[3.1.x] Fixed CVE-2020-24583, #31921 -- Fixed permissions on intermediate-level static and storage directories on Python 3.7+.

Thanks WhiteSage for the report.

Backport of ea0febbba531a3ecc8c77b570efbfb68ca7155db from master.

7 files changed, 86 insertions, 27 deletions

diff --git a/django/core/files/storage.py b/django/core/files/storage.py
index e9166d94ff..16f9d4e27b 100644
--- a/django/core/files/storage.py
+++ b/django/core/files/storage.py
@@ -237,9 +237,9 @@ class FileSystemStorage(Storage):
         directory = os.path.dirname(full_path)
         try:
             if self.directory_permissions_mode is not None:
-                # os.makedirs applies the global umask, so we reset it,
-                # for consistency with file_permissions_mode behavior.
-                old_umask = os.umask(0)
+                # Set the umask because os.makedirs() doesn't apply the "mode"
+                # argument to intermediate-level directories.
+                old_umask = os.umask(0o777 & ~self.directory_permissions_mode)
                 try:
                     os.makedirs(directory, self.directory_permissions_mode, exist_ok=True)
                 finally:
diff --git a/docs/releases/2.2.16.txt b/docs/releases/2.2.16.txt
index ce700e5043..f0c3ec894a 100644
--- a/docs/releases/2.2.16.txt
+++ b/docs/releases/2.2.16.txt
@@ -4,7 +4,18 @@ Django 2.2.16 release notes
 
 *Expected September 1, 2020*
 
-Django 2.2.16 fixes two data loss bugs in 2.2.15.
+Django 2.2.16 fixes a security issue and two data loss bugs in 2.2.15.
+
+CVE-2020-24583: Incorrect permissions on intermediate-level directories on Python 3.7+
+======================================================================================
+
+On Python 3.7+, :setting:`FILE_UPLOAD_DIRECTORY_PERMISSIONS` mode was not
+applied to intermediate-level directories created in the process of uploading
+files and to intermediate-level collected static directories when using the
+:djadmin:`collectstatic` management command.
+
+You should review and manually fix permissions on existing intermediate-level
+directories.
 
 Bugfixes
 ========
diff --git a/docs/releases/3.0.10.txt b/docs/releases/3.0.10.txt
index 9c60435a28..4238a9fd71 100644
--- a/docs/releases/3.0.10.txt
+++ b/docs/releases/3.0.10.txt
@@ -4,7 +4,18 @@ Django 3.0.10 release notes
 
 *Expected September 1, 2020*
 
-Django 3.0.10 fixes two data loss bugs in 3.0.9.
+Django 3.0.10 fixes a security issue and two data loss bugs in 3.0.9.
+
+CVE-2020-24583: Incorrect permissions on intermediate-level directories on Python 3.7+
+======================================================================================
+
+On Python 3.7+, :setting:`FILE_UPLOAD_DIRECTORY_PERMISSIONS` mode was not
+applied to intermediate-level directories created in the process of uploading
+files and to intermediate-level collected static directories when using the
+:djadmin:`collectstatic` management command.
+
+You should review and manually fix permissions on existing intermediate-level
+directories.
 
 Bugfixes
 ========
diff --git a/docs/releases/3.1.1.txt b/docs/releases/3.1.1.txt
index 359acfcffc..11a935dda7 100644
--- a/docs/releases/3.1.1.txt
+++ b/docs/releases/3.1.1.txt
@@ -4,7 +4,18 @@ Django 3.1.1 release notes
 
 *Expected September 1, 2020*
 
-Django 3.1.1 fixes several bugs in 3.1.
+Django 3.1.1 fixes a security issue and several bugs in 3.1.
+
+CVE-2020-24583: Incorrect permissions on intermediate-level directories on Python 3.7+
+======================================================================================
+
+On Python 3.7+, :setting:`FILE_UPLOAD_DIRECTORY_PERMISSIONS` mode was not
+applied to intermediate-level directories created in the process of uploading
+files and to intermediate-level collected static directories when using the
+:djadmin:`collectstatic` management command.
+
+You should review and manually fix permissions on existing intermediate-level
+directories.
 
 Bugfixes
 ========
diff --git a/tests/file_storage/tests.py b/tests/file_storage/tests.py
index 8f280ad13c..4bac3ca11d 100644
--- a/tests/file_storage/tests.py
+++ b/tests/file_storage/tests.py
@@ -972,16 +972,19 @@ class FileStoragePermissions(unittest.TestCase):
     @override_settings(FILE_UPLOAD_DIRECTORY_PERMISSIONS=0o765)
     def test_file_upload_directory_permissions(self):
         self.storage = FileSystemStorage(self.storage_dir)
-        name = self.storage.save("the_directory/the_file", ContentFile("data"))
-        dir_mode = os.stat(os.path.dirname(self.storage.path(name)))[0] & 0o777
-        self.assertEqual(dir_mode, 0o765)
+        name = self.storage.save('the_directory/subdir/the_file', ContentFile('data'))
+        file_path = Path(self.storage.path(name))
+        self.assertEqual(file_path.parent.stat().st_mode & 0o777, 0o765)
+        self.assertEqual(file_path.parent.parent.stat().st_mode & 0o777, 0o765)
 
