src: Add XXX.

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

details:   https://anonhg.NetBSD.org/src/rev/d21757ae0169
branches:  trunk
changeset: 318044:d21757ae0169
user:      maxv <maxv%NetBSD.org@localhost>
date:      Wed Apr 11 05:38:47 2018 +0000
description:
Add XXX.

diffstat:

 sys/netinet/if_arp.c |  13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diffs (34 lines):

diff -r 688497fb6b0f -r d21757ae0169 sys/netinet/if_arp.c
--- a/sys/netinet/if_arp.c      Wed Apr 11 03:25:25 2018 +0000
+++ b/sys/netinet/if_arp.c      Wed Apr 11 05:38:47 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: if_arp.c,v 1.272 2018/04/10 08:41:14 maxv Exp $        */
+/*     $NetBSD: if_arp.c,v 1.273 2018/04/11 05:38:47 maxv Exp $        */
 
 /*
  * Copyright (c) 1998, 2000, 2008 The NetBSD Foundation, Inc.
@@ -68,7 +68,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_arp.c,v 1.272 2018/04/10 08:41:14 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_arp.c,v 1.273 2018/04/11 05:38:47 maxv Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ddb.h"
@@ -1358,6 +1358,15 @@
        }
        ia4_release(ia, &psref_ia);
 
+       /*
+        * XXX XXX: Here we're recycling the mbuf. But the mbuf could have
+        * other mbufs in its chain, and just overwriting m->m_pkthdr.len
+        * would be wrong in this case (the length becomes smaller than the
+        * real chain size).
+        *
+        * This can theoretically cause bugs in the lower layers (drivers,
+        * and L2encap), in some corner cases.
+        */
        memcpy(ar_tpa(ah), ar_spa(ah), ah->ar_pln);
        memcpy(ar_spa(ah), &itaddr, ah->ar_pln);
        ah->ar_op = htons(ARPOP_REPLY);