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From: "Alexander V. Chernikov" <melifaro@FreeBSD.org>
Date: Thu, 16 Jan 2014 11:50:01 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r260702 - head/sys/netinet
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Author: melifaro
Date: Thu Jan 16 11:50:00 2014
New Revision: 260702
URL: http://svnweb.freebsd.org/changeset/base/260702

Log:
  Fix ipfw fwd for IPv4 traffic broken by r249894.
  
  Problem case:
  Original lookup returns route with GW set, so gw points to
  rte->rt_gateway.
  After that we're changing dst and performing lookup another time.
  Since fwd host is most probably directly reachable, resulting
  rte does not contain rt_gateway, so gw is not set. Finally, we
  end with packet transmitted to proper interface but wrong
  link-layer address.
  
  Found by:	lstewart
  Discussed with:	ae,lstewart
  MFC after:	2 weeks
  Sponsored by:	Yandex LLC

Modified:
  head/sys/netinet/ip_output.c

Modified: head/sys/netinet/ip_output.c
==============================================================================
--- head/sys/netinet/ip_output.c	Thu Jan 16 06:26:03 2014	(r260701)
+++ head/sys/netinet/ip_output.c	Thu Jan 16 11:50:00 2014	(r260702)
@@ -202,6 +202,13 @@ ip_output(struct mbuf *m, struct mbuf *o
 		hlen = ip->ip_hl << 2;
 	}
 
+	/*
+	 * dst/gw handling:
+	 *
+	 * dst can be rewritten but always point to &ro->ro_dst
+	 * gw is readonly but can be pointed either to dst OR rt_gatewy
+	 * therefore we need restore GW if we're re-doing lookup
+	 */
 	gw = dst = (struct sockaddr_in *)&ro->ro_dst;
 again:
 	ia = NULL;
@@ -221,6 +228,7 @@ again:
 		RO_RTFREE(ro);
 		ro->ro_lle = NULL;
 		rte = NULL;
+		gw = dst;
 	}
 	if (rte == NULL && fwd_tag == NULL) {
 		bzero(dst, sizeof(*dst));