2 files changed, 22 insertions, 3 deletions
diff --git a/pkg/chrootuser/user.go b/pkg/chrootuser/user.go
index 22ba5ff8a..54917b843 100644
--- a/pkg/chrootuser/user.go
+++ b/pkg/chrootuser/user.go
@@ -37,8 +37,8 @@ func GetUser(rootdir, userspec string) (uint32, uint32, error) {
 			userspec = name
 		} else {
 			// Leave userspec alone, but swallow the error and just
-			// use GID 0.
-			gid64 = 0
+			// use GID == UID.
+			gid64 = uid64
 			gerr = nil
 		}
 	}
@@ -70,6 +70,21 @@ func GetUser(rootdir, userspec string) (uint32, uint32, error) {
 	return 0, 0, err
 }
 
+// GetGroup returns the gid by looking it up in the /etc/passwd file
+// groupspec format [ group | gid ]
+func GetGroup(rootdir, groupspec string) (uint32, error) {
+	gid64, gerr := strconv.ParseUint(groupspec, 10, 32)
+	if gerr != nil {
+		// The group couldn't be parsed as a number, so look up
+		// the group's GID.
+		gid64, gerr = lookupGroupInContainer(rootdir, groupspec)
+	}
+	if gerr != nil {
+		return 0, errors.Wrapf(gerr, "error looking up group for gid %q", groupspec)
+	}
+	return uint32(gid64), nil
+}
+
 // GetAdditionalGroupsForUser returns a list of gids that userid is associated with
 func GetAdditionalGroupsForUser(rootdir string, userid uint64) ([]uint32, error) {
 	return lookupAdditionalGroupsForUIDInContainer(rootdir, userid)
diff --git a/pkg/chrootuser/user_linux.go b/pkg/chrootuser/user_linux.go
index 64ff7cef6..d48a1c7c2 100644
--- a/pkg/chrootuser/user_linux.go
+++ b/pkg/chrootuser/user_linux.go
@@ -4,6 +4,7 @@ package chrootuser
 
 import (
 	"bufio"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -78,6 +79,9 @@ func openChrootedFile(rootdir, filename string) (*exec.Cmd, io.ReadCloser, error
 
 var (
 	lookupUser, lookupGroup sync.Mutex
+	// ErrNoSuchUser indicates that the user provided by the caller does not
+	// exist in /etc/passws
+	ErrNoSuchUser = errors.New("user does not exist in /etc/passwd")
 )
 
 type lookupPasswdEntry struct {
@@ -207,7 +211,7 @@ func lookupGroupForUIDInContainer(rootdir string, userid uint64) (username strin
 		return pwd.name, pwd.gid, nil
 	}
 
-	return "", 0, user.UnknownUserError(fmt.Sprintf("error looking up user with UID %d", userid))
+	return "", 0, ErrNoSuchUser
 }
 
 func lookupAdditionalGroupsForUIDInContainer(rootdir string, userid uint64) (gid []uint32, err error) {