Fixed #23157 -- Removed O(n) algorithm when uploading duplicate file names.

This is a security fix. Disclosure following shortly.

1 files changed, 11 insertions, 2 deletions

diff --git a/docs/howto/custom-file-storage.txt b/docs/howto/custom-file-storage.txt
index 5109986d45..afa1c9a908 100644
--- a/docs/howto/custom-file-storage.txt
+++ b/docs/howto/custom-file-storage.txt
@@ -90,5 +90,14 @@ the provided filename into account. The ``name`` argument passed to this method
 will have already cleaned to a filename valid for the storage system, according
 to the ``get_valid_name()`` method described above.
 
-The code provided on ``Storage`` simply appends ``"_1"``, ``"_2"``, etc. to the
-filename until it finds one that's available in the destination directory.
+.. versionchanged:: 1.7
+
+    If a file with ``name`` already exists, an underscore plus a random 7
+    character alphanumeric string is appended to the filename before the
+    extension.
+
+    Previously, an underscore followed by a number (e.g. ``"_1"``, ``"_2"``,
+    etc.) was appended to the filename until an avaible name in the destination
+    directory was found. A malicious user could exploit this deterministic
+    algorithm to create a denial-of-service attack. This change was also made
+    in Django 1.6.6, 1.5.9, and 1.4.14.