Issue #16411: Fix a bug where zlib.decompressobj().flush() might try to access previously-freed memory.

Patch by Serhiy Storchaka.

1 files changed, 12 insertions, 0 deletions

diff --git a/Lib/test/test_zlib.py b/Lib/test/test_zlib.py
index 6d4b2c3..4661c1d 100644
--- a/Lib/test/test_zlib.py
+++ b/Lib/test/test_zlib.py
@@ -459,6 +459,18 @@ class CompressObjectTestCase(BaseCompressTestCase, unittest.TestCase):
                 self.assertEqual(dco.unconsumed_tail, b'')
                 self.assertEqual(dco.unused_data, remainder)
 
+    def test_flush_with_freed_input(self):
+        # Issue #16411: decompressor accesses input to last decompress() call
+        # in flush(), even if this object has been freed in the meanwhile.
+        input1 = b'abcdefghijklmnopqrstuvwxyz'
+        input2 = b'QWERTYUIOPASDFGHJKLZXCVBNM'
+        data = zlib.compress(input1)
+        dco = zlib.decompressobj()
+        dco.decompress(data, 1)
+        del data
+        data = zlib.compress(input2)
+        self.assertEqual(dco.flush(), input1[1:])
+
     if hasattr(zlib.compressobj(), "copy"):
         def test_compresscopy(self):
             # Test copying a compression object