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diff --git a/share/man/man4/blackhole.4 b/share/man/man4/blackhole.4
--- a/share/man/man4/blackhole.4
+++ b/share/man/man4/blackhole.4
@@ -12,7 +12,7 @@
.\"
.\"
.\" $FreeBSD$
-.Dd September 6, 2015
+.Dd November 3, 2021
.Dt BLACKHOLE 4
.Os
.Sh NAME
@@ -24,7 +24,9 @@
.Sh SYNOPSIS
.Cd sysctl net.inet.sctp.blackhole Ns Op = Ns Brq "0 | 1 | 2"
.Cd sysctl net.inet.tcp.blackhole Ns Op = Ns Brq "0 | 1 | 2"
+.Cd sysctl net.inet.tcp.blackhole_local Ns Op = Ns Brq "0 | 1"
.Cd sysctl net.inet.udp.blackhole Ns Op = Ns Brq "0 | 1"
+.Cd sysctl net.inet.udp.blackhole_local Ns Op = Ns Brq "0 | 1"
.Sh DESCRIPTION
The
.Nm
@@ -35,6 +37,14 @@
The blackhole behaviour is useful to slow down an attacker who is port-scanning
a system in an attempt to detect vulnerable services.
It might also slow down an attempted denial of service attack.
+.Pp
+The blackhole behaviour is disabled by default.
+If enabled, the locally originated packets would still be responded to,
+unless also
+.Va net.inet.tcp.blackhole_local
+(for TCP) and/or
+.Va net.inet.udp.blackhole_local
+(for UDP) are enforced.
.Ss SCTP
Setting the SCTP blackhole MIB to a numeric value of one
will prevent sending an ABORT packet in response to an incoming INIT.
diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -144,6 +144,12 @@
&VNET_NAME(blackhole), 0,
"Do not send RST on segments to closed ports");
+VNET_DEFINE(bool, blackhole_local) = false;
+#define V_blackhole_local VNET(blackhole_local)
+SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, blackhole_local, CTLFLAG_VNET |
+ CTLFLAG_RW, &VNET_NAME(blackhole_local), false,
+ "Enforce net.inet.tcp.blackhole for locally originated packets");
+
VNET_DEFINE(int, tcp_delack_enabled) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_delack_enabled), 0,
@@ -935,8 +941,17 @@
* When blackholing do not respond with a RST but
* completely ignore the segment and drop it.
*/
- if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
- V_blackhole == 2)
+ if (((V_blackhole == 1 && (thflags & TH_SYN)) ||
+ V_blackhole == 2) && (V_blackhole_local ||
+#ifdef INET6
+ isipv6 ? !in6_localaddr(&ip6->ip6_src) :
+#endif
+#ifdef INET
+ !in_localip(ip->ip_src)
+#else
+ true
+#endif
+ ))
goto dropunlock;
rstreason = BANDLIM_RST_CLOSEDPORT;
diff --git a/sys/netinet/udp_usrreq.c b/sys/netinet/udp_usrreq.c
--- a/sys/netinet/udp_usrreq.c
+++ b/sys/netinet/udp_usrreq.c
@@ -127,6 +127,10 @@
SYSCTL_INT(_net_inet_udp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(udp_blackhole), 0,
"Do not send port unreachables for refused connects");
+VNET_DEFINE(bool, udp_blackhole_local) = false;
+SYSCTL_BOOL(_net_inet_udp, OID_AUTO, blackhole_local, CTLFLAG_VNET |
+ CTLFLAG_RW, &VNET_NAME(udp_blackhole_local), false,
+ "Enforce net.inet.udp.blackhole for locally originated packets");
u_long udp_sendspace = 9216; /* really max datagram size */
SYSCTL_ULONG(_net_inet_udp, UDPCTL_MAXDGRAM, maxdgram, CTLFLAG_RW,
@@ -701,7 +705,8 @@
UDPSTAT_INC(udps_noportbcast);
goto badunlocked;
}
- if (V_udp_blackhole)
+ if (V_udp_blackhole && (V_udp_blackhole_local ||
+ !in_localip(ip->ip_src)))
goto badunlocked;
if (badport_bandlim(BANDLIM_ICMP_UNREACH) < 0)
goto badunlocked;
diff --git a/sys/netinet/udp_var.h b/sys/netinet/udp_var.h
--- a/sys/netinet/udp_var.h
+++ b/sys/netinet/udp_var.h
@@ -149,9 +149,11 @@
extern u_long udp_recvspace;
VNET_DECLARE(int, udp_cksum);
VNET_DECLARE(int, udp_blackhole);
+VNET_DECLARE(bool, udp_blackhole_local);
VNET_DECLARE(int, udp_log_in_vain);
#define V_udp_cksum VNET(udp_cksum)
#define V_udp_blackhole VNET(udp_blackhole)
+#define V_udp_blackhole_local VNET(udp_blackhole_local)
#define V_udp_log_in_vain VNET(udp_log_in_vain)
VNET_DECLARE(int, zero_checksum_port);
diff --git a/sys/netinet6/udp6_usrreq.c b/sys/netinet6/udp6_usrreq.c
--- a/sys/netinet6/udp6_usrreq.c
+++ b/sys/netinet6/udp6_usrreq.c
@@ -511,7 +511,8 @@
UDPSTAT_INC(udps_noportmcast);
goto badunlocked;
}
- if (V_udp_blackhole)
+ if (V_udp_blackhole && (V_udp_blackhole_local ||
+ !in6_localaddr(&ip6->ip6_src)))
goto badunlocked;
icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_NOPORT, 0);
*mp = NULL;

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