Issue #20078: Reading malformed zipfiles no longer hangs with 100% CPU

consumption.

2 files changed, 33 insertions, 0 deletions

diff --git a/Lib/test/test_zipfile.py b/Lib/test/test_zipfile.py
index 49eccbb..33602cf 100644
--- a/Lib/test/test_zipfile.py
+++ b/Lib/test/test_zipfile.py
@@ -297,6 +297,36 @@ class AbstractTestsWithSourceFile:
                     buf = fp.read(test_size)
                     self.assertEqual(len(buf), test_size)
 
+    def test_truncated_zipfile(self):
+        fp = io.BytesIO()
+        with zipfile.ZipFile(fp, mode='w') as zipf:
+            zipf.writestr('strfile', self.data, compress_type=self.compression)
+            end_offset = fp.tell()
+        zipfiledata = fp.getvalue()
+
+        fp = io.BytesIO(zipfiledata)
+        with zipfile.ZipFile(fp) as zipf:
+            with zipf.open('strfile') as zipopen:
+                fp.truncate(end_offset - 20)
+                with self.assertRaises(EOFError):
+                    zipopen.read()
+
+        fp = io.BytesIO(zipfiledata)
+        with zipfile.ZipFile(fp) as zipf:
+            with zipf.open('strfile') as zipopen:
+                fp.truncate(end_offset - 20)
+                with self.assertRaises(EOFError):
+                    while zipopen.read(100):
+                        pass
+
+        fp = io.BytesIO(zipfiledata)
+        with zipfile.ZipFile(fp) as zipf:
+            with zipf.open('strfile') as zipopen:
+                fp.truncate(end_offset - 20)
+                with self.assertRaises(EOFError):
+                    while zipopen.read1(100):
+                        pass
+
     def tearDown(self):
         unlink(TESTFN)
         unlink(TESTFN2)
@@ -393,6 +423,7 @@ class StoredTestsWithSourceFile(AbstractTestsWithSourceFile,
         with zipfile.ZipFile(TESTFN2, "w") as zipfp:
             self.assertRaises(ValueError, zipfp.write, TESTFN)
 
+
 @requires_zlib
 class DeflateTestsWithSourceFile(AbstractTestsWithSourceFile,
                                  unittest.TestCase):
diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 173d990..12c1754 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -862,6 +862,8 @@ class ZipExtFile(io.BufferedIOBase):
 
         data = self._fileobj.read(n)
         self._compress_left -= len(data)
+        if not data:
+            raise EOFError
 
         if self._decrypter is not None:
             data = bytes(map(self._decrypter, data))