On Tue, Nov 08, 2022 at 07:22:22AM +0100, Stefano Brivio wrote: > On Tue, 8 Nov 2022 16:51:35 +1100 > David Gibson wrote: > > > On Mon, Nov 07, 2022 at 10:51:21AM +0100, Stefano Brivio wrote: > > > On Mon, 7 Nov 2022 12:08:59 +1100 > > > David Gibson wrote: > > > > > > > On Sat, Nov 05, 2022 at 08:22:23AM +0100, Stefano Brivio wrote: > > > > > On Sat, 5 Nov 2022 12:19:55 +1100 > > > > > David Gibson 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 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 > > > > > > > > > --- > > > > > > > > > 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. > > > > > > > > Right, that's what I meant. > > > > > > > > > We could rename .dns_send[] back to .dns[] and change the current > > > > > > > > Right, I think dns[] is a better name for it. > > > > > > > > > .dns[] to .own_dns, or .fwd_dns_target, something like that. Other naming > > > > > ideas welcome. > > > > > > > > Yeah, I find the current dns_fwd name not very illuminating either. > > > > > > > > *thinks* does it even make sense for dns_fwd not to be in dns_send? > > > > We're intercepting queries the guest sends to @dns_fwd, so surely we > > > > should also be advertising it to the guest. > > > > > > I wouldn't be so sure of that "surely". In the Podman test case where I > > > hit this issue, I use Podman to write to /etc/resolv.conf directly, no > > > DHCP/NDP/DHCPv6 involved, and things work. > > > > > > That doesn't automatically imply a use case for *not* advertising it, > > > but we have several ways this can work without advertising anything, so > > > there are also chances somebody might not want to advertise that in some > > > obscure use case. > > > > Right, but only the case for not advertising it matters here, and I > > don't see one. @dns_fwd (or @dns_match, as we discussed calling it > > instead) is explicitly a virtual DNS server available to the guest. > > Whatever method the guest does use to configure itself, we should > > allow it to discover this via DHCP (or DHCPv6 or NDP). > > Rather hypothetical: you don't want the guest/container to use a given > address as resolver. You know that that address might be in its > resolv.conf(5) because you don't have control over the image, wish to > override it if possible, and at the same time keep a safety net. Yeah, I guess. Seems pretty contrived. > Slightly unrelated: we're talking about this in the perspective of > getting rid of an explicit @dns_fwd/@dns_match. This would become a > flag, indicating we should forward queries originally directed to > 1. dns[0]... or 2. anything in dns[]? > > If it's just about 1. dns[0], we're forcing that address to be the first > advertised resolver. > > If it's about 2. dns[], we're not giving anymore the possibility of > forwarding queries originally directed to one a single address. Hmm... yes, those are fair points. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson