From d8d96bce62e8597b8d35bed1d9e9cb103336fd6b Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 18 Nov 2022 16:52:06 +0100
Subject: [PATCH] resolved: when configuring 127.0.0.1 as per-interface DNS
 server, contact it via "lo" always

ussually if you specify a DNS server on some interface then we'll use
that interface to talk to it. Let's override this for localhost
addresses, as they only really make sense on "lo".

Fixes: #25397
(cherry picked from commit 6e32414a66ff8dbcef233981a7066684d903ee9f)

Related: #2138081
---
 src/resolve/resolved-dns-server.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c
index 04a4f53ed0..8ff513fa33 100644
--- a/src/resolve/resolved-dns-server.c
+++ b/src/resolve/resolved-dns-server.c
@@ -648,6 +648,11 @@ int dns_server_adjust_opt(DnsServer *server, DnsPacket *packet, DnsServerFeature
 int dns_server_ifindex(const DnsServer *s) {
         assert(s);
 
+        /* For loopback addresses, go via the loopback interface, regardless which interface this is linked
+         * to. */
+        if (in_addr_is_localhost(s->family, &s->address))
+                return LOOPBACK_IFINDEX;
+
         /* The link ifindex always takes precedence */
         if (s->link)
                 return s->link->ifindex;