Merge pull request #13918 from Luap99/hosts

use etchosts package from c/common

docs/source/markdown/podman-build.1.md

@@ -439,9 +439,9 @@ with a new set of cached layers.
 #### **--no-hosts**
 
 Do not create _/etc/hosts_ for the container.
-
+By default, Podman will manage _/etc/hosts_, adding the container's own IP address and any hosts from **--add-host**.
-By default, Buildah manages _/etc/hosts_, adding the container's own IP address.
+**--no-hosts** disables this, and the image's _/etc/hosts_ will be preserved unmodified.
-**--no-hosts** disables this, and the image's _/etc/hosts_ will be preserved unmodified. Conflicts with the --add-host option.
+This option conflicts with **--add-host**.
 
 #### **--os**=*string*
 

docs/source/markdown/podman-create.1.md

@@ -743,9 +743,9 @@ Disable any defined healthchecks for container.
 
 #### **--no-hosts**
 
-Do not create /etc/hosts for the container.
+Do not create _/etc/hosts_ for the container.
-By default, Podman will manage /etc/hosts, adding the container's own IP address and any hosts from **--add-host**.
+By default, Podman will manage _/etc/hosts_, adding the container's own IP address and any hosts from **--add-host**.
-#### **--no-hosts** disables this, and the image's **/etc/host** will be preserved unmodified.
+**--no-hosts** disables this, and the image's _/etc/hosts_ will be preserved unmodified.
 This option conflicts with **--add-host**.
 
 #### **--oom-kill-disable**

docs/source/markdown/podman-play-kube.1.md

@@ -216,7 +216,10 @@ Valid _mode_ values are:
 
 #### **--no-hosts**
 
-Do not create /etc/hosts within the pod's containers, instead use the version from the image
+Do not create /etc/hosts for the pod.
+By default, Podman will manage /etc/hosts, adding the container's own IP address and any hosts from **--add-host**.
+**--no-hosts** disables this, and the image's **/etc/host** will be preserved unmodified.
+This option conflicts with host added in the Kubernetes YAML.
 
 #### **--quiet**, **-q**
 

docs/source/markdown/podman-pod-create.1.md

@@ -17,7 +17,11 @@ containers added to it. The pod id is printed to STDOUT. You can then use
 
 #### **--add-host**=_host_:_ip_
 
-Add a host to the /etc/hosts file shared between all containers in the pod.
+Add a custom host-to-IP mapping (host:ip)
+
+Add a line to /etc/hosts. The format is hostname:ip. The **--add-host**
+option can be set multiple times.
+The /etc/hosts file is shared between all containers in the pod.
 
 #### **--cgroup-parent**=*path*
 
@@ -187,7 +191,10 @@ NOTE: A container will only have access to aliases on the first network that it
 
 #### **--no-hosts**
 
-Disable creation of /etc/hosts for the pod.
+Do not create _/etc/hosts_ for the pod.
+By default, Podman will manage _/etc/hosts_, adding the container's own IP address and any hosts from **--add-host**.
+**--no-hosts** disables this, and the image's _/etc/hosts_ will be preserved unmodified.
+This option conflicts with **--add-host**.
 
 #### **--pid**=*pid*
 

docs/source/markdown/podman-run.1.md

@@ -85,8 +85,10 @@ and specified with a _tag_.
 ## OPTIONS
 #### **--add-host**=_host_:_ip_
 
-Add a line to container's _/etc/hosts_ for custom host-to-IP mapping.
+Add a custom host-to-IP mapping (host:ip)
-This option can be set multiple times.
+
+Add a line to /etc/hosts. The format is hostname:ip. The **--add-host**
+option can be set multiple times.
 
 #### **--annotation**=_key_=_value_
 
@@ -768,9 +770,8 @@ Disable any defined healthchecks for container.
 #### **--no-hosts**
 
 Do not create _/etc/hosts_ for the container.
-
 By default, Podman will manage _/etc/hosts_, adding the container's own IP address and any hosts from **--add-host**.
-#### **--no-hosts** disables this, and the image's _/etc/hosts_ will be preserved unmodified.
+**--no-hosts** disables this, and the image's _/etc/hosts_ will be preserved unmodified.
 This option conflicts with **--add-host**.
 
 #### **--oom-kill-disable**

libpod/container.go

@@ -628,6 +628,15 @@ func (c *Container) RuntimeName() string {
 
 // Hostname gets the container's hostname
 func (c *Container) Hostname() string {
+	if c.config.UTSNsCtr != "" {
+		utsNsCtr, err := c.runtime.GetContainer(c.config.UTSNsCtr)
+		if err != nil {
+			// should we return an error here?
+			logrus.Errorf("unable to lookup uts namespace for container %s: %v", c.ID(), err)
+			return ""
+		}
+		return utsNsCtr.Hostname()
+	}
 	if c.config.Spec.Hostname != "" {
 		return c.config.Spec.Hostname
 	}

libpod/container_internal.go

@@ -1,7 +1,6 @@
 package libpod
 
 import (
-	"bufio"
 	"bytes"
 	"context"
 	"fmt"
@@ -17,8 +16,10 @@ import (
 	"github.com/containers/buildah/copier"
 	"github.com/containers/buildah/pkg/overlay"
 	butil "github.com/containers/buildah/util"
+	"github.com/containers/common/libnetwork/etchosts"
 	"github.com/containers/common/pkg/cgroups"
 	"github.com/containers/common/pkg/chown"
+	"github.com/containers/common/pkg/config"
 	"github.com/containers/podman/v4/libpod/define"
 	"github.com/containers/podman/v4/libpod/events"
 	"github.com/containers/podman/v4/pkg/ctime"
@@ -31,6 +32,7 @@ import (
 	"github.com/containers/storage"
 	"github.com/containers/storage/pkg/archive"
 	"github.com/containers/storage/pkg/idtools"
+	"github.com/containers/storage/pkg/lockfile"
 	"github.com/containers/storage/pkg/mount"
 	"github.com/coreos/go-systemd/v22/daemon"
 	securejoin "github.com/cyphar/filepath-securejoin"
@@ -1006,19 +1008,16 @@ func (c *Container) completeNetworkSetup() error {
 		}
 	}
 	// check if we have a bindmount for /etc/hosts
-	if hostsBindMount, ok := state.BindMounts["/etc/hosts"]; ok && len(c.cniHosts()) > 0 {
+	if hostsBindMount, ok := state.BindMounts[config.DefaultHostsFile]; ok {
-		ctrHostPath := filepath.Join(c.state.RunDir, "hosts")
+		entries, err := c.getHostsEntries()
-		if hostsBindMount == ctrHostPath {
-			// read the existing hosts
-			b, err := ioutil.ReadFile(hostsBindMount)
 		if err != nil {
 			return err
 		}
-			if err := ioutil.WriteFile(hostsBindMount, append(b, []byte(c.cniHosts())...), 0644); err != nil {
+		// add new container ips to the hosts file
+		if err := etchosts.Add(hostsBindMount, entries); err != nil {
 			return err
 		}
 	}
-	}
 
