sch);
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tcpstat.tcps_sc_stale++;
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continue;
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}
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(void) syncache_respond(sc, NULL);
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tcpstat.tcps_sc_retransmitted++;
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SYNCACHE_TIMEOUT(sc, sch, 0);
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}
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if (!TAILQ_EMPTY(&(sch)->sch_bucket))
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callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
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syncache_timer, (void *)(sch));
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}
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/*
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* Find an entry in the syncache.
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* Returns always with locked syncache_head plus a matching entry or NULL.
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*/
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struct syncache *
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syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
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{
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struct syncache *sc;
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struct syncache_head *sch;
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#ifdef INET6
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if (inc->inc_isipv6) {
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sch = &tcp_syncache.hashbase[
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SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
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*schp = sch;
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SCH_LOCK(sch);
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/* Circle through bucket row to find matching entry. */
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TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
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if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
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return (sc);
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}
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} else
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#endif
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{
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sch = &tcp_syncache.hashbase[
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SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
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*schp = sch;
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SCH_LOCK(sch);
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/* Circle through bucket row to find matching entry. */
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TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
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#ifdef INET6
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if (sc->sc_inc.inc_isipv6)
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continue;
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#endif
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if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
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return (sc);
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}
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}
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SCH_LOCK_ASSERT(*schp);
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return (NULL); /* always returns with locked sch */
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}
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/*
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* This function is called when we get a RST for a
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* non-existent connection, so that we can see if the
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* connection is in the syn cache. If it is, zap it.
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*/
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void
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syncache_chkrst(struct in_conninfo *inc, struct tcphdr *th)
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{
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struct syncache *sc;
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|
struct syncache_head *sch;
|
|
|
|
sc = syncache_lookup(inc, &sch); /* returns locked sch */
|
|
SCH_LOCK_ASSERT(sch);
|
|
if (sc == NULL)
|
|
goto done;
|
|
|
|
/*
|
|
* If the RST bit is set, check the sequence number to see
|
|
* if this is a valid reset segment.
|
|
* RFC 793 page 37:
|
|
* In all states except SYN-SENT, all reset (RST) segments
|
|
* are validated by checking their SEQ-fields. A reset is
|
|
* valid if its sequence number is in the window.
|
|
*
|
|
* The sequence number in the reset segment is normally an
|
|
* echo of our outgoing acknowlegement numbers, but some hosts
|
|
* send a reset with the sequence number at the rightmost edge
|
|
* of our receive window, and we have to handle this case.
|
|
*/
|
|
if (SEQ_GEQ(th->th_seq, sc->sc_irs) &&
|
|
SEQ_LEQ(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
|
|
syncache_drop(sc, sch);
|
|
tcpstat.tcps_sc_reset++;
|
|
}
|
|
done:
|
|
SCH_UNLOCK(sch);
|
|
}
|
|
|
|
void
|
|
syncache_badack(struct in_conninfo *inc)
|
|
{
|
|
struct syncache *sc;
|
|
struct syncache_head *sch;
|
|
|
|
sc = syncache_lookup(inc, &sch); /* returns locked sch */
|
|
SCH_LOCK_ASSERT(sch);
|
|
if (sc != NULL) {
|
|
syncache_drop(sc, sch);
|
|
tcpstat.tcps_sc_badack++;
|
|
}
|
|
SCH_UNLOCK(sch);
|
|
}
|
|
|
|
void
|
|
syncache_unreach(struct in_conninfo *inc, struct tcphdr *th)
|
|
{
|
|
struct syncache *sc;
|
|
struct syncache_head *sch;
|
|
|
|
sc = syncache_lookup(inc, &sch); /* returns locked sch */
|
|
SCH_LOCK_ASSERT(sch);
|
|
if (sc == NULL)
|
|
goto done;
|
|
|
|
/* If the sequence number != sc_iss, then it's a bogus ICMP msg */
|
|
if (ntohl(th->th_seq) != sc->sc_iss)
|
|
goto done;
|
|
|
|
/*
|
|
* If we've rertransmitted 3 times and this is our second error,
|
|
* we remove the entry. Otherwise, we allow it to continue on.
|
|
* This prevents us from incorrectly nuking an entry during a
|
|
* spurious network outage.
|
|
*
|
|
* See tcp_notify().
|
|
*/
|
|
if ((sc->sc_flags & SCF_UNREACH) == 0 || sc->sc_rxmits < 3 + 1) {
|
|
sc->sc_flags |= SCF_UNREACH;
|
|
goto done;
|
|
}
|
|
syncache_drop(sc, sch);
|
|
tcpstat.tcps_sc_unreach++;
|
|
done:
|
|
SCH_UNLOCK(sch);
|
|
}
|
|
|
|
/*
|
|
* Build a new TCP socket structure from a syncache entry.
|
|
*/
|
|
static struct socket *
|
|
syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
|
|
{
|
|
struct inpcb *inp = NULL;
|
|
struct socket *so;
|
|
struct tcpcb *tp;
|
|
|
|
NET_ASSERT_GIANT();
|
|
INP_INFO_WLOCK_ASSERT(&tcbinfo);
|
|
|
|
/*
|
|
* Ok, create the full blown connection, and set things up
|
|
* as they would have been set up if we had created the
|
|
* connection when the SYN arrived. If we can't create
|
|
* the connection, abort it.
