2026 lines
58 KiB
C
2026 lines
58 KiB
C
/*-
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* Copyright (c) 2001 McAfee, Inc.
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* Copyright (c) 2006,2013 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. [2001 McAfee, Inc.]
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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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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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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_pcbgroup.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/limits.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/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 <sys/syslog.h>
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#include <sys/ucred.h>
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#include <sys/md5.h>
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#include <crypto/siphash/siphash.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 <net/vnet.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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#include <netinet/tcp_syncache.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 TCP_OFFLOAD
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#include <netinet/toecore.h>
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#endif
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#ifdef 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 /*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 VNET_DEFINE(int, tcp_syncookies) = 1;
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#define V_tcp_syncookies VNET(tcp_syncookies)
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SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies, CTLFLAG_RW,
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&VNET_NAME(tcp_syncookies), 0,
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"Use TCP SYN cookies if the syncache overflows");
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static VNET_DEFINE(int, tcp_syncookiesonly) = 0;
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#define V_tcp_syncookiesonly VNET(tcp_syncookiesonly)
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SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
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&VNET_NAME(tcp_syncookiesonly), 0,
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"Use only TCP SYN cookies");
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#ifdef TCP_OFFLOAD
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#define ADDED_BY_TOE(sc) ((sc)->sc_tod != NULL)
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#endif
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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 *);
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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 int syncache_sysctl_count(SYSCTL_HANDLER_ARGS);
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static void syncache_timeout(struct syncache *sc, struct syncache_head *sch,
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int docallout);
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static void syncache_timer(void *);
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static uint32_t syncookie_mac(struct in_conninfo *, tcp_seq, uint8_t,
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uint8_t *, uintptr_t);
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static tcp_seq syncookie_generate(struct syncache_head *, struct syncache *);
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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 tcphdr *, struct tcpopt *,
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struct socket *);
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static void syncookie_reseed(void *);
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#ifdef INVARIANTS
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static int syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
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struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
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struct socket *lso);
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#endif
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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 3 * (1 + 2 + 4 + 8) == 45 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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static VNET_DEFINE(struct tcp_syncache, tcp_syncache);
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#define V_tcp_syncache VNET(tcp_syncache)
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static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, syncache, CTLFLAG_RW, 0,
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"TCP SYN cache");
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SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, bucketlimit, CTLFLAG_RDTUN,
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&VNET_NAME(tcp_syncache.bucket_limit), 0,
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"Per-bucket hash limit for syncache");
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SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, cachelimit, CTLFLAG_RDTUN,
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&VNET_NAME(tcp_syncache.cache_limit), 0,
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"Overall entry limit for syncache");
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SYSCTL_VNET_PROC(_net_inet_tcp_syncache, OID_AUTO, count, (CTLTYPE_UINT|CTLFLAG_RD),
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NULL, 0, &syncache_sysctl_count, "IU",
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"Current number of entries in syncache");
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SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, hashsize, CTLFLAG_RDTUN,
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&VNET_NAME(tcp_syncache.hashsize), 0,
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"Size of TCP syncache hashtable");
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SYSCTL_VNET_UINT(_net_inet_tcp_syncache, OID_AUTO, rexmtlimit, CTLFLAG_RW,
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&VNET_NAME(tcp_syncache.rexmt_limit), 0,
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"Limit on SYN/ACK retransmissions");
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VNET_DEFINE(int, tcp_sc_rst_sock_fail) = 1;
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SYSCTL_VNET_INT(_net_inet_tcp_syncache, OID_AUTO, rst_on_sock_fail,
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CTLFLAG_RW, &VNET_NAME(tcp_sc_rst_sock_fail), 0,
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"Send reset on socket allocation failure");
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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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((V_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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((V_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 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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if (sc->sc_cred)
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crfree(sc->sc_cred);
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#ifdef MAC
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mac_syncache_destroy(&sc->sc_label);
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#endif
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uma_zfree(V_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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V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
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V_tcp_syncache.bucket_limit = TCP_SYNCACHE_BUCKETLIMIT;
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V_tcp_syncache.rexmt_limit = SYNCACHE_MAXREXMTS;
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V_tcp_syncache.hash_secret = arc4random();
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TUNABLE_INT_FETCH("net.inet.tcp.syncache.hashsize",
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&V_tcp_syncache.hashsize);
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TUNABLE_INT_FETCH("net.inet.tcp.syncache.bucketlimit",
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&V_tcp_syncache.bucket_limit);
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if (!powerof2(V_tcp_syncache.hashsize) ||
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V_tcp_syncache.hashsize == 0) {
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printf("WARNING: syncache hash size is not a power of 2.\n");
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V_tcp_syncache.hashsize = TCP_SYNCACHE_HASHSIZE;
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}
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V_tcp_syncache.hashmask = V_tcp_syncache.hashsize - 1;
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/* Set limits. */
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V_tcp_syncache.cache_limit =
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V_tcp_syncache.hashsize * V_tcp_syncache.bucket_limit;
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TUNABLE_INT_FETCH("net.inet.tcp.syncache.cachelimit",
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&V_tcp_syncache.cache_limit);
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/* Allocate the hash table. */
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V_tcp_syncache.hashbase = malloc(V_tcp_syncache.hashsize *
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sizeof(struct syncache_head), M_SYNCACHE, M_WAITOK | M_ZERO);
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#ifdef VIMAGE
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V_tcp_syncache.vnet = curvnet;
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#endif
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/* Initialize the hash buckets. */
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for (i = 0; i < V_tcp_syncache.hashsize; i++) {
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TAILQ_INIT(&V_tcp_syncache.hashbase[i].sch_bucket);
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mtx_init(&V_tcp_syncache.hashbase[i].sch_mtx, "tcp_sc_head",
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NULL, MTX_DEF);
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callout_init_mtx(&V_tcp_syncache.hashbase[i].sch_timer,
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&V_tcp_syncache.hashbase[i].sch_mtx, 0);
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V_tcp_syncache.hashbase[i].sch_length = 0;
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V_tcp_syncache.hashbase[i].sch_sc = &V_tcp_syncache;
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}
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/* Create the syncache entry zone. */
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V_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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V_tcp_syncache.cache_limit = uma_zone_set_max(V_tcp_syncache.zone,
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V_tcp_syncache.cache_limit);
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/* Start the SYN cookie reseeder callout. */
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callout_init(&V_tcp_syncache.secret.reseed, 1);
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arc4rand(V_tcp_syncache.secret.key[0], SYNCOOKIE_SECRET_SIZE, 0);
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arc4rand(V_tcp_syncache.secret.key[1], SYNCOOKIE_SECRET_SIZE, 0);
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callout_reset(&V_tcp_syncache.secret.reseed, SYNCOOKIE_LIFETIME * hz,
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syncookie_reseed, &V_tcp_syncache);
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}
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#ifdef VIMAGE
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void
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syncache_destroy(void)
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{
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struct syncache_head *sch;
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struct syncache *sc, *nsc;
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int i;
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/* Cleanup hash buckets: stop timers, free entries, destroy locks. */
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for (i = 0; i < V_tcp_syncache.hashsize; i++) {
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sch = &V_tcp_syncache.hashbase[i];
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callout_drain(&sch->sch_timer);
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SCH_LOCK(sch);
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TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc)
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syncache_drop(sc, sch);
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SCH_UNLOCK(sch);
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KASSERT(TAILQ_EMPTY(&sch->sch_bucket),
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("%s: sch->sch_bucket not empty", __func__));
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KASSERT(sch->sch_length == 0, ("%s: sch->sch_length %d not 0",
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__func__, sch->sch_length));
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mtx_destroy(&sch->sch_mtx);
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}
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KASSERT(uma_zone_get_cur(V_tcp_syncache.zone) == 0,
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("%s: cache_count not 0", __func__));
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/* Free the allocated global resources. */
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uma_zdestroy(V_tcp_syncache.zone);
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free(V_tcp_syncache.hashbase, M_SYNCACHE);
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callout_drain(&V_tcp_syncache.secret.reseed);
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}
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#endif
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static int
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syncache_sysctl_count(SYSCTL_HANDLER_ARGS)
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{
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int count;
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count = uma_zone_get_cur(V_tcp_syncache.zone);
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return (sysctl_handle_int(oidp, &count, 0, req));
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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 >= V_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_INC(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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#ifdef TCP_OFFLOAD
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if (ADDED_BY_TOE(sc)) {
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struct toedev *tod = sc->sc_tod;
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tod->tod_syncache_added(tod, sc->sc_todctx);
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}
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#endif
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/* Reinitialize the bucket row's timer. */
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if (sch->sch_length == 1)
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sch->sch_nextc = ticks + INT_MAX;
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syncache_timeout(sc, sch, 1);
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SCH_UNLOCK(sch);
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TCPSTAT_INC(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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#ifdef TCP_OFFLOAD
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if (ADDED_BY_TOE(sc)) {
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struct toedev *tod = sc->sc_tod;
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tod->tod_syncache_removed(tod, sc->sc_todctx);
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}
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#endif
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syncache_free(sc);
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}
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/*
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* Engage/reengage time on bucket row.
