1 files changed, 15 insertions, 5 deletions
diff --git a/django/core/files/utils.py b/django/core/files/utils.py
index f83cb1a3cf..f28cea1077 100644
--- a/django/core/files/utils.py
+++ b/django/core/files/utils.py
@@ -1,16 +1,26 @@
 import os
+import pathlib
 
 from django.core.exceptions import SuspiciousFileOperation
 
 
-def validate_file_name(name):
-    if name != os.path.basename(name):
-        raise SuspiciousFileOperation("File name '%s' includes path elements" % name)
-
+def validate_file_name(name, allow_relative_path=False):
     # Remove potentially dangerous names
-    if name in {'', '.', '..'}:
+    if os.path.basename(name) in {'', '.', '..'}:
         raise SuspiciousFileOperation("Could not derive file name from '%s'" % name)
 
+    if allow_relative_path:
+        # Use PurePosixPath() because this branch is checked only in
+        # FileField.generate_filename() where all file paths are expected to be
+        # Unix style (with forward slashes).
+        path = pathlib.PurePosixPath(name)
+        if path.is_absolute() or '..' in path.parts:
+            raise SuspiciousFileOperation(
+                "Detected path traversal attempt in '%s'" % name
+            )
+    elif name != os.path.basename(name):
+        raise SuspiciousFileOperation("File name '%s' includes path elements" % name)
+
     return name