Pass container hostname to netavark

libpod/container.go

@@ -666,8 +666,12 @@ func (c *Container) RuntimeName() string {
 // Runtime spec accessors
 // Unlocked
 
-// Hostname gets the container's hostname
-func (c *Container) Hostname() string {
+// hostname determines the container's hostname.
+// If 'network' is true and the container isn't running in a
+// private UTS namespoace, an empty string will be returned
+// instead of the host's hostname because we never want to
+// send the host's hostname to a DHCP or DNS server.
+func (c *Container) hostname(network bool) string {
 	if c.config.UTSNsCtr != "" {
 		utsNsCtr, err := c.runtime.GetContainer(c.config.UTSNsCtr)
 		if err != nil {
@@ -677,25 +681,66 @@ func (c *Container) Hostname() string {
 		}
 		return utsNsCtr.Hostname()
 	}
+
 	if c.config.Spec.Hostname != "" {
 		return c.config.Spec.Hostname
 	}
 
-	// if the container is not running in a private UTS namespace,
-	// return the host's hostname.
+	// If the container is not running in a private UTS namespace,
+	// return the host's hostname unless 'network' is true in which
+	// case we return an empty string.
 	privateUTS := c.hasPrivateUTS()
 	if !privateUTS {
 		hostname, err := os.Hostname()
 		if err == nil {
+			if network {
+				return ""
+			}
 			return hostname
 		}
+		logrus.Errorf("unable to get host's hostname for container %s: %v", c.ID(), err)
+		return ""
+	}
+
+	// If container_name_as_hostname is set in the CONTAINERS table in
+	// containers.conf, use a sanitized version of the container's name
+	// as the hostname.  Since the container name must already match
+	// the set '[a-zA-Z0-9][a-zA-Z0-9_.-]*', we can just remove any
+	// underscores and limit it to 253 characters to make it a valid
+	// hostname.
+	if c.runtime.config.Containers.ContainerNameAsHostName {
+		sanitizedHostname := strings.ReplaceAll(c.Name(), "_", "")
+		if len(sanitizedHostname) <= 253 {
+			return sanitizedHostname
+		}
+		return sanitizedHostname[:253]
 	}
+
+	// Otherwise use the container's short ID as the hostname.
 	if len(c.ID()) < 11 {
 		return c.ID()
 	}
 	return c.ID()[:12]
 }
 
+// Hostname gets the container's hostname
+func (c *Container) Hostname() string {
+	return c.hostname(false)
+}
+
+// If the container isn't running in a private UTS namespace, Hostname()
+// will return the host's hostname as the container's hostname. If netavark
+// were to try and obtain a DHCP lease with the host's hostname in an environment
+// where DDNS was active, bad things could happen. NetworkHostname() on the
+// other hand, will return an empty string if the container isn't running
+// in a private UTS namespace.
+//
+// This function should only be used to populate the ContainerHostname member
+// of the common.libnetwork.types.NetworkOptions struct.
+func (c *Container) NetworkHostname() string {
+	return c.hostname(true)
+}
+
 // WorkingDir returns the containers working dir
 func (c *Container) WorkingDir() string {
 	if c.config.Spec.Process != nil {

libpod/networking_common.go

@@ -55,9 +55,10 @@ func (c *Container) getNetworkOptions(networkOpts map[string]types.PerNetworkOpt
 		nameservers = append(nameservers, ip.String())
 	}
 	opts := types.NetworkOptions{
-		ContainerID:   c.config.ID,
-		ContainerName: getNetworkPodName(c),
-		DNSServers:    nameservers,
+		ContainerID:       c.config.ID,
+		ContainerName:     getNetworkPodName(c),
+		DNSServers:        nameservers,
+		ContainerHostname: c.NetworkHostname(),
 	}
 	opts.PortMappings = c.convertPortMappings()
 