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*/
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static void
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syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
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{
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sc->sc_rxttime = ticks +
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TCPTV_RTOBASE * (tcp_syn_backoff[sc->sc_rxmits]);
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sc->sc_rxmits++;
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if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
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sch->sch_nextc = sc->sc_rxttime;
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if (docallout)
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callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
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syncache_timer, (void *)sch);
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}
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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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char *s;
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CURVNET_SET(sch->sch_sc->vnet);
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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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/*
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* In the following cycle we may remove some entries and/or
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* advance some timeouts, so re-initialize the bucket timer.
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*/
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sch->sch_nextc = tick + INT_MAX;
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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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|
*/
|
|
if (TSTMP_GT(sc->sc_rxttime, tick)) {
|
|
if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
|
|
sch->sch_nextc = sc->sc_rxttime;
|
|
continue;
|
|
}
|
|
if (sc->sc_rxmits > V_tcp_syncache.rexmt_limit) {
|
|
if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
|
|
"giving up and removing syncache entry\n",
|
|
s, __func__);
|
|
free(s, M_TCPLOG);
|
|
}
|
|
syncache_drop(sc, sch);
|
|
TCPSTAT_INC(tcps_sc_stale);
|
|
continue;
|
|
}
|
|
if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: Response timeout, "
|
|
"retransmitting (%u) SYN|ACK\n",
|
|
s, __func__, sc->sc_rxmits);
|
|
free(s, M_TCPLOG);
|
|
}
|
|
|
|
(void) syncache_respond(sc);
|
|
TCPSTAT_INC(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));
|
|
CURVNET_RESTORE();
|
|
}
|
|
|
|
/*
|
|
* 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_flags & INC_ISIPV6) {
|
|
sch = &V_tcp_syncache.hashbase[
|
|
SYNCACHE_HASH6(inc, V_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 = &V_tcp_syncache.hashbase[
|
|
SYNCACHE_HASH(inc, V_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_flags & 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;
|
|
char *s = NULL;
|
|
|
|
sc = syncache_lookup(inc, &sch); /* returns locked sch */
|
|
SCH_LOCK_ASSERT(sch);
|
|
|
|
/*
|
|
* Any RST to our SYN|ACK must not carry ACK, SYN or FIN flags.
|
|
* See RFC 793 page 65, section SEGMENT ARRIVES.
|
|
*/
|
|
if (th->th_flags & (TH_ACK|TH_SYN|TH_FIN)) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: Spurious RST with ACK, SYN or "
|
|
"FIN flag set, segment ignored\n", s, __func__);
|
|
TCPSTAT_INC(tcps_badrst);
|
|
goto done;
|
|
}
|
|
|
|
/*
|
|
* No corresponding connection was found in syncache.
|
|
* If syncookies are enabled and possibly exclusively
|
|
* used, or we are under memory pressure, a valid RST
|
|
* may not find a syncache entry. In that case we're
|
|
* done and no SYN|ACK retransmissions will happen.
|
|
* Otherwise the RST was misdirected or spoofed.
|
|
*/
|
|
if (sc == NULL) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: Spurious RST without matching "
|
|
"syncache entry (possibly syncookie only), "
|
|
"segment ignored\n", s, __func__);
|
|
TCPSTAT_INC(tcps_badrst);
|
|
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);
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: Our SYN|ACK was rejected, "
|
|
"connection attempt aborted by remote endpoint\n",
|
|
s, __func__);
|
|
TCPSTAT_INC(tcps_sc_reset);
|
|
} else {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: RST with invalid SEQ %u != "
|
|
"IRS %u (+WND %u), segment ignored\n",
|
|
s, __func__, th->th_seq, sc->sc_irs, sc->sc_wnd);
|
|
TCPSTAT_INC(tcps_badrst);
|
|
}
|
|
|
|
done:
|
|
if (s != NULL)
|
|
free(s, M_TCPLOG);
|
|
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_INC(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_INC(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;
|
|
int error;
|
|
char *s;
|
|
|
|
INP_INFO_WLOCK_ASSERT(&V_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 either send a RST or
|
|
* have the peer retransmit its SYN again after its
|
|
* RTO and try again.
|
|
*/
|
|
TCPSTAT_INC(tcps_listendrop);
|
|
if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: Socket create failed "
|
|
"due to limits or memory shortage\n",
|
|
s, __func__);
|
|
free(s, M_TCPLOG);
|
|
}
|
|
goto abort2;
|
|
}
|
|
#ifdef MAC
|
|
mac_socketpeer_set_from_mbuf(m, so);
|
|
#endif
|
|
|
|
inp = sotoinpcb(so);
|
|
inp->inp_inc.inc_fibnum = so->so_fibnum;
|
|
INP_WLOCK(inp);
|
|
INP_HASH_WLOCK(&V_tcbinfo);
|
|
|
|
/* Insert new socket into PCB hash list. */
|
|
inp->inp_inc.inc_flags = sc->sc_inc.inc_flags;
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_flags & 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
|
|
|
|
/*
|
|
* Install in the reservation hash table for now, but don't yet
|
|
* install a connection group since the full 4-tuple isn't yet
|
|
* configured.
|
|
*/
|
|
inp->inp_lport = sc->sc_inc.inc_lport;
|
|
if ((error = in_pcbinshash_nopcbgroup(inp)) != 0) {
|
|
/*
|
|
* Undo the assignments above if we failed to
|
|
* put the PCB on the hash lists.
