netdev - Re: switching network namespace midway

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87ip9zqqlv.fsf@xmission.com>
Date:	Wed, 24 Oct 2012 18:37:16 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	rsa <ravi.mlists@...il.com>, netdev@...r.kernel.org
Subject: Re: switching network namespace midway

Benjamin LaHaise <bcrl@...ck.org> writes:

> On Wed, Oct 24, 2012 at 02:11:14PM -0700, Eric W. Biederman wrote:
>> rsa <ravi.mlists@...il.com> writes:
>> 
>> > Assuming I have a tunnel interface where two route lookups are done --
>> > one for innter
>> > packet and the other for outer -- do you see any issues in switching
>> > the network
>> > namespace prior to second route lookup (and restore to the original namespace
>> > after the second lookup is done)?
>> >
>> > If so, are there any other calls other than sk_change_net() needed?
>> 
>> In general sk_change_net is a bad idea.
>> 
>> Most likely what you want to do is simply memorize both struct net's
>> that you care about and perform the routing lookup as appropriate.
>> 
>> Certainly you don't want to be calling sk_change_net for every packet
>> that goes through your tunnel.
>
> I've actually done this with L2TP.  The packets coming into the system from 
> the tunnel are received on one UDP socket in one "struct net", but the 
> decapsulated packets are received on a "struct net_device" that is in a 
> different "struct net".  No special coding is required -- just move the 
> tunnel's net_device into another namespace after creation and it works as 
> expected.  Using sk_change_net() would be full of races and is really not 
> required for the vast majority of use cases.

Yes.  Although L2TP is not an example of code I would copy.  Any other
tunnel would be better.  I haven't looked closely at L2TP but it keeps
popping up as a poster child for small little network namespace bugs
that I don't want to think about.

Last I looked to use L2TP it required a magic userspace that I couldn't
find and I haven't cared enough to write.  Ben would you be interested
in helping flush out the network namespace bugs out of L2TP?

Eric

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html