File: CVE-2015-5143.patch

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From 2e47f3e401c29bc2ba5ab794d483cb0820855fb9 Mon Sep 17 00:00:00 2001
From: Carl Meyer <carl@oddbird.net>
Date: Wed, 10 Jun 2015 15:45:20 -0600
Subject: [PATCH] [1.4.x] Fixed #19324 -- Avoided creating a session record
 when loading the session.

The session record is now only created if/when the session is modified. This
prevents a potential DoS via creation of many empty session records.

This is a security fix; disclosure to follow shortly.
---
 django/contrib/sessions/backends/cache.py     |  6 ++++--
 django/contrib/sessions/backends/cached_db.py |  5 +++--
 django/contrib/sessions/backends/db.py        |  5 +++--
 django/contrib/sessions/backends/file.py      |  7 ++++---
 django/contrib/sessions/tests.py              | 19 +++++++++++++++++++
 docs/releases/1.4.21.txt                      | 21 +++++++++++++++++++++
 6 files changed, 54 insertions(+), 9 deletions(-)

--- a/django/contrib/sessions/backends/cache.py
+++ b/django/contrib/sessions/backends/cache.py
@@ -15,7 +15,7 @@ class SessionStore(SessionBase):
         session_data = self._cache.get(KEY_PREFIX + self.session_key)
         if session_data is not None:
             return session_data
-        self.create()
+        self._session_key = None
         return {}
 
     def create(self):
@@ -35,6 +35,8 @@ class SessionStore(SessionBase):
         raise RuntimeError("Unable to create a new session key.")
 
     def save(self, must_create=False):
+        if self._session_key is None:
+            return self.create()
         if must_create:
             func = self._cache.add
         else:
@@ -45,7 +47,7 @@ class SessionStore(SessionBase):
             raise CreateError
 
     def exists(self, session_key):
-        if self._cache.has_key(KEY_PREFIX + session_key):
+        if session_key and self._cache.has_key(KEY_PREFIX + session_key):
             return True
         return False
 
--- a/django/contrib/sessions/backends/cached_db.py
+++ b/django/contrib/sessions/backends/cached_db.py
@@ -20,16 +20,19 @@ class SessionStore(DBStore):
         data = cache.get(KEY_PREFIX + self.session_key, None)
         if data is None:
             data = super(SessionStore, self).load()
-            cache.set(KEY_PREFIX + self.session_key, data, 
-                      settings.SESSION_COOKIE_AGE)
+            if self._session_key:
+                cache.set(KEY_PREFIX + self._session_key, data,
+                          settings.SESSION_COOKIE_AGE)
         return data
 
     def exists(self, session_key):
+        if session_key and cache.has_key(KEY_PREFIX + session_key):
+            return True
         return super(SessionStore, self).exists(session_key)
 
     def save(self, must_create=False):
         super(SessionStore, self).save(must_create)
-        cache.set(KEY_PREFIX + self.session_key, self._session, 
+        cache.set(KEY_PREFIX + self.session_key, self._session,
                   settings.SESSION_COOKIE_AGE)
 
     def delete(self, session_key=None):
@@ -43,4 +46,4 @@ class SessionStore(DBStore):
         """
         self.clear()
         self.delete(self.session_key)
-        self.create()
\ No newline at end of file
+        self.create()
--- a/django/contrib/sessions/backends/db.py
+++ b/django/contrib/sessions/backends/db.py
@@ -21,7 +21,7 @@ class SessionStore(SessionBase):
             )
             return self.decode(force_unicode(s.session_data))
         except (Session.DoesNotExist, SuspiciousOperation):
-            self.create()
+            self._session_key = None
             return {}
 
     def exists(self, session_key):
@@ -42,7 +42,6 @@ class SessionStore(SessionBase):
                 # Key wasn't unique. Try again.
                 continue
             self.modified = True
-            self._session_cache = {}
             return
 
