[Python-checkins] bpo-41175: Guard against a NULL pointer dereference within bytearrayobject (GH-21240)

[stratakis]

https://github.com/python/cpython/commit/61fc23ca106bc82955b0e59d1ab42285b94899e2
commit: 61fc23ca106bc82955b0e59d1ab42285b94899e2
branch: master
author: stratakis <cstratak at redhat.com>
committer: GitHub <noreply at github.com>
date: 2020-07-08T22:39:41+02:00
summary:

bpo-41175: Guard against a NULL pointer dereference within bytearrayobject (GH-21240)

The issue is triggered by the bytearray() + bytearray() operation.

Detected by GCC 10 static analysis tool.

files:
A Misc/NEWS.d/next/Core and Builtins/2020-06-30-20-17-31.bpo-41175.acJoXB.rst
M Objects/bytearrayobject.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-06-30-20-17-31.bpo-41175.acJoXB.rst b/Misc/NEWS.d/next/Core and Builtins/2020-06-30-20-17-31.bpo-41175.acJoXB.rst
new file mode 100644
index 0000000000000..844fb804c0c8d
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-06-30-20-17-31.bpo-41175.acJoXB.rst	
@@ -0,0 +1,2 @@
+Guard against a NULL pointer dereference within bytearrayobject triggered by
+the ``bytearray() + bytearray()`` operation.
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index 83c79b200a0a1..7035061933098 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -266,7 +266,9 @@ PyByteArray_Concat(PyObject *a, PyObject *b)
 
     result = (PyByteArrayObject *) \
         PyByteArray_FromStringAndSize(NULL, va.len + vb.len);
-    if (result != NULL) {
+    // result->ob_bytes is NULL if result is an empty string:
+    // if va.len + vb.len equals zero.
+    if (result != NULL && result->ob_bytes != NULL) {
         memcpy(result->ob_bytes, va.buf, va.len);
         memcpy(result->ob_bytes + va.len, vb.buf, vb.len);
     }