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Address issue pointed out in CVE-2020-25705

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Add jitter to the ICMP bandwidth limit to deny a side-channel port scan.

Reviewed by:	kp, philip, cy, emaste
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D27354
This commit is contained in:
George V. Neville-Neil 2022-03-19 17:48:16 +01:00 committed by Kristof Provost
parent ab8ac4c285
commit ca4cd20c4a
1 changed files with 28 additions and 2 deletions
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30
sys/netinet/ip_icmp.c
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@ -88,6 +88,14 @@ SYSCTL_INT(_net_inet_icmp, ICMPCTL_ICMPLIM, icmplim, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(icmplim), 0,
"Maximum number of ICMP responses per second");
VNET_DEFINE_STATIC(int, icmplim_curr_jitter) = 0;
#define V_icmplim_curr_jitter VNET(icmplim_curr_jitter)
VNET_DEFINE_STATIC(int, icmplim_jitter) = 16;
#define V_icmplim_jitter VNET(icmplim_jitter)
SYSCTL_INT(_net_inet_icmp, OID_AUTO, icmplim_jitter, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(icmplim_jitter), 0,
"Random icmplim jitter adjustment 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,
@ -1122,11 +1130,29 @@ badport_bandlim(int which)
KASSERT(which >= 0 && which < BANDLIM_MAX,
("%s: which %d", __func__, which));
pps = counter_ratecheck(&V_icmp_rates[which].cr, V_icmplim);
if ((V_icmplim + V_icmplim_curr_jitter) <= 0)
V_icmplim_curr_jitter = -V_icmplim + 1;
pps = counter_ratecheck(&V_icmp_rates[which].cr, V_icmplim +
V_icmplim_curr_jitter);
if (pps > 0) {
/*
* Adjust limit +/- to jitter the measurement to deny a
* side-channel port scan as in CVE-2020-25705
*/
if (V_icmplim_jitter > 0) {
int32_t inc =
arc4random_uniform(V_icmplim_jitter * 2 +1)
- V_icmplim_jitter;
V_icmplim_curr_jitter = inc;
}
}
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, V_icmplim +
V_icmplim_curr_jitter);
return (0);
}