Repair widespread misuse of _PyString_Resize. Since it's clear people

don't understand how this function works, also beefed up the docs.  The
most common usage error is of this form (often spread out across gotos):

	if (_PyString_Resize(&s, n) < 0) {
		Py_DECREF(s);
		s = NULL;
		goto outtahere;
	}

The error is that if _PyString_Resize runs out of memory, it automatically
decrefs the input string object s (which also deallocates it, since its
refcount must be 1 upon entry), and sets s to NULL.  So if the "if"
branch ever triggers, it's an error to call Py_DECREF(s):  s is already
NULL!  A correct way to write the above is the simpler (and intended)

	if (_PyString_Resize(&s, n) < 0)
		goto outtahere;

Bugfix candidate.

9 files changed, 23 insertions, 55 deletions

diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index f5ab2b6..1b05e40 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -331,8 +331,8 @@ static PyObject *PySSL_SSLread(PySSLObject *self, PyObject *args)
 		Py_DECREF(buf);
 		return PySSL_SetError(self, count);
 	}
-	if (count != len && _PyString_Resize(&buf, count) < 0)
-		return NULL;
+	if (count != len)
+		_PyString_Resize(&buf, count);
 	return buf;
 }
 
diff --git a/Modules/cPickle.c b/Modules/cPickle.c
index 2ffba48..a6c5e9d 100644
--- a/Modules/cPickle.c
+++ b/Modules/cPickle.c
@@ -1252,14 +1252,8 @@ modified_EncodeRawUnicodeEscape(const Py_UNICODE *s, int size)
 			*p++ = (char) ch;
 	}
 	*p = '\0';
-	if (_PyString_Resize(&repr, p - q))
-		goto onError;
-
+	_PyString_Resize(&repr, p - q);
 	return repr;
-
-  onError:
-	Py_DECREF(repr);
-	return NULL;
 }
 
 
diff --git a/Modules/cdmodule.c b/Modules/cdmodule.c
index b977277..25add3e 100644
--- a/Modules/cdmodule.c
+++ b/Modules/cdmodule.c
@@ -251,8 +251,7 @@ CD_readda(cdplayerobject *self, PyObject *args)
 		return NULL;
 	}
 	if (n < numframes)
-		if (_PyString_Resize(&result, n * sizeof(CDFRAME)))
-			return NULL;
+		_PyString_Resize(&result, n * sizeof(CDFRAME));
 
 	return result;
 }
diff --git a/Modules/clmodule.c b/Modules/clmodule.c
index ef3d77a..70e8f8e 100644
--- a/Modules/clmodule.c
+++ b/Modules/clmodule.c
@@ -135,8 +135,7 @@ cl_CompressImage(PyObject *self, PyObject *args)
 	}
 
 	if (compressedBufferSize < frameBufferSize)
-		if (_PyString_Resize(&compressedBuffer, compressedBufferSize))
-			return NULL;
+		_PyString_Resize(&compressedBuffer, compressedBufferSize);
 
 	return compressedBuffer;
 }
diff --git a/Modules/linuxaudiodev.c b/Modules/linuxaudiodev.c
index fa2e441..7d4abc9 100644
--- a/Modules/linuxaudiodev.c
+++ b/Modules/linuxaudiodev.c
@@ -158,8 +158,7 @@ lad_read(lad_t *self, PyObject *args)
         return NULL;
     }
     self->x_icount += count;
-    if (_PyString_Resize(&rv, count) == -1)
-	return NULL;
+    _PyString_Resize(&rv, count);
     return rv;
 }
 
diff --git a/Modules/regexmodule.c b/Modules/regexmodule.c
index d449604..4c7035e 100644
--- a/Modules/regexmodule.c
+++ b/Modules/regexmodule.c
@@ -516,11 +516,8 @@ symcomp(PyObject *pattern, PyObject *gdict)
 		return NULL;
 	}
 	/* _PyString_Resize() decrements npattern on failure */
-	if (_PyString_Resize(&npattern, n - v) == 0)
-		return npattern;
-	else {
-		return NULL;
-	}
+	_PyString_Resize(&npattern, n - v);
+	return npattern;
 
 }
 
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 53952fc..21fcab0 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -1402,8 +1402,8 @@ PySocketSock_recv(PySocketSockObject *s, PyObject *args)
 		Py_DECREF(buf);
 		return s->errorhandler();
 	}
-	if (n != len && _PyString_Resize(&buf, n) < 0)
-		return NULL;
+	if (n != len)
+		_PyString_Resize(&buf, n);
 	return buf;
 }
 
diff --git a/Modules/stropmodule.c b/Modules/stropmodule.c
index 0d5b75c..9a68b20 100644
--- a/Modules/stropmodule.c
+++ b/Modules/stropmodule.c
@@ -215,10 +215,8 @@ strop_joinfields(PyObject *self, PyObject *args)
 			}
 			slen = PyString_GET_SIZE(item);
 			while (reslen + slen + seplen >= sz) {
-				if (_PyString_Resize(&res, sz * 2)) {
-					Py_DECREF(res);
+				if (_PyString_Resize(&res, sz * 2) < 0)
 					return NULL;
-				}
 				sz *= 2;
 				p = PyString_AsString(res) + reslen;
 			}
@@ -231,10 +229,7 @@ strop_joinfields(PyObject *self, PyObject *args)
 			p += slen;
 			reslen += slen;
 		}
-		if (_PyString_Resize(&res, reslen)) {
-			Py_DECREF(res);
-			res = NULL;
-		}
+		_PyString_Resize(&res, reslen);
 		return res;
 	}
 
