CRI: An empty DNSConfig != unspecified

If we find that DNSConfig is provided and empty (not nil), we should not
replace it with the host's resolv.conf.

Also adds tests.

Signed-off-by: Tim Hockin <[email protected]>

Author: thockin

pkg/cri/server/podsandbox/sandbox_run_linux.go

@@ -268,25 +268,21 @@ func (c *Controller) setupSandboxFiles(id string, config *runtime.PodSandboxConf
 	}
 
 	// Set DNS options. Maintain a resolv.conf for the sandbox.
-	var err error
-	resolvContent := ""
+	resolvPath := c.getResolvPath(id)
+
 	if dnsConfig := config.GetDnsConfig(); dnsConfig != nil {
-		resolvContent, err = parseDNSOptions(dnsConfig.Servers, dnsConfig.Searches, dnsConfig.Options)
+		resolvContent, err := parseDNSOptions(dnsConfig.Servers, dnsConfig.Searches, dnsConfig.Options)
 		if err != nil {
 			return fmt.Errorf("failed to parse sandbox DNSConfig %+v: %w", dnsConfig, err)
 		}
-	}
-	resolvPath := c.getResolvPath(id)
-	if resolvContent == "" {
-		// copy host's resolv.conf to resolvPath
-		err = c.os.CopyFile(resolvConfPath, resolvPath, 0644)
-		if err != nil {
-			return fmt.Errorf("failed to copy host's resolv.conf to %q: %w", resolvPath, err)
+		if err := c.os.WriteFile(resolvPath, []byte(resolvContent), 0644); err != nil {
+			return fmt.Errorf("failed to write resolv content to %q: %w", resolvPath, err)
 		}
 	} else {
-		err = c.os.WriteFile(resolvPath, []byte(resolvContent), 0644)
-		if err != nil {
-			return fmt.Errorf("failed to write resolv content to %q: %w", resolvPath, err)
+		// The DnsConfig was nil - we interpret that to mean "use the global
+		// default", which is dubious but backwards-compatible.
+		if err := c.os.CopyFile(resolvConfPath, resolvPath, 0644); err != nil {
+			return fmt.Errorf("failed to copy host's resolv.conf to %q: %w", resolvPath, err)
 		}
 	}
 

pkg/cri/server/podsandbox/sandbox_run_linux_test.go

@@ -511,6 +511,82 @@ options timeout:1
 				},
 			},
 		},
+		{
+			desc:      "should create empty /etc/resolv.conf if DNSOptions is empty",
+			dnsConfig: &runtime.DNSConfig{},
+			ipcMode:   runtime.NamespaceMode_NODE,
+			expectedCalls: []ostesting.CalledDetail{
+				{
+					Name: "Hostname",
+				},
+				{
+					Name: "WriteFile",
+					Arguments: []interface{}{
+						filepath.Join(testRootDir, sandboxesDir, testID, "hostname"),
+						[]byte(realhostname + "\n"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name: "CopyFile",
+					Arguments: []interface{}{
+						"/etc/hosts",
+						filepath.Join(testRootDir, sandboxesDir, testID, "hosts"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name: "WriteFile",
+					Arguments: []interface{}{
+						filepath.Join(testRootDir, sandboxesDir, testID, "resolv.conf"),
+						[]byte{},
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name:      "Stat",
+					Arguments: []interface{}{"/dev/shm"},
+				},
+			},
+		},
+		{
+			desc:      "should copy host /etc/resolv.conf if DNSOptions is not set",
+			dnsConfig: nil,
+			ipcMode:   runtime.NamespaceMode_NODE,
+			expectedCalls: []ostesting.CalledDetail{
+				{
+					Name: "Hostname",
+				},
+				{
+					Name: "WriteFile",
+					Arguments: []interface{}{
+						filepath.Join(testRootDir, sandboxesDir, testID, "hostname"),
+						[]byte(realhostname + "\n"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name: "CopyFile",
+					Arguments: []interface{}{
+						"/etc/hosts",
+						filepath.Join(testRootDir, sandboxesDir, testID, "hosts"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name: "CopyFile",
+					Arguments: []interface{}{
+						filepath.Join("/etc/resolv.conf"),
+						filepath.Join(testRootDir, sandboxesDir, testID, "resolv.conf"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name:      "Stat",
+					Arguments: []interface{}{"/dev/shm"},
+				},
+			},
+		},
 		{
 			desc:    "should create sandbox shm when ipc namespace mode is not NODE",
 			ipcMode: runtime.NamespaceMode_POD,