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ntp: restrict use of sub-second polling intervals

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When the local polling interval is adjusted between minpoll and maxpoll
to a sub-second value, check if the source is reachable and the minimum
measured delay is 10 milliseconds or less. If it's not, ignore the
maxpoll value and set the interval to 1 second.

This should prevent clients (mis)configured with an extremely short
minpoll/maxpoll from flooding servers on the Internet.
This commit is contained in:
Miroslav Lichvar 2018-06-21 17:29:43 +02:00
parent 5b75d4afef
commit 59d1b41716
1 changed files with 12 additions and 0 deletions
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12
ntp_core.c
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@ -268,6 +268,11 @@ static ARR_Instance broadcasts;
#define MIN_MAXPOLL 0
#define MAX_POLL 24
/* Enable sub-second polling intervals only when the peer delay is not
longer than 10 milliseconds to restrict them to local networks */
#define MIN_NONLAN_POLL 0
#define MAX_LAN_PEER_DELAY 0.01
/* Kiss-o'-Death codes */
#define KOD_RATE 0x52415445UL /* RATE */
@ -742,6 +747,13 @@ adjust_poll(NCR_Instance inst, double adj)
inst->local_poll = inst->maxpoll;
inst->poll_score = 1.0;
}
/* Don't allow a sub-second polling interval if the source is not reachable
or it is not in a local network according to the measured delay */
if (inst->local_poll < MIN_NONLAN_POLL &&
(!SRC_IsReachable(inst->source) ||
SST_MinRoundTripDelay(SRC_GetSourcestats(inst->source)) > MAX_LAN_PEER_DELAY))
inst->local_poll = MIN_NONLAN_POLL;
}
/* ================================================== */