     @override_settings(FILE_UPLOAD_DIRECTORY_PERMISSIONS=None)
     def test_file_upload_directory_default_permissions(self):
         self.storage = FileSystemStorage(self.storage_dir)
-        name = self.storage.save("the_directory/the_file", ContentFile("data"))
-        dir_mode = os.stat(os.path.dirname(self.storage.path(name)))[0] & 0o777
-        self.assertEqual(dir_mode, 0o777 & ~self.umask)
+        name = self.storage.save('the_directory/subdir/the_file', ContentFile('data'))
+        file_path = Path(self.storage.path(name))
+        expected_mode = 0o777 & ~self.umask
+        self.assertEqual(file_path.parent.stat().st_mode & 0o777, expected_mode)
+        self.assertEqual(file_path.parent.parent.stat().st_mode & 0o777, expected_mode)
 
 
 class FileStoragePathParsing(SimpleTestCase):
diff --git a/tests/staticfiles_tests/project/documents/nested/css/base.css b/tests/staticfiles_tests/project/documents/nested/css/base.css
new file mode 100644
index 0000000000..06041ca25f
--- /dev/null
+++ b/tests/staticfiles_tests/project/documents/nested/css/base.css
@@ -0,0 +1 @@
+html {height: 100%;}
diff --git a/tests/staticfiles_tests/test_storage.py b/tests/staticfiles_tests/test_storage.py
index 02704fcbe8..dc45a0b839 100644
--- a/tests/staticfiles_tests/test_storage.py
+++ b/tests/staticfiles_tests/test_storage.py
@@ -4,6 +4,7 @@ import sys
 import tempfile
 import unittest
 from io import StringIO
+from pathlib import Path
 from unittest import mock
 
 from django.conf import settings
@@ -457,12 +458,19 @@ class TestStaticFilePermissions(CollectionTestCase):
     )
     def test_collect_static_files_permissions(self):
         call_command('collectstatic', **self.command_params)
-        test_file = os.path.join(settings.STATIC_ROOT, "test.txt")
-        test_dir = os.path.join(settings.STATIC_ROOT, "subdir")
-        file_mode = os.stat(test_file)[0] & 0o777
-        dir_mode = os.stat(test_dir)[0] & 0o777
+        static_root = Path(settings.STATIC_ROOT)
+        test_file = static_root / 'test.txt'
+        file_mode = test_file.stat().st_mode & 0o777
         self.assertEqual(file_mode, 0o655)
-        self.assertEqual(dir_mode, 0o765)
+        tests = [
+            static_root / 'subdir',
+            static_root / 'nested',
+            static_root / 'nested' / 'css',
+        ]
+        for directory in tests:
+            with self.subTest(directory=directory):
+                dir_mode = directory.stat().st_mode & 0o777
+                self.assertEqual(dir_mode, 0o765)
 
     @override_settings(
         FILE_UPLOAD_PERMISSIONS=None,
@@ -470,12 +478,19 @@ class TestStaticFilePermissions(CollectionTestCase):
     )
     def test_collect_static_files_default_permissions(self):
         call_command('collectstatic', **self.command_params)
-        test_file = os.path.join(settings.STATIC_ROOT, "test.txt")
-        test_dir = os.path.join(settings.STATIC_ROOT, "subdir")
-        file_mode = os.stat(test_file)[0] & 0o777
-        dir_mode = os.stat(test_dir)[0] & 0o777
+        static_root = Path(settings.STATIC_ROOT)
+        test_file = static_root / 'test.txt'
+        file_mode = test_file.stat().st_mode & 0o777
         self.assertEqual(file_mode, 0o666 & ~self.umask)
-        self.assertEqual(dir_mode, 0o777 & ~self.umask)
+        tests = [
+            static_root / 'subdir',
+            static_root / 'nested',
+            static_root / 'nested' / 'css',
+        ]
+        for directory in tests:
+            with self.subTest(directory=directory):
+                dir_mode = directory.stat().st_mode & 0o777
+                self.assertEqual(dir_mode, 0o777 & ~self.umask)
 
     @override_settings(
         FILE_UPLOAD_PERMISSIONS=0o655,
@@ -484,12 +499,19 @@ class TestStaticFilePermissions(CollectionTestCase):
     )
     def test_collect_static_files_subclass_of_static_storage(self):
         call_command('collectstatic', **self.command_params)
-        test_file = os.path.join(settings.STATIC_ROOT, "test.txt")
-        test_dir = os.path.join(settings.STATIC_ROOT, "subdir")
-        file_mode = os.stat(test_file)[0] & 0o777
-        dir_mode = os.stat(test_dir)[0] & 0o777
+        static_root = Path(settings.STATIC_ROOT)
+        test_file = static_root / 'test.txt'
+        file_mode = test_file.stat().st_mode & 0o777
         self.assertEqual(file_mode, 0o640)
-        self.assertEqual(dir_mode, 0o740)
+        tests = [
+            static_root / 'subdir',
+            static_root / 'nested',
+            static_root / 'nested' / 'css',
+        ]
+        for directory in tests:
+            with self.subTest(directory=directory):
+                dir_mode = directory.stat().st_mode & 0o777
+                self.assertEqual(dir_mode, 0o740)
 
 
 @override_settings(