Add username to /etc/passwd inside of container if --userns keep-id

If I enter a continer with --userns keep-id, my UID will be present
inside of the container, but most likely my user will not be defined.

This patch will take information about the user and stick it into the
container.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

4 files changed, 113 insertions, 9 deletions

diff --git a/libpod/container.go b/libpod/container.go
index 6a87ad3a9..9ad938a5c 100644
--- a/libpod/container.go
+++ b/libpod/container.go
@@ -277,6 +277,9 @@ type ContainerConfig struct {
 	User string `json:"user,omitempty"`
 	// Additional groups to add
 	Groups []string `json:"groups,omitempty"`
+	// AddCurrentUserPasswdEntry indicates that the current user passwd entry
+	// should be added to the /etc/passwd within the container
+	AddCurrentUserPasswdEntry bool `json:"addCurrentUserPasswdEntry,omitempty"`
 
 	// Namespace Config
 	// IDs of container to share namespaces with
@@ -774,7 +777,10 @@ func (c *Container) Hostname() string {
 
 // WorkingDir returns the containers working dir
 func (c *Container) WorkingDir() string {
-	return c.config.Spec.Process.Cwd
+	if c.config.Spec.Process != nil {
+		return c.config.Spec.Process.Cwd
+	}
+	return "/"
 }
 
 // State Accessors
diff --git a/libpod/container_internal_linux.go b/libpod/container_internal_linux.go
index cfcf9b823..f86903fd1 100644
--- a/libpod/container_internal_linux.go
+++ b/libpod/container_internal_linux.go
@@ -9,6 +9,7 @@ import (
 	"io/ioutil"
 	"net"
 	"os"
+	"os/user"
 	"path"
 	"path/filepath"
 	"strconv"
@@ -33,7 +34,7 @@ import (
 	"github.com/containers/libpod/v2/pkg/util"
 	"github.com/containers/storage/pkg/archive"
 	securejoin "github.com/cyphar/filepath-securejoin"
-	"github.com/opencontainers/runc/libcontainer/user"
+	User "github.com/opencontainers/runc/libcontainer/user"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/opencontainers/runtime-tools/generate"
 	"github.com/opencontainers/selinux/go-selinux/label"
@@ -1420,9 +1421,23 @@ func (c *Container) getHosts() string {
 	return hosts
 }
 
-// generatePasswd generates a container specific passwd file,
-// iff g.config.User is a number
-func (c *Container) generatePasswd() (string, error) {
+// generateCurrentUserPasswdEntry generates an /etc/passwd entry for the user
+// running the container engine
+func (c *Container) generateCurrentUserPasswdEntry() (string, error) {
+	uid := rootless.GetRootlessUID()
+	if uid == 0 {
+		return "", nil
+	}
+	u, err := user.LookupId(strconv.Itoa(rootless.GetRootlessUID()))
+	if err != nil {
+		return "", errors.Wrapf(err, "failed to get current user")
+	}
+	return fmt.Sprintf("%s:x:%s:%s:%s:%s:/bin/sh\n", u.Username, u.Uid, u.Gid, u.Username, c.WorkingDir()), nil
+}
+
+// generateUserPasswdEntry generates an /etc/passwd entry for the container user
+// to run in the container.
+func (c *Container) generateUserPasswdEntry() (string, error) {
 	var (
 		groupspec string
 		gid       int
@@ -1440,14 +1455,16 @@ func (c *Container) generatePasswd() (string, error) {
 	if err != nil {
 		return "", nil
 	}
+
 	// Lookup the user to see if it exists in the container image
 	_, err = lookup.GetUser(c.state.Mountpoint, userspec)
-	if err != nil && err != user.ErrNoPasswdEntries {
+	if err != nil && err != User.ErrNoPasswdEntries {
 		return "", err
 	}
 	if err == nil {
 		return "", nil
 	}
+
 	if groupspec != "" {
 		ugid, err := strconv.ParseUint(groupspec, 10, 32)
 		if err == nil {
@@ -1460,14 +1477,39 @@ func (c *Container) generatePasswd() (string, error) {
 			gid = group.Gid
 		}
 	}
+	return fmt.Sprintf("%d:x:%d:%d:container user:%s:/bin/sh\n", uid, uid, gid, c.WorkingDir()), nil
+}
+
+// generatePasswd generates a container specific passwd file,
+// iff g.config.User is a number
+func (c *Container) generatePasswd() (string, error) {
+	if !c.config.AddCurrentUserPasswdEntry && c.config.User == "" {
+		return "", nil
+	}
+	pwd := ""
+	if c.config.User != "" {
+		entry, err := c.generateUserPasswdEntry()
+		if err != nil {
+			return "", err
+		}
+		pwd += entry
+	}
+	if c.config.AddCurrentUserPasswdEntry {
+		entry, err := c.generateCurrentUserPasswdEntry()
+		if err != nil {
+			return "", err
+		}
+		pwd += entry
+	}
+	if pwd == "" {
+		return "", nil
+	}
 	originPasswdFile := filepath.Join(c.state.Mountpoint, "/etc/passwd")
 	orig, err := ioutil.ReadFile(originPasswdFile)
 	if err != nil && !os.IsNotExist(err) {
 		return "", errors.Wrapf(err, "unable to read passwd file %s", originPasswdFile)
 	}
-
-	pwd := fmt.Sprintf("%s%d:x:%d:%d:container user:%s:/bin/sh\n", orig, uid, uid, gid, c.WorkingDir())
-	passwdFile, err := c.writeStringToRundir("passwd", pwd)
+	passwdFile, err := c.writeStringToRundir("passwd", string(orig)+pwd)
 	if err != nil {
 		return "", errors.Wrapf(err, "failed to create temporary passwd file")
 	}
diff --git a/libpod/container_internal_linux_test.go b/libpod/container_internal_linux_test.go
new file mode 100644
index 000000000..078cc53a7
--- /dev/null
+++ b/libpod/container_internal_linux_test.go
@@ -0,0 +1,42 @@
+// +build linux
+
+package libpod
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGenerateUserPasswdEntry(t *testing.T) {
+	dir, err := ioutil.TempDir("", "libpod_test_")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	c := Container{
+		config: &ContainerConfig{
+			User: "123:456",
+			Spec: &spec.Spec{},
+		},
+		state: &ContainerState{
+			Mountpoint: "/does/not/exist/tmp/",
+		},
+	}
+	user, err := c.generateUserPasswdEntry()
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, user, "123:x:123:456:container user:/:/bin/sh\n")
+
+	c.config.User = "567"
+	user, err = c.generateUserPasswdEntry()
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, user, "567:x:567:0:container user:/:/bin/sh\n")
+}
diff --git a/libpod/options.go b/libpod/options.go
index bff3f3c18..560b406e2 100644
--- a/libpod/options.go
+++ b/libpod/options.go
@@ -844,6 +844,20 @@ func WithPIDNSFrom(nsCtr *Container) CtrCreateOption {
 	}
 }
 
+// WithAddCurrentUserPasswdEntry indicates that container should add current
+// user entry to /etc/passwd, since the UID will be mapped into the container,
+// via user namespace
+func WithAddCurrentUserPasswdEntry() CtrCreateOption {
+	return func(ctr *Container) error {
+		if ctr.valid {
+			return define.ErrCtrFinalized
+		}
+
+		ctr.config.AddCurrentUserPasswdEntry = true
+		return nil
+	}
+}
+
 // WithUserNSFrom indicates the the container should join the user namespace of
 // the given container.
 // If the container has joined a pod, it can only join the namespaces of