|
|
*/
|
|
so = sonewconn(lso, SS_ISCONNECTED);
|
|
if (so == NULL) {
|
|
/*
|
|
* Drop the connection; we will send a RST if the peer
|
|
* retransmits the ACK,
|
|
*/
|
|
tcpstat.tcps_listendrop++;
|
|
goto abort2;
|
|
}
|
|
#ifdef MAC
|
|
SOCK_LOCK(so);
|
|
mac_set_socket_peer_from_mbuf(m, so);
|
|
SOCK_UNLOCK(so);
|
|
#endif
|
|
|
|
inp = sotoinpcb(so);
|
|
INP_LOCK(inp);
|
|
|
|
/* Insert new socket into PCB hash list. */
|
|
inp->inp_inc.inc_isipv6 = sc->sc_inc.inc_isipv6;
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6) {
|
|
inp->in6p_laddr = sc->sc_inc.inc6_laddr;
|
|
} else {
|
|
inp->inp_vflag &= ~INP_IPV6;
|
|
inp->inp_vflag |= INP_IPV4;
|
|
#endif
|
|
inp->inp_laddr = sc->sc_inc.inc_laddr;
|
|
#ifdef INET6
|
|
}
|
|
#endif
|
|
inp->inp_lport = sc->sc_inc.inc_lport;
|
|
if (in_pcbinshash(inp) != 0) {
|
|
/*
|
|
* Undo the assignments above if we failed to
|
|
* put the PCB on the hash lists.
|
|
*/
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6)
|
|
inp->in6p_laddr = in6addr_any;
|
|
else
|
|
#endif
|
|
inp->inp_laddr.s_addr = INADDR_ANY;
|
|
inp->inp_lport = 0;
|
|
goto abort;
|
|
}
|
|
#ifdef IPSEC
|
|
/* Copy old policy into new socket's. */
|
|
if (ipsec_copy_pcbpolicy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
|
|
printf("syncache_socket: could not copy policy\n");
|
|
#endif
|
|
#ifdef FAST_IPSEC
|
|
/* Copy old policy into new socket's. */
|
|
if (ipsec_copy_policy(sotoinpcb(lso)->inp_sp, inp->inp_sp))
|
|
printf("syncache_socket: could not copy policy\n");
|
|
#endif
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6) {
|
|
struct inpcb *oinp = sotoinpcb(lso);
|
|
struct in6_addr laddr6;
|
|
struct sockaddr_in6 sin6;
|
|
/*
|
|
* Inherit socket options from the listening socket.
|
|
* Note that in6p_inputopts are not (and should not be)
|
|
* copied, since it stores previously received options and is
|
|
* used to detect if each new option is different than the
|
|
* previous one and hence should be passed to a user.
|
|
* If we copied in6p_inputopts, a user would not be able to
|
|
* receive options just after calling the accept system call.
|
|
*/
|
|
inp->inp_flags |= oinp->inp_flags & INP_CONTROLOPTS;
|
|
if (oinp->in6p_outputopts)
|
|
inp->in6p_outputopts =
|
|
ip6_copypktopts(oinp->in6p_outputopts, M_NOWAIT);
|
|
|
|
sin6.sin6_family = AF_INET6;
|
|
sin6.sin6_len = sizeof(sin6);
|
|
sin6.sin6_addr = sc->sc_inc.inc6_faddr;
|
|
sin6.sin6_port = sc->sc_inc.inc_fport;
|
|
sin6.sin6_flowinfo = sin6.sin6_scope_id = 0;
|
|
laddr6 = inp->in6p_laddr;
|
|
if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
|
|
inp->in6p_laddr = sc->sc_inc.inc6_laddr;
|
|
if (in6_pcbconnect(inp, (struct sockaddr *)&sin6,
|
|
thread0.td_ucred)) {
|
|
inp->in6p_laddr = laddr6;
|
|
goto abort;
|
|
}
|
|
/* Override flowlabel from in6_pcbconnect. */
|
|
inp->in6p_flowinfo &= ~IPV6_FLOWLABEL_MASK;
|
|
inp->in6p_flowinfo |= sc->sc_flowlabel;
|
|
} else
|
|
#endif
|
|
{
|
|
struct in_addr laddr;
|
|
struct sockaddr_in sin;
|
|
|
|
inp->inp_options = ip_srcroute(m);
|
|
if (inp->inp_options == NULL) {
|
|
inp->inp_options = sc->sc_ipopts;
|
|
sc->sc_ipopts = NULL;
|
|
}
|
|
|
|
sin.sin_family = AF_INET;
|
|
sin.sin_len = sizeof(sin);
|
|
sin.sin_addr = sc->sc_inc.inc_faddr;
|
|
sin.sin_port = sc->sc_inc.inc_fport;
|
|
bzero((caddr_t)sin.sin_zero, sizeof(sin.sin_zero));
|
|
laddr = inp->inp_laddr;
|
|
if (inp->inp_laddr.s_addr == INADDR_ANY)
|
|
inp->inp_laddr = sc->sc_inc.inc_laddr;
|
|
if (in_pcbconnect(inp, (struct sockaddr *)&sin,
|
|
thread0.td_ucred)) {
|
|
inp->inp_laddr = laddr;
|
|
goto abort;
|
|
}
|
|
}
|
|
tp = intotcpcb(inp);
|
|
tp->t_state = TCPS_SYN_RECEIVED;
|
|
tp->iss = sc->sc_iss;
|
|
tp->irs = sc->sc_irs;
|
|
tcp_rcvseqinit(tp);
|
|
tcp_sendseqinit(tp);
|
|
tp->snd_wl1 = sc->sc_irs;
|
|
tp->rcv_up = sc->sc_irs + 1;
|
|
tp->rcv_wnd = sc->sc_wnd;
|
|
tp->rcv_adv += tp->rcv_wnd;
|
|
|
|
tp->t_flags = sototcpcb(lso)->t_flags & (TF_NOPUSH|TF_NODELAY);
|
|
if (sc->sc_flags & SCF_NOOPT)
|
|
tp->t_flags |= TF_NOOPT;
|
|
else {
|
|
if (sc->sc_flags & SCF_WINSCALE) {
|
|
tp->t_flags |= TF_REQ_SCALE|TF_RCVD_SCALE;
|
|
tp->snd_scale = sc->sc_requested_s_scale;
|
|
tp->request_r_scale = sc->sc_requested_r_scale;
|
|
}
|
|
if (sc->sc_flags & SCF_TIMESTAMP) {
|
|
tp->t_flags |= TF_REQ_TSTMP|TF_RCVD_TSTMP;
|
|
tp->ts_recent = sc->sc_tsreflect;
|
|
tp->ts_recent_age = ticks;
|
|
tp->ts_offset = sc->sc_tsoff;
|
|
}
|
|
#ifdef TCP_SIGNATURE
|
|
if (sc->sc_flags & SCF_SIGNATURE)
|
|
tp->t_flags |= TF_SIGNATURE;
|
|
#endif
|
|
if (sc->sc_flags & SCF_SACK) {
|
|
tp->sack_enable = 1;
|
|
tp->t_flags |= TF_SACK_PERMIT;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Set up MSS and get cached values from tcp_hostcache.
