In the forwarding case refragment the reassembled packets with the same

size as they arrived in. This allows the sender to determine the optimal
fragment size by Path MTU Discovery.

Roughly based on the OpenBSD work by Alexander Bluhm.

Submitted by:		Kristof Provost
Differential Revision:	D1767

4 files changed, 93 insertions, 2 deletions

diff --git a/sys/netpfil/pf/pf.c b/sys/netpfil/pf/pf.c
index d8c35b3..b32288b 100644
--- a/sys/netpfil/pf/pf.c
+++ b/sys/netpfil/pf/pf.c
@@ -5499,7 +5499,7 @@ pf_route6(struct mbuf **m, struct pf_rule *r, int dir, struct ifnet *oifp,
 		goto bad;
 
 	if (oifp != ifp) {
-		if (pf_test6(PF_OUT, ifp, &m0, NULL) != PF_PASS)
+		if (pf_test6(PF_FWD, ifp, &m0, NULL) != PF_PASS)
 			goto bad;
 		else if (m0 == NULL)
 			goto done;
@@ -6057,15 +6057,20 @@ pf_test6(int dir, struct ifnet *ifp, struct mbuf **m0, struct inpcb *inp)
 	struct pfi_kif		*kif;
 	u_short			 action, reason = 0, log = 0;
 	struct mbuf		*m = *m0, *n = NULL;
+	struct m_tag		*mtag;
 	struct ip6_hdr		*h = NULL;
 	struct pf_rule		*a = NULL, *r = &V_pf_default_rule, *tr, *nr;
 	struct pf_state		*s = NULL;
 	struct pf_ruleset	*ruleset = NULL;
 	struct pf_pdesc		 pd;
 	int			 off, terminal = 0, dirndx, rh_cnt = 0;
+	int			 fwdir = dir;
 
 	M_ASSERTPKTHDR(m);
 
+	if (ifp != m->m_pkthdr.rcvif)
+		fwdir = PF_FWD;
+
 	if (!V_pf_status.running)
 		return (PF_PASS);
 
@@ -6427,6 +6432,11 @@ done:
 	if (s)
 		PF_STATE_UNLOCK(s);
 
+	/* If reassembled packet passed, create new fragments. */
+	if (action == PF_PASS && *m0 && fwdir == PF_FWD &&
+	    (mtag = m_tag_find(m, PF_REASSEMBLED, NULL)) != NULL)
+		action = pf_refragment6(ifp, m0, mtag);
+
 	return (action);
 }
 #endif /* INET6 */
diff --git a/sys/netpfil/pf/pf.h b/sys/netpfil/pf/pf.h
index 96f638e..ac0e0fb 100644
--- a/sys/netpfil/pf/pf.h
+++ b/sys/netpfil/pf/pf.h
@@ -43,7 +43,7 @@
 #endif
 #endif
 
-enum	{ PF_INOUT, PF_IN, PF_OUT };
+enum	{ PF_INOUT, PF_IN, PF_OUT, PF_FWD };
 enum	{ PF_PASS, PF_DROP, PF_SCRUB, PF_NOSCRUB, PF_NAT, PF_NONAT,
 	  PF_BINAT, PF_NOBINAT, PF_RDR, PF_NORDR, PF_SYNPROXY_DROP, PF_DEFER };
 enum	{ PF_RULESET_SCRUB, PF_RULESET_FILTER, PF_RULESET_NAT,
diff --git a/sys/netpfil/pf/pf_mtag.h b/sys/netpfil/pf/pf_mtag.h
index baff00a..3aacb2e 100644
--- a/sys/netpfil/pf/pf_mtag.h
+++ b/sys/netpfil/pf/pf_mtag.h
@@ -39,6 +39,7 @@
 #define	PF_TAG_TRANSLATE_LOCALHOST	0x04
 #define	PF_PACKET_LOOPED		0x08
 #define	PF_FASTFWD_OURS_PRESENT		0x10
+#define	PF_REASSEMBLED			0x20
 
