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From: Cy Schubert <cy@FreeBSD.org>
Date: Tue, 6 Oct 2015 03:41:12 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: svn commit: r288910 - head/sys/contrib/ipfilter/netinet
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Author: cy
Date: Tue Oct  6 03:41:11 2015
New Revision: 288910
URL: https://svnweb.freebsd.org/changeset/base/288910

Log:
  On some interfaces, ipfilter drops UDP packets with zero checkum.
  This commit fixes that.
  
  PR:		166372
  Submitted by:	mk@neon1.net
  Reviewed by:	Darren Reed <darrenr@reed.wattle.id.au>
  MFC after:	1 week

Modified:
  head/sys/contrib/ipfilter/netinet/ip_fil_freebsd.c

Modified: head/sys/contrib/ipfilter/netinet/ip_fil_freebsd.c
==============================================================================
--- head/sys/contrib/ipfilter/netinet/ip_fil_freebsd.c	Tue Oct  6 01:24:46 2015	(r288909)
+++ head/sys/contrib/ipfilter/netinet/ip_fil_freebsd.c	Tue Oct  6 03:41:11 2015	(r288910)
@@ -1104,6 +1104,22 @@ ipf_checkv4sum(fin)
 		return -1;
 	}
 	if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
+		/* Depending on the driver, UDP may have zero checksum */
+		if (fin->fin_p == IPPROTO_UDP && (fin->fin_flx &
+		    (FI_FRAG|FI_SHORT|FI_BAD)) == 0) {
+			udphdr_t *udp = fin->fin_dp;
+			if (udp->uh_sum == 0) {
+				/*
+				 * we're good no matter what the hardware
+				 * checksum flags and csum_data say (handling
+				 * of csum_data for zero UDP checksum is not
+				 * consistent across all drivers)
+				 */
+				fin->fin_cksum = 1;
+				return 0;
+			}
+		}
+
 		if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
 			sum = m->m_pkthdr.csum_data;
 		else