conf: Don't warn if nameservers were found, but won't be advertised

Starting from commit 3a2afde87dd1 ("conf, udp: Drop mostly duplicated
dns_send arrays, rename related fields"), we won't add to c->ip4.dns
and c->ip6.dns nameservers that can't be used by the guest or
container, and we won't advertise them.

However, the fact that we don't advertise any nameserver doesn't mean
that we didn't find any, and we should warn only if we couldn't find
any.

This is particularly relevant in case both --dns-forward and
--no-map-gw are passed, and a single loopback address is listed in
/etc/resolv.conf: we'll forward queries directed to the address
specified by --dns-forward to the loopback address we found, we
won't advertise that address, so we shouldn't warn: this is a
perfectly legitimate usage.

Reported-by: Paul Holzinger <pholzing@redhat.com>
Link: https://github.com/containers/podman/issues/19213
Fixes: 3a2afde87dd1 ("conf, udp: Drop mostly duplicated dns_send arrays, rename related fields")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Tested-by: Paul Holzinger <pholzing@redhat.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/conf.c b/conf.c
index 4a783b8..c50c039 100644
--- a/conf.c
+++ b/conf.c
@@ -399,6 +399,7 @@ static void get_dns(struct ctx *c)
 	int dns4_set, dns6_set, dnss_set, dns_set, fd;
 	struct fqdn *s = c->dns_search;
 	struct lineread resolvconf;
+	unsigned int added = 0;
 	char *line, *end;
 	const char *p;
 	int line_len;
@@ -427,13 +428,17 @@ static void get_dns(struct ctx *c)
 
 			if (!dns4_set &&
 			    dns4 - &c->ip4.dns[0] < ARRAY_SIZE(c->ip4.dns) - 1
-			    && inet_pton(AF_INET, p + 1, &dns4_tmp))
+			    && inet_pton(AF_INET, p + 1, &dns4_tmp)) {
 				add_dns4(c, &dns4_tmp, &dns4);
+				added++;
+			}
 
 			if (!dns6_set &&
 			    dns6 - &c->ip6.dns[0] < ARRAY_SIZE(c->ip6.dns) - 1
-			    && inet_pton(AF_INET6, p + 1, &dns6_tmp))
+			    && inet_pton(AF_INET6, p + 1, &dns6_tmp)) {
 				add_dns6(c, &dns6_tmp, &dns6);
+				added++;
+			}
 		} else if (!dnss_set && strstr(line, "search ") == line &&
 			   s == c->dns_search) {
 			end = strpbrk(line, "\n");
@@ -459,7 +464,7 @@ static void get_dns(struct ctx *c)
 	close(fd);
 
 out:
-	if (!dns_set && dns4 == c->ip4.dns && dns6 == c->ip6.dns)
+	if (!dns_set && !added)
 		warn("Couldn't get any nameserver address");
 }