|
|
* This might overwrite some of the defaults we just set.
|
|
*/
|
|
tcp_mss(tp, sc->sc_peer_mss);
|
|
|
|
/*
|
|
* If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
|
|
*/
|
|
if (sc->sc_rxmits > 1)
|
|
tp->snd_cwnd = tp->t_maxseg;
|
|
callout_reset(tp->tt_keep, tcp_keepinit, tcp_timer_keep, tp);
|
|
|
|
INP_UNLOCK(inp);
|
|
|
|
tcpstat.tcps_accepts++;
|
|
return (so);
|
|
|
|
abort:
|
|
INP_UNLOCK(inp);
|
|
abort2:
|
|
if (so != NULL)
|
|
soabort(so);
|
|
return (NULL);
|
|
}
|
|
|
|
/*
|
|
* This function gets called when we receive an ACK for a
|
|
* socket in the LISTEN state. We look up the connection
|
|
* in the syncache, and if its there, we pull it out of
|
|
* the cache and turn it into a full-blown connection in
|
|
* the SYN-RECEIVED state.
|
|
*/
|
|
int
|
|
syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
|
|
struct socket **lsop, struct mbuf *m)
|
|
{
|
|
struct syncache *sc;
|
|
struct syncache_head *sch;
|
|
struct socket *so;
|
|
struct syncache scs;
|
|
|
|
/*
|
|
* Global TCP locks are held because we manipulate the PCB lists
|
|
* and create a new socket.
|
|
*/
|
|
INP_INFO_WLOCK_ASSERT(&tcbinfo);
|
|
|
|
sc = syncache_lookup(inc, &sch); /* returns locked sch */
|
|
SCH_LOCK_ASSERT(sch);
|
|
if (sc == NULL) {
|
|
/*
|
|
* There is no syncache entry, so see if this ACK is
|
|
* a returning syncookie. To do this, first:
|
|
* A. See if this socket has had a syncache entry dropped in
|
|
* the past. We don't want to accept a bogus syncookie
|
|
* if we've never received a SYN.
|
|
* B. check that the syncookie is valid. If it is, then
|
|
* cobble up a fake syncache entry, and return.
|
|
*/
|
|
if (!tcp_syncookies) {
|
|
SCH_UNLOCK(sch);
|
|
goto failed;
|
|
}
|
|
bzero(&scs, sizeof(scs));
|
|
sc = syncookie_lookup(inc, sch, &scs, to, th, *lsop);
|
|
SCH_UNLOCK(sch);
|
|
if (sc == NULL)
|
|
goto failed;
|
|
tcpstat.tcps_sc_recvcookie++;
|
|
} else {
|
|
/* Pull out the entry to unlock the bucket row. */
|
|
TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
|
|
sch->sch_length--;
|
|
tcp_syncache.cache_count--;
|
|
SCH_UNLOCK(sch);
|
|
}
|
|
|
|
/*
|
|
* If seg contains an ACK, but not for our SYN/ACK, send a RST.
|
|
*/
|
|
if (th->th_ack != sc->sc_iss + 1)
|
|
goto failed;
|
|
|
|
so = syncache_socket(sc, *lsop, m);
|
|
|
|
if (so == NULL) {
|
|
#if 0
|
|
resetandabort:
|
|
/* XXXjlemon check this - is this correct? */
|
|
(void) tcp_respond(NULL, m, m, th,
|
|
th->th_seq + tlen, (tcp_seq)0, TH_RST|TH_ACK);
|
|
#endif
|
|
m_freem(m); /* XXX: only needed for above */
|
|
tcpstat.tcps_sc_aborted++;
|
|
if (sc != &scs) {
|
|
syncache_insert(sc, sch); /* try again later */
|
|
sc = NULL;
|
|
}
|
|
goto failed;
|
|
} else
|
|
tcpstat.tcps_sc_completed++;
|
|
*lsop = so;
|
|
|
|
if (sc != &scs)
|
|
syncache_free(sc);
|
|
return (1);
|
|
failed:
|
|
if (sc != NULL && sc != &scs)
|
|
syncache_free(sc);
|
|
return (0);
|
|
}
|
|
|
|
/*
|
|
* Given a LISTEN socket and an inbound SYN request, add
|
|
* this to the syn cache, and send back a segment:
|
|
* <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
|
|
* to the source.
|
|
*
|
|
* IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN.
|
|
* Doing so would require that we hold onto the data and deliver it
|
|
* to the application. However, if we are the target of a SYN-flood
|
|
* DoS attack, an attacker could send data which would eventually
|
|
* consume all available buffer space if it were ACKed. By not ACKing
|
|
* the data, we avoid this DoS scenario.
|
|
*/
|
|
int
|
|
syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
|
|
struct inpcb *inp, struct socket **lsop, struct mbuf *m)
|
|
{
|
|
struct tcpcb *tp;
|
|
struct socket *so;
|
|
struct syncache *sc = NULL;
|
|
struct syncache_head *sch;
|
|
struct mbuf *ipopts = NULL;
|
|
u_int32_t flowtmp;
|
|
int win, sb_hiwat, ip_ttl, ip_tos, noopt;
|
|
#ifdef INET6
|
|
int autoflowlabel = 0;
|
|
#endif
|
|
struct syncache scs;
|
|
|
|
INP_INFO_WLOCK_ASSERT(&tcbinfo);
|
|
INP_LOCK_ASSERT(inp); /* listen socket */
|
|
|
|
/*
|
|
* Combine all so/tp operations very early to drop the INP lock as
|
|
* soon as possible.