test/e2e/containers_conf_test.go

@@ -763,4 +763,109 @@ var _ = Describe("Verify podman containers.conf usage", func() {
 			Expect(inspect.OutputToString()).Should(Equal(mode))
 		}
 	})
+
+	startContainer := func(params ...string) string {
+		args := []string{"create"}
+		for _, param := range params {
+			if param == "--name" {
+				args = append(args, "--replace")
+				break
+			}
+		}
+		args = append(args, params...)
+		args = append(args, ALPINE, "true")
+
+		result := podmanTest.Podman(args)
+		result.WaitWithDefaultTimeout()
+		Expect(result).Should(ExitCleanly())
+		containerID := result.OutputToString()
+
+		return containerID
+	}
+
+	getContainerConfig := func(containerID string, formatParam string) string {
+		inspect := podmanTest.Podman([]string{"inspect", "--format", formatParam, containerID})
+		inspect.WaitWithDefaultTimeout()
+		value := inspect.OutputToString()
+		return value
+	}
+
+	It("podman containers.conf container_name_as_hostname", func() {
+
+		// With default containers.conf
+
+		// Start container with no options
+		containerID := startContainer()
+		hostname := getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should be the first 12 characters of the containerID
+		Expect(hostname).To(Equal(containerID[:12]))
+
+		// Start container with name
+		containerID = startContainer("--name", "cname1")
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should still be the first 12 characters of the containerID
+		Expect(hostname).To(Equal(containerID[:12]))
+
+		// Start container with just hostname
+		containerID = startContainer("--hostname", "cname1.dev")
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should now be "cname1.dev"
+		Expect(hostname).To(Equal("cname1.dev"))
+
+		// Start container with name and hostname
+		containerID = startContainer("--name", "cname1", "--hostname", "cname1.dev")
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should now be "cname1.dev"
+		Expect(hostname).To(Equal("cname1.dev"))
+
+		// Create containers.conf override with container_name_as_hostname=true
+		conffile := filepath.Join(podmanTest.TempDir, "container.conf")
+		err := os.WriteFile(conffile, []byte("[containers]\ncontainer_name_as_hostname=true\n"), 0755)
+		Expect(err).ToNot(HaveOccurred())
+		os.Setenv("CONTAINERS_CONF_OVERRIDE", conffile)
+		if IsRemote() {
+			podmanTest.RestartRemoteService()
+		}
+
+		// Start container with no options
+		containerID = startContainer()
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		name := getContainerConfig(containerID, "{{ .Name }}")
+		// Hostname should be the auto generated container name with '_' removed
+		Expect(hostname).To(Equal(strings.ReplaceAll(name, "_", "")))
+
+		// Start container with name
+		containerID = startContainer("--name", "cname1")
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should be the container name
+		Expect(hostname).To(Equal("cname1"))
+
+		// Start container with name containing '_'
+		containerID = startContainer("--name", "cname1_2_3")
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should be the set container name with all '_' removed
+		Expect(hostname).To(Equal("cname123"))
+
+		// Start container with just hostname
+		containerID = startContainer("--hostname", "cname1.dev")
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should now be "cname1.dev"
+		Expect(hostname).To(Equal("cname1.dev"))
+
+		// Start container with name and hostname
+		containerID = startContainer("--name", "cname1", "--hostname", "cname1.dev")
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		// Hostname should still be "cname1.dev"
+		Expect(hostname).To(Equal("cname1.dev"))
+
+		// Start container with name = 260 characters
+		longHostname := "cnabcdefghijklmnopqrstuvwxyz1234567890.abcdefghijklmnopqrstuvwxyz1234567890.abcdefghijklmnopqrstuvwxyz1234567890.abcdefghijklmnopqrstuvwxyz1234567890.abcdefghijklmnopqrstuvwxyz1234567890.abcdefghijklmnopqrstuvwxyz1234567890.abcdefghijklmnopqrstuvwxyz1234567890"
+		containerID = startContainer("--name", longHostname)
+		hostname = getContainerConfig(containerID, "{{ .Config.Hostname }}")
+		name = getContainerConfig(containerID, "{{ .Name }}")
+		// Double check that name actually got set correctly
+		Expect(name).To(Equal(longHostname))
+		// Hostname should be the container name truncated to 253 characters
+		Expect(hostname).To(Equal(name[:253]))
+	})
 })