9eab54debf
to free the oldest entry in the current bucket row. The global entry limit may be smaller than the bucket rows and their limit combined however. Thus only try to free a syncache entry if we found one in this bucket row. Reported by: kris
1507 lines
42 KiB
C
1507 lines
42 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/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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#include <security/mac/mac_framework.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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#ifdef MAC
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struct label *sc_label; /* MAC label reference */
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#endif
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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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#ifdef MAC
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mac_destroy_syncache(&sc->sc_label);
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#endif
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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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|
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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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|
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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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|
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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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|
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SCH_LOCK_ASSERT(sch);
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|
|
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TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
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sch->sch_length--;
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|
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syncache_free(sc);
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tcp_syncache.cache_count--;
|
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}
|
|
|
|
/*
|
|
* Walk the timer queues, looking for SYN,ACKs that need to be retransmitted.
|
|
* If we have retransmitted an entry the maximum number of times, expire it.
|
|
* One separate timer for each bucket row.
|
|
*/
|
|
static void
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|
syncache_timer(void *xsch)
|
|
{
|
|
struct syncache_head *sch = (struct syncache_head *)xsch;
|
|
struct syncache *sc, *nsc;
|
|
int tick = ticks;
|
|
|
|
/* NB: syncache_head has already been locked by the callout. */
|
|
SCH_LOCK_ASSERT(sch);
|
|
|
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TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
|
|
/*
|
|
* We do not check if the listen socket still exists
|
|
* and accept the case where the listen socket may be
|
|
* gone by the time we resend the SYN/ACK. We do
|
|
* not expect this to happens often. If it does,
|
|
* then the RST will be sent by the time the remote
|
|
* host does the SYN/ACK->ACK.
|
|
*/
|
|
if (sc->sc_rxttime >= tick) {
|
|
if (sc->sc_rxttime < sch->sch_nextc)
|
|
sch->sch_nextc = sc->sc_rxttime;
|
|
continue;
|
|
}
|
|
|
|
if (sc->sc_rxmits > tcp_syncache.rexmt_limit) {
|
|
syncache_drop(sc, sch);
|
|
tcpstat.tcps_sc_stale++;
|
|
continue;
|
|
}
|
|
|
|
(void) syncache_respond(sc, NULL);
|
|
tcpstat.tcps_sc_retransmitted++;
|
|
SYNCACHE_TIMEOUT(sc, sch, 0);
|
|
}
|
|
if (!TAILQ_EMPTY(&(sch)->sch_bucket))
|
|
callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
|
|
syncache_timer, (void *)(sch));
|
|
}
|
|
|
|
/*
|
|
* Find an entry in the syncache.
|
|
* Returns always with locked syncache_head plus a matching entry or NULL.
|
|
*/
|
|
struct syncache *
|
|
syncache_lookup(struct in_conninfo *inc, struct syncache_head **schp)
|
|
{
|
|
struct syncache *sc;
|
|
struct syncache_head *sch;
|
|
|
|
#ifdef INET6
|
|
if (inc->inc_isipv6) {
|
|
sch = &tcp_syncache.hashbase[
|
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SYNCACHE_HASH6(inc, tcp_syncache.hashmask)];
|
|
*schp = sch;
|
|
|
|
SCH_LOCK(sch);
|
|
|
|
/* Circle through bucket row to find matching entry. */
|
|
TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
|
|
if (ENDPTS6_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
|
|
return (sc);
|
|
}
|
|
} else
|
|
#endif
|
|
{
|
|
sch = &tcp_syncache.hashbase[
|
|
SYNCACHE_HASH(inc, tcp_syncache.hashmask)];
|
|
*schp = sch;
|
|
|
|
SCH_LOCK(sch);
|
|
|
|
/* Circle through bucket row to find matching entry. */
|
|
TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6)
|
|
continue;
|
|
#endif
|
|
if (ENDPTS_EQ(&inc->inc_ie, &sc->sc_inc.inc_ie))
|
|
return (sc);
|
|
}
|
|
}
|
|
SCH_LOCK_ASSERT(*schp);
|
|
return (NULL); /* always returns with locked sch */
|
|
}
|
|
|
|
/*
|
|
* This function is called when we get a RST for a
|
|
* non-existent connection, so that we can see if the
|
|
* connection is in the syn cache. If it is, zap it.
|
|
*/
|
|
void
|
|
syncache_chkrst(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 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->snd_max = tp->iss + 1;
|
|
tp->snd_nxt = tp->iss + 1;
|
|
tp->rcv_up = sc->sc_irs + 1;
|
|
tp->rcv_wnd = sc->sc_wnd;
|
|
tp->rcv_adv += tp->rcv_wnd;
|
|
tp->last_ack_sent = tp->rcv_nxt;
|
|
|
|
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;
|
|
tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
|
|
|
|
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
|
|
#ifdef MAC
|
|
struct label *maclabel;
|
|
#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;
|
|
|
|
#ifdef MAC
|
|
if (mac_init_syncache(&maclabel) != 0) {
|
|
*lsop = NULL;
|
|
INP_UNLOCK(inp);
|
|
INP_INFO_WUNLOCK(&tcbinfo);
|
|
return (1);
|
|
} else
|
|
mac_init_syncache_from_inpcb(maclabel, inp);
|
|
#endif
|
|
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;
|
|
#ifdef MAC
|
|
/*
|
|
* Since we have already unconditionally allocated label
|
|
* storage, free it up. The syncache entry will already
|
|
* have an initialized label we can use.