|
|
*/
|
|
so = *lsop;
|
|
tp = sototcpcb(so);
|
|
|
|
#ifdef INET6
|
|
if (inc->inc_isipv6 &&
|
|
(inp->in6p_flags & IN6P_AUTOFLOWLABEL))
|
|
autoflowlabel = 1;
|
|
#endif
|
|
ip_ttl = inp->inp_ip_ttl;
|
|
ip_tos = inp->inp_ip_tos;
|
|
win = sbspace(&so->so_rcv);
|
|
sb_hiwat = so->so_rcv.sb_hiwat;
|
|
noopt = (tp->t_flags & TF_NOOPT);
|
|
|
|
so = NULL;
|
|
tp = NULL;
|
|
|
|
INP_UNLOCK(inp);
|
|
INP_INFO_WUNLOCK(&tcbinfo);
|
|
|
|
/*
|
|
* Remember the IP options, if any.
|
|
*/
|
|
#ifdef INET6
|
|
if (!inc->inc_isipv6)
|
|
#endif
|
|
ipopts = ip_srcroute(m);
|
|
|
|
/*
|
|
* See if we already have an entry for this connection.
|
|
* If we do, resend the SYN,ACK, and reset the retransmit timer.
|
|
*
|
|
* XXX: should the syncache be re-initialized with the contents
|
|
* of the new SYN here (which may have different options?)
|
|
*/
|
|
sc = syncache_lookup(inc, &sch); /* returns locked entry */
|
|
SCH_LOCK_ASSERT(sch);
|
|
if (sc != NULL) {
|
|
tcpstat.tcps_sc_dupsyn++;
|
|
if (ipopts) {
|
|
/*
|
|
* If we were remembering a previous source route,
|
|
* forget it and use the new one we've been given.
|
|
*/
|
|
if (sc->sc_ipopts)
|
|
(void) m_free(sc->sc_ipopts);
|
|
sc->sc_ipopts = ipopts;
|
|
}
|
|
/*
|
|
* Update timestamp if present.
|
|
*/
|
|
if (sc->sc_flags & SCF_TIMESTAMP)
|
|
sc->sc_tsreflect = to->to_tsval;
|
|
if (syncache_respond(sc, m) == 0) {
|
|
SYNCACHE_TIMEOUT(sc, sch, 1);
|
|
tcpstat.tcps_sndacks++;
|
|
tcpstat.tcps_sndtotal++;
|
|
}
|
|
SCH_UNLOCK(sch);
|
|
goto done;
|
|
}
|
|
|
|
sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
|
|
if (sc == NULL) {
|
|
/*
|
|
* The zone allocator couldn't provide more entries.
|
|
* Treat this as if the cache was full; drop the oldest
|
|
* entry and insert the new one.
|
|
*/
|
|
tcpstat.tcps_sc_zonefail++;
|
|
sc = TAILQ_LAST(&sch->sch_bucket, sch_head);
|
|
syncache_drop(sc, sch);
|
|
sc = uma_zalloc(tcp_syncache.zone, M_NOWAIT | M_ZERO);
|
|
if (sc == NULL) {
|
|
if (tcp_syncookies) {
|
|
bzero(&scs, sizeof(scs));
|
|
sc = &scs;
|
|
} else {
|
|
SCH_UNLOCK(sch);
|
|
if (ipopts)
|
|
(void) m_free(ipopts);
|
|
goto done;
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Fill in the syncache values.
|
|
*/
|
|
sc->sc_ipopts = ipopts;
|
|
bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
|
|
#ifdef INET6
|
|
if (!inc->inc_isipv6)
|
|
#endif
|
|
{
|
|
sc->sc_ip_tos = ip_tos;
|
|
sc->sc_ip_ttl = ip_ttl;
|
|
}
|
|
|
|
sc->sc_irs = th->th_seq;
|
|
sc->sc_iss = arc4random();
|
|
sc->sc_flags = 0;
|
|
sc->sc_flowlabel = 0;
|
|
|
|
/*
|
|
* Initial receive window: clip sbspace to [0 .. TCP_MAXWIN].
|
|
* win was derived from socket earlier in the function.
|
|
*/
|
|
win = imax(win, 0);
|
|
win = imin(win, TCP_MAXWIN);
|
|
sc->sc_wnd = win;
|
|
|
|
if (tcp_do_rfc1323) {
|
|
/*
|
|
* A timestamp received in a SYN makes
|
|
* it ok to send timestamp requests and replies.
|
|
*/
|
|
if (to->to_flags & TOF_TS) {
|
|
sc->sc_tsreflect = to->to_tsval;
|
|
sc->sc_flags |= SCF_TIMESTAMP;
|
|
}
|
|
if (to->to_flags & TOF_SCALE) {
|
|
int wscale = 0;
|
|
|
|
/* Compute proper scaling value from buffer space */
|
|
while (wscale < TCP_MAX_WINSHIFT &&
|
|
(TCP_MAXWIN << wscale) < sb_hiwat)
|
|
wscale++;
|
|
sc->sc_requested_r_scale = wscale;
|
|
sc->sc_requested_s_scale = to->to_requested_s_scale;
|
|
sc->sc_flags |= SCF_WINSCALE;
|
|
}
|
|
}
|
|
#ifdef TCP_SIGNATURE
|
|
/*
|
|
* If listening socket requested TCP digests, and received SYN
|
|
* contains the option, flag this in the syncache so that
|
|
* syncache_respond() will do the right thing with the SYN+ACK.
|
|
* XXX: Currently we always record the option by default and will
|
|
* attempt to use it in syncache_respond().
