From 72af4b325aa9ffd96b18ef68d26ec2260e982c2a Mon Sep 17 00:00:00 2001
From: nkrapp <nico.krapp@suse.com>
Date: Wed, 24 Jul 2024 17:08:23 +0200
Subject: [PATCH] Fixed CVE-2024-39330 -- Added extra file name validation in
 Storage's save method.

Thanks to Josh Schneier for the report, and to Carlton Gibson and Sarah
Boyce for the reviews.
---
 django/core/files/storage.py    | 11 ++++++
 django/core/files/utils.py      |  7 ++--
 tests/file_storage/test_base.py | 64 +++++++++++++++++++++++++++++++++
 tests/file_storage/tests.py     |  6 ----
 4 files changed, 78 insertions(+), 10 deletions(-)
 create mode 100644 tests/file_storage/test_base.py

diff --git a/django/core/files/storage.py b/django/core/files/storage.py
index ea5bbc82d0..8c633ec040 100644
--- a/django/core/files/storage.py
+++ b/django/core/files/storage.py
@@ -50,7 +50,18 @@ class Storage:
         if not hasattr(content, 'chunks'):
             content = File(content, name)
 
+        # Ensure that the name is valid, before and after having the storage
+        # system potentially modifying the name. This duplicates the check made
+        # inside `get_available_name` but it's necessary for those cases where
+        # `get_available_name` is overriden and validation is lost.
+        validate_file_name(name, allow_relative_path=True)
+
+        # Potentially find a different name depending on storage constraints.
         name = self.get_available_name(name, max_length=max_length)
+        # Validate the (potentially) new name.
+        validate_file_name(name, allow_relative_path=True)
+
+        # The save operation should return the actual name of the file saved.
         name = self._save(name, content)
         # Ensure that the name returned from the storage system is still valid.
         validate_file_name(name, allow_relative_path=True)
diff --git a/django/core/files/utils.py b/django/core/files/utils.py
index f28cea1077..a1fea44ded 100644
--- a/django/core/files/utils.py
+++ b/django/core/files/utils.py
@@ -10,10 +10,9 @@ def validate_file_name(name, allow_relative_path=False):
         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)
+        # Ensure that name can be treated as a pure posix path, i.e. Unix
+        # style (with forward slashes).
+        path = pathlib.PurePosixPath(str(name).replace("\\", "/"))
         if path.is_absolute() or '..' in path.parts:
             raise SuspiciousFileOperation(
                 "Detected path traversal attempt in '%s'" % name
diff --git a/tests/file_storage/test_base.py b/tests/file_storage/test_base.py
new file mode 100644
index 0000000000..7a0838f7a5
--- /dev/null
+++ b/tests/file_storage/test_base.py
@@ -0,0 +1,64 @@
+import os
+from unittest import mock
+
+from django.core.exceptions import SuspiciousFileOperation
+from django.core.files.storage import Storage
+from django.test import SimpleTestCase
+
+
+class CustomStorage(Storage):
+    """Simple Storage subclass implementing the bare minimum for testing."""
+
+    def exists(self, name):
+        return False
+
+    def _save(self, name):
+        return name
+
+
+class StorageValidateFileNameTests(SimpleTestCase):
+    invalid_file_names = [
+        os.path.join("path", "to", os.pardir, "test.file"),
+        os.path.join(os.path.sep, "path", "to", "test.file"),
+    ]
+    error_msg = "Detected path traversal attempt in '%s'"
+
+    def test_validate_before_get_available_name(self):
+        s = CustomStorage()
+        # The initial name passed to `save` is not valid nor safe, fail early.
+        for name in self.invalid_file_names:
+            with self.subTest(name=name):
+                with mock.patch.object(s, "get_available_name") as mock_get_available_names:
+                    with mock.patch.object(s, "_save") as mock_internal_save:
+                        with self.assertRaisesMessage(
+                            SuspiciousFileOperation, self.error_msg % name
+                        ):
+                            s.save(name, content="irrelevant")
+                        self.assertEqual(mock_get_available_names.mock_calls, [])
+                        self.assertEqual(mock_internal_save.mock_calls, [])
+
+    def test_validate_after_get_available_name(self):
+        s = CustomStorage()
+        # The initial name passed to `save` is valid and safe, but the returned
+        # name from `get_available_name` is not.
+        for name in self.invalid_file_names:
+            with self.subTest(name=name):
+                with mock.patch.object(s, "get_available_name", return_value=name):
+                    with mock.patch.object(s, "_save") as mock_internal_save:
+                        with self.assertRaisesMessage(
+                            SuspiciousFileOperation, self.error_msg % name
+                        ):
+                            s.save("valid-file-name.txt", content="irrelevant")
+                        self.assertEqual(mock_internal_save.mock_calls, [])
+
+    def test_validate_after_internal_save(self):
+        s = CustomStorage()
+        # The initial name passed to `save` is valid and safe, but the result
+        # from `_save` is not (this is achieved by monkeypatching _save).
+        for name in self.invalid_file_names:
+            with self.subTest(name=name):
+                with mock.patch.object(s, "_save", return_value=name):
+                    with self.assertRaisesMessage(
+                        SuspiciousFileOperation, self.error_msg % name
+                    ):
+                        s.save("valid-file-name.txt", content="irrelevant")
diff --git a/tests/file_storage/tests.py b/tests/file_storage/tests.py
index 4c6f6920ed..0e692644b7 100644
--- a/tests/file_storage/tests.py
+++ b/tests/file_storage/tests.py
@@ -291,12 +291,6 @@ class FileStorageTests(SimpleTestCase):
 
         self.storage.delete('path/to/test.file')
 
-    def test_file_save_abs_path(self):
-        test_name = 'path/to/test.file'
-        f = ContentFile('file saved with path')
-        f_name = self.storage.save(os.path.join(self.temp_dir, test_name), f)
-        self.assertEqual(f_name, test_name)
-
     def test_save_doesnt_close(self):
         with TemporaryUploadedFile('test', 'text/plain', 1, 'utf8') as file:
             file.write(b'1')
-- 
2.45.2

