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From: "Bjoern A. Zeeb" <bz@FreeBSD.org>
Date: Sun, 8 Jul 2012 15:30:24 +0000 (UTC)
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Subject: svn commit: r238248 - head/sys/netinet6
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Author: bz
Date: Sun Jul  8 15:30:24 2012
New Revision: 238248
URL: http://svn.freebsd.org/changeset/base/238248

Log:
  Implement handling of "atomic fragements" as outlined in
  draft-gont-6man-ipv6-atomic-fragments to mitigate one class of
  possible fragmentation-based attacks.
  
  MFC after:	5 days

Modified:
  head/sys/netinet6/frag6.c

Modified: head/sys/netinet6/frag6.c
==============================================================================
--- head/sys/netinet6/frag6.c	Sun Jul  8 14:21:36 2012	(r238247)
+++ head/sys/netinet6/frag6.c	Sun Jul  8 15:30:24 2012	(r238248)
@@ -221,6 +221,19 @@ frag6_input(struct mbuf **mp, int *offp,
 	/* offset now points to data portion */
 	offset += sizeof(struct ip6_frag);
 
+	/*
+	 * XXX-BZ RFC XXXX (draft-gont-6man-ipv6-atomic-fragments)
+	 * Handle "atomic" fragments (offset and m bit set to 0) upfront,
+	 * unrelated to any reassembly.  Just skip the fragment header.
+	 */
+	if ((ip6f->ip6f_offlg & ~IP6F_RESERVED_MASK) == 0) {
+		/* XXX-BZ we want dedicated counters for this. */
+		V_ip6stat.ip6s_reassembled++;
+		in6_ifstat_inc(dstifp, ifs6_reass_ok);
+		*offp = offset;
+		return (ip6f->ip6f_nxt);
+	}
+
 	IP6Q_LOCK();
 
 	/*