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o Move setting/resetting logic of syncache timer from macro
SYNCACHE_TIMEOUT to new function syncache_timeout(). o Fix inverted timeout callout engagement logic to actually enable the timer for the bucket row. Before SYN|ACK was not retransmitted. o Simplify SYN|ACK retransmit timeout backoff calculation. o Improve logging of retransmit and timeout events. o Reset timeout when duplicate SYN arrives. o Add comments. o Rearrange SYN cookie statistics counting. Bug found by: silby Submitted by: silby (different version) Approved by: re (rwatson)
This commit is contained in:
Andre Oppermann
parent
19bc77c549
commit
cdaf208d09
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=171639
@ -158,6 +158,8 @@ 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 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 void syncookie_generate(struct syncache_head *, struct syncache *,
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u_int32_t *);
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@ -234,18 +236,6 @@ static MALLOC_DEFINE(M_SYNCACHE, "syncache", "TCP syncache");
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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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@ -341,7 +331,7 @@ syncache_insert(struct syncache *sc, struct syncache_head *sch)
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sch->sch_length++;
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/* Reinitialize the bucket row's timer. */
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SYNCACHE_TIMEOUT(sc, sch, 1);
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syncache_timeout(sc, sch, 1);
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SCH_UNLOCK(sch);
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@ -366,6 +356,22 @@ syncache_drop(struct syncache *sc, struct syncache_head *sch)
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tcp_syncache.cache_count--;
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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_backoff[sc->sc_rxmits]);
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sc->sc_rxmits++;
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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) && 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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* 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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@ -391,7 +397,7 @@ syncache_timer(void *xsch)
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* then the RST will be sent by the time the remote
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* host does the SYN/ACK->ACK.
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*/
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if (sc->sc_rxttime >= tick) {
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if (sc->sc_rxttime > tick) {
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if (sc->sc_rxttime < sch->sch_nextc)
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sch->sch_nextc = sc->sc_rxttime;
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continue;
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@ -399,7 +405,8 @@ syncache_timer(void *xsch)
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if (sc->sc_rxmits > tcp_syncache.rexmt_limit) {
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if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
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log(LOG_DEBUG, "%s; %s: Response timeout\n",
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log(LOG_DEBUG, "%s; %s: Retransmits exhausted, "
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"giving up and removing syncache entry\n",
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s, __func__);
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free(s, M_TCPLOG);
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}
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@ -407,10 +414,16 @@ syncache_timer(void *xsch)
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tcpstat.tcps_sc_stale++;
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continue;
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}
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if ((s = tcp_log_addrs(&sc->sc_inc, NULL, NULL, NULL))) {
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log(LOG_DEBUG, "%s; %s: Response timeout, "
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"retransmitting (%u) SYN|ACK\n",
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s, __func__, sc->sc_rxmits);
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free(s, M_TCPLOG);
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}
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(void) syncache_respond(sc);
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tcpstat.tcps_sc_retransmitted++;
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SYNCACHE_TIMEOUT(sc, sch, 0);
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syncache_timeout(sc, sch, 0);
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}
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if (!TAILQ_EMPTY(&(sch)->sch_bucket))
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callout_reset(&(sch)->sch_timer, (sch)->sch_nextc - tick,
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@ -774,7 +787,7 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
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/*
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* If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
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*/
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if (sc->sc_rxmits > 1)
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if (sc->sc_rxmits)
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tp->snd_cwnd = tp->t_maxseg;
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tcp_timer_activate(tp, TT_KEEP, tcp_keepinit);
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@ -845,7 +858,6 @@ syncache_expand(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
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"(probably spoofed)\n", s, __func__);
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goto failed;
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}
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tcpstat.tcps_sc_recvcookie++;
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} else {
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/* Pull out the entry to unlock the bucket row. */
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TAILQ_REMOVE(&sch->sch_bucket, sc, sc_hash);
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@ -947,6 +959,7 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
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struct mbuf *ipopts = NULL;
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u_int32_t flowtmp;
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int win, sb_hiwat, ip_ttl, ip_tos, noopt;
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char *s;
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#ifdef INET6
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int autoflowlabel = 0;
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#endif
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@ -957,6 +970,8 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
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INP_INFO_WLOCK_ASSERT(&tcbinfo);
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INP_LOCK_ASSERT(inp); /* listen socket */
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KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
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("%s: unexpected tcp flags", __func__));
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/*
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* Combine all so/tp operations very early to drop the INP lock as
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@ -1004,6 +1019,11 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
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*
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* XXX: should the syncache be re-initialized with the contents
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* of the new SYN here (which may have different options?)
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*
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* XXX: We do not check the sequence number to see if this is a
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* real retransmit or a new connection attempt. The question is
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* how to handle such a case; either ignore it as spoofed, or
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* drop the current entry and create a new one?
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*/
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sc = syncache_lookup(inc, &sch); /* returns locked entry */
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SCH_LOCK_ASSERT(sch);
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@ -1035,8 +1055,16 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
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KASSERT(sc->sc_label != NULL,
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("%s: label not initialized", __func__));
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#endif
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/* Retransmit SYN|ACK and reset retransmit count. */
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if ((s = tcp_log_addrs(&sc->sc_inc, th, NULL, NULL))) {
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log(LOG_DEBUG, "%s; %s: Reveived duplicate SYN, "
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"resetting timer and retransmitting SYN|ACK\n",
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s, __func__);
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free(s, M_TCPLOG);
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}
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if (syncache_respond(sc) == 0) {
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SYNCACHE_TIMEOUT(sc, sch, 1);
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sc->sc_rxmits = 0;
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syncache_timeout(sc, sch, 1);
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tcpstat.tcps_sndacks++;
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tcpstat.tcps_sndtotal++;
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}
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@ -1488,6 +1516,7 @@ syncookie_generate(struct syncache_head *sch, struct syncache *sc,
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sc->sc_tsoff = data - ticks; /* after XOR */
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}
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tcpstat.tcps_sc_sendcookie++;
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return;
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}
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@ -1590,6 +1619,7 @@ syncookie_lookup(struct in_conninfo *inc, struct syncache_head *sch,
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sc->sc_rxmits = 0;
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sc->sc_peer_mss = tcp_sc_msstab[mss];
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tcpstat.tcps_sc_recvcookie++;
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return (sc);
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}
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