 	// check if we have a bindmount for resolv.conf
 	resolvBindMount := state.BindMounts["/etc/resolv.conf"]
@@ -1041,18 +1040,6 @@ func (c *Container) completeNetworkSetup() error {
 	return ioutil.WriteFile(resolvBindMount, []byte(strings.Join(outResolvConf, "\n")), 0644)
 }
 
-func (c *Container) cniHosts() string {
-	var hosts string
-	for _, status := range c.getNetworkStatus() {
-		for _, netInt := range status.Interfaces {
-			for _, netAddress := range netInt.Subnets {
-				hosts += fmt.Sprintf("%s\t%s %s\n", netAddress.IPNet.IP.String(), c.Hostname(), c.config.Name)
-			}
-		}
-	}
-	return hosts
-}
-
 // Initialize a container, creating it in the runtime
 func (c *Container) init(ctx context.Context, retainRetries bool) error {
 	// Unconditionally remove conmon temporary files.
@@ -1894,6 +1881,24 @@ func (c *Container) cleanup(ctx context.Context) error {
 		lastError = errors.Wrapf(err, "error removing container %s network", c.ID())
 	}
 
+	// cleanup host entry if it is shared
+	if c.config.NetNsCtr != "" {
+		if hoststFile, ok := c.state.BindMounts[config.DefaultHostsFile]; ok {
+			if _, err := os.Stat(hoststFile); err == nil {
+				// we cannot use the dependency container lock due ABBA deadlocks
+				if lock, err := lockfile.GetLockfile(hoststFile); err == nil {
+					lock.Lock()
+					// make sure to ignore ENOENT error in case the netns container was cleanup before this one
+					if err := etchosts.Remove(hoststFile, getLocalhostHostEntry(c)); err != nil && !errors.Is(err, os.ErrNotExist) {
+						// this error is not fatal we still want to do proper cleanup
+						logrus.Errorf("failed to remove hosts entry from the netns containers /etc/hosts: %v", err)
+					}
+					lock.Unlock()
+				}
+			}
+		}
+	}
+
 	// Remove the container from the runtime, if necessary.
 	// Do this *before* unmounting storage - some runtimes (e.g. Kata)
 	// apparently object to having storage removed while the container still
@@ -2030,33 +2035,6 @@ func (c *Container) writeStringToStaticDir(filename, contents string) (string, e
 	return destFileName, nil
 }
 
-// appendStringToRunDir appends the provided string to the runtimedir file
-func (c *Container) appendStringToRunDir(destFile, output string) (string, error) {
-	destFileName := filepath.Join(c.state.RunDir, destFile)
-
-	f, err := os.OpenFile(destFileName, os.O_APPEND|os.O_RDWR, 0600)
-	if err != nil {
-		return "", err
-	}
-	defer f.Close()
-
-	compareStr := strings.TrimRight(output, "\n")
-	scanner := bufio.NewScanner(f)
-	scanner.Split(bufio.ScanLines)
-
-	for scanner.Scan() {
-		if strings.Compare(scanner.Text(), compareStr) == 0 {
-			return filepath.Join(c.state.RunDir, destFile), nil
-		}
-	}
-
-	if _, err := f.WriteString(output); err != nil {
-		return "", errors.Wrapf(err, "unable to write %s", destFileName)
-	}
-
-	return filepath.Join(c.state.RunDir, destFile), nil
-}
-
 // saveSpec saves the OCI spec to disk, replacing any existing specs for the container
 func (c *Container) saveSpec(spec *spec.Spec) error {
 	// If the OCI spec already exists, we need to replace it

libpod/container_internal_linux.go

@@ -28,6 +28,7 @@ import (
 	"github.com/containers/buildah/pkg/chrootuser"
 	"github.com/containers/buildah/pkg/overlay"
 	butil "github.com/containers/buildah/util"
+	"github.com/containers/common/libnetwork/etchosts"
 	"github.com/containers/common/libnetwork/types"
 	"github.com/containers/common/pkg/apparmor"
 	"github.com/containers/common/pkg/cgroups"
@@ -49,6 +50,7 @@ import (
 	"github.com/containers/podman/v4/version"
 	"github.com/containers/storage/pkg/archive"
 	"github.com/containers/storage/pkg/idtools"
+	"github.com/containers/storage/pkg/lockfile"
 	securejoin "github.com/cyphar/filepath-securejoin"
 	runcuser "github.com/opencontainers/runc/libcontainer/user"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
@@ -2079,23 +2081,25 @@ func (c *Container) makeBindMounts() error {
 
 			// check if dependency container has an /etc/hosts file.
 			// It may not have one, so only use it if it does.
-			hostsPath, exists := bindMounts["/etc/hosts"]
+			hostsPath, exists := bindMounts[config.DefaultHostsFile]
 			if !c.config.UseImageHosts && exists {
-				depCtr.lock.Lock()
+				// we cannot use the dependency container lock due ABBA deadlocks in cleanup()
-				// generate a hosts file for the dependency container,
+				lock, err := lockfile.GetLockfile(hostsPath)
-				// based on either its old hosts file, or the default,
+				if err != nil {
-				// and add the relevant information from the new container (hosts and IP)
+					return fmt.Errorf("failed to lock hosts file: %w", err)
-				hostsPath, err = depCtr.appendHosts(hostsPath, c)
+				}
-
+				lock.Lock()
+
+				// add the newly added container to the hosts file
+				// we always use 127.0.0.1 as ip since they have the same netns
+				err = etchosts.Add(hostsPath, getLocalhostHostEntry(c))
+				lock.Unlock()
 				if err != nil {
-					depCtr.lock.Unlock()
 					return errors.Wrapf(err, "error creating hosts file for container %s which depends on container %s", c.ID(), depCtr.ID())
 				}
-				depCtr.lock.Unlock()
 
 				// finally, save it in the new container
-				err := c.mountIntoRootDirs("/etc/hosts", hostsPath)
+				err = c.mountIntoRootDirs(config.DefaultHostsFile, hostsPath)
-
 				if err != nil {
 					return errors.Wrapf(err, "error assigning mounts to container %s", c.ID())
 				}
@@ -2123,7 +2127,7 @@ func (c *Container) makeBindMounts() error {
 			}
 
 			if !c.config.UseImageHosts {
-				if err := c.updateHosts("/etc/hosts"); err != nil {
+				if err := c.createHosts(); err != nil {
 					return errors.Wrapf(err, "error creating hosts file for container %s", c.ID())
 				}
 			}
@@ -2142,7 +2146,7 @@ func (c *Container) makeBindMounts() error {
 		}
 	} else {
 		if !c.config.UseImageHosts && c.state.BindMounts["/etc/hosts"] == "" {
-			if err := c.updateHosts("/etc/hosts"); err != nil {
+			if err := c.createHosts(); err != nil {
 				return errors.Wrapf(err, "error creating hosts file for container %s", c.ID())
 			}
 		}
@@ -2528,169 +2532,79 @@ func (c *Container) removeNameserver(ips []string) error {
 	return nil
 }
 
