The function ip6_get_prevhdr() did return a pointer into a mbuf.

It was not guaranteed that the mbuf data was not somewhere else in
the chain.  So return an offset and do a proper mbuf pulldown.
found by Maxime Villard; from NetBSD; with markus@; OK deraadt@

4 files changed, 40 insertions, 40 deletions

diff --git a/sys/netinet6/frag6.c b/sys/netinet6/frag6.c
index 7b874e37bab..f3abef22fa1 100644
--- a/sys/netinet6/frag6.c
+++ b/sys/netinet6/frag6.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: frag6.c,v 1.81 2017/11/14 14:46:49 bluhm Exp $	*/
+/*	$OpenBSD: frag6.c,v 1.82 2018/02/01 21:11:33 bluhm Exp $	*/
 /*	$KAME: frag6.c,v 1.40 2002/05/27 21:40:31 itojun Exp $	*/
 
 /*
@@ -422,14 +422,6 @@ frag6_input(struct mbuf **mp, int *offp, int proto, int af)
 		goto dropfrag;
 	}
 
-	/*
-	 * Store NXT to the original.
-	 */
-	{
-		u_int8_t *prvnxtp = ip6_get_prevhdr(m, offset); /* XXX */
-		*prvnxtp = nxt;
-	}
-
 	TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
 	frag6_nfrags -= q6->ip6q_nfrag;
 	frag6_nfragpackets--;
@@ -445,6 +437,20 @@ frag6_input(struct mbuf **mp, int *offp, int proto, int af)
 		m->m_pkthdr.len = plen;
 	}
 
+	/*
+	 * Restore NXT to the original.
+	 */
+	{
+		int prvnxt = ip6_get_prevhdr(m, offset);
+		uint8_t *prvnxtp;
+
+		IP6_EXTHDR_GET(prvnxtp, uint8_t *, m, prvnxt,
+		    sizeof(*prvnxtp));
+		if (prvnxtp == NULL)
+			goto dropfrag;
+		*prvnxtp = nxt;
+	}
+
 	ip6stat_inc(ip6s_reassembled);
 
 	/*
diff --git a/sys/netinet6/ip6_input.c b/sys/netinet6/ip6_input.c
index 6f07b36d9d3..b7dc6287e5a 100644
--- a/sys/netinet6/ip6_input.c
+++ b/sys/netinet6/ip6_input.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip6_input.c,v 1.210 2017/11/23 13:45:46 mpi Exp $	*/
+/*	$OpenBSD: ip6_input.c,v 1.211 2018/02/01 21:11:33 bluhm Exp $	*/
 /*	$KAME: ip6_input.c,v 1.188 2001/03/29 05:34:31 itojun Exp $	*/
 
 /*
@@ -1188,50 +1188,44 @@ ip6_pullexthdr(struct mbuf *m, size_t off, int nxt)
 }
 
 /*
- * Get pointer to the previous header followed by the header
+ * Get offset to the previous header followed by the header
  * currently processed.
- * XXX: This function supposes that
- *	M includes all headers,
- *	the next header field and the header length field of each header
- *	are valid, and
- *	the sum of each header length equals to OFF.
- * Because of these assumptions, this function must be called very
- * carefully. Moreover, it will not be used in the near future when
- * we develop `neater' mechanism to process extension headers.
  */
-u_int8_t *
+int
 ip6_get_prevhdr(struct mbuf *m, int off)
 {
 	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
 
