From 202ed2506c84cd98e9e35621b5b2929ceb717864 Mon Sep 17 00:00:00 2001
From: Sam Ezeh <sam.z.ezeh@gmail.com>
Date: Mon, 23 May 2022 18:59:21 +0100
Subject: gh-83245: Raise BadZipFile instead of ValueError when reading a
 corrupt ZIP file (GH-32291)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
---
 Lib/test/test_zipfile.py                                      | 11 +++++++++++
 Lib/zipfile.py                                                |  2 ++
 .../next/Library/2022-04-03-19-40-09.bpo-39064.76PbIz.rst     |  2 ++
 3 files changed, 15 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2022-04-03-19-40-09.bpo-39064.76PbIz.rst

diff --git a/Lib/test/test_zipfile.py b/Lib/test/test_zipfile.py
index 848bf4f..f4c11d8 100644
--- a/Lib/test/test_zipfile.py
+++ b/Lib/test/test_zipfile.py
@@ -1740,6 +1740,17 @@ class OtherTests(unittest.TestCase):
             fp.write("short file")
         self.assertRaises(zipfile.BadZipFile, zipfile.ZipFile, TESTFN)
 
+    def test_negative_central_directory_offset_raises_BadZipFile(self):
+        # Zip file containing an empty EOCD record
+        buffer = bytearray(b'PK\x05\x06' + b'\0'*18)
+
+        # Set the size of the central directory bytes to become 1,
+        # causing the central directory offset to become negative
+        for dirsize in 1, 2**32-1:
+            buffer[12:16] = struct.pack('<L', dirsize)
+            f = io.BytesIO(buffer)
+            self.assertRaises(zipfile.BadZipFile, zipfile.ZipFile, f)
+
     def test_closed_zip_raises_ValueError(self):
         """Verify that testzip() doesn't swallow inappropriate exceptions."""
         data = io.BytesIO()
diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 9f44375..fc6ca65 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -1381,6 +1381,8 @@ class ZipFile:
             print("given, inferred, offset", offset_cd, inferred, concat)
         # self.start_dir:  Position of start of central directory
         self.start_dir = offset_cd + concat
+        if self.start_dir < 0:
+            raise BadZipFile("Bad offset for central directory")
         fp.seek(self.start_dir, 0)
         data = fp.read(size_cd)
         fp = io.BytesIO(data)
diff --git a/Misc/NEWS.d/next/Library/2022-04-03-19-40-09.bpo-39064.76PbIz.rst b/Misc/NEWS.d/next/Library/2022-04-03-19-40-09.bpo-39064.76PbIz.rst
new file mode 100644
index 0000000..34d3152
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-04-03-19-40-09.bpo-39064.76PbIz.rst
@@ -0,0 +1,2 @@
+:class:`zipfile.ZipFile` now raises :exc:`zipfile.BadZipFile` instead of ``ValueError`` when reading a
+corrupt zip file in which the central directory offset is negative.
-- 
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