Improve systemd-resolved detection

When 127.0.0.53 is the only nameserver in /etc/resolv.conf assume systemd-resolved is used. This is better because /etc/resolv.conf does not have to be symlinked to /run/systemd/resolve/stub-resolv.conf in order to use systemd-resolved. [NO TESTS NEEDED] Fixes: containers#10570 Signed-off-by: Paul Holzinger <[email protected]>
Luap99 · Jun 8, 2021 · 18fa124 · 18fa124
1 parent 9a3a732
commit 18fa124
Showing 1 changed file with 9 additions and 11 deletions.
diff --git a/libpod/container_internal_linux.go b/libpod/container_internal_linux.go
@@ -1650,22 +1650,20 @@ func (c *Container) generateResolvConf() (string, error) {
 		}
 	}
 
-	// Determine the endpoint for resolv.conf in case it is a symlink
-	resolvPath, err := filepath.EvalSymlinks(resolvConf)
+	contents, err := ioutil.ReadFile(resolvConf)
 	// resolv.conf doesn't have to exists
 	if err != nil && !os.IsNotExist(err) {
 		return "", err
 	}
 
-	// Determine if symlink points to any of the systemd-resolved files
-	if strings.HasPrefix(resolvPath, "/run/systemd/resolve/") {
-		resolvPath = "/run/systemd/resolve/resolv.conf"
-	}
-
-	contents, err := ioutil.ReadFile(resolvPath)
-	// resolv.conf doesn't have to exists
-	if err != nil && !os.IsNotExist(err) {
-		return "", err
+	ns := resolvconf.GetNameservers(contents)
+	// check if systemd-resolved is used, assume it is used when 127.0.0.53 is the only nameserver
+	if len(ns) == 1 && ns[0] == "127.0.0.53" {
+		// read the actual resolv.conf file for systemd-resolved
+		contents, err = ioutil.ReadFile("/run/systemd/resolve/resolv.conf")
+		if err != nil {
+			return "", errors.Wrapf(err, "detected that systemd-resolved is in use, but could not locate real resolv.conf")
+		}
 	}
 
 	ipv6 := false