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Index: sys/netinet/ip_icmp.c
===================================================================
--- sys/netinet/ip_icmp.c
+++ sys/netinet/ip_icmp.c
@@ -89,6 +89,12 @@
&VNET_NAME(icmplim), 0,
"Maximum number of ICMP responses per second");
+VNET_DEFINE_STATIC(int, icmplim_jitter) = 16;
+#define V_icmplim_jitter VNET(icmplim_jitter)
+SYSCTL_INT(_net_inet_icmp, ICMPCTL_ICMPLIM, icmplim_jitter, CTLFLAG_VNET | CTLFLAG_RW,
+ &VNET_NAME(icmplim_jitter), 0,
+ "Jitter value for randomizing the bandwidth limit");
+
VNET_DEFINE_STATIC(int, icmplim_output) = 1;
#define V_icmplim_output VNET(icmplim_output)
SYSCTL_INT(_net_inet_icmp, OID_AUTO, icmplim_output, CTLFLAG_VNET | CTLFLAG_RW,
@@ -1094,6 +1100,11 @@
};
#define V_icmp_rates VNET(icmp_rates)
+/*
+ * Adjust limit +/- to jitter the measurement for security Paper
+ * forthcoming.
+ */
+
static void
icmp_bandlimit_init(void)
{
@@ -1120,18 +1131,32 @@
badport_bandlim(int which)
{
int64_t pps;
-
+ uint32_t jitter, limit;
+
if (V_icmplim == 0 || which == BANDLIM_UNLIMITED)
return (0);
KASSERT(which >= 0 && which < BANDLIM_MAX,
("%s: which %d", __func__, which));
- pps = counter_ratecheck(&V_icmp_rates[which].cr, V_icmplim);
+ /*
+ * Add random jitter to the administratively set limit.
+ * If the returned random number is even then add the jitter
+ * and if odd then subtract.
+ */
+ jitter = arc4random_uniform(V_icmplim_jitter);
+
+ if (jitter % 2 == 0)
+ limit = V_icmplim + jitter;
+ else
+ limit = V_icmplim - jitter;
+
+ pps = counter_ratecheck(&V_icmp_rates[which].cr, limit);
+
if (pps == -1)
return (-1);
if (pps > 0 && V_icmplim_output)
log(LOG_NOTICE, "Limiting %s from %jd to %d packets/sec\n",
- V_icmp_rates[which].descr, (intmax_t )pps, V_icmplim);
+ V_icmp_rates[which].descr, (intmax_t )pps, limit);
return (0);
}

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