[3.12] gh-105967: Work around a macOS bug, limit zlib C library crc32 API calls to 1gig (GH-112615) (#112724)

miss-islington · gpshead · web-flow · commit 88ec2a4fef5e · 2023-12-04T20:29:23.000Z
gh-105967: Work around a macOS bug, limit zlib C library crc32 API calls to 1gig (GH-112615) Work around a macOS bug, limit zlib crc32 calls to 1GiB. Without this, `zlib.crc32` and `binascii.crc32` could produce incorrect results on multi-gigabyte inputs depending on the macOS version's Apple supplied zlib implementation. (cherry picked from commit 4eddb4c) Co-authored-by: Gregory P. Smith <greg@krypto.org>
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-12-01-19-02-21.gh-issue-105967.Puq5Cn.rst b/Misc/NEWS.d/next/Core and Builtins/2023-12-01-19-02-21.gh-issue-105967.Puq5Cn.rst
@@ -0,0 +1,4 @@
+Workaround a bug in Apple's macOS platform zlib library where
+:func:`zlib.crc32` and :func:`binascii.crc32` could produce incorrect results
+on multi-gigabyte inputs. Including when using :mod:`zipfile` on zips
+containing large data.
diff --git a/Modules/binascii.c b/Modules/binascii.c
@@ -780,12 +780,20 @@ binascii_crc32_impl(PyObject *module, Py_buffer *data, unsigned int crc)
 
         Py_BEGIN_ALLOW_THREADS
         /* Avoid truncation of length for very large buffers. crc32() takes
-           length as an unsigned int, which may be narrower than Py_ssize_t. */
-        while ((size_t)len > UINT_MAX) {
-            crc = crc32(crc, buf, UINT_MAX);
-            buf += (size_t) UINT_MAX;
-            len -= (size_t) UINT_MAX;
+           length as an unsigned int, which may be narrower than Py_ssize_t.
+           We further limit size due to bugs in Apple's macOS zlib.
+           See https://github.com/python/cpython/issues/105967
+         */
+#define ZLIB_CRC_CHUNK_SIZE 0x40000000
+#if ZLIB_CRC_CHUNK_SIZE > INT_MAX
+# error "unsupported less than 32-bit platform?"
+#endif
+        while ((size_t)len > ZLIB_CRC_CHUNK_SIZE) {
+            crc = crc32(crc, buf, ZLIB_CRC_CHUNK_SIZE);
+            buf += (size_t) ZLIB_CRC_CHUNK_SIZE;
+            len -= (size_t) ZLIB_CRC_CHUNK_SIZE;
         }
+#undef ZLIB_CRC_CHUNK_SIZE
         crc = crc32(crc, buf, (unsigned int)len);
         Py_END_ALLOW_THREADS
     } else {
diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
@@ -1890,12 +1890,20 @@ zlib_crc32_impl(PyObject *module, Py_buffer *data, unsigned int value)
 
         Py_BEGIN_ALLOW_THREADS
         /* Avoid truncation of length for very large buffers. crc32() takes
-           length as an unsigned int, which may be narrower than Py_ssize_t. */
-        while ((size_t)len > UINT_MAX) {
-            value = crc32(value, buf, UINT_MAX);
-            buf += (size_t) UINT_MAX;
-            len -= (size_t) UINT_MAX;
+           length as an unsigned int, which may be narrower than Py_ssize_t.
+           We further limit size due to bugs in Apple's macOS zlib.
+           See https://github.com/python/cpython/issues/105967.
+         */
+#define ZLIB_CRC_CHUNK_SIZE 0x40000000
+#if ZLIB_CRC_CHUNK_SIZE > INT_MAX
+# error "unsupported less than 32-bit platform?"
+#endif
+        while ((size_t)len > ZLIB_CRC_CHUNK_SIZE) {
+            value = crc32(value, buf, ZLIB_CRC_CHUNK_SIZE);
+            buf += (size_t) ZLIB_CRC_CHUNK_SIZE;
+            len -= (size_t) ZLIB_CRC_CHUNK_SIZE;
         }
+#undef ZLIB_CRC_CHUNK_SIZE
         value = crc32(value, buf, (unsigned int)len);
         Py_END_ALLOW_THREADS
     } else {
