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From: Stefano Brivio <sbrivio@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: passt-dev@passt.top, Paul Holzinger <pholzing@redhat.com>
Subject: Re: [PATCH 3/3] udp: Check for answers to forwarded DNS queries before handling local redirects
Date: Sun, 06 Nov 2022 23:22:51	[thread overview]
Message-ID: <20221105082223.4a447ac5@elisabeth> (raw)
In-Reply-To: <Y2W6O+7kF1mkV/3d@yekko>

On Sat, 5 Nov 2022 12:19:55 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Thu, Nov 03, 2022 at 07:42:51AM +0100, Stefano Brivio wrote:
> > On Thu, 3 Nov 2022 14:42:13 +1100
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > On Thu, Nov 03, 2022 at 12:04:43AM +0100, Stefano Brivio wrote:  
> > > > Now that we allow loopback DNS addresses to be used as targets for
> > > > forwarding, we need to check if DNS answers come from those targets,
> > > > before deciding to eventually remap traffic for local redirects.
> > > > 
> > > > Otherwise, the source address won't match the one configured as
> > > > forwarder, which means that the guest or the container will refuse
> > > > those responses.
> > > > 
> > > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> > > > ---
> > > >  udp.c | 17 ++++++++---------
> > > >  1 file changed, 8 insertions(+), 9 deletions(-)
> > > > 
> > > > diff --git a/udp.c b/udp.c
> > > > index 4b201d3..7c77e09 100644
> > > > --- a/udp.c
> > > > +++ b/udp.c
> > > > @@ -680,8 +680,10 @@ static void udp_sock_fill_data_v4(const struct ctx *c, int n,
> > > >  	src = ntohl(b->s_in.sin_addr.s_addr);
> > > >  	src_port = ntohs(b->s_in.sin_port);
> > > >  
> > > > -	if (src >> IN_CLASSA_NSHIFT == IN_LOOPBACKNET ||
> > > > -	    src == INADDR_ANY || src == ntohl(c->ip4.addr_seen)) {
> > > > +	if (c->ip4.dns_fwd && src == htonl(c->ip4.dns[0]) && src_port == 53) {    
> > > 
> > > I guess this is not a newly introduced bug, but for the case of
> > > multiple host nameservers, don't you need to check against everything
> > > in the ip4.dns[] array, not just entry 0?  
> > 
> > No, because that's the only one we're using as target for forwarded
> > queries -- and DNS answers we want to check here are only the forwarded
> > ones.  
> 
> *thinks*  .. ok, that makes sense.  But if that's the case, won't
> ip4.dns[0] be the only entry in ip4.dns[] we use for anything at all?
> Can we drop the table and just keep one entry?

Now that we have ip{4,6}.dns_send[], yes.

We could rename .dns_send[] back to .dns[] and change the current
.dns[] to .own_dns, or .fwd_dns_target, something like that. Other naming
ideas welcome.

I wanted the change in 2/3 to be simple and fix-like, but I can do this
rework soon so that you don't _have_ to. :)

-- 
Stefano


  reply	other threads:[~2022-11-06 23:22 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-02 23:04 [PATCH 0/3] Fixes and workarounds for pasta with Podman in Google Cloud Stefano Brivio
2022-11-02 23:04 ` [PATCH 1/3] conf: Consistency check between configured IPv4 netmask and gateway Stefano Brivio
2022-11-03  3:17   ` David Gibson
2022-11-03  6:39     ` Stefano Brivio
2022-11-02 23:04 ` [PATCH 2/3] conf: Split the notions of read DNS addresses and offered ones Stefano Brivio
2022-11-03  3:37   ` David Gibson
2022-11-03  6:42     ` Stefano Brivio
2022-11-02 23:04 ` [PATCH 3/3] udp: Check for answers to forwarded DNS queries before handling local redirects Stefano Brivio
2022-11-03  3:42   ` David Gibson
2022-11-03  6:42     ` Stefano Brivio
2022-11-05  1:19       ` David Gibson
2022-11-06 22:22         ` Stefano Brivio [this message]
2022-11-07  1:08           ` David Gibson
2022-11-07  9:51             ` Stefano Brivio
2022-11-08  5:51               ` David Gibson
2022-11-08  6:22                 ` Stefano Brivio
2022-11-10  4:30                   ` David Gibson
2022-11-03  3:13 ` [PATCH 0/3] Fixes and workarounds for pasta with Podman in Google Cloud David Gibson
2022-11-03  6:36   ` Stefano Brivio

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