-// updateHosts updates the container's hosts file
+func getLocalhostHostEntry(c *Container) etchosts.HostEntries {
-func (c *Container) updateHosts(path string) error {
+	return etchosts.HostEntries{{IP: "127.0.0.1", Names: []string{c.Hostname(), c.config.Name}}}
-	var hosts string
-
-	orig, err := ioutil.ReadFile(path)
-	if err != nil {
-		// Ignore if the path does not exist
-		if !os.IsNotExist(err) {
-			return err
-		}
-	} else {
-		hosts = string(orig)
-	}
-
-	hosts += c.getHosts()
-	hosts = c.appendLocalhost(hosts)
-
-	newHosts, err := c.writeStringToRundir("hosts", hosts)
-	if err != nil {
-		return err
-	}
-
-	if err = c.mountIntoRootDirs("/etc/hosts", newHosts); err != nil {
-		return err
-	}
-
-	return nil
 }
 
-// based on networking mode we may want to append the localhost
+// getHostsEntries returns the container ip host entries for the correct netmode
-// if there isn't any record for it and also this should happen
+func (c *Container) getHostsEntries() (etchosts.HostEntries, error) {
-// in slirp4netns and similar network modes.
+	var entries etchosts.HostEntries
-func (c *Container) appendLocalhost(hosts string) string {
+	names := []string{c.Hostname(), c.config.Name}
-	if !strings.Contains(hosts, "localhost") &&
+	switch {
-		!c.config.NetMode.IsHost() {
+	case c.config.NetMode.IsBridge():
-		hosts += "127.0.0.1\tlocalhost\n::1\tlocalhost\n"
+		entries = etchosts.GetNetworkHostEntries(c.state.NetworkStatus, names...)
-	}
+	case c.config.NetMode.IsSlirp4netns():
-
+		ip, err := GetSlirp4netnsIP(c.slirp4netnsSubnet)
-	return hosts
-}
-
-// appendHosts appends a container's config and state pertaining to hosts to a container's
-// local hosts file. netCtr is the container from which the netNS information is
-// taken.
-// path is the basis of the hosts file, into which netCtr's netNS information will be appended.
-// FIXME.  Path should be used by this function,but I am not sure what is correct; remove //lint
-// once this is fixed
-func (c *Container) appendHosts(path string, netCtr *Container) (string, error) { //nolint
-	return c.appendStringToRunDir("hosts", netCtr.getHosts())
-}
-
-// getHosts finds the pertinent information for a container's host file in its config and state
-// and returns a string in a format that can be written to the host file
-func (c *Container) getHosts() string {
-	var hosts string
-
-	if len(c.config.HostAdd) > 0 {
-		for _, host := range c.config.HostAdd {
-			// the host format has already been verified at this point
-			fields := strings.SplitN(host, ":", 2)
-			hosts += fmt.Sprintf("%s %s\n", fields[1], fields[0])
-		}
-	}
-
-	hosts += c.cniHosts()
-
-	// Add hostname for slirp4netns
-	if c.Hostname() != "" {
-		if c.config.NetMode.IsSlirp4netns() {
-			// When using slirp4netns, the interface gets a static IP
-			slirp4netnsIP, err := GetSlirp4netnsIP(c.slirp4netnsSubnet)
 		if err != nil {
-				logrus.Warnf("Failed to determine slirp4netnsIP: %v", err.Error())
+			return nil, err
-			} else {
-				hosts += fmt.Sprintf("# used by slirp4netns\n%s\t%s %s\n", slirp4netnsIP.String(), c.Hostname(), c.config.Name)
 		}
-		}
+		entries = etchosts.HostEntries{{IP: ip.String(), Names: names}}
-
+	default:
-		// Do we have a network namespace?
+		// check for net=none
-		netNone := false
+		if !c.config.CreateNetNS {
-		if c.config.NetNsCtr == "" && !c.config.CreateNetNS {
 			for _, ns := range c.config.Spec.Linux.Namespaces {
 				if ns.Type == spec.NetworkNamespace {
 					if ns.Path == "" {
-						netNone = true
+						entries = etchosts.HostEntries{{IP: "127.0.0.1", Names: names}}
 					}
 					break
 				}
 			}
 		}
-		// If we are net=none (have a network namespace, but not connected to
-		// anything) add the container's name and hostname to localhost.
-		if netNone {
-			hosts += fmt.Sprintf("127.0.0.1 %s %s\n", c.Hostname(), c.config.Name)
-		}
 	}
+	return entries, nil
+}
 
-	// Add gateway entry if we are not in a machine. If we use podman machine
+func (c *Container) createHosts() error {
-	// the gvproxy dns server will take care of host.containers.internal.
+	var containerIPsEntries etchosts.HostEntries
-	// https://github.com/containers/gvisor-tap-vsock/commit/1108ea45162281046d239047a6db9bc187e64b08
+	var err error
-	if !c.runtime.config.Engine.MachineEnabled {
+	// if we configure the netns after the container create we should not add
-		var depCtr *Container
+	// the hosts here since we have no information about the actual ips
-		netStatus := c.getNetworkStatus()
+	// instead we will add them in c.completeNetworkSetup()
-		if c.config.NetNsCtr != "" {
+	if !c.config.PostConfigureNetNS {
-			// ignoring the error because there isn't anything to do
+		containerIPsEntries, err = c.getHostsEntries()
-			depCtr, _ = c.getRootNetNsDepCtr()
-		} else if len(netStatus) != 0 {
-			depCtr = c
-		}
-
-		// getLocalIP returns the non loopback local IP of the host
-		getLocalIP := func() string {
-			addrs, err := net.InterfaceAddrs()
 		if err != nil {
-				return ""
+			return fmt.Errorf("failed to get container ip host entries: %w", err)
-			}
-			for _, address := range addrs {
-				// check the address type and if it is not a loopback the display it
-				if ipnet, ok := address.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
-					if ipnet.IP.To4() != nil {
-						return ipnet.IP.String()
 		}
 	}
-			}
+	baseHostFile, err := etchosts.GetBaseHostFile(c.runtime.config.Containers.BaseHostsFile, c.state.Mountpoint)
-			return ""
+	if err != nil {
+		return err
 	}
 
