Pass container hostname to netavark

Passing the hostname allows netavark to include it in DHCP lease
requests which, in an environment where DDNS is used, can cause
DNS entries to be created automatically.

* The current Hostname() function in container.go was updated to
check the new `use_container_name_as_hostname` option in the
CONTAINERS table of containers.conf.  If set and no hostname
was configured for the container, it causes the hostname to be
set to a version of the container's name with the characters not
valid for a hostname removed.  If not set (the default), the original
behavior of setting the hostname to the short container ID is
preserved.

* Because the Hostname() function can return the host's hostname
if the container isn't running in a private UTS namespace, and we'd
NEVER want to send _that_ in a DHCP request for a container, a new
function NetworkHostname() was added which functions like Hostname()
except that it will return an empty string instead of the host's
hostname if the container is not running in a private UTS namespace.

* networking_common.getNetworkOptions() now uses NetworkHostname()
to set the ContainerHostname member of the NetworkOptions structure.
That member was added to the structure in a corresponding commit in
common/libnetwork/types/network.go.

Signed-off-by: George Joseph <g.devel@wxy78.net>

libpod/container.go

@@ -20,6 +20,7 @@ import (
 	"github.com/containers/podman/v5/libpod/define"
 	"github.com/containers/podman/v5/libpod/lock"
 	"github.com/containers/storage"
+	"github.com/containers/storage/pkg/regexp"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
@@ -667,7 +668,7 @@ func (c *Container) RuntimeName() string {
 // Unlocked
 
 // Hostname gets the container's hostname
-func (c *Container) Hostname() string {
+func (c *Container) ConfiguredHostname() string {
 	if c.config.UTSNsCtr != "" {
 		utsNsCtr, err := c.runtime.GetContainer(c.config.UTSNsCtr)
 		if err != nil {
@@ -680,6 +681,18 @@ func (c *Container) Hostname() string {
 	if c.config.Spec.Hostname != "" {
 		return c.config.Spec.Hostname
 	}
+	return ""
+}
+
+// Characters valid in a hostname are in the set [0-9a-zA-Z.-]
+var invalidHostnameCharacters = regexp.Delayed("[^0-9a-zA-Z.-]")
+
+// Hostname gets the container's hostname
+func (c *Container) Hostname() string {
+	hostname := c.ConfiguredHostname()
+	if hostname != "" {
+		return hostname
+	}
 
 	// if the container is not running in a private UTS namespace,
 	// return the host's hostname.
@@ -690,6 +703,51 @@ func (c *Container) Hostname() string {
 			return hostname
 		}
 	}
+
+	// If use_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.
+	if c.runtime.config.Containers.UseContainerNameAsHostName {
+		sanitizedHostname := invalidHostnameCharacters.ReplaceAllString(c.Name(), "")
+		return sanitizedHostname
+	}
+
+	// Otherwise use the container's short ID as the hostname.
+	if len(c.ID()) < 11 {
+		return c.ID()
+	}
+	return c.ID()[:12]
+}
+
+// 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 {
+	hostname := c.ConfiguredHostname()
+	if hostname != "" {
+		return hostname
+	}
+
+	// if the container is not running in a private UTS namespace,
+	// return an empty string.
+	privateUTS := c.hasPrivateUTS()
+	if !privateUTS {
+		return ""
+	}
+
+	// If use_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.
+	if c.runtime.config.Containers.UseContainerNameAsHostName {
+		sanitizedHostname := invalidHostnameCharacters.ReplaceAllString(c.Name(), "")
+		return sanitizedHostname
+	}
+
+	// Otherwise use the container's short ID as the hostname.
 	if len(c.ID()) < 11 {
 		return c.ID()
 	}

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()