[3.12] gh-113977, gh-120754: Remove unbounded reads from zipfile (GH-122101) (#126347)

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.

(cherry picked from commit 556dc9b)

Co-authored-by: Cody Maloney <[email protected]>
Co-authored-by: Daniel Hillier <[email protected]>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Author: 4 people

Lib/zipfile/__init__.py

@@ -295,7 +295,7 @@ 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"):
@@ -315,9 +315,9 @@ 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

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.