|
|
*/
|
|
if (to->to_flags & TOF_SIGNATURE)
|
|
sc->sc_flags |= SCF_SIGNATURE;
|
|
#endif
|
|
if (to->to_flags & TOF_SACK)
|
|
sc->sc_flags |= SCF_SACK;
|
|
if (to->to_flags & TOF_MSS)
|
|
sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
|
|
if (noopt)
|
|
sc->sc_flags |= SCF_NOOPT;
|
|
|
|
if (tcp_syncookies) {
|
|
syncookie_generate(sch, sc, &flowtmp);
|
|
#ifdef INET6
|
|
if (autoflowlabel)
|
|
sc->sc_flowlabel = flowtmp;
|
|
#endif
|
|
} else {
|
|
#ifdef INET6
|
|
if (autoflowlabel)
|
|
sc->sc_flowlabel =
|
|
(htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
|
|
#endif
|
|
}
|
|
SCH_UNLOCK(sch);
|
|
|
|
/*
|
|
* Do a standard 3-way handshake.
|
|
*/
|
|
if (syncache_respond(sc, m) == 0) {
|
|
if (tcp_syncookies && tcp_syncookiesonly && sc != &scs)
|
|
syncache_free(sc);
|
|
else if (sc != &scs)
|
|
syncache_insert(sc, sch); /* locks and unlocks sch */
|
|
tcpstat.tcps_sndacks++;
|
|
tcpstat.tcps_sndtotal++;
|
|
} else {
|
|
syncache_free(sc);
|
|
tcpstat.tcps_sc_dropped++;
|
|
}
|
|
|
|
done:
|
|
*lsop = NULL;
|
|
return (1);
|
|
}
|
|
|
|
static int
|
|
syncache_respond(struct syncache *sc, struct mbuf *m)
|
|
{
|
|
struct ip *ip = NULL;
|
|
struct tcphdr *th;
|
|
int optlen, error;
|
|
u_int16_t tlen, hlen, mssopt;
|
|
u_int8_t *optp;
|
|
#ifdef INET6
|
|
struct ip6_hdr *ip6 = NULL;
|
|
#endif
|
|
#ifdef MAC
|
|
struct inpcb *inp = NULL;
|
|
#endif
|
|
|
|
hlen =
|
|
#ifdef INET6
|
|
(sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) :
|
|
#endif
|
|
sizeof(struct ip);
|
|
|
|
/* Determine MSS we advertize to other end of connection. */
|
|
mssopt = tcp_mssopt(&sc->sc_inc);
|
|
if (sc->sc_peer_mss)
|
|
mssopt = max( min(sc->sc_peer_mss, mssopt), tcp_minmss);
|
|
|
|
/* Compute the size of the TCP options. */
|
|
if (sc->sc_flags & SCF_NOOPT) {
|
|
optlen = 0;
|
|
} else {
|
|
optlen = TCPOLEN_MAXSEG +
|
|
((sc->sc_flags & SCF_WINSCALE) ? 4 : 0) +
|
|
((sc->sc_flags & SCF_TIMESTAMP) ? TCPOLEN_TSTAMP_APPA : 0);
|
|
#ifdef TCP_SIGNATURE
|
|
if (sc->sc_flags & SCF_SIGNATURE)
|
|
optlen += TCPOLEN_SIGNATURE;
|
|
#endif
|
|
if (sc->sc_flags & SCF_SACK)
|
|
optlen += TCPOLEN_SACK_PERMITTED;
|
|
optlen = roundup2(optlen, 4);
|
|
}
|
|
tlen = hlen + sizeof(struct tcphdr) + optlen;
|
|
|
|
/*
|
|
* XXX: Assume that the entire packet will fit in a header mbuf.
|
|
*/
|
|
KASSERT(max_linkhdr + tlen <= MHLEN, ("syncache: mbuf too small"));
|
|
|
|
/* Create the IP+TCP header from scratch. */
|
|
if (m)
|
|
m_freem(m);
|
|
|
|
m = m_gethdr(M_DONTWAIT, MT_DATA);
|
|
if (m == NULL)
|
|
return (ENOBUFS);
|
|
m->m_data += max_linkhdr;
|
|
m->m_len = tlen;
|
|
m->m_pkthdr.len = tlen;
|
|
m->m_pkthdr.rcvif = NULL;
|
|
|
|
#ifdef MAC
|
|
/*
|
|
* For MAC look up the inpcb to get access to the label information.
|
|
* We don't store the inpcb pointer in struct syncache to make locking
|
|
* less complicated and to save locking operations. However for MAC
|
|
* this gives a slight overhead as we have to do a full pcblookup here.
