From ff63ac922a4017de8a5d384b1c0be36433436ed8 Mon Sep 17 00:00:00 2001
From: David Gibson <david@gibson.dropbear.id.au>
Date: Thu, 3 Oct 2024 15:14:02 +1000
Subject: conf: Add --dns-host option to configure host side nameserver
When redirecting DNS queries with the --dns-forward option, passt/pasta
needs a host side nameserver to redirect the queries to. This is
controlled by the c->ip[46].dns_host variables. This is set to the first
first nameserver listed in the host's /etc/resolv.conf, and there isn't
currently a way to override it from the command line.
Prior to 0b25cac9 ("conf: Treat --dns addresses as guest visible
addresses") it was possible to alter this with the -D/--dns option.
However, doing so was confusing and had some nonsensical edge cases because
-D generally takes guest side addresses, rather than host side addresses.
Add a new --dns-host option to restore this functionality in a more
sensible way.
Link: https://bugs.passt.top/show_bug.cgi?id=102
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
conf.c | 16 ++++++++++++++++
passt.1 | 17 +++++++++++++----
2 files changed, 29 insertions(+), 4 deletions(-)
diff --git a/conf.c b/conf.c
index e360fb9..c631019 100644
--- a/conf.c
+++ b/conf.c
@@ -829,6 +829,9 @@ static void usage(const char *name, FILE *f, int status)
" --dns-forward ADDR Forward DNS queries sent to ADDR\n"
" can be specified zero to two times (for IPv4 and IPv6)\n"
" default: don't forward DNS queries\n"
+ " --dns-host ADDR Host nameserver to direct queries to\n"
+ " can be specified zero to two times (for IPv4 and IPv6)\n"
+ " default: first nameserver from host's /etc/resolv.conf\n"
" --no-tcp Disable TCP protocol handler\n"
" --no-udp Disable UDP protocol handler\n"
" --no-icmp Disable ICMP/ICMPv6 protocol handler\n"
@@ -1286,6 +1289,7 @@ 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 },
+ {"dns-host", required_argument, NULL, 24 },
{ 0 },
};
const char *logname = (c->mode == MODE_PASTA) ? "pasta" : "passt";
@@ -1463,6 +1467,18 @@ 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 24:
+ if (inet_pton(AF_INET6, optarg, &c->ip6.dns_host) &&
+ !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_host))
+ break;
+
+ if (inet_pton(AF_INET, optarg, &c->ip4.dns_host) &&
+ !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_host) &&
+ !IN4_IS_ADDR_BROADCAST(&c->ip4.dns_host))
+ break;
+
+ die("Invalid host nameserver address: %s", optarg);
+ break;
case 'd':
c->debug = 1;
c->quiet = 0;
diff --git a/passt.1 b/passt.1
index 5ac2962..ef33267 100644
--- a/passt.1
+++ b/passt.1
@@ -249,10 +249,19 @@ the host.
.TP
.BR \-\-dns-forward " " \fIaddr
Map \fIaddr\fR (IPv4 or IPv6) as seen from guest or namespace to the
-first configured DNS resolver (with corresponding IP version). Maps
-only UDP and TCP traffic to port 53 or port 853. Replies are
-translated back with a reverse mapping. This option can be specified
-zero to two times (once for IPv4, once for IPv6).
+nameserver (with corresponding IP version) specified by the
+\fB\-\-dns-host\fR option. Maps only UDP and TCP traffic to port 53 or
+port 853. Replies are translated back with a reverse mapping. This
+option can be specified zero to two times (once for IPv4, once for
+IPv6).
+
+.TP
+.BR \-\-dns-host " " \fIaddr
+Configure the host nameserver which guest or namespace queries to the
+\fB\-\-dns-forward\fR address will be redirected to. This option can
+be specified zero to two times (once for IPv4, once for IPv6).
+By default, the first nameserver from the host's
+\fI/etc/resolv.conf\fR.
.TP
.BR \-S ", " \-\-search " " \fIlist
--
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