|
|
*/
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_flags & INC_ISIPV6)
|
|
inp->in6p_laddr = in6addr_any;
|
|
else
|
|
#endif
|
|
inp->inp_laddr.s_addr = INADDR_ANY;
|
|
inp->inp_lport = 0;
|
|
if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: in_pcbinshash failed "
|
|
"with error %i\n",
|
|
s, __func__, error);
|
|
free(s, M_TCPLOG);
|
|
}
|
|
INP_HASH_WUNLOCK(&V_tcbinfo);
|
|
goto abort;
|
|
}
|
|
#ifdef 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_flags & 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 ((error = in6_pcbconnect_mbuf(inp, (struct sockaddr *)&sin6,
|
|
thread0.td_ucred, m)) != 0) {
|
|
inp->in6p_laddr = laddr6;
|
|
if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: in6_pcbconnect failed "
|
|
"with error %i\n",
|
|
s, __func__, error);
|
|
free(s, M_TCPLOG);
|
|
}
|
|
INP_HASH_WUNLOCK(&V_tcbinfo);
|
|
goto abort;
|
|
}
|
|
/* Override flowlabel from in6_pcbconnect. */
|
|
inp->inp_flow &= ~IPV6_FLOWLABEL_MASK;
|
|
inp->inp_flow |= sc->sc_flowlabel;
|
|
}
|
|
#endif /* INET6 */
|
|
#if defined(INET) && defined(INET6)
|
|
else
|
|
#endif
|
|
#ifdef INET
|
|
{
|
|
struct in_addr laddr;
|
|
struct sockaddr_in sin;
|
|
|
|
inp->inp_options = (m) ? ip_srcroute(m) : NULL;
|
|
|
|
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 ((error = in_pcbconnect_mbuf(inp, (struct sockaddr *)&sin,
|
|
thread0.td_ucred, m)) != 0) {
|
|
inp->inp_laddr = laddr;
|
|
if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: in_pcbconnect failed "
|
|
"with error %i\n",
|
|
s, __func__, error);
|
|
free(s, M_TCPLOG);
|
|
}
|
|
INP_HASH_WUNLOCK(&V_tcbinfo);
|
|
goto abort;
|
|
}
|
|
}
|
|
#endif /* INET */
|
|
INP_HASH_WUNLOCK(&V_tcbinfo);
|
|
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 = tcp_ts_getticks();
|
|
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->t_flags |= TF_SACK_PERMIT;
|
|
}
|
|
|
|
if (sc->sc_flags & SCF_ECN)
|
|
tp->t_flags |= TF_ECN_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, indicate that CWND to be
|
|
* limited to one segment in cc_conn_init().
|
|
* NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
|
|
*/
|
|
if (sc->sc_rxmits > 1)
|
|
tp->snd_cwnd = 1;
|
|
|
|
#ifdef TCP_OFFLOAD
|
|
/*
|
|
* Allow a TOE driver to install its hooks. Note that we hold the
|
|
* pcbinfo lock too and that prevents tcp_usr_accept from accepting a
|
|
* new connection before the TOE driver has done its thing.
|
|
*/
|
|
if (ADDED_BY_TOE(sc)) {
|
|
struct toedev *tod = sc->sc_tod;
|
|
|
|
tod->tod_offload_socket(tod, sc->sc_todctx, so);
|
|
}
|
|
#endif
|
|
/*
|
|
* Copy and activate timers.
|
|
*/
|
|
tp->t_keepinit = sototcpcb(lso)->t_keepinit;
|
|
tp->t_keepidle = sototcpcb(lso)->t_keepidle;
|
|
tp->t_keepintvl = sototcpcb(lso)->t_keepintvl;
|
|
tp->t_keepcnt = sototcpcb(lso)->t_keepcnt;
|
|
tcp_timer_activate(tp, TT_KEEP, TP_KEEPINIT(tp));
|
|
|
|
INP_WUNLOCK(inp);
|
|
|
|
TCPSTAT_INC(tcps_accepts);
|
|
return (so);
|
|
|
|
abort:
|
|
INP_WUNLOCK(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 syncache scs;
|
|
char *s;
|
|
|
|
/*
|
|
* Global TCP locks are held because we manipulate the PCB lists
|
|
* and create a new socket.
|
|
*/
|
|
INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
|
|
KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
|
|
("%s: can handle only ACK", __func__));
|
|
|
|
sc = syncache_lookup(inc, &sch); /* returns locked sch */
|
|
SCH_LOCK_ASSERT(sch);
|
|
|
|
#ifdef INVARIANTS
|
|
/*
|
|
* Test code for syncookies comparing the syncache stored
|
|
* values with the reconstructed values from the cookie.
|
|
*/
|
|
if (sc != NULL)
|
|
syncookie_cmp(inc, sch, sc, th, to, *lsop);
|
|
#endif
|
|
|
|
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 (!V_tcp_syncookies) {
|
|
SCH_UNLOCK(sch);
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: Spurious ACK, "
|
|
"segment rejected (syncookies disabled)\n",
|
|
s, __func__);
|
|
goto failed;
|
|
}
|
|
bzero(&scs, sizeof(scs));
|
|
sc = syncookie_lookup(inc, sch, &scs, th, to, *lsop);
|
|
SCH_UNLOCK(sch);
|
|
if (sc == NULL) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: Segment failed "
|
|
"SYNCOOKIE authentication, segment rejected "
|
|
"(probably spoofed)\n", s, __func__);
|
|
goto failed;
|
|
}
|
|
} else {
|
|
/* Pull out the entry to unlock the bucket row. */
|
|
TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
|
|
sch->sch_length--;
|
|
#ifdef TCP_OFFLOAD
|
|
if (ADDED_BY_TOE(sc)) {
|
|
struct toedev *tod = sc->sc_tod;
|
|
|
|
tod->tod_syncache_removed(tod, sc->sc_todctx);
|
|
}
|
|
#endif
|
|
SCH_UNLOCK(sch);
|
|
}
|
|
|
|
/*
|
|
* Segment validation:
|
|
* ACK must match our initial sequence number + 1 (the SYN|ACK).
|
|
*/
|
|
if (th->th_ack != sc->sc_iss + 1) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: ACK %u != ISS+1 %u, segment "
|
|
"rejected\n", s, __func__, th->th_ack, sc->sc_iss);
|
|
goto failed;
|
|
}
|
|
|
|
/*
|
|
* The SEQ must fall in the window starting at the received
|
|
* initial receive sequence number + 1 (the SYN).
|
|
*/
|
|
if (SEQ_LEQ(th->th_seq, sc->sc_irs) ||
|
|
SEQ_GT(th->th_seq, sc->sc_irs + sc->sc_wnd)) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: SEQ %u != IRS+1 %u, segment "
|
|
"rejected\n", s, __func__, th->th_seq, sc->sc_irs);
|
|
goto failed;
|
|
}
|
|
|
|
/*
|
|
* If timestamps were not negotiated during SYN/ACK they
|
|
* must not appear on any segment during this session.
|
|
*/
|
|
if (!(sc->sc_flags & SCF_TIMESTAMP) && (to->to_flags & TOF_TS)) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
|
|
"segment rejected\n", s, __func__);
|
|
goto failed;
|
|
}
|
|
|
|
/*
|
|
* If timestamps were negotiated during SYN/ACK they should
|
|
* appear on every segment during this session.
|
|
* XXXAO: This is only informal as there have been unverified
|
|
* reports of non-compliants stacks.
|
|
*/
|
|
if ((sc->sc_flags & SCF_TIMESTAMP) && !(to->to_flags & TOF_TS)) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: Timestamp missing, "
|
|
"no action\n", s, __func__);
|
|
free(s, M_TCPLOG);
|
|
s = NULL;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If timestamps were negotiated the reflected timestamp
|
|
* must be equal to what we actually sent in the SYN|ACK.
|
|
*/
|
|
if ((to->to_flags & TOF_TS) && to->to_tsecr != sc->sc_ts) {
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)))
|
|
log(LOG_DEBUG, "%s; %s: TSECR %u != TS %u, "
|
|
"segment rejected\n",
|
|
s, __func__, to->to_tsecr, sc->sc_ts);
|
|
goto failed;
|
|
}
|
|
|
|
*lsop = syncache_socket(sc, *lsop, m);
|
|
|
|
if (*lsop == NULL)
|
|
TCPSTAT_INC(tcps_sc_aborted);
|
|
else
|
|
TCPSTAT_INC(tcps_sc_completed);
|
|
|
|
/* how do we find the inp for the new socket? */
|
|
if (sc != &scs)
|
|
syncache_free(sc);
|
|
return (1);
|
|
failed:
|
|
if (sc != NULL && sc != &scs)
|
|
syncache_free(sc);
|
|
if (s != NULL)
|
|
free(s, M_TCPLOG);
|
|
*lsop = NULL;
|
|
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.
|
|
*/
|
|
void
|
|
syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
|
|
struct inpcb *inp, struct socket **lsop, struct mbuf *m, void *tod,
|
|
void *todctx)
|
|
{
|
|
struct tcpcb *tp;
|
|
struct socket *so;
|
|
struct syncache *sc = NULL;
|
|
struct syncache_head *sch;
|
|
struct mbuf *ipopts = NULL;
|
|
u_int ltflags;
|
|
int win, sb_hiwat, ip_ttl, ip_tos;
|
|
char *s;
|
|
#ifdef INET6
|
|
int autoflowlabel = 0;
|
|
#endif
|
|
#ifdef MAC
|
|
struct label *maclabel;
|
|
#endif
|
|
struct syncache scs;
|
|
struct ucred *cred;
|
|
|
|
INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
|
|
INP_WLOCK_ASSERT(inp); /* listen socket */
|
|
KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
|
|
("%s: unexpected tcp flags", __func__));
|
|
|
|
/*
|
|
* Combine all so/tp operations very early to drop the INP lock as
|
|
* soon as possible.
|
|
*/
|
|
so = *lsop;
|
|
tp = sototcpcb(so);
|
|
cred = crhold(so->so_cred);
|
|
|
|
#ifdef INET6
|
|
if ((inc->inc_flags & INC_ISIPV6) &&
|
|
(inp->inp_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;
|
|
ltflags = (tp->t_flags & (TF_NOOPT | TF_SIGNATURE));
|
|
|
|
/* By the time we drop the lock these should no longer be used. */
|
|
so = NULL;
|
|
tp = NULL;
|
|
|
|
#ifdef MAC
|
|
if (mac_syncache_init(&maclabel) != 0) {
|
|
INP_WUNLOCK(inp);
|
|
INP_INFO_WUNLOCK(&V_tcbinfo);
|
|
goto done;
|
|
} else
|
|
mac_syncache_create(maclabel, inp);
|
|
#endif
|
|
INP_WUNLOCK(inp);
|
|
INP_INFO_WUNLOCK(&V_tcbinfo);
|
|
|
|
/*
|
|
* Remember the IP options, if any.
|
|
*/
|
|
#ifdef INET6
|
|
if (!(inc->inc_flags & INC_ISIPV6))
|
|
#endif
|
|
#ifdef INET
|
|
ipopts = (m) ? ip_srcroute(m) : NULL;
|
|
#else
|
|
ipopts = NULL;
|
|
#endif
|
|
|
|
/*
|
|
* 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?)
|
|
*
|
|
* XXX: We do not check the sequence number to see if this is a
|
|
* real retransmit or a new connection attempt. The question is
|
|
* how to handle such a case; either ignore it as spoofed, or
|
|
* drop the current entry and create a new one?
|
|
*/
|
|
sc = syncache_lookup(inc, &sch); /* returns locked entry */
|
|
SCH_LOCK_ASSERT(sch);
|
|
if (sc != NULL) {
|
|
TCPSTAT_INC(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) && (to->to_flags & TOF_TS))
|
|
sc->sc_tsreflect = to->to_tsval;
|
|
else
|
|
sc->sc_flags &= ~SCF_TIMESTAMP;
|
|
#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_syncache_destroy(&maclabel);
|
|
#endif
|
|
/* Retransmit SYN|ACK and reset retransmit count. */
|
|
if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
|
|
log(LOG_DEBUG, "%s; %s: Received duplicate SYN, "
|
|
"resetting timer and retransmitting SYN|ACK\n",
|
|
s, __func__);
|
|
free(s, M_TCPLOG);
|
|
}
|
|
if (syncache_respond(sc) == 0) {
|
|
sc->sc_rxmits = 0;
|
|
syncache_timeout(sc, sch, 1);
|
|
TCPSTAT_INC(tcps_sndacks);
|
|
TCPSTAT_INC(tcps_sndtotal);
|
|
}
|
|
SCH_UNLOCK(sch);
|
|
goto done;
|
|
}
|
|
|
|
sc = uma_zalloc(V_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_INC(tcps_sc_zonefail);
|
|
if ((sc = TAILQ_LAST(&sch->sch_bucket, sch_head)) != NULL)
|
|
syncache_drop(sc, sch);
|
|
sc = uma_zalloc(V_tcp_syncache.zone, M_NOWAIT | M_ZERO);
|
|
if (sc == NULL) {
|
|
if (V_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_cred = cred;
|
|
cred = NULL;
|
|
sc->sc_ipopts = ipopts;
|
|
bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
|
|
#ifdef INET6
|
|
if (!(inc->inc_flags & INC_ISIPV6))
|
|
#endif
|
|
{
|
|
sc->sc_ip_tos = ip_tos;
|
|
sc->sc_ip_ttl = ip_ttl;
|
|
}
|
|
#ifdef TCP_OFFLOAD
|
|
sc->sc_tod = tod;
|
|
sc->sc_todctx = todctx;
|
|
#endif
|
|
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 (V_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_ts = tcp_ts_getticks();
|
|
sc->sc_flags |= SCF_TIMESTAMP;
|
|
}
|
|
if (to->to_flags & TOF_SCALE) {
|
|
int wscale = 0;
|
|
|
|
/*
|
|
* Pick the smallest possible scaling factor that
|
|
* will still allow us to scale up to sb_max, aka
|
|
* kern.ipc.maxsockbuf.
