netdev - Re: [PATCH ipsec] xfrm: check DST_NOPOLICY as well as DST

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Date:   Thu, 05 Dec 2019 11:11:56 +0000
From:   Mark Gillott <mgillott@...tta.att-mail.com>
To:     nicolas.dichtel@...nd.com, netdev@...r.kernel.org
Cc:     steffen.klassert@...unet.com, herbert@...dor.apana.org.au
Subject: Re: [PATCH ipsec] xfrm: check DST_NOPOLICY as well as DST_NOXFRM

On Thu, 2019-12-05 at 11:51 +0100, Nicolas Dichtel wrote:
> Le 05/12/2019 à 11:05, Mark Gillott a écrit :
> > On Thu, 2019-12-05 at 09:52 +0100, Nicolas Dichtel wrote:
> > > Le 05/12/2019 à 09:10, Mark Gillott a écrit :
> > > > On Wed, 2019-12-04 at 17:57 +0100, Nicolas Dichtel wrote:
> > > > > Le 04/12/2019 à 16:17, Mark Gillott a écrit :
> > > > > > Before performing a policy bundle lookup, check the
> > > > > > DST_NOPOLICY
> > > > > > option, as well as DST_NOXFRM. That is, skip further
> > > > > > processing
> > > > > > if
> > > > > > either of the disable_policy or disable_xfrm sysctl
> > > > > > attributes
> > > > > > are
> > > > > > set.
> > > > > 
> > > > > Can you elaborate why this change is needed?
> > > > 
> > > > We have a separate DPDK-based dataplane that is responsible for
> > > > all
> > > > IPsec processing - policy handing/encryption/decryption.
> > > > Consequently
> > > > we set the net.ipv[4|6].conf.<if>.disable_policy sysctl to 1
> > > > for
> > > > all
> > > > "interesting" interfaces. That is we want the kernel to ignore
> > > > any
> > > > IPsec policies.
> > > > 
> > > > Despite the above & depending on configuration, we found that
> > > > originating traffic was ending up deep inside XFRM where it
> > > > would
> > > > get
> > > > dropped because of a route lookup problem.
> > > 
> > > And why don't you set disable_xfrm to thoses interfaces also?
> > > disable_policy means no xfrm policy lookup on output,
> > > disable_xfrm
> > > means no xfrm
> > > policy check on input.
> 
> I inverted them! :/
> disable_policy => no xfrm policy check on input
> disable_xfrm => no xfrm encryption on output
> 
> > > 
> > 
> > True, setting disable_xfrm=1 would solve the issue. Except this is
> > output - the test case is a ping from a peer, the corresponding
> > ICMP
> > response is discarded by the kernel. Feels like disable_policy is
> > the
> > right check (the kernel is doing XFRM output).
> 
> If you don't want to perform xfrm encryption on output, you have to
> set
> disable_xfrm. disable_policy is for input path only.
> 

Alright happy to drop this patch and we'll use disable_xfrm (as well
as/instead of disable_policy).

Many thanks,
Mark