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fwd: Direct inbound spliced forwards to the guest's external address

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In pasta mode, where addressing permits we "splice" connections, forwarding
directly from host socket to guest/container socket without any L2 or L3
processing.  This gives us a very large performance improvement when it's
possible.

Since the traffic is from a local socket within the guest, it will go over
the guest's 'lo' interface, and accordingly we set the guest side address
to be the loopback address.  However this has a surprising side effect:
sometimes guests will run services that are only supposed to be used within
the guest and are therefore bound to only 127.0.0.1 and/or ::1.  pasta's
forwarding exposes those services to the host, which isn't generally what
we want.

Correct this by instead forwarding inbound "splice" flows to the guest's
external address.

Link: https://github.com/containers/podman/issues/24045
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2024-10-18 12:35:56 +11:00 • committed by Stefano Brivio
parent 58e6d68599
commit b4dace8f46
4 changed files with 53 additions and 12 deletions

9
conf.c
View file

@ -912,6 +912,9 @@ pasta_opts:
" -U, --udp-ns SPEC UDP port forwarding to init namespace\n"
" SPEC is as described above\n"
" default: auto\n"
" --host-lo-to-ns-lo DEPRECATED:\n"
" Translate host-loopback forwards to\n"
" namespace loopback\n"
" --userns NSPATH Target user namespace to join\n"
" --netns PATH|NAME Target network namespace to join\n"
" --netns-only Don't join existing user namespace\n"
@ -1289,6 +1292,7 @@ void conf(struct ctx *c, int argc, char **argv)
{"netns-only", no_argument, NULL, 20 },
{"map-host-loopback", required_argument, NULL, 21 },
{"map-guest-addr", required_argument, NULL, 22 },
{"host-lo-to-ns-lo", no_argument, NULL, 23 },
{"dns-host", required_argument, NULL, 24 },
{ 0 },
};
@ -1467,6 +1471,11 @@ void conf(struct ctx *c, int argc, char **argv)
conf_nat(optarg, &c->ip4.map_guest_addr,
&c->ip6.map_guest_addr, NULL);
break;
case 23:
if (c->mode != MODE_PASTA)
die("--host-lo-to-ns-lo is for pasta mode only");
c->host_lo_to_ns_lo = 1;
break;
case 24:
if (inet_pton(AF_INET6, optarg, &c->ip6.dns_host) &&
!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_host))