|
|
*
|
|
* We do this because there are broken firewalls that
|
|
* will corrupt the window scale option, leading to
|
|
* the other endpoint believing that our advertised
|
|
* window is unscaled. At scale factors larger than
|
|
* 5 the unscaled window will drop below 1500 bytes,
|
|
* leading to serious problems when traversing these
|
|
* broken firewalls.
|
|
*
|
|
* With the default maxsockbuf of 256K, a scale factor
|
|
* of 3 will be chosen by this algorithm. Those who
|
|
* choose a larger maxsockbuf should watch out
|
|
* for the compatiblity problems mentioned above.
|
|
*
|
|
* RFC1323: The Window field in a SYN (i.e., a <SYN>
|
|
* or <SYN,ACK>) segment itself is never scaled.
|
|
*/
|
|
while (wscale < TCP_MAX_WINSHIFT &&
|
|
(TCP_MAXWIN << wscale) < sb_max)
|
|
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 || ltflags & TF_SIGNATURE)
|
|
sc->sc_flags |= SCF_SIGNATURE;
|
|
#endif
|
|
if (to->to_flags & TOF_SACKPERM)
|
|
sc->sc_flags |= SCF_SACK;
|
|
if (to->to_flags & TOF_MSS)
|
|
sc->sc_peer_mss = to->to_mss; /* peer mss may be zero */
|
|
if (ltflags & TF_NOOPT)
|
|
sc->sc_flags |= SCF_NOOPT;
|
|
if ((th->th_flags & (TH_ECE|TH_CWR)) && V_tcp_do_ecn)
|
|
sc->sc_flags |= SCF_ECN;
|
|
|
|
if (V_tcp_syncookies)
|
|
sc->sc_iss = syncookie_generate(sch, sc);
|
|
#ifdef INET6
|
|
if (autoflowlabel) {
|
|
if (V_tcp_syncookies)
|
|
sc->sc_flowlabel = sc->sc_iss;
|
|
else
|
|
sc->sc_flowlabel = ip6_randomflowlabel();
|
|
sc->sc_flowlabel = htonl(sc->sc_flowlabel) & IPV6_FLOWLABEL_MASK;
|
|
}
|
|
#endif
|
|
SCH_UNLOCK(sch);
|
|
|
|
/*
|
|
* Do a standard 3-way handshake.
|
|
*/
|
|
if (syncache_respond(sc) == 0) {
|
|
if (V_tcp_syncookies && V_tcp_syncookiesonly && sc != &scs)
|
|
syncache_free(sc);
|
|
else if (sc != &scs)
|
|
syncache_insert(sc, sch); /* locks and unlocks sch */
|
|
TCPSTAT_INC(tcps_sndacks);
|
|
TCPSTAT_INC(tcps_sndtotal);
|
|
} else {
|
|
if (sc != &scs)
|
|
syncache_free(sc);
|
|
TCPSTAT_INC(tcps_sc_dropped);
|
|
}
|
|
|
|
done:
|
|
if (cred != NULL)
|
|
crfree(cred);
|
|
#ifdef MAC
|
|
if (sc == &scs)
|
|
mac_syncache_destroy(&maclabel);
|
|
#endif
|
|
if (m) {
|
|
|
|
*lsop = NULL;
|
|
m_freem(m);
|
|
}
|
|
}
|
|
|
|
static int
|
|
syncache_respond(struct syncache *sc)
|
|
{
|
|
struct ip *ip = NULL;
|
|
struct mbuf *m;
|
|
struct tcphdr *th = NULL;
|
|
int optlen, error = 0; /* Make compiler happy */
|
|
u_int16_t hlen, tlen, mssopt;
|
|
struct tcpopt to;
|
|
#ifdef INET6
|
|
struct ip6_hdr *ip6 = NULL;
|
|
#endif
|
|
|
|
hlen =
|
|
#ifdef INET6
|
|
(sc->sc_inc.inc_flags & 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), V_tcp_minmss);
|
|
|
|
/* XXX: Assume that the entire packet will fit in a header mbuf. */
|
|
KASSERT(max_linkhdr + tlen + TCP_MAXOLEN <= MHLEN,
|
|
("syncache: mbuf too small"));
|
|
|
|
/* Create the IP+TCP header from scratch. */
|
|
m = m_gethdr(M_NOWAIT, MT_DATA);
|
|
if (m == NULL)
|
|
return (ENOBUFS);
|
|
#ifdef MAC
|
|
mac_syncache_create_mbuf(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_flags & 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);
|
|
}
|
|
#endif
|
|
#if defined(INET6) && defined(INET)
|
|
else
|
|
#endif
|
|
#ifdef INET
|
|
{
|
|
ip = mtod(m, struct ip *);
|
|
ip->ip_v = IPVERSION;
|
|
ip->ip_hl = sizeof(struct ip) >> 2;
|
|
ip->ip_len = htons(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 (V_path_mtu_discovery && ((sc->sc_flags & SCF_UNREACH) == 0))
|
|
ip->ip_off |= htons(IP_DF);
|
|
|
|
th = (struct tcphdr *)(ip + 1);
|
|
}
|
|
#endif /* INET */
|
|
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;
|
|
|
|
if (sc->sc_flags & SCF_ECN) {
|
|
th->th_flags |= TH_ECE;
|
|
TCPSTAT_INC(tcps_ecn_shs);
|
|
}
|
|
|
|
/* 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;
|
|
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));
|
|
|
|
/* Adjust headers by option size. */
|
|
th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
|
|
m->m_len += optlen;
|
|
m->m_pkthdr.len += optlen;
|
|
|
|
#ifdef TCP_SIGNATURE
|
|
if (sc->sc_flags & SCF_SIGNATURE)
|
|
tcp_signature_compute(m, 0, 0, optlen,
|
|
to.to_signature, IPSEC_DIR_OUTBOUND);
|
|
#endif
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_flags & INC_ISIPV6)
|
|
ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) + optlen);
|
|
else
|
|
#endif
|
|
ip->ip_len = htons(ntohs(ip->ip_len) + optlen);
|
|
} else
|
|
optlen = 0;
|
|
|
|
M_SETFIB(m, sc->sc_inc.inc_fibnum);
|
|
m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
|
|
#ifdef INET6
|
|
if (sc->sc_inc.inc_flags & INC_ISIPV6) {
|
|
m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
|
|
th->th_sum = in6_cksum_pseudo(ip6, tlen + optlen - hlen,
|
|
IPPROTO_TCP, 0);
|
|
ip6->ip6_hlim = in6_selecthlim(NULL, NULL);
|
|
#ifdef TCP_OFFLOAD
|
|
if (ADDED_BY_TOE(sc)) {
|
|
struct toedev *tod = sc->sc_tod;
|
|
|
|
error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
|
|
|
|
return (error);
|
|
}
|
|
#endif
|
|
error = ip6_output(m, NULL, NULL, 0, NULL, NULL, NULL);
|
|
}
|
|
#endif
|
|
#if defined(INET6) && defined(INET)
|
|
else
|
|
#endif
|
|
#ifdef INET
|
|
{
|
|
m->m_pkthdr.csum_flags = CSUM_TCP;
|
|
th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
|
|
htons(tlen + optlen - hlen + IPPROTO_TCP));
|
|
#ifdef TCP_OFFLOAD
|
|
if (ADDED_BY_TOE(sc)) {
|
|
struct toedev *tod = sc->sc_tod;
|
|
|
|
error = tod->tod_syncache_respond(tod, sc->sc_todctx, m);
|
|
|
|
return (error);
|
|
}
|
|
#endif
|
|
error = ip_output(m, sc->sc_ipopts, NULL, 0, NULL, NULL);
|
|
}
|
|
#endif
|
|
return (error);
|
|
}
|
|
|
|
/*
|
|
* The purpose of syncookies is to handle spoofed SYN flooding DoS attacks
|
|
* that exceed the capacity of the syncache by avoiding the storage of any
|
|
* of the SYNs we receive. Syncookies defend against blind SYN flooding
|
|
* attacks where the attacker does not have access to our responses.
|
|
*
|
|
* Syncookies encode and include all necessary information about the
|
|
* connection setup within the SYN|ACK that we send back. That way we
|
|
* can avoid keeping any local state until the ACK to our SYN|ACK returns
|
|
* (if ever). Normally the syncache and syncookies are running in parallel
|
|
* with the latter taking over when the former is exhausted. When matching
|
|
* syncache entry is found the syncookie is ignored.
|
|
*
|
|
* The only reliable information persisting the 3WHS is our inital sequence
|
|
* number ISS of 32 bits. Syncookies embed a cryptographically sufficient
|
|
* strong hash (MAC) value and a few bits of TCP SYN options in the ISS
|
|
* of our SYN|ACK. The MAC can be recomputed when the ACK to our SYN|ACK
|
|
* returns and signifies a legitimate connection if it matches the ACK.
|
|
*
|
|
* The available space of 32 bits to store the hash and to encode the SYN
|
|
* option information is very tight and we should have at least 24 bits for
|
|
* the MAC to keep the number of guesses by blind spoofing reasonably high.
|
|
*
|
|
* SYN option information we have to encode to fully restore a connection:
|
|
* MSS: is imporant to chose an optimal segment size to avoid IP level
|
|
* fragmentation along the path. The common MSS values can be encoded
|
|
* in a 3-bit table. Uncommon values are captured by the next lower value
|
|
* in the table leading to a slight increase in packetization overhead.
|
|
* WSCALE: is necessary to allow large windows to be used for high delay-
|
|
* bandwidth product links. Not scaling the window when it was initially
|
|
* negotiated is bad for performance as lack of scaling further decreases
|
|
* the apparent available send window. We only need to encode the WSCALE
|
|
* we received from the remote end. Our end can be recalculated at any
|
|
* time. The common WSCALE values can be encoded in a 3-bit table.
|
|
* Uncommon values are captured by the next lower value in the table
|
|
* making us under-estimate the available window size halving our
|
|
* theoretically possible maximum throughput for that connection.
|
|
* SACK: Greatly assists in packet loss recovery and requires 1 bit.
|
|
* TIMESTAMP and SIGNATURE is not encoded because they are permanent options
|
|
* that are included in all segments on a connection. We enable them when
|
|
* the ACK has them.
|
|
*
|
|
* Security of syncookies and attack vectors:
|
|
*
|
|
* The MAC is computed over (faddr||laddr||fport||lport||irs||flags||secmod)
|
|
* together with the gloabl secret to make it unique per connection attempt.
|
|
* Thus any change of any of those parameters results in a different MAC output
|
|
* in an unpredictable way unless a collision is encountered. 24 bits of the
|
|
* MAC are embedded into the ISS.
|
|
*
|
|
* To prevent replay attacks two rotating global secrets are updated with a
|
|
* new random value every 15 seconds. The life-time of a syncookie is thus
|
|
* 15-30 seconds.
|
|
*
|
|
* Vector 1: Attacking the secret. This requires finding a weakness in the
|
|
* MAC itself or the way it is used here. The attacker can do a chosen plain
|
|
* text attack by varying and testing the all parameters under his control.
|
|
* The strength depends on the size and randomness of the secret, and the
|
|
* cryptographic security of the MAC function. Due to the constant updating
|
|
* of the secret the attacker has at most 29.999 seconds to find the secret
|
|
* and launch spoofed connections. After that he has to start all over again.
|
|
*
|
|
* Vector 2: Collision attack on the MAC of a single ACK. With a 24 bit MAC
|
|
* size an average of 4,823 attempts are required for a 50% chance of success
|
|
* to spoof a single syncookie (birthday collision paradox). However the
|
|
* attacker is blind and doesn't know if one of his attempts succeeded unless
|
|
* he has a side channel to interfere success from. A single connection setup
|
|
* success average of 90% requires 8,790 packets, 99.99% requires 17,578 packets.
|
|
* This many attempts are required for each one blind spoofed connection. For
|
|
* every additional spoofed connection he has to launch another N attempts.
|
|
* Thus for a sustained rate 100 spoofed connections per second approximately
|
|
* 1,800,000 packets per second would have to be sent.
|
|
*
|
|
* NB: The MAC function should be fast so that it doesn't become a CPU
|
|
* exhaustion attack vector itself.
|
|
*
|
|
* References:
|
|
* RFC4987 TCP SYN Flooding Attacks and Common Mitigations
|
|
* SYN cookies were first proposed by cryptographer Dan J. Bernstein in 1996
|
|
* http://cr.yp.to/syncookies.html (overview)
|
|
* http://cr.yp.to/syncookies/archive (details)
|
|
*
|
|
*
|
|
* Schematic construction of a syncookie enabled Initial Sequence Number:
|
|
* 0 1 2 3
|
|
* 12345678901234567890123456789012
|
|
* |xxxxxxxxxxxxxxxxxxxxxxxxWWWMMMSP|
|
|
*
|
|
* x 24 MAC (truncated)
|
|
* W 3 Send Window Scale index
|
|
* M 3 MSS index
|
|
* S 1 SACK permitted
|
|
* P 1 Odd/even secret
|
|
*/
|
|
|
|
/*
|
|
* Distribution and probability of certain MSS values. Those in between are
|
|
* rounded down to the next lower one.
|
|
* [An Analysis of TCP Maximum Segment Sizes, S. Alcock and R. Nelson, 2011]
|
|
* .2% .3% 5% 7% 7% 20% 15% 45%
|
|
*/
|
|
static int tcp_sc_msstab[] = { 216, 536, 1200, 1360, 1400, 1440, 1452, 1460 };
|
|
|
|
/*
|
|
* Distribution and probability of certain WSCALE values. We have to map the
|
|
* (send) window scale (shift) option with a range of 0-14 from 4 bits into 3
|
|
* bits based on prevalence of certain values. Where we don't have an exact
|
|
* match for are rounded down to the next lower one letting us under-estimate
|
|
* the true available window. At the moment this would happen only for the
|
|
* very uncommon values 3, 5 and those above 8 (more than 16MB socket buffer
|
|
* and window size). The absence of the WSCALE option (no scaling in either
|
|
* direction) is encoded with index zero.
