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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
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