From df2e7e00fccaac87e558c29032eabc9fe8d5c465 Mon Sep 17 00:00:00 2001
From: Paul Holzinger <pholzing@redhat.com>
Date: Wed, 2 Jun 2021 21:00:26 +0200
Subject: add ipv6 nameservers only when the container has ipv6 enabled

The containers /etc/resolv.conf allways preserved the ipv6 nameserves
from the host even when the container did not supported ipv6. Check
if the cni result contains an ipv6 address or slirp4netns has ipv6
support enabled and only add the ipv6 nameservers when this is the case.

The test needs to have an ipv6 nameserver in the hosts /etc/hosts but we
should never mess with this file on the host. Therefore the test is
skipped when no ipv6 is detected.

Fixes #10158

Signed-off-by: Paul Holzinger <pholzing@redhat.com>
---
 libpod/container_internal_linux.go | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

(limited to 'libpod/container_internal_linux.go')

diff --git a/libpod/container_internal_linux.go b/libpod/container_internal_linux.go
index 1b2f5a496..74a3fec32 100644
--- a/libpod/container_internal_linux.go
+++ b/libpod/container_internal_linux.go
@@ -1668,17 +1668,16 @@ func (c *Container) generateResolvConf() (string, error) {
 		return "", err
 	}
 
-	// Ensure that the container's /etc/resolv.conf is compatible with its
-	// network configuration.
-	// TODO: set ipv6 enable bool more sanely
-	resolv, err := resolvconf.FilterResolvDNS(contents, true, c.config.CreateNetNS)
-	if err != nil {
-		return "", errors.Wrapf(err, "error parsing host resolv.conf")
-	}
-
+	ipv6 := false
 	// Check if CNI gave back and DNS servers for us to add in
 	cniResponse := c.state.NetworkStatus
 	for _, i := range cniResponse {
+		for _, ip := range i.IPs {
+			// Note: only using To16() does not work since it also returns a vaild ip for ipv4
+			if ip.Address.IP.To4() == nil && ip.Address.IP.To16() != nil {
+				ipv6 = true
+			}
+		}
 		if i.DNS.Nameservers != nil {
 			cniNameServers = append(cniNameServers, i.DNS.Nameservers...)
 			logrus.Debugf("adding nameserver(s) from cni response of '%q'", i.DNS.Nameservers)
@@ -1689,6 +1688,25 @@ func (c *Container) generateResolvConf() (string, error) {
 		}
 	}
 
+	if c.config.NetMode.IsSlirp4netns() {
+		ctrNetworkSlipOpts := []string{}
+		if c.config.NetworkOptions != nil {
+			ctrNetworkSlipOpts = append(ctrNetworkSlipOpts, c.config.NetworkOptions["slirp4netns"]...)
+		}
+		slirpOpts, err := parseSlirp4netnsNetworkOptions(c.runtime, ctrNetworkSlipOpts)
+		if err != nil {
+			return "", err
+		}
+		ipv6 = slirpOpts.enableIPv6
+	}
+
+	// Ensure that the container's /etc/resolv.conf is compatible with its
+	// network configuration.
+	resolv, err := resolvconf.FilterResolvDNS(contents, ipv6, c.config.CreateNetNS)
+	if err != nil {
+		return "", errors.Wrapf(err, "error parsing host resolv.conf")
+	}
+
 	dns := make([]net.IP, 0, len(c.runtime.config.Containers.DNSServers))
 	for _, i := range c.runtime.config.Containers.DNSServers {
 		result := net.ParseIP(i)
-- 
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