@@ -257,8 +252,7 @@ strop_joinfields(PyObject *self, PyObject *args)
 		}
 		slen = PyString_GET_SIZE(item);
 		while (reslen + slen + seplen >= sz) {
-			if (_PyString_Resize(&res, sz * 2)) {
-				Py_DECREF(res);
+			if (_PyString_Resize(&res, sz * 2) < 0) {
 				Py_DECREF(item);
 				return NULL;
 			}
@@ -275,10 +269,7 @@ strop_joinfields(PyObject *self, PyObject *args)
 		reslen += slen;
 		Py_DECREF(item);
 	}
-	if (_PyString_Resize(&res, reslen)) {
-		Py_DECREF(res);
-		res = NULL;
-	}
+	_PyString_Resize(&res, reslen);
 	return res;
 }
 
@@ -989,8 +980,8 @@ strop_translate(PyObject *self, PyObject *args)
 		return input_obj;
 	}
 	/* Fix the size of the resulting string */
-	if (inlen > 0 &&_PyString_Resize(&result, output-output_start))
-		return NULL;
+	if (inlen > 0)
+		_PyString_Resize(&result, output - output_start);
 	return result;
 }
 
diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index a3891f7..cfb71ae 100644
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -255,9 +255,8 @@ PyZlib_decompress(PyObject *self, PyObject *args)
 	    /* fall through */
 	case(Z_OK):
 	    /* need more memory */
-	    if (_PyString_Resize(&result_str, r_strlen << 1) == -1) {
+	    if (_PyString_Resize(&result_str, r_strlen << 1) < 0) {
 		inflateEnd(&zst);
-		result_str = NULL;
 		goto error;
 	    }
 	    zst.next_out = (unsigned char *)PyString_AS_STRING(result_str) \
@@ -414,10 +413,8 @@ PyZlib_objcompress(compobject *self, PyObject *args)
     /* while Z_OK and the output buffer is full, there might be more output,
        so extend the output buffer and try again */
     while (err == Z_OK && self->zst.avail_out == 0) {
-	if (_PyString_Resize(&RetVal, length << 1) == -1) {
-	    RetVal = NULL;
+	if (_PyString_Resize(&RetVal, length << 1) < 0)
 	    goto error;
-	}
 	self->zst.next_out = (unsigned char *)PyString_AS_STRING(RetVal) \
 	    + length;
 	self->zst.avail_out = length;
@@ -438,9 +435,7 @@ PyZlib_objcompress(compobject *self, PyObject *args)
 	RetVal = NULL;
 	goto error;
     }
-    if (_PyString_Resize(&RetVal,
-			 self->zst.total_out - start_total_out) < 0)
-	RetVal = NULL;
+    _PyString_Resize(&RetVal, self->zst.total_out - start_total_out);
 
  error:
     LEAVE_ZLIB
@@ -510,10 +505,8 @@ PyZlib_objdecompress(compobject *self, PyObject *args)
 	if (max_length && length > max_length)
 	    length = max_length;
 
-	if (_PyString_Resize(&RetVal, length) == -1) {
-	    RetVal = NULL;
+	if (_PyString_Resize(&RetVal, length) < 0)
 	    goto error;
-	}
 	self->zst.next_out = (unsigned char *)PyString_AS_STRING(RetVal) \
 	    + old_length;
 	self->zst.avail_out = length - old_length;
@@ -561,8 +554,7 @@ PyZlib_objdecompress(compobject *self, PyObject *args)
 	goto error;
     }
 
-    if (_PyString_Resize(&RetVal, self->zst.total_out - start_total_out) < 0)
-	RetVal = NULL;
+    _PyString_Resize(&RetVal, self->zst.total_out - start_total_out);
 
  error:
     LEAVE_ZLIB
@@ -612,10 +604,8 @@ PyZlib_flush(compobject *self, PyObject *args)
     /* while Z_OK and the output buffer is full, there might be more output,
        so extend the output buffer and try again */
     while (err == Z_OK && self->zst.avail_out == 0) {
-	if (_PyString_Resize(&RetVal, length << 1) == -1)  {
-	    RetVal = NULL;
+	if (_PyString_Resize(&RetVal, length << 1) < 0)
 	    goto error;
-	}
 	self->zst.next_out = (unsigned char *)PyString_AS_STRING(RetVal) \
 	    + length;
 	self->zst.avail_out = length;
@@ -651,8 +641,7 @@ PyZlib_flush(compobject *self, PyObject *args)
 	goto error;
     }
 
-    if (_PyString_Resize(&RetVal, self->zst.total_out - start_total_out) < 0)
-	RetVal = NULL;
+    _PyString_Resize(&RetVal, self->zst.total_out - start_total_out);
 
  error:
     LEAVE_ZLIB