|
|
*/
|
|
INP_INFO_RLOCK(&tcbinfo);
|
|
if (inp == NULL) {
|
|
#ifdef INET6 /* && MAC */
|
|
if (sc->sc_inc.inc_isipv6)
|
|
inp = in6_pcblookup_hash(&tcbinfo,
|
|
&sc->sc_inc.inc6_faddr, sc->sc_inc.inc_fport,
|
|
&sc->sc_inc.inc6_laddr, sc->sc_inc.inc_lport,
|
|
1, NULL);
|
|
else
|
|
#endif /* INET6 */
|
|
inp = in_pcblookup_hash(&tcbinfo,
|
|
sc->sc_inc.inc_faddr, sc->sc_inc.inc_fport,
|
|
sc->sc_inc.inc_laddr, sc->sc_inc.inc_lport,
|
|
1, NULL);
|
|
if (inp == NULL) {
|
|
m_freem(m);
|
|
INP_INFO_RUNLOCK(&tcbinfo);
|
|
return (ESHUTDOWN);
|
|
}
|
|
}
|
|
INP_LOCK(inp);
|
|
if (!inp->inp_socket->so_options & SO_ACCEPTCONN) {
|
|
m_freem(m);
|
|
INP_UNLOCK(inp);
|
|
INP_INFO_RUNLOCK(&tcbinfo);
|
|
return (ESHUTDOWN);
|
|
}
|
|
mac_create_mbuf_from_inpcb(inp, m);
|
|
INP_UNLOCK(inp);
|
|
INP_INFO_RUNLOCK(&tcbinfo);
|
|
#endif /* MAC */
|
|
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6) {
|
|
ip6 = mtod(m, struct ip6_hdr *);
|
|
ip6->ip6_vfc = IPV6_VERSION;
|
|
ip6->ip6_nxt = IPPROTO_TCP;
|
|
ip6->ip6_src = sc->sc_inc.inc6_laddr;
|
|
ip6->ip6_dst = sc->sc_inc.inc6_faddr;
|
|
ip6->ip6_plen = htons(tlen - hlen);
|
|
/* ip6_hlim is set after checksum */
|
|
ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
|
|
ip6->ip6_flow |= sc->sc_flowlabel;
|
|
|
|
th = (struct tcphdr *)(ip6 + 1);
|
|
} else
|
|
#endif
|
|
{
|
|
ip = mtod(m, struct ip *);
|
|
ip->ip_v = IPVERSION;
|
|
ip->ip_hl = sizeof(struct ip) >> 2;
|
|
ip->ip_len = tlen;
|
|
ip->ip_id = 0;
|
|
ip->ip_off = 0;
|
|
ip->ip_sum = 0;
|
|
ip->ip_p = IPPROTO_TCP;
|
|
ip->ip_src = sc->sc_inc.inc_laddr;
|
|
ip->ip_dst = sc->sc_inc.inc_faddr;
|
|
ip->ip_ttl = sc->sc_ip_ttl;
|
|
ip->ip_tos = sc->sc_ip_tos;
|
|
|
|
/*
|
|
* See if we should do MTU discovery. Route lookups are
|
|
* expensive, so we will only unset the DF bit if:
|
|
*
|
|
* 1) path_mtu_discovery is disabled
|
|
* 2) the SCF_UNREACH flag has been set
|
|
*/
|
|
if (path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
|
|
ip->ip_off |= IP_DF;
|
|
|
|
th = (struct tcphdr *)(ip + 1);
|
|
}
|
|
th->th_sport = sc->sc_inc.inc_lport;
|
|
th->th_dport = sc->sc_inc.inc_fport;
|
|
|
|
th->th_seq = htonl(sc->sc_iss);
|
|
th->th_ack = htonl(sc->sc_irs + 1);
|
|
th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
|
|
th->th_x2 = 0;
|
|
th->th_flags = TH_SYN|TH_ACK;
|
|
th->th_win = htons(sc->sc_wnd);
|
|
th->th_urp = 0;
|
|
|
|
/* Tack on the TCP options. */
|
|
if (optlen != 0) {
|
|
optp = (u_int8_t *)(th + 1);
|
|
*optp++ = TCPOPT_MAXSEG;
|
|
*optp++ = TCPOLEN_MAXSEG;
|
|
*optp++ = (mssopt >> 8) & 0xff;
|
|
*optp++ = mssopt & 0xff;
|
|
|
|
if (sc->sc_flags & SCF_WINSCALE) {
|
|
*((u_int32_t *)optp) = htonl(TCPOPT_NOP << 24 |
|
|
TCPOPT_WINDOW << 16 | TCPOLEN_WINDOW << 8 |
|
|
sc->sc_requested_r_scale);
|
|
optp += 4;
|
|
}
|
|
|
|
if (sc->sc_flags & SCF_TIMESTAMP) {
|
|
u_int32_t *lp = (u_int32_t *)(optp);
|
|
|
|
/* Form timestamp option per appendix A of RFC 1323. */
|
|
*lp++ = htonl(TCPOPT_TSTAMP_HDR);
|
|
if (sc->sc_ts)
|
|
*lp++ = htonl(sc->sc_ts);
|
|
else
|
|
*lp++ = htonl(ticks);
|
|
*lp = htonl(sc->sc_tsreflect);
|
|
optp += TCPOLEN_TSTAMP_APPA;
|
|
}
|
|
|
|
#ifdef TCP_SIGNATURE
|
|
/*
|
|
* Handle TCP-MD5 passive opener response.
|
|
*/
|
|
if (sc->sc_flags & SCF_SIGNATURE) {
|
|
u_int8_t *bp = optp;
|
|
int i;
|
|
|
|
*bp++ = TCPOPT_SIGNATURE;
|
|
*bp++ = TCPOLEN_SIGNATURE;
|
|
for (i = 0; i < TCP_SIGLEN; i++)
|
|
*bp++ = 0;
|
|
tcp_signature_compute(m, sizeof(struct ip), 0, optlen,
|
|
optp + 2, IPSEC_DIR_OUTBOUND);
|
|
optp += TCPOLEN_SIGNATURE;
|
|
}
|
|
#endif /* TCP_SIGNATURE */
|
|
|
|
if (sc->sc_flags & SCF_SACK) {
|
|
*optp++ = TCPOPT_SACK_PERMITTED;
|
|
*optp++ = TCPOLEN_SACK_PERMITTED;
|
|
}
|
|
|
|
{
|
|
/* Pad TCP options to a 4 byte boundary */
|
|
int padlen = optlen - (optp - (u_int8_t *)(th + 1));
|
|
while (padlen-- > 0)
|
|
*optp++ = TCPOPT_EOL;
|
|
}
|
|
}
|
|
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6) {
|
|
th->th_sum = 0;
|
|
th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen, tlen - hlen);
|
|
ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
|
|
error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
|
|
} else
|
|
#endif
|
|
{
|
|
th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
|
|
htons(tlen - hlen + IPPROTO_TCP));
|
|
m->m_pkthdr.csum_flags = CSUM_TCP;
|
|
m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
|
|
error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
|
|
}
|
|
return (error);
|
|
}
|
|
|
|
/*
|
|
* The purpose of SYN cookies is to avoid keeping track of all SYN's we
|
|
* receive and to be able to handle SYN floods from bogus source addresses
|
|
* (where we will never receive any reply). SYN floods try to exhaust all
|
|
* our memory and available slots in the SYN cache table to cause a denial
|
|
* of service to legitimate users of the local host.
|
|
*
|
|
* The idea of SYN cookies is to encode and include all necessary information
|
|
* about the connection setup state within the SYN-ACK we send back and thus
|
|
* to get along without keeping any local state until the ACK to the SYN-ACK
|
|
* arrives (if ever). Everything we need to know should be available from
|
|
* the information we encoded in the SYN-ACK.
