src: Pull up following revision(s) (requested by knakahara in ti...

[Repository Conversion <srcmastr%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/bb3e2959368c
branches:  netbsd-8
changeset: 318059:bb3e2959368c
user:      martin <martin%NetBSD.org@localhost>
date:      Wed Apr 11 14:15:45 2018 +0000
description:
Pull up following revision(s) (requested by knakahara in ticket #730):

        sys/net/if_l2tp.c: revision 1.22
        sys/net/if_l2tp.c: revision 1.23

Improve comment. Pointed out by maxv@n.o, thanks.

Fix previous my mistake and odd unaligned case. Pointed out by maxv@n.o, thanks.
It must be rare case to be required this copy routine...

diffstat:

 sys/net/if_l2tp.c |  25 +++++++++++++++++++++----
 1 files changed, 21 insertions(+), 4 deletions(-)

diffs (57 lines):

diff -r fbf1ea51908f -r bb3e2959368c sys/net/if_l2tp.c
--- a/sys/net/if_l2tp.c Wed Apr 11 03:00:03 2018 +0000
+++ b/sys/net/if_l2tp.c Wed Apr 11 14:15:45 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: if_l2tp.c,v 1.11.2.6 2018/04/09 13:40:20 bouyer Exp $  */
+/*     $NetBSD: if_l2tp.c,v 1.11.2.7 2018/04/11 14:15:45 martin Exp $  */
 
 /*
  * Copyright (c) 2017 Internet Initiative Japan Inc.
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_l2tp.c,v 1.11.2.6 2018/04/09 13:40:20 bouyer Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_l2tp.c,v 1.11.2.7 2018/04/11 14:15:45 martin Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_inet.h"
@@ -477,11 +477,16 @@
                return;
        }
 
+       /*
+        * If the head of the payload is not aligned, align it.
+        */
        addr = mtod(m, vaddr_t);
-       if ((addr & 0x03) == 0) {
+       if ((addr & 0x03) != 0x2) {
                /* copy and align head of payload */
                struct mbuf *m_head;
                int copy_length;
+               u_int pad = roundup(sizeof(struct ether_header), 4)
+                       - sizeof(struct ether_header);
 
 #define L2TP_COPY_LENGTH               60
 
@@ -504,7 +509,19 @@
                }
                M_COPY_PKTHDR(m_head, m);
 
-               MH_ALIGN(m_head, L2TP_COPY_LENGTH);
+               /*
+                * m_head should be:
+                *                             L2TP_COPY_LENGTH
+                *                          <-  + roundup(pad, 4) - pad ->
+                *   +-------+--------+-----+--------------+-------------+
+                *   | m_hdr | pkthdr | ... | ether header |   payload   |
+                *   +-------+--------+-----+--------------+-------------+
+                *                          ^              ^
+                *                          m_data         4 byte aligned
+                */
+               MH_ALIGN(m_head, L2TP_COPY_LENGTH + roundup(pad, 4));
+               m_head->m_data += pad;
+
                memcpy(mtod(m_head, void *), mtod(m, void *), copy_length);
                m_head->m_len = copy_length;
                m->m_data += copy_length;