[2.2.x] Fixed #32718 -- Relaxed file name validation in FileField.

- Validate filename returned by FileField.upload_to() not a filename
  passed to the FileField.generate_filename() (upload_to() may
  completely ignored passed filename).
- Allow relative paths (without dot segments) in the generated filename.

Thanks to Jakub Kleň for the report and review.
Thanks to all folks for checking this patch on existing projects.
Thanks Florian Apolloner and Markus Holtermann for the discussion and
implementation idea.

Regression in 0b79eb36915d178aef5c6a7bbce71b1e76d376d3.

Backport of b55699968fc9ee985384c64e37f6cc74a0a23683 from main.

2 files changed, 16 insertions, 0 deletions

diff --git a/docs/releases/2.2.23.txt b/docs/releases/2.2.23.txt
new file mode 100644
index 0000000000..6c39361e5f
--- /dev/null
+++ b/docs/releases/2.2.23.txt
@@ -0,0 +1,15 @@
+===========================
+Django 2.2.23 release notes
+===========================
+
+*May 13, 2021*
+
+Django 2.2.23 fixes a regression in 2.2.21.
+
+Bugfixes
+========
+
+* Fixed a regression in Django 2.2.21 where saving ``FileField`` would raise a
+  ``SuspiciousFileOperation`` even when a custom
+  :attr:`~django.db.models.FileField.upload_to` returns a valid file path
+  (:ticket:`32718`).
diff --git a/docs/releases/index.txt b/docs/releases/index.txt
index 4262a97ac1..53cc50b419 100644
--- a/docs/releases/index.txt
+++ b/docs/releases/index.txt
@@ -25,6 +25,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   2.2.23
    2.2.22
    2.2.21
    2.2.20