|
|
* [WSCALE values histograms, Allman, 2012]
|
|
* X 10 10 35 5 6 14 10% by host
|
|
* X 11 4 5 5 18 49 3% by connections
|
|
*/
|
|
static int tcp_sc_wstab[] = { 0, 0, 1, 2, 4, 6, 7, 8 };
|
|
|
|
/*
|
|
* Compute the MAC for the SYN cookie. SIPHASH-2-4 is chosen for its speed
|
|
* and good cryptographic properties.
|
|
*/
|
|
static uint32_t
|
|
syncookie_mac(struct in_conninfo *inc, tcp_seq irs, uint8_t flags,
|
|
uint8_t *secbits, uintptr_t secmod)
|
|
{
|
|
SIPHASH_CTX ctx;
|
|
uint32_t siphash[2];
|
|
|
|
SipHash24_Init(&ctx);
|
|
SipHash_SetKey(&ctx, secbits);
|
|
switch (inc->inc_flags & INC_ISIPV6) {
|
|
#ifdef INET
|
|
case 0:
|
|
SipHash_Update(&ctx, &inc->inc_faddr, sizeof(inc->inc_faddr));
|
|
SipHash_Update(&ctx, &inc->inc_laddr, sizeof(inc->inc_laddr));
|
|
break;
|
|
#endif
|
|
#ifdef INET6
|
|
case INC_ISIPV6:
|
|
SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(inc->inc6_faddr));
|
|
SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(inc->inc6_laddr));
|
|
break;
|
|
#endif
|
|
}
|
|
SipHash_Update(&ctx, &inc->inc_fport, sizeof(inc->inc_fport));
|
|
SipHash_Update(&ctx, &inc->inc_lport, sizeof(inc->inc_lport));
|
|
SipHash_Update(&ctx, &flags, sizeof(flags));
|
|
SipHash_Update(&ctx, &secmod, sizeof(secmod));
|
|
SipHash_Final((u_int8_t *)&siphash, &ctx);
|
|
|
|
return (siphash[0] ^ siphash[1]);
|
|
}
|
|
|
|
static tcp_seq
|
|
syncookie_generate(struct syncache_head *sch, struct syncache *sc)
|
|
{
|
|
u_int i, mss, secbit, wscale;
|
|
uint32_t iss, hash;
|
|
uint8_t *secbits;
|
|
union syncookie cookie;
|
|
|
|
SCH_LOCK_ASSERT(sch);
|
|
|
|
cookie.cookie = 0;
|
|
|
|
/* Map our computed MSS into the 3-bit index. */
|
|
mss = min(tcp_mssopt(&sc->sc_inc), max(sc->sc_peer_mss, V_tcp_minmss));
|
|
for (i = sizeof(tcp_sc_msstab) / sizeof(*tcp_sc_msstab) - 1;
|
|
tcp_sc_msstab[i] > mss && i > 0;
|
|
i--)
|
|
;
|
|
cookie.flags.mss_idx = i;
|
|
|
|
/*
|
|
* Map the send window scale into the 3-bit index but only if
|
|
* the wscale option was received.
|
|
*/
|
|
if (sc->sc_flags & SCF_WINSCALE) {
|
|
wscale = sc->sc_requested_s_scale;
|
|
for (i = sizeof(tcp_sc_wstab) / sizeof(*tcp_sc_wstab) - 1;
|
|
tcp_sc_wstab[i] > wscale && i > 0;
|
|
i--)
|
|
;
|
|
cookie.flags.wscale_idx = i;
|
|
}
|
|
|
|
/* Can we do SACK? */
|
|
if (sc->sc_flags & SCF_SACK)
|
|
cookie.flags.sack_ok = 1;
|
|
|
|
/* Which of the two secrets to use. */
|
|
secbit = sch->sch_sc->secret.oddeven & 0x1;
|
|
cookie.flags.odd_even = secbit;
|
|
|
|
secbits = sch->sch_sc->secret.key[secbit];
|
|
hash = syncookie_mac(&sc->sc_inc, sc->sc_irs, cookie.cookie, secbits,
|
|
(uintptr_t)sch);
|
|
|
|
/*
|
|
* Put the flags into the hash and XOR them to get better ISS number
|
|
* variance. This doesn't enhance the cryptographic strength and is
|
|
* done to prevent the 8 cookie bits from showing up directly on the
|
|
* wire.
|
|
*/
|
|
iss = hash & ~0xff;
|
|
iss |= cookie.cookie ^ (hash >> 24);
|
|
|
|
/* Randomize the timestamp. */
|
|
if (sc->sc_flags & SCF_TIMESTAMP) {
|
|
sc->sc_ts = arc4random();
|
|
sc->sc_tsoff = sc->sc_ts - tcp_ts_getticks();
|
|
}
|
|
|
|
TCPSTAT_INC(tcps_sc_sendcookie);
|
|
return (iss);
|
|
}
|
|
|
|
static struct syncache *
|
|
syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
|
|
struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
|
|
struct socket *lso)
|
|
{
|
|
uint32_t hash;
|
|
uint8_t *secbits;
|
|
tcp_seq ack, seq;
|
|
int wnd, wscale = 0;
|
|
union syncookie cookie;
|
|
|
|
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;
|
|
|
|
/*
|
|
* Unpack the flags containing enough information to restore the
|
|
* connection.
