Prevent modify mutable cached value

The cached values are copied when set and copied again when returned so the
stored values can never be modified.

Closes #9558

trytond/trytond/cache.py

@@ -7,6 +7,7 @@ import os
 import selectors
 import threading
 from collections import OrderedDict, defaultdict
+from copy import deepcopy
 from weakref import WeakKeyDictionary
 
 from sql import Table
@@ -190,7 +191,7 @@ class MemoryCache(BaseCache):
                 return default
             cache[key] = (expire, result)
             self.hit += 1
-            return result
+            return deepcopy(result)
         except (KeyError, TypeError):
             self.miss += 1
             return default
@@ -203,7 +204,7 @@ class MemoryCache(BaseCache):
         else:
             expire = None
         try:
-            cache[key] = (expire, value)
+            cache[key] = (expire, deepcopy(value))
         except TypeError:
             pass
         return value

trytond/trytond/tests/test_cache.py

@@ -121,6 +121,15 @@ class MemoryCacheTestCase(unittest.TestCase):
 
         self.assertEqual(cache.get('foo'), 'bar')
 
+    @with_transaction()
+    def test_memory_cache_mutable(self):
+        "Test MemoryCache with mutable value"
+        value = ['bar']
+        cache.set('foo', value)
+        value.remove('bar')
+
+        self.assertEqual(cache.get('foo'), ['bar'])
+
     @with_transaction()
     def test_memory_cache_drop(self):
         "Test MemoryCache drop"