[3.10] bpo-41486: zlib uses an UINT32_MAX sliding window for the output buffer (GH-26143)

Misc/NEWS.d/next/Core and Builtins/2021-07-04-17-41-47.bpo-41486.DiM24a.rst

@@ -0,0 +1,3 @@
+Fix a memory consumption and copying performance regression in earlier 3.10
+beta releases if someone used an output buffer larger than 4GiB with
+zlib.decompress on input data that expands that large.

Modules/zlibmodule.c

@@ -30,28 +30,6 @@ OutputBuffer_InitAndGrow(_BlocksOutputBuffer *buffer, Py_ssize_t max_length,
  return allocated;
 }
 
-/* On success, return value >= 0
- On failure, return -1 */
-static inline Py_ssize_t
-OutputBuffer_InitWithSize(_BlocksOutputBuffer *buffer, Py_ssize_t init_size,
- Bytef **next_out, uint32_t *avail_out)
-{
- Py_ssize_t allocated;
-
- if (init_size >= 0 && // ensure (size_t) cast is safe
- (size_t)init_size > UINT32_MAX)
- {
- /* In 32-bit build, never reach this conditional branch.
- The maximum block size accepted by zlib is UINT32_MAX. */
- init_size = UINT32_MAX;
- }
-
- allocated = _BlocksOutputBuffer_InitWithSize(
- buffer, init_size, (void**) next_out);
- *avail_out = (uint32_t) allocated;
- return allocated;
-}
-
 /* On success, return value >= 0
  On failure, return -1 */
 static inline Py_ssize_t
@@ -84,6 +62,106 @@ OutputBuffer_OnError(_BlocksOutputBuffer *buffer)
  _BlocksOutputBuffer_OnError(buffer);
 }
 
+/* The max buffer size accepted by zlib is UINT32_MAX, the initial buffer size
+ `init_size` may > it in 64-bit build. These wrapper functions maintain an
+ UINT32_MAX sliding window for the first block:
+ 1. OutputBuffer_WindowInitWithSize()
+ 2. OutputBuffer_WindowGrow()
+ 3. OutputBuffer_WindowFinish()
+ 4. OutputBuffer_WindowOnError()
+
+ ==== is the sliding window:
+ 1. ====------
+ ^ next_posi, left_bytes is 6
+ 2. ----====--
+ ^ next_posi, left_bytes is 2
+ 3. --------==
+ ^ next_posi, left_bytes is 0 */
+typedef struct {
+ Py_ssize_t left_bytes;
+ Bytef *next_posi;
+} _Uint32Window;
+
+/* Initialize the buffer with an inital buffer size.
+
+ On success, return value >= 0
+ On failure, return value < 0 */
+static inline Py_ssize_t
+OutputBuffer_WindowInitWithSize(_BlocksOutputBuffer *buffer, _Uint32Window *window,
+ Py_ssize_t init_size,
+ Bytef **next_out, uint32_t *avail_out)
+{
+ Py_ssize_t allocated = _BlocksOutputBuffer_InitWithSize(
+ buffer, init_size, (void**) next_out);
+
+ if (allocated >= 0) {
+ // the UINT32_MAX sliding window
+ Py_ssize_t window_size = Py_MIN((size_t)allocated, UINT32_MAX);
+ *avail_out = (uint32_t) window_size;
+
+ window->left_bytes = allocated - window_size;
+ window->next_posi = *next_out + window_size;
+ }
+ return allocated;
+}
+
+/* Grow the buffer.
+
+ On success, return value >= 0
+ On failure, return value < 0 */
+static inline Py_ssize_t
+OutputBuffer_WindowGrow(_BlocksOutputBuffer *buffer, _Uint32Window *window,
+ Bytef **next_out, uint32_t *avail_out)
+{
+ Py_ssize_t allocated;
+
+ /* ensure no gaps in the data.
+ if inlined, this check could be optimized away.*/
+ if (*avail_out != 0) {
+ PyErr_SetString(PyExc_SystemError,
+ "*avail_out != 0 in OutputBuffer_WindowGrow().");
+ return -1;
+ }
+
+ // slide the UINT32_MAX sliding window
+ if (window->left_bytes > 0) {
+ Py_ssize_t window_size = Py_MIN((size_t)window->left_bytes, UINT32_MAX);
+
+ *next_out = window->next_posi;
+ *avail_out = (uint32_t) window_size;
+
+ window->left_bytes -= window_size;
+ window->next_posi += window_size;
+
+ return window_size;
+ }
+ assert(window->left_bytes == 0);
+
+ // only the first block may > UINT32_MAX
+ allocated = _BlocksOutputBuffer_Grow(
+ buffer, (void**) next_out, (Py_ssize_t) *avail_out);
+ *avail_out = (uint32_t) allocated;
+ return allocated;
+}
+
+/* Finish the buffer.
+
+ On success, return a bytes object
+ On failure, return NULL */
+static inline PyObject *
+OutputBuffer_WindowFinish(_BlocksOutputBuffer *buffer, _Uint32Window *window,
+ uint32_t avail_out)
+{
+ Py_ssize_t real_avail_out = (Py_ssize_t) avail_out + window->left_bytes;
+ return _BlocksOutputBuffer_Finish(buffer, real_avail_out);
+}
+
+static inline void
+OutputBuffer_WindowOnError(_BlocksOutputBuffer *buffer, _Uint32Window *window)
+{
+ _BlocksOutputBuffer_OnError(buffer);
+}
+
 