|
|
*/
|
|
mac_destroy_syncache(&maclabel);
|
|
KASSERT(sc->sc_label != NULL,
|
|
("%s: label not initialized", __func__));
|
|
#endif
|
|
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++;
|
|
if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
|
|
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.
|
|
*/
|
|
#ifdef MAC
|
|
sc->sc_label = maclabel;
|
|
#endif
|
|
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.
|
|
* Leave enough room for the socket buffer to grow
|
|
* with auto sizing. This allows us to scale the
|
|
* receive buffer over a wide range while not losing
|
|
* any efficiency or fine granularity.
|
|
*
|
|
* RFC1323: The Window field in a SYN (i.e., a <SYN>
|
|
* or <SYN,ACK>) segment itself is never scaled.
|
|
*/
|
|
while (wscale < TCP_MAX_WINSHIFT &&
|
|
(0x1 << wscale) < tcp_minmss)
|
|
wscale++;
|
|
sc->sc_requested_r_scale = wscale;
|
|
sc->sc_requested_s_scale = to->to_wscale;
|
|
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 */
|
|
#ifdef MAC
|
|
else
|
|
mac_destroy_syncache(&sc->sc_label);
|
|
#endif
|
|
tcpstat.tcps_sndacks++;
|
|
tcpstat.tcps_sndtotal++;
|
|
} else {
|
|
if (sc != &scs)
|
|
syncache_free(sc);
|
|
#ifdef MAC
|
|
else
|
|
mac_destroy_syncache(&sc->sc_label);
|
|
#endif
|
|
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 hlen, tlen, mssopt;
|
|
struct tcpopt to;
|
|
#ifdef INET6
|
|
struct ip6_hdr *ip6 = NULL;
|
|
#endif
|
|
|
|
hlen =
|
|
#ifdef INET6
|
|
(sc->sc_inc.inc_isipv6) ? sizeof(struct ip6_hdr) :
|
|
#endif
|
|
sizeof(struct ip);
|
|
tlen = hlen + sizeof(struct tcphdr);
|
|
|
|
/* 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);
|
|
|
|
/* XXX: Assume that the entire packet will fit in a header mbuf. */
|
|
KASSERT(max_linkhdr + tlen + MAX_TCPOPTLEN <= 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);
|
|
#ifdef MAC
|
|
mac_create_mbuf_from_syncache(sc->sc_label, m);
|
|
#endif
|
|
m->m_data += max_linkhdr;
|
|
m->m_len = tlen;
|
|
m->m_pkthdr.len = tlen;
|
|
m->m_pkthdr.rcvif = NULL;
|
|
|
|
#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) >> 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 ((sc->sc_flags & SCF_NOOPT) == 0) {
|
|
to.to_flags = 0;
|
|
|
|
to.to_mss = mssopt;
|
|
to.to_flags = TOF_MSS;
|
|
if (sc->sc_flags & SCF_WINSCALE) {
|
|
to.to_wscale = sc->sc_requested_r_scale;
|
|
to.to_flags |= TOF_SCALE;
|
|
}
|
|
if (sc->sc_flags & SCF_TIMESTAMP) {
|
|
/* Virgin timestamp or TCP cookie enhanced one. */
|
|
to.to_tsval = sc->sc_ts ? sc->sc_ts : ticks;
|
|
to.to_tsecr = sc->sc_tsreflect;
|
|
to.to_flags |= TOF_TS;
|
|
}
|
|
if (sc->sc_flags & SCF_SACK)
|
|
to.to_flags |= TOF_SACKPERM;
|
|
#ifdef TCP_SIGNATURE
|
|
if (sc->sc_flags & SCF_SIGNATURE)
|
|
to.to_flags |= TOF_SIGNATURE;
|
|
#endif
|
|
optlen = tcp_addoptions(&to, (u_char *)(th + 1));
|
|
|
|
#ifdef TCP_SIGNATURE
|
|
tcp_signature_compute(m, sizeof(struct ip), 0, optlen,
|
|
to.to_signature, IPSEC_DIR_OUTBOUND);
|
|
#endif
|
|
|
|
/* Adjust headers by option size. */
|
|
th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
|
|
m->m_len += optlen;
|
|
m->m_pkthdr.len += optlen;
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6)
|
|
ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
|
|
else
|
|
#endif
|
|
ip->ip_len += optlen;
|
|
} else
|
|
optlen = 0;
|
|
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_isipv6) {
|
|
th->th_sum = 0;
|
|
th->th_sum = in6_cksum(m, IPPROTO_TCP, hlen,
|
|
tlen + optlen - 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 + optlen - 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);
|
|
}
|