-	if (off == sizeof(struct ip6_hdr))
-		return (&ip6->ip6_nxt);
-	else {
-		int len, nxt;
-		struct ip6_ext *ip6e = NULL;
+	if (off == sizeof(struct ip6_hdr)) {
+		return offsetof(struct ip6_hdr, ip6_nxt);
+	} else if (off < sizeof(struct ip6_hdr)) {
+		panic("%s: off < sizeof(struct ip6_hdr)", __func__);
+	} else {
+		int len, nlen, nxt;
+		struct ip6_ext ip6e;
 
 		nxt = ip6->ip6_nxt;
 		len = sizeof(struct ip6_hdr);
+		nlen = 0;
 		while (len < off) {
-			ip6e = (struct ip6_ext *)(mtod(m, caddr_t) + len);
+			m_copydata(m, len, sizeof(ip6e), (caddr_t)&ip6e);
 
 			switch (nxt) {
 			case IPPROTO_FRAGMENT:
-				len += sizeof(struct ip6_frag);
+				nlen = sizeof(struct ip6_frag);
 				break;
 			case IPPROTO_AH:
-				len += (ip6e->ip6e_len + 2) << 2;
+				nlen = (ip6e.ip6e_len + 2) << 2;
 				break;
 			default:
-				len += (ip6e->ip6e_len + 1) << 3;
+				nlen = (ip6e.ip6e_len + 1) << 3;
 				break;
 			}
-			nxt = ip6e->ip6e_nxt;
+			len += nlen;
+			nxt = ip6e.ip6e_nxt;
 		}
-		if (ip6e)
-			return (&ip6e->ip6e_nxt);
-		else
-			return NULL;
+
+		return (len - nlen);
 	}
 }
 
diff --git a/sys/netinet6/ip6_var.h b/sys/netinet6/ip6_var.h
index 370f23f804b..2e62ac01540 100644
--- a/sys/netinet6/ip6_var.h
+++ b/sys/netinet6/ip6_var.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip6_var.h,v 1.81 2017/11/05 13:19:59 florian Exp $	*/
+/*	$OpenBSD: ip6_var.h,v 1.82 2018/02/01 21:11:33 bluhm Exp $	*/
 /*	$KAME: ip6_var.h,v 1.33 2000/06/11 14:59:20 jinmei Exp $	*/
 
 /*
@@ -303,7 +303,7 @@ int	ip6_input_if(struct mbuf **, int *, int, int, struct ifnet *);
 void	ip6_freepcbopts(struct ip6_pktopts *);
 void	ip6_freemoptions(struct ip6_moptions *);
 int	ip6_unknown_opt(u_int8_t *, struct mbuf *, int);
-u_int8_t *ip6_get_prevhdr(struct mbuf *, int);
+int	ip6_get_prevhdr(struct mbuf *, int);
 int	ip6_nexthdr(struct mbuf *, int, int, int *);
 int	ip6_lasthdr(struct mbuf *, int, int, int *);
 int	ip6_mforward(struct ip6_hdr *, struct ifnet *, struct mbuf *);
diff --git a/sys/netinet6/raw_ip6.c b/sys/netinet6/raw_ip6.c
index 8824f88987d..464e44090d9 100644
--- a/sys/netinet6/raw_ip6.c
+++ b/sys/netinet6/raw_ip6.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: raw_ip6.c,v 1.125 2017/12/04 13:40:35 bluhm Exp $	*/
+/*	$OpenBSD: raw_ip6.c,v 1.126 2018/02/01 21:11:33 bluhm Exp $	*/
 /*	$KAME: raw_ip6.c,v 1.69 2001/03/04 15:55:44 itojun Exp $	*/
 
 /*
@@ -236,10 +236,10 @@ rip6_input(struct mbuf **mp, int *offp, int proto, int af)
 		if (proto == IPPROTO_NONE || proto == IPPROTO_ICMPV6) {
 			m_freem(m);
 		} else {
-			u_int8_t *prvnxtp = ip6_get_prevhdr(m, *offp); /* XXX */
+			int prvnxt = ip6_get_prevhdr(m, *offp);
+
 			icmp6_error(m, ICMP6_PARAM_PROB,
-			    ICMP6_PARAMPROB_NEXTHEADER,
-			    prvnxtp - mtod(m, u_int8_t *));
+			    ICMP6_PARAMPROB_NEXTHEADER, prvnxt);
 		}
 		counters = counters_enter(&ref, ip6counters);
 		counters[ip6s_delivered]--;