     def save(self, must_create=False):
@@ -52,6 +51,8 @@ class SessionStore(SessionBase):
         create a *new* entry (as opposed to possibly updating an existing
         entry).
         """
+        if self.session_key is None:
+            return self.create()
         obj = Session(
             session_key = self.session_key,
             session_data = self.encode(self._get_session(no_load=must_create)),
--- a/django/contrib/sessions/backends/file.py
+++ b/django/contrib/sessions/backends/file.py
@@ -56,11 +56,11 @@ class SessionStore(SessionBase):
                     try:
                         session_data = self.decode(file_data)
                     except (EOFError, SuspiciousOperation):
-                        self.create()
+                        self._session_key = None
             finally:
                 session_file.close()
         except IOError:
-            pass
+            self._session_key = None
         return session_data
 
     def create(self):
@@ -71,10 +71,11 @@ class SessionStore(SessionBase):
             except CreateError:
                 continue
             self.modified = True
-            self._session_cache = {}
             return
 
     def save(self, must_create=False):
+        if self.session_key is None:
+            return self.create()
         # Get the session data now, before we start messing
         # with the file it is stored within.
         session_data = self._get_session(no_load=must_create)
--- a/django/contrib/sessions/tests.py
+++ b/django/contrib/sessions/tests.py
@@ -40,6 +40,8 @@ False
 (True, True)
 >>> db_session['a'], db_session['b'] = 'c', 'd'
 >>> db_session.save()
+>>> db_session['a']
+'c'
 >>> prev_key = db_session.session_key
 >>> prev_data = db_session.items()
 >>> db_session.cycle_key()
@@ -55,6 +57,16 @@ True
 >>> db_session.save()
 >>> DatabaseSession('1').get('cat')
 
+# Loading an unknown session key does not create a session record
+# Creating session records on load is a DOS vulnerability.
+>>> session = DatabaseSession('deadbeef')
+>>> session.load()
+{}
+>>> session.exists(session.session_key)
+False
+>>> session.session_key != 'deadbeef'
+True
+
 #
 # Cached DB session tests
 #
@@ -75,6 +87,20 @@ True
 >>> cdb_session.delete(cdb_session.session_key)
 >>> cdb_session.exists(cdb_session.session_key)
 False
+>>> cdb_session['a'] = 'b'
+>>> cdb_session.save()
+>>> cdb_session['a']
+'b'
+
+# Loading an unknown session key does not create a session record
+# Creating session records on load is a DOS vulnerability.
+>>> session = CacheDBSession('deadbeef')
+>>> session.load()
+{}
+>>> session.exists(session.session_key)
+False
+>>> session.session_key != 'deadbeef'
+True
 
 #
 # File session tests.
@@ -117,6 +143,8 @@ False
 (True, True)
 >>> file_session['a'], file_session['b'] = 'c', 'd'
 >>> file_session.save()
+>>> file_session['a']
+'c'
 >>> prev_key = file_session.session_key
 >>> prev_data = file_session.items()
 >>> file_session.cycle_key()
@@ -129,6 +157,16 @@ True
 >>> file_session = FileSession(file_session.session_key)
 >>> file_session.save()
 
+# Loading an unknown session key does not create a session record
+# Creating session records on load is a DOS vulnerability.
+>>> session = FileSession('deadbeef')
+>>> session.load()
+{}
+>>> session.exists(session.session_key)
+False
+>>> session.session_key != 'deadbeef'
+True
+
 # Ensure we don't allow directory traversal
 >>> FileSession("a/b/c").load()
 Traceback (innermost last):
@@ -186,6 +224,8 @@ False
 (True, True)
 >>> cache_session['a'], cache_session['b'] = 'c', 'd'
 >>> cache_session.save()
+>>> cache_session['a']
+'c'
 >>> prev_key = cache_session.session_key
 >>> prev_data = cache_session.items()
 >>> cache_session.cycle_key()
@@ -204,6 +244,16 @@ True
 >>> cache_session.save()
 >>> cache_session.delete(cache_session.session_key)
 
+# Loading an unknown session key does not create a session record
+# Creating session records on load is a DOS vulnerability.
+>>> session = CacheSession('deadbeef')
+>>> session.load()
+{}
+>>> session.exists(session.session_key)
+False
+>>> session.session_key != 'deadbeef'
+True
+
 >>> s = SessionBase()
 >>> s._session['some key'] = 'exists' # Pre-populate the session with some data
 >>> s.accessed = False   # Reset to pretend this wasn't accessed previously