|
|
*/
|
|
cookie.cookie = (ack & 0xff) ^ (ack >> 24);
|
|
|
|
/* Which of the two secrets to use. */
|
|
secbits = sch->sch_sc->secret.key[cookie.flags.odd_even];
|
|
|
|
hash = syncookie_mac(inc, seq, cookie.cookie, secbits, (uintptr_t)sch);
|
|
|
|
/* The recomputed hash matches the ACK if this was a genuine cookie. */
|
|
if ((ack & ~0xff) != (hash & ~0xff))
|
|
return (NULL);
|
|
|
|
/* Fill in the syncache values. */
|
|
sc->sc_flags = 0;
|
|
bcopy(inc, &sc->sc_inc, sizeof(struct in_conninfo));
|
|
sc->sc_ipopts = NULL;
|
|
|
|
sc->sc_irs = seq;
|
|
sc->sc_iss = ack;
|
|
|
|
switch (inc->inc_flags & INC_ISIPV6) {
|
|
#ifdef INET
|
|
case 0:
|
|
sc->sc_ip_ttl = sotoinpcb(lso)->inp_ip_ttl;
|
|
sc->sc_ip_tos = sotoinpcb(lso)->inp_ip_tos;
|
|
break;
|
|
#endif
|
|
#ifdef INET6
|
|
case INC_ISIPV6:
|
|
if (sotoinpcb(lso)->inp_flags & IN6P_AUTOFLOWLABEL)
|
|
sc->sc_flowlabel = sc->sc_iss & IPV6_FLOWLABEL_MASK;
|
|
break;
|
|
#endif
|
|
}
|
|
|
|
sc->sc_peer_mss = tcp_sc_msstab[cookie.flags.mss_idx];
|
|
|
|
/* We can simply recompute receive window scale we sent earlier. */
|
|
while (wscale < TCP_MAX_WINSHIFT && (TCP_MAXWIN << wscale) < sb_max)
|
|
wscale++;
|
|
|
|
/* Only use wscale if it was enabled in the orignal SYN. */
|
|
if (cookie.flags.wscale_idx > 0) {
|
|
sc->sc_requested_r_scale = wscale;
|
|
sc->sc_requested_s_scale = tcp_sc_wstab[cookie.flags.wscale_idx];
|
|
sc->sc_flags |= SCF_WINSCALE;
|
|
}
|
|
|
|
wnd = sbspace(&lso->so_rcv);
|
|
wnd = imax(wnd, 0);
|
|
wnd = imin(wnd, TCP_MAXWIN);
|
|
sc->sc_wnd = wnd;
|
|
|
|
if (cookie.flags.sack_ok)
|
|
sc->sc_flags |= SCF_SACK;
|
|
|
|
if (to->to_flags & TOF_TS) {
|
|
sc->sc_flags |= SCF_TIMESTAMP;
|
|
sc->sc_tsreflect = to->to_tsval;
|
|
sc->sc_ts = to->to_tsecr;
|
|
sc->sc_tsoff = to->to_tsecr - tcp_ts_getticks();
|
|
}
|
|
|
|
if (to->to_flags & TOF_SIGNATURE)
|
|
sc->sc_flags |= SCF_SIGNATURE;
|
|
|
|
sc->sc_rxmits = 0;
|
|
|
|
TCPSTAT_INC(tcps_sc_recvcookie);
|
|
return (sc);
|
|
}
|
|
|
|
#ifdef INVARIANTS
|
|
static int
|
|
syncookie_cmp(struct in_conninfo *inc, struct syncache_head *sch,
|
|
struct syncache *sc, struct tcphdr *th, struct tcpopt *to,
|
|
struct socket *lso)
|
|
{
|
|
struct syncache scs, *scx;
|
|
char *s;
|
|
|
|
bzero(&scs, sizeof(scs));
|
|
scx = syncookie_lookup(inc, sch, &scs, th, to, lso);
|
|
|
|
if ((s = tcp_log_addrs(inc, th, NULL, NULL)) == NULL)
|
|
return (0);
|
|
|
|
if (scx != NULL) {
|
|
if (sc->sc_peer_mss != scx->sc_peer_mss)
|
|
log(LOG_DEBUG, "%s; %s: mss different %i vs %i\n",
|
|
s, __func__, sc->sc_peer_mss, scx->sc_peer_mss);
|
|
|
|
if (sc->sc_requested_r_scale != scx->sc_requested_r_scale)
|
|
log(LOG_DEBUG, "%s; %s: rwscale different %i vs %i\n",
|
|
s, __func__, sc->sc_requested_r_scale,
|
|
scx->sc_requested_r_scale);
|
|
|
|
if (sc->sc_requested_s_scale != scx->sc_requested_s_scale)
|
|
log(LOG_DEBUG, "%s; %s: swscale different %i vs %i\n",
|
|
s, __func__, sc->sc_requested_s_scale,
|
|
scx->sc_requested_s_scale);
|
|
|
|
if ((sc->sc_flags & SCF_SACK) != (scx->sc_flags & SCF_SACK))
|
|
log(LOG_DEBUG, "%s; %s: SACK different\n", s, __func__);
|
|
}
|
|
|
|
if (s != NULL)
|
|
free(s, M_TCPLOG);
|
|
return (0);
|
|
}
|
|
#endif /* INVARIANTS */
|
|
|
|
static void
|
|
syncookie_reseed(void *arg)
|
|
{
|
|
struct tcp_syncache *sc = arg;
|
|
uint8_t *secbits;
|
|
int secbit;
|
|
|
|
/*
|
|
* Reseeding the secret doesn't have to be protected by a lock.
|
|
* It only must be ensured that the new random values are visible
|
|
* to all CPUs in a SMP environment. The atomic with release
|
|
* semantics ensures that.
|
|
*/
|
|
secbit = (sc->secret.oddeven & 0x1) ? 0 : 1;
|
|
secbits = sc->secret.key[secbit];
|
|
arc4rand(secbits, SYNCOOKIE_SECRET_SIZE, 0);
|
|
atomic_add_rel_int(&sc->secret.oddeven, 1);
|
|
|
|
/* Reschedule ourself. */
|
|
callout_schedule(&sc->secret.reseed, SYNCOOKIE_LIFETIME * hz);
|
|
}
|
|
|
|
/*
|
|
* Returns the current number of syncache entries. This number
|
|
* will probably change before you get around to calling
|
|
* syncache_pcblist.
|
|
*/
|
|
int
|
|
syncache_pcbcount(void)
|
|
{
|
|
struct syncache_head *sch;
|
|
int count, i;
|
|
|
|
for (count = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
|
|
/* No need to lock for a read. */
|
|
sch = &V_tcp_syncache.hashbase[i];
|
|
count += sch->sch_length;
|
|
}
|
|
return count;
|
|
}
|
|
|
|
/*
|
|
* Exports the syncache entries to userland so that netstat can display
|
|
* them alongside the other sockets. This function is intended to be
|
|
* called only from tcp_pcblist.
|
|
*
|
|
* Due to concurrency on an active system, the number of pcbs exported
|
|
* may have no relation to max_pcbs. max_pcbs merely indicates the
|
|
* amount of space the caller allocated for this function to use.
|
|
*/
|
|
int
|
|
syncache_pcblist(struct sysctl_req *req, int max_pcbs, int *pcbs_exported)
|
|
{
|
|
struct xtcpcb xt;
|
|
struct syncache *sc;
|
|
struct syncache_head *sch;
|
|
int count, error, i;
|
|
|
|
for (count = 0, error = 0, i = 0; i < V_tcp_syncache.hashsize; i++) {
|
|
sch = &V_tcp_syncache.hashbase[i];
|
|
SCH_LOCK(sch);
|
|
TAILQ_FOREACH(sc, &sch->sch_bucket, sc_hash) {
|
|
if (count >= max_pcbs) {
|
|
SCH_UNLOCK(sch);
|
|
goto exit;
|
|
}
|
|
if (cr_cansee(req->td->td_ucred, sc->sc_cred) != 0)
|
|
continue;
|
|
bzero(&xt, sizeof(xt));
|
|
xt.xt_len = sizeof(xt);
|
|
if (sc->sc_inc.inc_flags & INC_ISIPV6)
|
|
xt.xt_inp.inp_vflag = INP_IPV6;
|
|
else
|
|
xt.xt_inp.inp_vflag = INP_IPV4;
|
|
bcopy(&sc->sc_inc, &xt.xt_inp.inp_inc, sizeof (struct in_conninfo));
|
|
xt.xt_tp.t_inpcb = &xt.xt_inp;
|
|
xt.xt_tp.t_state = TCPS_SYN_RECEIVED;
|
|
xt.xt_socket.xso_protocol = IPPROTO_TCP;
|
|
xt.xt_socket.xso_len = sizeof (struct xsocket);
|
|
xt.xt_socket.so_type = SOCK_STREAM;
|
|
xt.xt_socket.so_state = SS_ISCONNECTING;
|
|
error = SYSCTL_OUT(req, &xt, sizeof xt);
|
|
if (error) {
|
|
SCH_UNLOCK(sch);
|
|
goto exit;
|
|
}
|
|
count++;
|
|
}
|
|
SCH_UNLOCK(sch);
|
|
}
|
|
exit:
|
|
*pcbs_exported = count;
|
|
return error;
|
|
}
|