|
|
*
|
|
* More information about the theory behind SYN cookies and its first
|
|
* discussion and specification can be found at:
|
|
* http://cr.yp.to/syncookies.html (overview)
|
|
* http://cr.yp.to/syncookies/archive (gory details)
|
|
*
|
|
* This implementation extends the orginal idea and first implementation
|
|
* of FreeBSD by using not only the initial sequence number field to store
|
|
* information but also the timestamp field if present. This way we can
|
|
* keep track of the entire state we need to know to recreate the session in
|
|
* its original form. Almost all TCP speakers implement RFC1323 timestamps
|
|
* these days. For those that do not we still have to live with the known
|
|
* shortcomings of the ISN only SYN cookies.
|
|
*
|
|
* Cookie layers:
|
|
*
|
|
* Initial sequence number we send:
|
|
* 31|................................|0
|
|
* DDDDDDDDDDDDDDDDDDDDDDDDDMMMRRRP
|
|
* D = MD5 Digest (first dword)
|
|
* M = MSS index
|
|
* R = Rotation of secret
|
|
* P = Odd or Even secret
|
|
*
|
|
* The MD5 Digest is computed with over following parameters:
|
|
* a) randomly rotated secret
|
|
* b) struct in_conninfo containing the remote/local ip/port (IPv4&IPv6)
|
|
* c) the received initial sequence number from remote host
|
|
* d) the rotation offset and odd/even bit
|
|
*
|
|
* Timestamp we send:
|
|
* 31|................................|0
|
|
* DDDDDDDDDDDDDDDDDDDDDDSSSSRRRRA5
|
|
* D = MD5 Digest (third dword) (only as filler)
|
|
* S = Requested send window scale
|
|
* R = Requested receive window scale
|
|
* A = SACK allowed
|
|
* 5 = TCP-MD5 enabled (not implemented yet)
|
|
* XORed with MD5 Digest (forth dword)
|
|
*
|
|
* The timestamp isn't cryptographically secure and doesn't need to be.
|
|
* The double use of the MD5 digest dwords ties it to a specific remote/
|
|
* local host/port, remote initial sequence number and our local time
|
|
* limited secret. A received timestamp is reverted (XORed) and then
|
|
* the contained MD5 dword is compared to the computed one to ensure the
|
|
* timestamp belongs to the SYN-ACK we sent. The other parameters may
|
|
* have been tampered with but this isn't different from supplying bogus
|
|
* values in the SYN in the first place.
|
|
*
|
|
* Some problems with SYN cookies remain however:
|
|
* Consider the problem of a recreated (and retransmitted) cookie. If the
|
|
* original SYN was accepted, the connection is established. The second
|
|
* SYN is inflight, and if it arrives with an ISN that falls within the
|
|
* receive window, the connection is killed.
|
|
*
|
|
* Notes:
|
|
* A heuristic to determine when to accept syn cookies is not necessary.
|
|
* An ACK flood would cause the syncookie verification to be attempted,
|
|
* but a SYN flood causes syncookies to be generated. Both are of equal
|
|
* cost, so there's no point in trying to optimize the ACK flood case.
|
|
* Also, if you don't process certain ACKs for some reason, then all someone
|
|
* would have to do is launch a SYN and ACK flood at the same time, which
|
|
* would stop cookie verification and defeat the entire purpose of syncookies.
|
|
*/
|
|
static int tcp_sc_msstab[] = { 0, 256, 468, 536, 996, 1452, 1460, 8960 };
|
|
|
|
static void
|
|
syncookie_generate(struct syncache_head *sch, struct syncache *sc,
|
|
u_int32_t *flowlabel)
|
|
{
|
|
MD5_CTX ctx;
|
|
u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
|
|
u_int32_t data;
|
|
u_int32_t *secbits;
|
|
u_int off, pmss, mss;
|
|
int i;
|
|
|
|
SCH_LOCK_ASSERT(sch);
|
|
|
|
/* Which of the two secrets to use. */
|
|
secbits = sch->sch_oddeven ?
|
|
sch->sch_secbits_odd : sch->sch_secbits_even;
|
|
|
|
/* Reseed secret if too old. */
|
|
if (sch->sch_reseed < time_uptime) {
|
|
sch->sch_oddeven = sch->sch_oddeven ? 0 : 1; /* toggle */
|
|
secbits = sch->sch_oddeven ?