-		if depCtr != nil {
+	targetFile := filepath.Join(c.state.RunDir, "hosts")
-			host := ""
+	err = etchosts.New(&etchosts.Params{
-		outer:
+		BaseFile:                 baseHostFile,
-			for net, status := range depCtr.getNetworkStatus() {
+		ExtraHosts:               c.config.HostAdd,
-				network, err := c.runtime.network.NetworkInspect(net)
+		ContainerIPs:             containerIPsEntries,
-				// only add the host entry for bridge networks
+		HostContainersInternalIP: etchosts.GetHostContainersInternalIP(c.runtime.config, c.state.NetworkStatus, c.runtime.network),
-				// ip/macvlan gateway is normally not on the host
+		TargetFile:               targetFile,
-				if err != nil || network.Driver != types.BridgeNetworkDriver {
+	})
-					continue
+	if err != nil {
-				}
+		return err
-				for _, netInt := range status.Interfaces {
-					for _, netAddress := range netInt.Subnets {
-						if netAddress.Gateway != nil {
-							host = fmt.Sprintf("%s host.containers.internal\n", netAddress.Gateway.String())
-							break outer
-						}
-					}
-				}
-			}
-			// if no bridge gw was found try to use a local ip
-			if host == "" {
-				if ip := getLocalIP(); ip != "" {
-					host = fmt.Sprintf("%s\t%s\n", ip, "host.containers.internal")
-				}
-			}
-			hosts += host
-		} else if c.config.NetMode.IsSlirp4netns() {
-			if ip := getLocalIP(); ip != "" {
-				hosts += fmt.Sprintf("%s\t%s\n", ip, "host.containers.internal")
-			}
-		} else {
-			logrus.Debug("Network configuration does not support host.containers.internal address")
-		}
 	}
 
-	return hosts
+	if err := os.Chown(targetFile, c.RootUID(), c.RootGID()); err != nil {
+		return err
+	}
+	if err := label.Relabel(targetFile, c.MountLabel(), false); err != nil {
+		return err
+	}
+
+	if err = c.mountIntoRootDirs(config.DefaultHostsFile, targetFile); err != nil {
+		return err
+	}
+	return nil
 }
 
 // generateGroupEntry generates an entry or entries into /etc/group as

libpod/container_internal_linux_test.go

@@ -8,7 +8,6 @@ import (
 	"os"
 	"testing"
 
-	"github.com/containers/podman/v4/pkg/namespaces"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/stretchr/testify/assert"
 )
@@ -70,30 +69,3 @@ func TestGenerateUserGroupEntry(t *testing.T) {
 	}
 	assert.Equal(t, group, "567:x:567:567\n")
 }
-
-func TestAppendLocalhost(t *testing.T) {
-	{
-		c := Container{
-			config: &ContainerConfig{
-				ContainerNetworkConfig: ContainerNetworkConfig{
-					NetMode: namespaces.NetworkMode("slirp4netns"),
-				},
-			},
-		}
-
-		assert.Equal(t, "127.0.0.1\tlocalhost\n::1\tlocalhost\n", c.appendLocalhost(""))
-		assert.Equal(t, "127.0.0.1\tlocalhost", c.appendLocalhost("127.0.0.1\tlocalhost"))
-	}
-	{
-		c := Container{
-			config: &ContainerConfig{
-				ContainerNetworkConfig: ContainerNetworkConfig{
-					NetMode: namespaces.NetworkMode("host"),
-				},
-			},
-		}
-
-		assert.Equal(t, "", c.appendLocalhost(""))
-		assert.Equal(t, "127.0.0.1\tlocalhost", c.appendLocalhost("127.0.0.1\tlocalhost"))
-	}
-}

libpod/networking_linux.go

@@ -20,7 +20,9 @@ import (
 	"time"
 
 	"github.com/containernetworking/plugins/pkg/ns"
+	"github.com/containers/common/libnetwork/etchosts"
 	"github.com/containers/common/libnetwork/types"
+	"github.com/containers/common/pkg/config"
 	"github.com/containers/common/pkg/netns"
 	"github.com/containers/podman/v4/libpod/define"
 	"github.com/containers/podman/v4/libpod/events"
@@ -1282,15 +1284,35 @@ func (c *Container) NetworkDisconnect(nameOrID, netName string, force bool) erro
 		for _, ip := range oldStatus.DNSServerIPs {
 			stringIPs = append(stringIPs, ip.String())
 		}
-		if len(stringIPs) == 0 {
+		if len(stringIPs) > 0 {
-			return nil
-		}
 			logrus.Debugf("Removing DNS Servers %v from resolv.conf", stringIPs)
 			if err := c.removeNameserver(stringIPs); err != nil {
 				return err
 			}
 		}
 
+		// update /etc/hosts file
+		if file, ok := c.state.BindMounts[config.DefaultHostsFile]; ok {
+			// sync the names with c.getHostsEntries()
+			names := []string{c.Hostname(), c.config.Name}
+			rm := etchosts.GetNetworkHostEntries(map[string]types.StatusBlock{netName: oldStatus}, names...)
+			if len(rm) > 0 {
+				// make sure to lock this file to prevent concurrent writes when
+				// this is used a net dependency container
+				lock, err := lockfile.GetLockfile(file)
+				if err != nil {
+					return fmt.Errorf("failed to lock hosts file: %w", err)
+				}
+				logrus.Debugf("Remove /etc/hosts entries %v", rm)
+				lock.Lock()
+				err = etchosts.Remove(file, rm)
+				lock.Unlock()
+				if err != nil {
+					return err
+				}
+			}
+		}
+	}
 	return nil
 }
 
@@ -1361,6 +1383,13 @@ func (c *Container) NetworkConnect(nameOrID, netName string, netOpts types.PerNe
 		return errors.New("when adding aliases, results must be of length 1")
 	}
 
+	// we need to get the old host entries before we add the new one to the status
+	// if we do not add do it here we will get the wrong existing entries which will throw of the logic
+	// we could also copy the map but this does not seem worth it
+	// sync the hostNames with c.getHostsEntries()
+	hostNames := []string{c.Hostname(), c.config.Name}
+	oldHostEntries := etchosts.GetNetworkHostEntries(networkStatus, hostNames...)
+
 	// update network status
 	if networkStatus == nil {
 		networkStatus = make(map[string]types.StatusBlock, 1)
@@ -1394,13 +1423,32 @@ func (c *Container) NetworkConnect(nameOrID, netName string, netOpts types.PerNe
 		}
 		stringIPs = append(stringIPs, ip.String())
 	}
-	if len(stringIPs) == 0 {
+	if len(stringIPs) > 0 {
-		return nil
-	}
 		logrus.Debugf("Adding DNS Servers %v to resolv.conf", stringIPs)
 		if err := c.addNameserver(stringIPs); err != nil {
 			return err
 		}
+	}
+
+	// update /etc/hosts file
+	if file, ok := c.state.BindMounts[config.DefaultHostsFile]; ok {
+		// make sure to lock this file to prevent concurrent writes when
+		// this is used a net dependency container
+		lock, err := lockfile.GetLockfile(file)
+		if err != nil {
+			return fmt.Errorf("failed to lock hosts file: %w", err)
+		}
+		new := etchosts.GetNetworkHostEntries(results, hostNames...)
+		logrus.Debugf("Add /etc/hosts entries %v", new)
+		// use special AddIfExists API to make sure we only add new entries if an old one exists
+		// see the AddIfExists() comment for more information
+		lock.Lock()
+		err = etchosts.AddIfExists(file, oldHostEntries, new)
+		lock.Unlock()
+		if err != nil {
+			return err
+		}
+	}
 
 	return nil
 }

pkg/specgen/container_validate.go

@@ -38,6 +38,13 @@ func (s *SpecGenerator) Validate() error {
 		if len(s.PortMappings) > 0 || s.PublishExposedPorts {
 			return errors.Wrap(define.ErrNetworkOnPodContainer, "published or exposed ports must be defined when the pod is created")
 		}
+		if len(s.HostAdd) > 0 {
+			return errors.Wrap(define.ErrNetworkOnPodContainer, "extra host entries must be specified on the pod")
+		}
+	}
+
+	if s.NetNS.IsContainer() && len(s.HostAdd) > 0 {
+		return errors.Wrap(ErrInvalidSpecConfig, "cannot set extra host entries when the container is joined to another containers network namespace")
 	}
 
