Issue #25626: Change zlib to accept Py_ssize_t and cap to UINT_MAX

The underlying zlib library stores sizes in “unsigned int”. The corresponding
Python parameters are all sizes of buffers filled in by zlib, so it is okay
to reduce higher values to the UINT_MAX internal cap. OverflowError is still
raised for sizes that do not fit in Py_ssize_t.

Sizes are now limited to Py_ssize_t rather than unsigned long, because Python
byte strings cannot be larger than Py_ssize_t. Previously this could result
in a SystemError on 32-bit platforms.

This resolves a regression in the gzip module when reading more than UINT_MAX
or LONG_MAX bytes in one call, introduced by revision 62723172412c.

1 files changed, 29 insertions, 29 deletions

diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index 1997b40..37307be 100644
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -226,42 +226,42 @@ zlib_compress_impl(PyModuleDef *module, Py_buffer *bytes, int level)
 
 /*[python input]
 
-class uint_converter(CConverter):
+class capped_uint_converter(CConverter):
     type = 'unsigned int'
-    converter = 'uint_converter'
+    converter = 'capped_uint_converter'
     c_ignored_default = "0"
 
 [python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=22263855f7a3ebfd]*/
+/*[python end generated code: output=da39a3ee5e6b4b0d input=35521e4e733823c7]*/
 
 static int
-uint_converter(PyObject *obj, void *ptr)
+capped_uint_converter(PyObject *obj, void *ptr)
 {
-    long val;
-    unsigned long uval;
+    PyObject *long_obj;
+    Py_ssize_t val;
 
-    val = PyLong_AsLong(obj);
-    if (val == -1 && PyErr_Occurred()) {
-        uval = PyLong_AsUnsignedLong(obj);
-        if (uval == (unsigned long)-1 && PyErr_Occurred())
-            return 0;
+    long_obj = (PyObject *)_PyLong_FromNbInt(obj);
+    if (long_obj == NULL) {
+        return 0;
     }
-    else {
-        if (val < 0) {
-            PyErr_SetString(PyExc_ValueError,
-                            "value must be positive");
-            return 0;
-        }
-        uval = (unsigned long)val;
+    val = PyLong_AsSsize_t(long_obj);
+    Py_DECREF(long_obj);
+    if (val == -1 && PyErr_Occurred()) {
+        return 0;
     }
-
-    if (uval > UINT_MAX) {
-        PyErr_SetString(PyExc_OverflowError,
-                        "Python int too large for C unsigned int");
+    if (val < 0) {
+        PyErr_SetString(PyExc_ValueError,
+                        "value must be positive");
         return 0;
     }
 
-    *(unsigned int *)ptr = Py_SAFE_DOWNCAST(uval, unsigned long, unsigned int);
+    if ((size_t)val > UINT_MAX) {
+        *(unsigned int *)ptr = UINT_MAX;
+    }
+    else {
+        *(unsigned int *)ptr = Py_SAFE_DOWNCAST(val, Py_ssize_t,
+            unsigned int);
+    }
     return 1;
 }
 
@@ -272,7 +272,7 @@ zlib.decompress
         Compressed data.
     wbits: int(c_default="MAX_WBITS") = MAX_WBITS
         The window buffer size.
-    bufsize: uint(c_default="DEF_BUF_SIZE") = DEF_BUF_SIZE
+    bufsize: capped_uint(c_default="DEF_BUF_SIZE") = DEF_BUF_SIZE
         The initial output buffer size.
     /
 
@@ -282,7 +282,7 @@ Returns a bytes object containing the uncompressed data.
 static PyObject *
 zlib_decompress_impl(PyModuleDef *module, Py_buffer *data, int wbits,
                      unsigned int bufsize)
-/*[clinic end generated code: output=444d0987f3429574 input=0f4b9abb7103f50e]*/
+/*[clinic end generated code: output=444d0987f3429574 input=da095118b3243b27]*/
 {
     PyObject *result_str = NULL;
     Byte *input;
@@ -691,7 +691,7 @@ zlib.Decompress.decompress
 
     data: Py_buffer
         The binary data to decompress.
-    max_length: uint = 0
+    max_length: capped_uint = 0
         The maximum allowable length of the decompressed data.
         Unconsumed input data will be stored in
         the unconsumed_tail attribute.
@@ -707,7 +707,7 @@ Call the flush() method to clear these buffers.
 static PyObject *
 zlib_Decompress_decompress_impl(compobject *self, Py_buffer *data,
                                 unsigned int max_length)
-/*[clinic end generated code: output=b82e2a2c19f5fe7b input=02cfc047377cec86]*/
+/*[clinic end generated code: output=b82e2a2c19f5fe7b input=68b6508ab07c2cf0]*/
 {
     int err;
     unsigned int old_length, length = DEF_BUF_SIZE;
@@ -1048,7 +1048,7 @@ error:
 /*[clinic input]
 zlib.Decompress.flush
 
-    length: uint(c_default="DEF_BUF_SIZE") = zlib.DEF_BUF_SIZE
+    length: capped_uint(c_default="DEF_BUF_SIZE") = zlib.DEF_BUF_SIZE
         the initial size of the output buffer.
     /
 
@@ -1057,7 +1057,7 @@ Return a bytes object containing any remaining decompressed data.
 
 static PyObject *
 zlib_Decompress_flush_impl(compobject *self, unsigned int length)
-/*[clinic end generated code: output=db6fb753ab698e22 input=1580956505978993]*/
+/*[clinic end generated code: output=db6fb753ab698e22 input=1bb961eb21b62aa0]*/
 {
     int err;
     unsigned int new_length;