 struct pf_mtag {
 	void		*hdr;		/* saved hdr pos in mbuf, for ECN */
diff --git a/sys/netpfil/pf/pf_norm.c b/sys/netpfil/pf/pf_norm.c
index 5109ab2..1801919 100644
--- a/sys/netpfil/pf/pf_norm.c
+++ b/sys/netpfil/pf/pf_norm.c
@@ -678,6 +678,8 @@ pf_reassemble6(struct mbuf **m0, struct ip6_hdr *ip6, struct ip6_frag *fraghdr,
 	struct pf_frent		*frent;
 	struct pf_fragment	*frag;
 	struct pf_fragment_cmp	 key;
+	struct m_tag		*mtag;
+	struct pf_fragment_tag	*ftag;
 	int			 off;
 	uint16_t		 total, maxlen;
 	uint8_t			 proto;
@@ -750,6 +752,15 @@ pf_reassemble6(struct mbuf **m0, struct ip6_hdr *ip6, struct ip6_frag *fraghdr,
 		m->m_pkthdr.len = plen;
 	}
 
+	if ((mtag = m_tag_get(PF_REASSEMBLED, sizeof(struct pf_fragment_tag),
+	    M_NOWAIT)) == NULL)
+		goto fail;
+	ftag = (struct pf_fragment_tag *)(mtag + 1);
+	ftag->ft_hdrlen = hdrlen;
+	ftag->ft_extoff = extoff;
+	ftag->ft_maxlen = maxlen;
+	m_tag_prepend(m, mtag);
+
 	ip6 = mtod(m, struct ip6_hdr *);
 	ip6->ip6_plen = htons(hdrlen - sizeof(struct ip6_hdr) + total);
 	if (extoff) {
@@ -1084,6 +1095,75 @@ pf_fragcache(struct mbuf **m0, struct ip *h, struct pf_fragment **frag, int mff,
 }
 
 int
+pf_refragment6(struct ifnet *ifp, struct mbuf **m0, struct m_tag *mtag)
+{
+	struct mbuf		*m = *m0, *t;
+	struct pf_fragment_tag	*ftag = (struct pf_fragment_tag *)(mtag + 1);
+	struct pf_pdesc		 pd;
+	uint16_t		 hdrlen, extoff, maxlen;
+	uint8_t			 proto;
+	int			 error, action;
+
+	hdrlen = ftag->ft_hdrlen;
+	extoff = ftag->ft_extoff;
+	maxlen = ftag->ft_maxlen;
+	m_tag_delete(m, mtag);
+	mtag = NULL;
+	ftag = NULL;
+
+	if (extoff) {
+		int off;
+
+		/* Use protocol from next field of last extension header */
+		m = m_getptr(m, extoff + offsetof(struct ip6_ext, ip6e_nxt),
+		    &off);
+		KASSERT((m != NULL), ("pf_refragment6: short mbuf chain"));
+		proto = *(mtod(m, caddr_t) + off);
+		*(mtod(m, char *) + off) = IPPROTO_FRAGMENT;
+		m = *m0;
+	} else {
+		struct ip6_hdr *hdr;
+
+		hdr = mtod(m, struct ip6_hdr *);
+		proto = hdr->ip6_nxt;
+		hdr->ip6_nxt = IPPROTO_FRAGMENT;
+	}
+
+	/*
+	 * Maxlen may be less than 8 if there was only a single
+	 * fragment.  As it was fragmented before, add a fragment
+	 * header also for a single fragment.  If total or maxlen
+	 * is less than 8, ip6_fragment() will return EMSGSIZE and
+	 * we drop the packet.
+	 */
+	error = ip6_fragment(ifp, m, hdrlen, proto, maxlen);
+	m = (*m0)->m_nextpkt;
+	(*m0)->m_nextpkt = NULL;
+	if (error == 0) {
+		/* The first mbuf contains the unfragmented packet. */
+		m_freem(*m0);
+		*m0 = NULL;
+		action = PF_PASS;
+	} else {
+		/* Drop expects an mbuf to free. */
+		DPFPRINTF(("refragment error %d", error));
+		action = PF_DROP;
+	}
+	for (t = m; m; m = t) {
+		t = m->m_nextpkt;
+		m->m_nextpkt = NULL;
+		memset(&pd, 0, sizeof(pd));
+		pd.pf_mtag = pf_find_mtag(m);
+		if (error == 0)
+			ip6_forward(m, 0);
+		else
+			m_freem(m);
+	}
+
+	return (action);
+}
+
+int
 pf_normalize_ip(struct mbuf **m0, int dir, struct pfi_kif *kif, u_short *reason,
     struct pf_pdesc *pd)
 {