 	//

test/e2e/pod_infra_container_test.go

@@ -377,21 +377,19 @@ var _ = Describe("Podman pod create", func() {
 		Expect(result.OutputToString()).To(ContainSubstring(infraID))
 	})
 
-	It("podman run --add-host in pod", func() {
+	It("podman run --add-host in pod should fail", func() {
-		session := podmanTest.Podman([]string{"pod", "create"})
+		session := podmanTest.Podman([]string{"pod", "create", "--add-host", "host1:127.0.0.1"})
 		session.WaitWithDefaultTimeout()
 		Expect(session).Should(Exit(0))
 		podID := session.OutputToString()
 
-		// verify we can add a host to the infra's /etc/hosts
+		session = podmanTest.Podman([]string{"create", "--pod", podID, "--add-host", "foobar:127.0.0.1", ALPINE, "ping", "-c", "1", "foobar"})
-		// N/B: Using alpine for ping, since BB ping throws
-		//      permission denied error as of Fedora 33.
-		session = podmanTest.Podman([]string{"run", "--pod", podID, "--add-host", "foobar:127.0.0.1", ALPINE, "ping", "-c", "1", "foobar"})
 		session.WaitWithDefaultTimeout()
-		Expect(session).Should(Exit(0))
+		Expect(session).Should(ExitWithError())
+		Expect(session.ErrorToString()).To(ContainSubstring("extra host entries must be specified on the pod: network cannot be configured when it is shared with a pod"))
 
-		// verify we can see the other hosts of infra's /etc/hosts
+		// verify we can see the pods hosts
-		session = podmanTest.Podman([]string{"run", "--pod", podID, ALPINE, "ping", "-c", "1", "foobar"})
+		session = podmanTest.Podman([]string{"run", "--pod", podID, ALPINE, "ping", "-c", "1", "host1"})
 		session.WaitWithDefaultTimeout()
 		Expect(session).Should(Exit(0))
 	})

test/e2e/run_dns_test.go

@@ -78,8 +78,7 @@ var _ = Describe("Podman run dns", func() {
 		session := podmanTest.Podman([]string{"run", "--add-host=foobar:1.1.1.1", "--add-host=foobaz:2001:db8::68", ALPINE, "cat", "/etc/hosts"})
 		session.WaitWithDefaultTimeout()
 		Expect(session).Should(Exit(0))
-		Expect(session.OutputToStringArray()).To(ContainElement(HavePrefix("1.1.1.1 foobar")))
+		Expect(session.OutputToStringArray()).To(ContainElements(HavePrefix("1.1.1.1\tfoobar"), HavePrefix("2001:db8::68\tfoobaz")))
-		Expect(session.OutputToStringArray()).To(ContainElement(HavePrefix("2001:db8::68 foobaz")))
 	})
 
 	It("podman run add hostname", func() {

test/e2e/run_networking_test.go

@@ -608,6 +608,18 @@ EXPOSE 2004-2005/tcp`, ALPINE)
 		Expect(ctr2).Should(Exit(0))
 	})
 
+	It("podman run --net container: and --add-host should fail", func() {
+		ctrName := "ctrToJoin"
+		ctr1 := podmanTest.RunTopContainer(ctrName)
+		ctr1.WaitWithDefaultTimeout()
+		Expect(ctr1).Should(Exit(0))
+
+		ctr2 := podmanTest.Podman([]string{"run", "-d", "--net=container:" + ctrName, "--add-host", "host1:127.0.0.1", ALPINE, "true"})
+		ctr2.WaitWithDefaultTimeout()
+		Expect(ctr2).Should(ExitWithError())
+		Expect(ctr2.ErrorToString()).Should(ContainSubstring("cannot set extra host entries when the container is joined to another containers network namespace: invalid configuration"))
+	})
+
 	It("podman run --net container: copies hosts and resolv", func() {
 		ctrName := "ctr1"
 		ctr1 := podmanTest.RunTopContainer(ctrName)

test/system/030-run.bats

@@ -786,7 +786,7 @@ EOF
     mv $hosts_tmp /etc/hosts
     assert "$status" = 0 \
            "podman run without /etc/hosts file should work"
-    assert "$output" =~ "^1\.2\.3\.4 foo.com.*" \
+    assert "$output" =~ "^1\.2\.3\.4[[:blank:]]foo\.com.*" \
            "users can add hosts even without /etc/hosts"
 }
 

test/system/200-pod.bats

@@ -250,7 +250,7 @@ EOF
     is "$output" ".*invalid config provided: cannot set hostname when joining the pod UTS namespace: invalid configuration" "--hostname should not be allowed in share UTS pod"
 
     run_podman run --rm --pod $pod_id $IMAGE cat /etc/hosts
-    is "$output" ".*$add_host_ip $add_host_n" "--add-host was added"
+    is "$output" ".*$add_host_ip[[:blank:]]$add_host_n" "--add-host was added"
     is "$output" ".*	$hostname"            "--hostname is in /etc/hosts"
     #               ^^^^ this must be a tab, not a space
 