 #define ENTER_ZLIB(obj) do { \
  if (!PyThread_acquire_lock((obj)->lock, 0)) { \
@@ -344,6 +422,7 @@ zlib_decompress_impl(PyObject *module, Py_buffer *data, int wbits,
  int err, flush;
  z_stream zst;
  _BlocksOutputBuffer buffer = {.list = NULL};
+ _Uint32Window window; // output buffer's UINT32_MAX sliding window
 
  zlibstate *state = get_zlib_state(module);
 
@@ -354,7 +433,8 @@ zlib_decompress_impl(PyObject *module, Py_buffer *data, int wbits,
  bufsize = 1;
  }
 
- if (OutputBuffer_InitWithSize(&buffer, bufsize, &zst.next_out, &zst.avail_out) < 0) {
+ if (OutputBuffer_WindowInitWithSize(&buffer, &window, bufsize,
+ &zst.next_out, &zst.avail_out) < 0) {
  goto error;
  }
 
@@ -387,7 +467,8 @@ zlib_decompress_impl(PyObject *module, Py_buffer *data, int wbits,
 
  do {
  if (zst.avail_out == 0) {
- if (OutputBuffer_Grow(&buffer, &zst.next_out, &zst.avail_out) < 0) {
+ if (OutputBuffer_WindowGrow(&buffer, &window,
+ &zst.next_out, &zst.avail_out) < 0) {
  inflateEnd(&zst);
  goto error;
  }
@@ -430,13 +511,13 @@ zlib_decompress_impl(PyObject *module, Py_buffer *data, int wbits,
  goto error;
  }
 
- RetVal = OutputBuffer_Finish(&buffer, zst.avail_out);
+ RetVal = OutputBuffer_WindowFinish(&buffer, &window, zst.avail_out);
  if (RetVal != NULL) {
  return RetVal;
  }
 
  error:
- OutputBuffer_OnError(&buffer);
+ OutputBuffer_WindowOnError(&buffer, &window);
  return NULL;
 }
 
@@ -1171,6 +1252,7 @@ zlib_Decompress_flush_impl(compobject *self, PyTypeObject *cls,
  PyObject *RetVal;
  Py_ssize_t ibuflen;
  _BlocksOutputBuffer buffer = {.list = NULL};
+ _Uint32Window window; // output buffer's UINT32_MAX sliding window
 
  PyObject *module = PyType_GetModule(cls);
  if (module == NULL) {
@@ -1193,7 +1275,8 @@ zlib_Decompress_flush_impl(compobject *self, PyTypeObject *cls,
  self->zst.next_in = data.buf;
  ibuflen = data.len;
 
- if (OutputBuffer_InitWithSize(&buffer, length, &self->zst.next_out, &self->zst.avail_out) < 0) {
+ if (OutputBuffer_WindowInitWithSize(&buffer, &window, length,
+ &self->zst.next_out, &self->zst.avail_out) < 0) {
  goto abort;
  }
 
@@ -1203,7 +1286,8 @@ zlib_Decompress_flush_impl(compobject *self, PyTypeObject *cls,
 
  do {
  if (self->zst.avail_out == 0) {
- if (OutputBuffer_Grow(&buffer, &self->zst.next_out, &self->zst.avail_out) < 0) {
+ if (OutputBuffer_WindowGrow(&buffer, &window,
+ &self->zst.next_out, &self->zst.avail_out) < 0) {
  goto abort;
  }
  }
@@ -1248,13 +1332,13 @@ zlib_Decompress_flush_impl(compobject *self, PyTypeObject *cls,
  }
  }
 
- RetVal = OutputBuffer_Finish(&buffer, self->zst.avail_out);
+ RetVal = OutputBuffer_WindowFinish(&buffer, &window, self->zst.avail_out);
  if (RetVal != NULL) {
  goto success;
  }
 
  abort:
- OutputBuffer_OnError(&buffer);
+ OutputBuffer_WindowOnError(&buffer, &window);
  RetVal = NULL;
  success:
  PyBuffer_Release(&data);