provide m_dup_pkt() for doing fast deep mbuf copies with a specified alignment

if a physical interface receives a multicast/broadcast packet and
has carp interfaces on it, that packet needs to be copied for
reception by each of those carp interfaces.

previously it was using m_copym2, but that doesn't respect the
alignment of the source packet. this meant the ip header in the
copies were aligned incorrectly for the network stack, which breaks
strict alignment archs.

m_dup_pkt lets carp specify that the payload needs an ETHER_ALIGN
adjustment, so the ip header inside will be aligned correctly.

reported and tested by anthony eden who hit this on armv7
i reproduced the problem on sparc64 and verified the fix on amd64
and sparc64
ok mpi@ mikeb@ deraadt@

3 files changed, 39 insertions, 4 deletions

diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index f839241b8c3..147fc1c2db9 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uipc_mbuf.c,v 1.218 2016/01/31 00:18:07 sashan Exp $	*/
+/*	$OpenBSD: uipc_mbuf.c,v 1.219 2016/02/23 01:39:14 dlg Exp $	*/
 /*	$NetBSD: uipc_mbuf.c,v 1.15.4.1 1996/06/13 17:11:44 cgd Exp $	*/
 
 /*
@@ -1213,6 +1213,40 @@ m_dup_pkthdr(struct mbuf *to, struct mbuf *from, int wait)
 	return (0);
 }
 
+struct mbuf *
+m_dup_pkt(struct mbuf *m0, unsigned int adj, int wait)
+{
+	struct mbuf *m;
+	int len;
+
+	len = m0->m_pkthdr.len + adj;
+	if (len > MAXMCLBYTES) /* XXX */
+		return (NULL);
+
+	m = m_get(m0->m_type, wait);
+	if (m == NULL)
+		return (NULL);
+
+	if (m_dup_pkthdr(m, m0, wait) != 0)
+		goto fail;
+
+	if (len > MHLEN) {
+		MCLGETI(m, len, NULL, wait);
+		if (!ISSET(m->m_flags, M_EXT))
+			goto fail;
+	}
+
+	m->m_len = m->m_pkthdr.len = len;
+	m_adj(m, adj);
+	m_copydata(m0, 0, m0->m_pkthdr.len, mtod(m, caddr_t));
+
+	return (m);
+
+fail:
+	m_freem(m);
+	return (NULL);
+}
+
 #ifdef DDB
 void
 m_print(void *v,
diff --git a/sys/netinet/ip_carp.c b/sys/netinet/ip_carp.c
index e0220d74ca3..795189c71f1 100644
--- a/sys/netinet/ip_carp.c
+++ b/sys/netinet/ip_carp.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip_carp.c,v 1.286 2016/01/21 11:23:48 mpi Exp $	*/
+/*	$OpenBSD: ip_carp.c,v 1.287 2016/02/23 01:39:14 dlg Exp $	*/
 
 /*
  * Copyright (c) 2002 Michael Shalayeff. All rights reserved.
@@ -1429,7 +1429,7 @@ carp_input(struct ifnet *ifp0, struct mbuf *m, void *cookie)
 			if (!(sc->sc_if.if_flags & IFF_UP))
 				continue;
 
-			m0 = m_copym2(m, 0, M_COPYALL, M_DONTWAIT);
+			m0 = m_dup_pkt(m, ETHER_ALIGN, M_DONTWAIT);
 			if (m0 == NULL)
 				continue;
 
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index 451c8c68c68..7e80483f338 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mbuf.h,v 1.207 2016/01/31 00:18:07 sashan Exp $	*/
+/*	$OpenBSD: mbuf.h,v 1.208 2016/02/23 01:39:14 dlg Exp $	*/
 /*	$NetBSD: mbuf.h,v 1.19 1996/02/09 18:25:14 christos Exp $	*/
 
 /*
@@ -447,6 +447,7 @@ void	m_cat(struct mbuf *, struct mbuf *);
 struct mbuf *m_devget(char *, int, int);
 int	m_apply(struct mbuf *, int, int,
 	    int (*)(caddr_t, caddr_t, unsigned int), caddr_t);
+struct mbuf *m_dup_pkt(struct mbuf *, unsigned int, int);
 int	m_dup_pkthdr(struct mbuf *, struct mbuf *, int);
 
 /* Packet tag routines */