test/system/500-networking.bats

@@ -134,14 +134,50 @@ load helpers
     done
 }
 
+@test "podman pod manages /etc/hosts correctly" {
+    local pod_name=pod-$(random_string 10)
+    local infra_name=infra-$(random_string 10)
+    local con1_name=con1-$(random_string 10)
+    local con2_name=con2-$(random_string 10)
+    run_podman pod create --name $pod_name  --infra-name $infra_name
+    pid="$output"
+    run_podman run --pod $pod_name --name $con1_name $IMAGE cat /etc/hosts
+    is "$output" ".*\s$pod_name $infra_name.*" "Pod hostname in /etc/hosts"
+    is "$output" ".*127.0.0.1\s$con1_name.*" "Container1 name in /etc/hosts"
+    # get the length of the hosts file
+    old_lines=${#lines[@]}
+
+    # since the first container should be cleaned up now we should only see the
+    # new host entry and the old one should be removed (lines check)
+    run_podman run --pod $pod_name --name $con2_name $IMAGE cat /etc/hosts
+    is "$output" ".*\s$pod_name $infra_name.*" "Pod hostname in /etc/hosts"
+    is "$output" ".*127.0.0.1\s$con2_name.*" "Container2 name in /etc/hosts"
+    is "${#lines[@]}" "$old_lines" "Number of hosts lines is equal"
+
+    run_podman run --pod $pod_name  $IMAGE sh -c  "hostname && cat /etc/hostname"
+    is "${lines[0]}" "$pod_name" "hostname is the pod hostname"
+    is "${lines[1]}" "$pod_name" "/etc/hostname contains correct pod hostname"
+
+    run_podman pod rm $pod_name
+    is "$output" "$pid" "Only ID in output (no extra errors)"
+}
+
 @test "podman run with slirp4ns assigns correct addresses to /etc/hosts" {
     CIDR="$(random_rfc1918_subnet)"
     IP=$(hostname -I | cut -f 1 -d " ")
     local conname=con-$(random_string 10)
     run_podman run --rm --network slirp4netns:cidr="${CIDR}.0/24" \
                 --name $conname --hostname $conname $IMAGE cat /etc/hosts
-    is "$output"   ".*${IP}	host.containers.internal"   "host.containers.internal should be the cidr+2 address"
+    is "$output"   ".*${IP}	host.containers.internal"   "host.containers.internal should be host address"
     is "$output"   ".*${CIDR}.100	$conname $conname"   "$conname should be the cidr+100 address"
+
+    if is_rootless; then
+    # check the slirp ip also works correct with userns
+        run_podman run --rm --userns keep-id --network slirp4netns:cidr="${CIDR}.0/24" \
+                --name $conname --hostname $conname $IMAGE cat /etc/hosts
+        is "$output"   ".*${IP}	host.containers.internal"   "host.containers.internal should be host address"
+        is "$output"   ".*${CIDR}.100	$conname $conname"   "$conname should be the cidr+100 address"
+    fi
 }
 
 @test "podman run with slirp4ns adds correct dns address to resolv.conf" {
@@ -434,9 +470,17 @@ load helpers
     run_podman inspect $cid --format "{{(index .NetworkSettings.Networks \"$netname\").Aliases}}"
     is "$output" "[${cid:0:12}]" "short container id in network aliases"
 
+    # check /etc/hosts for our entry
+    run_podman exec $cid cat /etc/hosts
+    is "$output" ".*$ip.*" "hosts contain expected ip"
+
     run_podman network disconnect $netname $cid
     is "$output" "" "Output should be empty (no errors)"
 
+    # check /etc/hosts again, the entry should be gone now
+    run_podman exec $cid cat /etc/hosts
+    assert "$output" !~ "$ip" "IP ($ip) should no longer be in /etc/hosts"
+
     # check that we cannot curl (timeout after 3 sec)
     run curl --max-time 3 -s $SERVER/index.txt
     assert $status -ne 0 \
@@ -452,13 +496,18 @@ load helpers
     # check that we have a new ip and mac
     # if the ip is still the same this whole test turns into a nop
     run_podman inspect $cid --format "{{(index .NetworkSettings.Networks \"$netname\").IPAddress}}"
-    assert "$output" != "$ip" \
+    new_ip="$output"
+    assert "$new_ip" != "$ip" \
            "IP address did not change after podman network disconnect/connect"
 
     run_podman inspect $cid --format "{{(index .NetworkSettings.Networks \"$netname\").MacAddress}}"
     assert "$output" != "$mac" \
            "MAC address did not change after podman network disconnect/connect"
 
+    # check /etc/hosts for the new entry
+    run_podman exec $cid cat /etc/hosts
+    is "$output" ".*$new_ip.*" "hosts contain expected new ip"
+
     # Disconnect/reconnect of a container *with no ports* should succeed quietly
     run_podman network disconnect $netname $background_cid
     is "$output" "" "disconnect of container with no open ports"
@@ -629,4 +678,48 @@ EOF
     done
 }
 
+@test "podman run CONTAINERS_CONF /etc/hosts options" {
+    skip_if_remote "CONTAINERS_CONF redirect does not work on remote"
+
+    containersconf=$PODMAN_TMPDIR/containers.conf
+    basehost=$PODMAN_TMPDIR/host
+
+    ip1="$(random_rfc1918_subnet).$((RANDOM % 256))"
+    name1=host1$(random_string)
+    ip2="$(random_rfc1918_subnet).$((RANDOM % 256))"
+    name2=host2$(random_string)
+
+    cat >$basehost <<EOF
+$ip1 $name1
+$ip2 $name2 #some comment
+EOF
+
+    containersinternal_ip="$(random_rfc1918_subnet).$((RANDOM % 256))"
+    cat >$containersconf <<EOF
+[containers]
+  base_hosts_file = "$basehost"
+  host_containers_internal_ip = "$containersinternal_ip"
+EOF
+
+    ip3="$(random_rfc1918_subnet).$((RANDOM % 256))"
+    name3=host3$(random_string)
+
+    CONTAINERS_CONF=$containersconf run_podman run --rm --add-host $name3:$ip3 $IMAGE cat /etc/hosts
+    is "$output" ".*$ip3[[:blank:]]$name3.*" "--add-host entry in /etc/host"
+    is "$output" ".*$ip1[[:blank:]]$name1.*" "first base entry in /etc/host"
+    is "$output" ".*$ip2[[:blank:]]$name2.*" "second base entry in /etc/host"
+    is "$output" ".*127.0.0.1[[:blank:]]localhost.*" "ipv4 localhost entry added"
+    is "$output" ".*::1[[:blank:]]localhost.*" "ipv6 localhost entry added"
+    is "$output" ".*$containersinternal_ip[[:blank:]]host\.containers\.internal.*" "host.containers.internal ip from config in /etc/host"
+    is "${#lines[@]}" "7" "expect 7 host entries in /etc/hosts"
+
+    # now try again with container name and hostname == host entry name
+    # in this case podman should not add its own entry thus we only have 5 entries (-1 for the removed --add-host)
+    CONTAINERS_CONF=$containersconf run_podman run --rm --name $name1 --hostname $name1 $IMAGE cat /etc/hosts
+    is "$output" ".*$ip1[[:blank:]]$name1.*" "first base entry in /etc/host"
+    is "$output" ".*$ip2[[:blank:]]$name2.*" "second base entry in /etc/host"
+    is "$output" ".*$containersinternal_ip[[:blank:]]host\.containers\.internal.*" "host.containers.internal ip from config in /etc/host"
+    is "${#lines[@]}" "5" "expect 5 host entries in /etc/hosts"
+}
+
 # vim: filetype=sh

