Make TCP_DROP_SYNFIN a standard part of TCP. Disabled by default it
doesn't impede normal operation negatively and is only a few lines of code. It's close relatives blackhole and log_in_vain aren't options either.
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@ -875,12 +875,6 @@ options MBUF_STRESS_TEST
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options ACCEPT_FILTER_DATA
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options ACCEPT_FILTER_HTTP
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# TCP_DROP_SYNFIN adds support for ignoring TCP packets with SYN+FIN. This
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# prevents nmap et al. from identifying the TCP/IP stack, but breaks support
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# for RFC1644 extensions and is not recommended for web servers.
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#
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options TCP_DROP_SYNFIN #drop TCP packets with SYN+FIN
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# TCP_SIGNATURE adds support for RFC 2385 (TCP-MD5) digests. These are
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# carried in TCP option 19. This option is commonly used to protect
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# TCP sessions (e.g. BGP) where IPSEC is not available nor desirable.
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@ -389,7 +389,6 @@ SLIP_IFF_OPTS opt_slip.h
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TCPDEBUG
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TCP_SIGNATURE opt_inet.h
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TCP_SACK_DEBUG opt_tcp_sack.h
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TCP_DROP_SYNFIN opt_tcp_input.h
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DEV_VLAN opt_vlan.h
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VLAN_ARRAY opt_vlan.h
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XBONEHACK
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@ -36,7 +36,6 @@
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#include "opt_ipsec.h"
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#include "opt_mac.h"
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#include "opt_tcpdebug.h"
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#include "opt_tcp_input.h"
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#include "opt_tcp_sack.h"
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#include <sys/param.h>
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@ -118,11 +117,9 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
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&tcp_delack_enabled, 0,
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"Delay ACK to try and piggyback it onto a data packet");
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#ifdef TCP_DROP_SYNFIN
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static int drop_synfin = 0;
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SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
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&drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
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#endif
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static int tcp_do_rfc3042 = 1;
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SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
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@ -601,7 +598,6 @@ tcp_input(m, off0)
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}
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thflags = th->th_flags;
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#ifdef TCP_DROP_SYNFIN
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/*
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* If the drop_synfin option is enabled, drop all packets with
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* both the SYN and FIN bits set. This prevents e.g. nmap from
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@ -611,7 +607,6 @@ tcp_input(m, off0)
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*/
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if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
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goto drop;
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#endif
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/*
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* Convert TCP protocol specific fields to host format.
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@ -36,7 +36,6 @@
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#include "opt_ipsec.h"
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#include "opt_mac.h"
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#include "opt_tcpdebug.h"
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#include "opt_tcp_input.h"
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#include "opt_tcp_sack.h"
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#include <sys/param.h>
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@ -118,11 +117,9 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_RW,
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&tcp_delack_enabled, 0,
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"Delay ACK to try and piggyback it onto a data packet");
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#ifdef TCP_DROP_SYNFIN
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static int drop_synfin = 0;
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SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_RW,
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&drop_synfin, 0, "Drop TCP packets with SYN+FIN set");
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#endif
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static int tcp_do_rfc3042 = 1;
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SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_RW,
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@ -601,7 +598,6 @@ tcp_input(m, off0)
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}
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thflags = th->th_flags;
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#ifdef TCP_DROP_SYNFIN
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/*
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* If the drop_synfin option is enabled, drop all packets with
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* both the SYN and FIN bits set. This prevents e.g. nmap from
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@ -611,7 +607,6 @@ tcp_input(m, off0)
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*/
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if (drop_synfin && (thflags & (TH_SYN|TH_FIN)) == (TH_SYN|TH_FIN))
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goto drop;
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#endif
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/*
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* Convert TCP protocol specific fields to host format.
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@ -99,7 +99,6 @@
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#include "opt_inet.h"
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#include "opt_inet6.h"
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#include "opt_tcpdebug.h"
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#include "opt_tcp_input.h"
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#include "opt_tcp_sack.h"
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#include <sys/param.h>
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