From 556dc9b8a78bad296513221f3f414a3f8fd0ae70 Mon Sep 17 00:00:00 2001
From: Cody Maloney <cmaloney@users.noreply.github.com>
Date: Sat, 2 Nov 2024 22:28:51 -0700
Subject: [PATCH] gh-113977, gh-120754: Remove unbounded reads from zipfile
 (GH-122101)

GH-113977, GH-120754: Remove unbounded reads from zipfile

Read without a size may read an unbounded amount of data + allocate
unbounded size buffers. Move to capped size reads to prevent potential
issues.

Co-authored-by: Daniel Hillier <daniel.hillier@gmail.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
---
 Lib/zipfile/__init__.py                                     | 6 +++---
 .../Library/2024-07-23-02-24-50.gh-issue-120754.nHb5mG.rst  | 1 +
 2 files changed, 4 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-07-23-02-24-50.gh-issue-120754.nHb5mG.rst

diff --git a/Lib/zipfile/__init__.py b/Lib/zipfile/__init__.py
index e2aaf8bab49..08c83cfb760 100644
--- a/Lib/zipfile/__init__.py
+++ b/Lib/zipfile/__init__.py
@@ -309,7 +309,7 @@ def _EndRecData(fpin):
         fpin.seek(-sizeEndCentDir, 2)
     except OSError:
         return None
-    data = fpin.read()
+    data = fpin.read(sizeEndCentDir)
     if (len(data) == sizeEndCentDir and
         data[0:4] == stringEndArchive and
         data[-2:] == b"\000\000"):
@@ -329,9 +329,9 @@ def _EndRecData(fpin):
     # record signature. The comment is the last item in the ZIP file and may be
     # up to 64K long.  It is assumed that the "end of central directory" magic
     # number does not appear in the comment.
-    maxCommentStart = max(filesize - (1 << 16) - sizeEndCentDir, 0)
+    maxCommentStart = max(filesize - ZIP_MAX_COMMENT - sizeEndCentDir, 0)
     fpin.seek(maxCommentStart, 0)
-    data = fpin.read()
+    data = fpin.read(ZIP_MAX_COMMENT + sizeEndCentDir)
     start = data.rfind(stringEndArchive)
     if start >= 0:
         # found the magic number; attempt to unpack and interpret
diff --git a/Misc/NEWS.d/next/Library/2024-07-23-02-24-50.gh-issue-120754.nHb5mG.rst b/Misc/NEWS.d/next/Library/2024-07-23-02-24-50.gh-issue-120754.nHb5mG.rst
new file mode 100644
index 00000000000..6c33e7b7ec7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-07-23-02-24-50.gh-issue-120754.nHb5mG.rst
@@ -0,0 +1 @@
+Update unbounded ``read`` calls in :mod:`zipfile` to specify an explicit ``size`` putting a limit on how much data they may read. This also updates handling around ZIP max comment size to match the standard instead of reading comments that are one byte too long.