vendor/github.com/containers/common/libnetwork/etchosts/hosts.go

@@ -0,0 +1,339 @@
+package etchosts
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/containers/common/pkg/config"
+	"github.com/containers/common/pkg/util"
+)
+
+const (
+	hostContainersInternal = "host.containers.internal"
+	localhost              = "localhost"
+)
+
+type HostEntries []HostEntry
+
+type HostEntry struct {
+	IP    string
+	Names []string
+}
+
+// Params for the New() function call
+type Params struct {
+	// BaseFile is the file where we read entries from and add entries to
+	// the target hosts file. If the name is empty it will not read any entries.
+	BaseFile string
+	// ExtraHosts is a slice of entries in the "hostname:ip" format.
+	// Optional.
+	ExtraHosts []string
+	// ContainerIPs should contain the main container ipv4 and ipv6 if available
+	// with the container name and host name as names set.
+	// Optional.
+	ContainerIPs HostEntries
+	// HostContainersInternalIP is the IP for the host.containers.internal entry.
+	// Optional.
+	HostContainersInternalIP string
+	// TargetFile where the hosts are written to.
+	TargetFile string
+}
+
+// New will create a new hosts file and write this to the target file.
+// This function does not prevent any kind of concurrency problems, it is
+// the callers responsibility to avoid concurrent writes to this file.
+// The extraHosts are written first, then the hosts from the file baseFile and the
+// containerIps. The container ip entry is only added when the name was not already
+// added before.
+func New(params *Params) error {
+	if err := new(params); err != nil {
+		return fmt.Errorf("failed to create new hosts file: %w", err)
+	}
+	return nil
+}
+
+// Add adds the given entries to the hosts file, entries are only added if
+// they are not already present.
+// Add is not atomic because it will keep the current file inode. This is
+// required to keep bind mounts for containers working.
+func Add(file string, entries HostEntries) error {
+	if err := add(file, entries); err != nil {
+		return fmt.Errorf("failed to add entries to hosts file: %w", err)
+	}
+	return nil
+}
+
+// AddIfExists will add the given entries only if one of the existsEntries
+// is in the hosts file. This API is required for podman network connect.
+// Since we want to add the same host name for each network ip we want to
+// add duplicates and the normal Add() call prevents us from doing so.
+// However since we also do not want to overwrite potential entries that
+// were added by users manually we first have to check if there are the
+// current expected entries in the file. Note that this will only check
+// for one match not all. It will also only check that the ip and one of
+// the hostnames match like Remove().
+func AddIfExists(file string, existsEntries, newEntries HostEntries) error {
+	if err := addIfExists(file, existsEntries, newEntries); err != nil {
+		return fmt.Errorf("failed to add entries to hosts file: %w", err)
+	}
+	return nil
+}
+
+// Remove will remove the given entries from the file. An entry will be
+// removed when the ip and at least one name matches. Not all names have
+// to match. If the given entries are not present in the file no error is
+// returned.
+// Remove is not atomic because it will keep the current file inode. This is
+// required to keep bind mounts for containers working.
+func Remove(file string, entries HostEntries) error {
+	if err := remove(file, entries); err != nil {
+		return fmt.Errorf("failed to remove entries from hosts file: %w", err)
+	}
+	return nil
+}
+
+// new see comment on New()
+func new(params *Params) error {
+	entries, err := parseExtraHosts(params.ExtraHosts)
+	if err != nil {
+		return err
+	}
+	entries2, err := parseHostsFile(params.BaseFile)
+	if err != nil {
+		return err
+	}
+	entries = append(entries, entries2...)
+
+	// preallocate the slice with enough space for the 3 special entries below
+	containerIPs := make(HostEntries, 0, len(params.ContainerIPs)+3)
+
+	// if localhost was not added we add it
+	// https://github.com/containers/podman/issues/11411
+	lh := []string{localhost}
+	l1 := HostEntry{IP: "127.0.0.1", Names: lh}
+	l2 := HostEntry{IP: "::1", Names: lh}
+	containerIPs = append(containerIPs, l1, l2)
+	if params.HostContainersInternalIP != "" {
+		e := HostEntry{IP: params.HostContainersInternalIP, Names: []string{hostContainersInternal}}
+		containerIPs = append(containerIPs, e)
+	}
+	containerIPs = append(containerIPs, params.ContainerIPs...)
+
+	if err := writeHostFile(params.TargetFile, entries, containerIPs); err != nil {
+		return err
+	}
+	return nil
+}
+
+// add see comment on Add()
+func add(file string, entries HostEntries) error {
+	currentEntries, err := parseHostsFile(file)
+	if err != nil {
+		return err
+	}
+
+	names := make(map[string]struct{})
+	for _, entry := range currentEntries {
+		for _, name := range entry.Names {
+			names[name] = struct{}{}
+		}
+	}
+
+	// open file in append mode since we only add, we do not have to write existing entries again
+	f, err := os.OpenFile(file, os.O_WRONLY|os.O_APPEND, 0o644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	return addEntriesIfNotExists(f, entries, names)
+}
+
+// addIfExists see comment on AddIfExists()
+func addIfExists(file string, existsEntries, newEntries HostEntries) error {
+	// special case when there are no existing entries do a normal add
+	// this can happen when we connect a network which was not connected
+	// to any other networks before
+	if len(existsEntries) == 0 {
+		return add(file, newEntries)
+	}
+
+	currentEntries, err := parseHostsFile(file)
+	if err != nil {
+		return err
+	}
+
+	for _, entry := range currentEntries {
+		if !checkIfEntryExists(entry, existsEntries) {
+			// keep looking for existing entries
+			continue
+		}
+		// if we have a matching existing entry add the new entries
+		// open file in append mode since we only add, we do not have to write existing entries again
+		f, err := os.OpenFile(file, os.O_WRONLY|os.O_APPEND, 0o644)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+
+		for _, e := range newEntries {
+			if _, err = f.WriteString(formatLine(e.IP, e.Names)); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+	// no match found is no error
+	return nil
+}
+
+// remove see comment on Remove()
+func remove(file string, entries HostEntries) error {
+	currentEntries, err := parseHostsFile(file)
+	if err != nil {
+		return err
+	}
+
+	f, err := os.Create(file)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	for _, entry := range currentEntries {
+		if checkIfEntryExists(entry, entries) {
+			continue
+		}
+		if _, err = f.WriteString(formatLine(entry.IP, entry.Names)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func checkIfEntryExists(current HostEntry, entries HostEntries) bool {
+	//  check if the current entry equals one of the given entries
+	for _, rm := range entries {
+		if current.IP == rm.IP {
+			// it is enough if one of the names match, in this case we remove the full entry
+			for _, name := range current.Names {
+				if util.StringInSlice(name, rm.Names) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+// parseExtraHosts converts a slice of "name:ip" string to entries.
+// Because podman and buildah both store the extra hosts in this format
+// we convert it here instead of having to this on the caller side.
+func parseExtraHosts(extraHosts []string) (HostEntries, error) {
+	entries := make(HostEntries, 0, len(extraHosts))
+	for _, entry := range extraHosts {
+		values := strings.SplitN(entry, ":", 2)
+		if len(values) != 2 {
+			return nil, fmt.Errorf("unable to parse host entry %q: incorrect format", entry)
+		}
+		if values[0] == "" {
+			return nil, fmt.Errorf("hostname in host entry %q is empty", entry)
+		}
+		if values[1] == "" {
+			return nil, fmt.Errorf("IP address in host entry %q is empty", entry)
+		}
+		e := HostEntry{IP: values[1], Names: []string{values[0]}}
+		entries = append(entries, e)
+	}
+	return entries, nil
+}
+
+// parseHostsFile parses a given host file and returns all entries in it.
+// Note that this will remove all comments and spaces.
+func parseHostsFile(file string) (HostEntries, error) {
+	// empty file is valid, in this case we skip adding entries from the file
+	if file == "" {
+		return nil, nil
+	}
+
+	f, err := os.Open(file)
+	if err != nil {
+		// do not error when the default hosts file does not exists
+		// https://github.com/containers/podman/issues/12667
+		if errors.Is(err, os.ErrNotExist) && file == config.DefaultHostsFile {
+			return nil, nil
+		}
+		return nil, err
+	}
+	defer f.Close()
+
+	entries := HostEntries{}
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		// split of the comments
+		line := scanner.Text()
+		if c := strings.IndexByte(line, '#'); c != -1 {
+			line = line[:c]
+		}
+		fields := strings.Fields(line)
+		// if we only have a ip without names we skip it
+		if len(fields) < 2 {
+			continue
+		}
+
+		e := HostEntry{IP: fields[0], Names: fields[1:]}
+		entries = append(entries, e)
+	}
+
+	return entries, scanner.Err()
+}
+
+// writeHostFile write the entries to the given file
+func writeHostFile(file string, userEntries, containerIPs HostEntries) error {
+	f, err := os.Create(file)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	names := make(map[string]struct{})
+	for _, entry := range userEntries {
+		for _, name := range entry.Names {
+			names[name] = struct{}{}
+		}
+		if _, err = f.WriteString(formatLine(entry.IP, entry.Names)); err != nil {
+			return err
+		}
+	}
+
+	return addEntriesIfNotExists(f, containerIPs, names)
+}
+
+// addEntriesIfNotExists only adds the entries for names that are not already
+// in the hosts file, otherwise we start overwriting user entries
+func addEntriesIfNotExists(f io.StringWriter, containerIPs HostEntries, names map[string]struct{}) error {
+	for _, entry := range containerIPs {
+		freeNames := make([]string, 0, len(entry.Names))
+		for _, name := range entry.Names {
+			if _, ok := names[name]; !ok {
+				freeNames = append(freeNames, name)
+			}
+		}
+		if len(freeNames) > 0 {
+			if _, err := f.WriteString(formatLine(entry.IP, freeNames)); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// formatLine converts the given ip and names to a valid hosts line.
+// The returned string includes the newline.
+func formatLine(ip string, names []string) string {
+	return ip + "\t" + strings.Join(names, " ") + "\n"
+}

