From 2fa60ae0b4ab7115e25c8c341570488bb29e7294 Mon Sep 17 00:00:00 2001 From: Kevin Mehall Date: Sun, 20 Mar 2022 08:26:09 -0600 Subject: [PATCH] bpo-42369: Fix thread safety of zipfile._SharedFile.tell (GH-26974) The `_SharedFile` tracks its own virtual position into the file as `self._pos` and updates it after reading or seeking. `tell()` should return this position instead of calling into the underlying file object, since if multiple `_SharedFile` instances are being used concurrently on the same file, another one may have moved the real file position. Additionally, calling into the underlying `tell` may expose thread safety issues in the underlying file object because it was called without taking the lock. (cherry picked from commit e730ae7effe4f13b24f1b5fb1fca005709c86acb) Co-authored-by: Kevin Mehall --- Lib/zipfile.py | 4 +++- .../next/Library/2022-03-19-19-56-04.bpo-42369.Ok828t.rst | 1 + 2 files changed, 4 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Library/2022-03-19-19-56-04.bpo-42369.Ok828t.rst diff --git a/Lib/zipfile.py b/Lib/zipfile.py index f72c6a4e0c2539..1e942a503e8ee1 100644 --- a/Lib/zipfile.py +++ b/Lib/zipfile.py @@ -720,7 +720,9 @@ def __init__(self, file, pos, close, lock, writing): self._lock = lock self._writing = writing self.seekable = file.seekable - self.tell = file.tell + + def tell(self): + return self._pos def seek(self, offset, whence=0): with self._lock: diff --git a/Misc/NEWS.d/next/Library/2022-03-19-19-56-04.bpo-42369.Ok828t.rst b/Misc/NEWS.d/next/Library/2022-03-19-19-56-04.bpo-42369.Ok828t.rst new file mode 100644 index 00000000000000..86dc3a0b81b9c2 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2022-03-19-19-56-04.bpo-42369.Ok828t.rst @@ -0,0 +1 @@ +Fix thread safety of :meth:`zipfile._SharedFile.tell` to avoid a "zipfile.BadZipFile: Bad CRC-32 for file" exception when reading a :class:`ZipFile` from multiple threads.