From: Hannes Frederic Sowa <hannes@stressinduktion.org>
To: Werner Almesberger <werner@almesberger.net>
Cc: netdev@vger.kernel.org, davem@davemloft.net
Subject: Re: minimum ICMPv6 message size vs. RPL's DIS
Date: Fri, 26 Jul 2013 01:31:34 +0200 [thread overview]
Message-ID: <20130725233134.GA24247@order.stressinduktion.org> (raw)
In-Reply-To: <20130725214749.GD29572@ws>
On Thu, Jul 25, 2013 at 06:47:49PM -0300, Werner Almesberger wrote:
> Hannes Frederic Sowa wrote:
> > I don't know how they could do this if they want to let other RFCs extend
> > icmp types.
>
> Oh, ICMPs can have padding. That's used to enforce "nice" alignment.
> Even RFC 6550 (RPL) has that. For example, you could simply pad the
> troublesome DIS, message which is
>
> Offset Value Description
> ------ ----- ------------------------------------------------
> 0 0x9b ICMPv6 Type = RPL (155, section 6)
> 1 0x00 ICMPv6 Code = DODAG Information Solicitation (0)
> 2 0x?? Checksum
> 3 0x?? (continued)
>
> 4 0x00 Flags = 0 (section 6.2.1)
> 5 0x00 Reserved
>
> to eight bytes (i.e., four bytes of body) by adding
>
> 6 0x01 Option Type = PadN (section 6.7.3)
> 7 0x00 Option Length = 0
>
> But if nothing obliges the sender to do so, there's no excuse for
> Linux to expect such padding.
Yes, of course, that's possible but not specified at all in the general
ICMPv6 RFC. If packets are too short for some medium, I guess, one
would stretch it with extension header paddings before the icmpv6 header.
> > Yes, that could be an issue. I would be willing to accept this fallout. :)
>
> I'm kinda curious what sort of policy we have on that. The worst
> case would be that there's a bunch of 64 bit Linux machines out
> there, doing critical infrastructure things in the Internet (not an
> unlikely role, given the API in question), and their user space has
> some vulnerability if the kernel lets a "short" ICMPv6 packet
> through.
You forgot one critical aspect: Important infrastructure is *never*
going to be updated and definitely never runs IPv6. ;)
I don't think there is a policy, just intuition.
> Of course, "The Almesberger-Sowa Internet Meltdown of 2013" does
> have a nice ring to it, in an apocalyptic kind of way ...
I would like to avoid such a scenario, but have seen enough patches that
I kind of cooled down a bit. ;)
In summary, I agree, we should get both changes at once into the tree or
none (of course I would still change the pointer to something reasonable
and describe the circumstances in a comment if we don't change the
current behaviour).
Greetings,
Hannes
next prev parent reply other threads:[~2013-07-25 23:31 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-24 23:28 minimum ICMPv6 message size vs. RPL's DIS Werner Almesberger
2013-07-25 6:17 ` Hannes Frederic Sowa
2013-07-25 10:30 ` Werner Almesberger
2013-07-25 13:03 ` Hannes Frederic Sowa
2013-07-25 13:58 ` Hannes Frederic Sowa
2013-07-25 14:32 ` Werner Almesberger
2013-07-25 18:40 ` Hannes Frederic Sowa
2013-07-25 21:47 ` Werner Almesberger
2013-07-25 23:31 ` Hannes Frederic Sowa [this message]
2013-08-01 5:48 ` Hannes Frederic Sowa
2013-08-02 1:10 ` David Miller
2013-08-02 4:51 ` Werner Almesberger
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20130725233134.GA24247@order.stressinduktion.org \
--to=hannes@stressinduktion.org \
--cc=davem@davemloft.net \
--cc=netdev@vger.kernel.org \
--cc=werner@almesberger.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).