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Date:      Fri, 18 Sep 2020 02:21:15 +0000 (UTC)
From:      Navdeep Parhar <np@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r365869 - in head/sys: netinet netinet6
Message-ID:  <202009180221.08I2LFop096309@repo.freebsd.org>
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Author: np
Date: Fri Sep 18 02:21:15 2020
New Revision: 365869
URL: https://svnweb.freebsd.org/changeset/base/365869

Log:
  Add a knob to allow zero UDP checksums for UDP/IPv6 traffic on the given UDP port.
  
  This will be used by some upcoming changes to if_vxlan(4).  RFC 7348 (VXLAN)
  says that the UDP checksum "SHOULD be transmitted as zero.  When a packet is
  received with a UDP checksum of zero, it MUST be accepted for decapsulation."
  But the original IPv6 RFCs did not allow zero UDP checksum.  RFC 6935 attempts
  to resolve this.
  
  Reviewed by:	kib@
  Sponsored by:	Chelsio Communications
  Differential Revision:	https://reviews.freebsd.org/D25873

Modified:
  head/sys/netinet/udp_var.h
  head/sys/netinet6/udp6_usrreq.c

Modified: head/sys/netinet/udp_var.h
==============================================================================
--- head/sys/netinet/udp_var.h	Fri Sep 18 02:10:28 2020	(r365868)
+++ head/sys/netinet/udp_var.h	Fri Sep 18 02:21:15 2020	(r365869)
@@ -154,6 +154,9 @@ VNET_DECLARE(int, udp_log_in_vain);
 #define	V_udp_blackhole		VNET(udp_blackhole)
 #define	V_udp_log_in_vain	VNET(udp_log_in_vain)
 
+VNET_DECLARE(int, zero_checksum_port);
+#define	V_zero_checksum_port	VNET(zero_checksum_port)
+
 static __inline struct inpcbinfo *
 udp_get_inpcbinfo(int protocol)
 {

Modified: head/sys/netinet6/udp6_usrreq.c
==============================================================================
--- head/sys/netinet6/udp6_usrreq.c	Fri Sep 18 02:10:28 2020	(r365868)
+++ head/sys/netinet6/udp6_usrreq.c	Fri Sep 18 02:21:15 2020	(r365869)
@@ -124,6 +124,11 @@ __FBSDID("$FreeBSD$");
 
 #include <security/mac/mac_framework.h>
 
+VNET_DEFINE(int, zero_checksum_port) = 0;
+#define	V_zero_checksum_port	VNET(zero_checksum_port)
+SYSCTL_INT(_net_inet6_udp6, OID_AUTO, rfc6935_port, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(zero_checksum_port), 0,
+    "Zero UDP checksum allowed for traffic to/from this port.");
 /*
  * UDP protocol implementation.
  * Per RFC 768, August, 1980.
@@ -267,7 +272,14 @@ udp6_input(struct mbuf **mp, int *offp, int proto)
 		}
 		if (uh->uh_sum == 0) {
 			UDPSTAT_INC(udps_nosum);
-			goto badunlocked;
+			/*
+			 * dport 0 was rejected earlier so this is OK even if
+			 * zero_checksum_port is 0 (which is its default value).
+			 */
+			if (ntohs(uh->uh_dport) == V_zero_checksum_port)
+				goto skip_checksum;
+			else
+				goto badunlocked;
 		}
 	}
 
@@ -287,6 +299,7 @@ udp6_input(struct mbuf **mp, int *offp, int proto)
 		goto badunlocked;
 	}
 
+skip_checksum:
 	/*
 	 * Construct sockaddr format source address.
 	 */

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