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Fix bugs in the TCP syncache timeout code. including:

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When system ticks are positive, for entries in the cache
bucket, syncache_timer() ran on every tick (doing nothing
useful) instead of the supposed 3, 6, 12, and 24 seconds
later (when it's time to retransmit SYN,ACK).

When ticks are negative, syncache_timer() was scheduled
for the too far future (up to ~25 days on systems with
HZ=1000), no SYN,ACK retransmits were attempted at all,
and syncache entries added in that period that correspond
to non-established connections stay there forever.

Only HEAD and RELENG_7 are affected.

Reviewed by:	silby, kmacy (earlier version)
Submitted by:	Maxim Dounin, ru
This commit is contained in:
Ruslan Ermilov 2007-12-19 16:56:28 +00:00
parent 0c40d5be19
commit 9eb1b6aabb
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=174775
1 changed files with 18 additions and 8 deletions
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26
sys/netinet/tcp_syncache.c
View File

@ -42,6 +42,7 @@ __FBSDID("$FreeBSD$");
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/malloc.h>
@ -111,7 +112,7 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, syncookies_only, CTLFLAG_RW,
struct syncache {
TAILQ_ENTRY(syncache) sc_hash;
struct in_conninfo sc_inc; /* addresses */
u_long sc_rxttime; /* retransmit time */
int sc_rxttime; /* retransmit time */
u_int16_t sc_rxmits; /* retransmit counter */
u_int32_t sc_tsreflect; /* timestamp to reflect */
@ -183,7 +184,7 @@ static struct syncache
/*
* Transmit the SYN,ACK fewer times than TCP_MAXRXTSHIFT specifies.
* 3 retransmits corresponds to a timeout of (1 + 2 + 4 + 8 == 15) seconds,
* 3 retransmits corresponds to a timeout of 3 * (1 + 2 + 4 + 8) == 45 seconds,
* the odds are that the user has given up attempting to connect by then.
*/
#define SYNCACHE_MAXREXMTS 3
@ -344,6 +345,8 @@ syncache_insert(struct syncache *sc, struct syncache_head *sch)
sch->sch_length++;
/* Reinitialize the bucket row's timer. */
if (sch->sch_length == 1)
sch->sch_nextc = ticks + INT_MAX;
syncache_timeout(sc, sch, 1);
SCH_UNLOCK(sch);
@ -382,11 +385,12 @@ syncache_timeout(struct syncache *sc, struct syncache_head *sch, int docallout)
sc->sc_rxttime = ticks +
TCPTV_RTOBASE * (tcp_backoff[sc->sc_rxmits]);
sc->sc_rxmits++;
if (sch->sch_nextc > sc->sc_rxttime)
if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc)) {
sch->sch_nextc = sc->sc_rxttime;
if (!TAILQ_EMPTY(&sch->sch_bucket) && docallout)
callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
syncache_timer, (void *)sch);
if (docallout)
callout_reset(&sch->sch_timer, sch->sch_nextc - ticks,
syncache_timer, (void *)sch);
}
}
/*
@ -405,6 +409,12 @@ syncache_timer(void *xsch)
/* NB: syncache_head has already been locked by the callout. */
SCH_LOCK_ASSERT(sch);
/*
* In the following cycle we may remove some entries and/or
* advance some timeouts, so re-initialize the bucket timer.
*/
sch->sch_nextc = tick + INT_MAX;
TAILQ_FOREACH_SAFE(sc, &sch->sch_bucket, sc_hash, nsc) {
/*
* We do not check if the listen socket still exists
@ -414,8 +424,8 @@ syncache_timer(void *xsch)
* then the RST will be sent by the time the remote
* host does the SYN/ACK->ACK.
*/
if (sc->sc_rxttime > tick) {
if (sc->sc_rxttime < sch->sch_nextc)
if (TSTMP_GT(sc->sc_rxttime, tick)) {
if (TSTMP_LT(sc->sc_rxttime, sch->sch_nextc))
sch->sch_nextc = sc->sc_rxttime;
continue;
}