vendor/github.com/containers/common/libnetwork/etchosts/ip.go

@@ -0,0 +1,91 @@
+package etchosts
+
+import (
+	"net"
+
+	"github.com/containers/common/libnetwork/types"
+	"github.com/containers/common/libnetwork/util"
+	"github.com/containers/common/pkg/config"
+	"github.com/containers/storage/pkg/unshare"
+)
+
+// GetHostContainersInternalIP return the host.containers.internal ip
+// if netStatus is not nil then networkInterface also must be non nil otherwise this function panics
+func GetHostContainersInternalIP(conf *config.Config, netStatus map[string]types.StatusBlock, networkInterface types.ContainerNetwork) string {
+	switch conf.Containers.HostContainersInternalIP {
+	case "":
+		// if empty (default) we will automatically choose one below
+		// if machine we let the gvproxy dns server handle the dns name so do not add it
+		if conf.Engine.MachineEnabled {
+			return ""
+		}
+	case "none":
+		return ""
+	default:
+		return conf.Containers.HostContainersInternalIP
+	}
+	ip := ""
+	// Only use the bridge ip when root, as rootless the interfaces are created
+	// inside the special netns and not the host so we cannot use them.
+	if unshare.IsRootless() {
+		return getLocalIP()
+	}
+	for net, status := range netStatus {
+		network, err := networkInterface.NetworkInspect(net)
+		// only add the host entry for bridge networks
+		// ip/macvlan gateway is normally not on the host
+		if err != nil || network.Driver != types.BridgeNetworkDriver {
+			continue
+		}
+		for _, netInt := range status.Interfaces {
+			for _, netAddress := range netInt.Subnets {
+				if netAddress.Gateway != nil {
+					if util.IsIPv4(netAddress.Gateway) {
+						return netAddress.Gateway.String()
+					}
+					// ipv6 address but keep looking since we prefer to use ipv4
+					ip = netAddress.Gateway.String()
+				}
+			}
+		}
+	}
+	if ip != "" {
+		return ip
+	}
+	return getLocalIP()
+}
+
+// getLocalIP returns the non loopback local IP of the host
+func getLocalIP() string {
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		return ""
+	}
+	ip := ""
+	for _, address := range addrs {
+		// check the address type and if it is not a loopback the display it
+		if ipnet, ok := address.(*net.IPNet); ok && ipnet.IP.IsGlobalUnicast() {
+			if util.IsIPv4(ipnet.IP) {
+				return ipnet.IP.String()
+			}
+			// if ipv6 we keep looking for an ipv4 address
+			ip = ipnet.IP.String()
+		}
+	}
+	return ip
+}
+
+// GetNetworkHostEntries returns HostEntries for all ips in the network status
+// with the given hostnames.
+func GetNetworkHostEntries(netStatus map[string]types.StatusBlock, names ...string) HostEntries {
+	hostEntries := make(HostEntries, 0, len(netStatus))
+	for _, status := range netStatus {
+		for _, netInt := range status.Interfaces {
+			for _, netAddress := range netInt.Subnets {
+				e := HostEntry{IP: netAddress.IPNet.IP.String(), Names: names}
+				hostEntries = append(hostEntries, e)
+			}
+		}
+	}
+	return hostEntries
+}

vendor/github.com/containers/common/libnetwork/etchosts/util.go

@@ -0,0 +1,30 @@
+package etchosts
+
+import (
+	"fmt"
+
+	"github.com/containers/common/pkg/config"
+	securejoin "github.com/cyphar/filepath-securejoin"
+)
+
+// GetBaseHostFile return the hosts file which should be used as base.
+// The first param should be the config value config.Containers.BaseHostsFile
+// The second param should be the root path to the mounted image. This is
+// required when the user conf value is set to "image".
+func GetBaseHostFile(confValue, imageRoot string) (string, error) {
+	switch confValue {
+	case "":
+		return config.DefaultHostsFile, nil
+	case "none":
+		return "", nil
+	case "image":
+		// use secure join to prevent problems with symlinks
+		path, err := securejoin.SecureJoin(imageRoot, config.DefaultHostsFile)
+		if err != nil {
+			return "", fmt.Errorf("failed to get /etc/hosts path in image: %w", err)
+		}
+		return path, nil
+	default:
+		return confValue, nil
+	}
+}

vendor/modules.txt

@@ -114,6 +114,7 @@ github.com/containers/buildah/util
 github.com/containers/common/libimage
 github.com/containers/common/libimage/manifests
 github.com/containers/common/libnetwork/cni
+github.com/containers/common/libnetwork/etchosts
 github.com/containers/common/libnetwork/internal/util
 github.com/containers/common/libnetwork/netavark
 github.com/containers/common/libnetwork/network