Index: uipc_mbuf.c
===================================================================
RCS file: /cvs/src/sys/kern/uipc_mbuf.c,v
retrieving revision 1.231
diff -u -p -r1.231 uipc_mbuf.c
--- uipc_mbuf.c	15 Sep 2016 02:00:16 -0000	1.231
+++ uipc_mbuf.c	7 Oct 2016 05:21:43 -0000
@@ -603,9 +603,13 @@ m_copym(struct mbuf *m0, int off, int le
 			n->m_data = m->m_data + off;
 			n->m_ext = m->m_ext;
 			MCLADDREFERENCE(m, n);
-		} else
+		} else {
+			n->m_data += m->m_data -
+			    (m->m_flags & M_PKTHDR ? m->m_pktdat : m->m_dat);
+			n->m_data += off;
 			memcpy(mtod(n, caddr_t), mtod(m, caddr_t) + off,
 			    n->m_len);
+		}
 		if (len != M_COPYALL)
 			len -= n->m_len;
 		off += n->m_len;