|
|
sch->sch_secbits_odd : sch->sch_secbits_even;
|
|
for (i = 0; i < SYNCOOKIE_SECRET_SIZE; i++)
|
|
secbits[i] = arc4random();
|
|
sch->sch_reseed = time_uptime + SYNCOOKIE_LIFETIME;
|
|
}
|
|
|
|
/* Secret rotation offset. */
|
|
off = sc->sc_iss & 0x7; /* iss was randomized before */
|
|
|
|
/* Maximum segment size calculation. */
|
|
pmss = max( min(sc->sc_peer_mss, tcp_mssopt(&sc->sc_inc)), tcp_minmss);
|
|
for (mss = sizeof(tcp_sc_msstab) / sizeof(int) - 1; mss > 0; mss--)
|
|
if (tcp_sc_msstab[mss] <= pmss)
|
|
break;
|
|
|
|
/* Fold parameters and MD5 digest into the ISN we will send. */
|
|
data = sch->sch_oddeven;/* odd or even secret, 1 bit */
|
|
data |= off << 1; /* secret offset, derived from iss, 3 bits */
|
|
data |= mss << 4; /* mss, 3 bits */
|
|
|
|
MD5Init(&ctx);
|
|
MD5Update(&ctx, ((u_int8_t *)secbits) + off,
|
|
SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
|
|
MD5Update(&ctx, secbits, off);
|
|
MD5Update(&ctx, &sc->sc_inc, sizeof(sc->sc_inc));
|
|
MD5Update(&ctx, &sc->sc_irs, sizeof(sc->sc_irs));
|
|
MD5Update(&ctx, &data, sizeof(data));
|
|
MD5Final((u_int8_t *)&md5_buffer, &ctx);
|
|
|
|
data |= (md5_buffer[0] << 7);
|
|
sc->sc_iss = data;
|
|
|
|
#ifdef INET6
|
|
*flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
|
|
#endif
|
|
|
|
/* Additional parameters are stored in the timestamp if present. */
|
|
if (sc->sc_flags & SCF_TIMESTAMP) {
|
|
data = ((sc->sc_flags & SCF_SIGNATURE) ? 1 : 0); /* TCP-MD5, 1 bit */
|
|
data |= ((sc->sc_flags & SCF_SACK) ? 1 : 0) << 1; /* SACK, 1 bit */
|
|
data |= sc->sc_requested_s_scale << 2; /* SWIN scale, 4 bits */
|
|
data |= sc->sc_requested_r_scale << 6; /* RWIN scale, 4 bits */
|
|
data |= md5_buffer[2] << 10; /* more digest bits */
|
|
data ^= md5_buffer[3];
|
|
sc->sc_ts = data;
|
|
sc->sc_tsoff = data - ticks; /* after XOR */
|
|
} else
|
|
sc->sc_ts = 0;
|
|
|
|
return;
|
|
}
|
|
|
|
static struct syncache *
|
|
syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
|
|
struct syncache *sc, struct tcpopt *to, struct tcphdr *th,
|
|
struct socket *so)
|
|
{
|
|
MD5_CTX ctx;
|
|
u_int32_t md5_buffer[MD5_DIGEST_LENGTH / sizeof(u_int32_t)];
|
|
u_int32_t data = 0;
|
|
u_int32_t *secbits;
|
|
tcp_seq ack, seq;
|
|
int off, mss, wnd, flags;
|
|
|
|
SCH_LOCK_ASSERT(sch);
|
|
|
|
/*
|
|
* Pull information out of SYN-ACK/ACK and
|
|
* revert sequence number advances.
|
|
*/
|
|
ack = th->th_ack - 1;
|
|
seq = th->th_seq - 1;
|
|
off = (ack >> 1) & 0x7;
|
|
mss = (ack >> 4) & 0x7;
|
|
flags = ack & 0x7f;
|
|
|
|
/* Which of the two secrets to use. */
|
|
secbits = (flags & 0x1) ? sch->sch_secbits_odd : sch->sch_secbits_even;
|
|
|
|
/*
|
|
* The secret wasn't updated for the lifetime of a syncookie,
|
|
* so this SYN-ACK/ACK is either too old (replay) or totally bogus.
|
|
*/
|
|
if (sch->sch_reseed < time_uptime) {
|
|
return (NULL);
|
|
}
|
|
|
|
/* Recompute the digest so we can compare it. */
|
|
MD5Init(&ctx);
|
|
MD5Update(&ctx, ((u_int8_t *)secbits) + off,
|
|
SYNCOOKIE_SECRET_SIZE * sizeof(*secbits) - off);
|
|
MD5Update(&ctx, secbits, off);
|
|
MD5Update(&ctx, inc, sizeof(*inc));
|
|
MD5Update(&ctx, &seq, sizeof(seq));
|
|
MD5Update(&ctx, &flags, sizeof(flags));
|
|
MD5Final((u_int8_t *)&md5_buffer, &ctx);
|
|
|
|
/* Does the digest part of or ACK'ed ISS match? */
|
|
if ((ack & (~0x7f)) != (md5_buffer[0] << 7))
|
|
return (NULL);
|
|
|
|
/* Does the digest part of our reflected timestamp match? */
|
|
if (to->to_flags & TOF_TS) {
|
|
data = md5_buffer[3] ^ to->to_tsecr;
|
|
if ((data & (~0x3ff)) != (md5_buffer[2] << 10))
|
|
return (NULL);
|
|
}
|
|
|
|
/* Fill in the syncache values. */
|
|
bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
|
|
sc->sc_ipopts = NULL;
|
|
|
|
sc->sc_irs = seq;
|
|
sc->sc_iss = ack;
|
|
|
|
#ifdef INET6
|
|
if (inc->inc_isipv6) {
|
|
if (sotoinpcb(so)->in6p_flags & IN6P_AUTOFLOWLABEL)
|
|
sc->sc_flowlabel = md5_buffer[1] & IPV6_FLOWLABEL_MASK;
|
|
} else
|
|
#endif
|
|
{
|
|
sc->sc_ip_ttl = sotoinpcb(so)->inp_ip_ttl;
|
|
sc->sc_ip_tos = sotoinpcb(so)->inp_ip_tos;
|
|
}
|
|
|
|
/* Additional parameters that were encoded in the timestamp. */
|
|
if (data) {
|
|
sc->sc_flags |= SCF_TIMESTAMP;
|
|
sc->sc_tsreflect = to->to_tsval;
|
|
sc->sc_tsoff = to->to_tsecr - ticks;
|
|
sc->sc_flags |= (data & 0x1) ? SCF_SIGNATURE : 0;
|
|
sc->sc_flags |= ((data >> 1) & 0x1) ? SCF_SACK : 0;
|
|
sc->sc_requested_s_scale = min((data >> 2) & 0xf,
|
|
TCP_MAX_WINSHIFT);
|
|
sc->sc_requested_r_scale = min((data >> 6) & 0xf,
|
|
TCP_MAX_WINSHIFT);
|
|
if (sc->sc_requested_s_scale || sc->sc_requested_r_scale)
|
|
sc->sc_flags |= SCF_WINSCALE;
|
|
} else
|
|
sc->sc_flags |= SCF_NOOPT;
|
|
|
|
wnd = sbspace(&so->so_rcv);
|
|
wnd = imax(wnd, 0);
|
|
wnd = imin(wnd, TCP_MAXWIN);
|
|
sc->sc_wnd = wnd;
|
|
|
|
sc->sc_rxmits = 0;
|
|
sc->sc_peer_mss = tcp_sc_msstab[mss];
|
|
|
|
return (sc);
|
|
}
|