NetBSD Problem Report #49834

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Date: Fri, 10 Apr 2015 22:20:41 +0000 (UTC)
From: nbsd.pr@fenyo.net
Reply-To: nbsd.pr@fenyo.net
To: gnats-bugs@NetBSD.org
Subject: invalid mbuf size comparison when dealing with neighbor solicitations and advertisements
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>Number:         49834
>Category:       kern
>Synopsis:       invalid mbuf size comparison when dealing with neighbor solicitations and advertisements
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Apr 10 22:25:00 +0000 2015
>Closed-Date:    Thu May 17 12:11:23 +0000 2018
>Last-Modified:  Thu May 17 12:11:23 +0000 2018
>Originator:     Alexandre FENYO
>Release:        NetBSD current
>Organization:
>Environment:
every ports (I think the bug comes from KAME, since it was integrated in NetBSD 1.5)
>Description:
In kernel file src/sys/netinet6/nd6_nbr.c, two mbuf size comparisons are erroneous:

Excerpt from line 374 to 477:
	if (max_linkhdr + maxlen >= MCLBYTES) {
		printf("nd6_ns_output: max_linkhdr + maxlen >= MCLBYTES "
		    "(%d + %d > %d)\n", max_linkhdr, maxlen, MCLBYTES);
		panic("nd6_ns_output: insufficient MCLBYTES");

The two tests ">=" should be ">", like it is correctly written in the last second line of the printf: "(%d + %d > %d)\n"

This is a bug because if max_linkhdr + maxlen == MCLBYTES, the packet can be handled correctly: there is enough space in the mbuf cluster.

The same mistake is done in the same file, from line 873 to 876:
	if (max_linkhdr + maxlen >= MCLBYTES) {
		printf("nd6_na_output: max_linkhdr + maxlen >= MCLBYTES "
		    "(%d + %d > %d)\n", max_linkhdr, maxlen, MCLBYTES);
		panic("nd6_na_output: insufficient MCLBYTES");

Anyway, this is a very minor bug since this case should never happen: the Neigbor Advertisement and Neighbor Solicitation packets are always small enough to be contained in a single MBUF cluster. But the code is wrong, the code would be nicer if it was corrected.
>How-To-Repeat:

>Fix:
Rewrite code like that:

from line 374 to 477:
	if (max_linkhdr + maxlen > MCLBYTES) {
		printf("nd6_ns_output: max_linkhdr + maxlen > MCLBYTES "
		    "(%d + %d > %d)\n", max_linkhdr, maxlen, MCLBYTES);
		panic("nd6_ns_output: insufficient MCLBYTES");

And from line 873 to 876:
	if (max_linkhdr + maxlen > MCLBYTES) {
		printf("nd6_na_output: max_linkhdr + maxlen > MCLBYTES "
		    "(%d + %d > %d)\n", max_linkhdr, maxlen, MCLBYTES);
		panic("nd6_na_output: insufficient MCLBYTES");


>Release-Note:

>Audit-Trail:
From: "Maxime Villard" <maxv@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/49834 CVS commit: src/sys/netinet6
Date: Thu, 17 May 2018 12:07:48 +0000

 Module Name:	src
 Committed By:	maxv
 Date:		Thu May 17 12:07:48 UTC 2018

 Modified Files:
 	src/sys/netinet6: nd6_nbr.c

 Log Message:
 Fix the KASSERTs. It doesn't matter at all since the packet can't be this
 big anyway, and there are many other places that have this kind of typo;
 but still fix it, for the sake of closing PR/49834.


 To generate a diff of this commit:
 cvs rdiff -u -r1.154 -r1.155 src/sys/netinet6/nd6_nbr.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->closed
State-Changed-By: maxv@NetBSD.org
State-Changed-When: Thu, 17 May 2018 12:11:23 +0000
State-Changed-Why:
Fixed, thanks.


>Unformatted:

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