3 files changed, 37 insertions, 0 deletions
diff --git a/pkg/chrootuser/user.go b/pkg/chrootuser/user.go
index 3de138b86..c83dcc230 100644
--- a/pkg/chrootuser/user.go
+++ b/pkg/chrootuser/user.go
@@ -99,3 +99,10 @@ func GetAdditionalGroupsForUser(rootdir string, userid uint64) ([]uint32, error)
 	}
 	return gids, nil
 }
+
+// LookupUIDInContainer returns username and gid associated with a UID in a container
+// it will use the /etc/passwd files inside of the rootdir
+// to return this information.
+func LookupUIDInContainer(rootdir string, uid uint64) (user string, gid uint64, err error) {
+	return lookupUIDInContainer(rootdir, uid)
+}
diff --git a/pkg/chrootuser/user_basic.go b/pkg/chrootuser/user_basic.go
index 4ed7918e9..79b0b24b5 100644
--- a/pkg/chrootuser/user_basic.go
+++ b/pkg/chrootuser/user_basic.go
@@ -21,3 +21,7 @@ func lookupGroupForUIDInContainer(rootdir string, userid uint64) (string, uint64
 func lookupAdditionalGroupsForUIDInContainer(rootdir string, userid uint64) (gid []uint32, err error) {
 	return nil, errors.New("supplemental groups list lookup by uid not supported")
 }
+
+func lookupUIDInContainer(rootdir string, uid uint64) (string, uint64, error) {
+	return "", 0, errors.New("UID lookup not supported")
+}
diff --git a/pkg/chrootuser/user_linux.go b/pkg/chrootuser/user_linux.go
index acd0af822..583eca569 100644
--- a/pkg/chrootuser/user_linux.go
+++ b/pkg/chrootuser/user_linux.go
@@ -265,3 +265,29 @@ func lookupGroupInContainer(rootdir, groupname string) (gid uint64, err error) {
 
 	return 0, user.UnknownGroupError(fmt.Sprintf("error looking up group %q", groupname))
 }
+
+func lookupUIDInContainer(rootdir string, uid uint64) (string, uint64, error) {
+	cmd, f, err := openChrootedFile(rootdir, "/etc/passwd")
+	if err != nil {
+		return "", 0, err
+	}
+	defer func() {
+		_ = cmd.Wait()
+	}()
+	rc := bufio.NewReader(f)
+	defer f.Close()
+
+	lookupUser.Lock()
+	defer lookupUser.Unlock()
+
+	pwd := parseNextPasswd(rc)
+	for pwd != nil {
+		if pwd.uid != uid {
+			pwd = parseNextPasswd(rc)
+			continue
+		}
+		return pwd.name, pwd.gid, nil
+	}
+
+	return "", 0, user.UnknownUserError(fmt.Sprintf("error looking up uid %q", uid))
+}