[Python-checkins] bpo-24618: Add a check in the code constructor. (GH-8283)

[Serhiy Storchaka]

https://github.com/python/cpython/commit/bd47384e07bde38a8f18b90b4cea02a505d95c75
commit: bd47384e07bde38a8f18b90b4cea02a505d95c75
branch: master
author: Serhiy Storchaka <storchaka at gmail.com>
committer: GitHub <noreply at github.com>
date: 2018-07-16T09:10:19+03:00
summary:

bpo-24618: Add a check in the code constructor. (GH-8283)

Check that the size of the varnames tuple is enough at least for all arguments.

files:
A Misc/NEWS.d/next/Core and Builtins/2018-07-14-14-01-37.bpo-24618.iTKjD_.rst
M Objects/codeobject.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-07-14-14-01-37.bpo-24618.iTKjD_.rst b/Misc/NEWS.d/next/Core and Builtins/2018-07-14-14-01-37.bpo-24618.iTKjD_.rst
new file mode 100644
index 000000000000..180b56501211
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-07-14-14-01-37.bpo-24618.iTKjD_.rst	
@@ -0,0 +1,2 @@
+Fixed reading invalid memory when create the code object with too small
+varnames tuple or too large argument counts.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index aa373a075d7d..b07667c28df1 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -103,7 +103,7 @@ PyCode_New(int argcount, int kwonlyargcount,
 {
     PyCodeObject *co;
     Py_ssize_t *cell2arg = NULL;
-    Py_ssize_t i, n_cellvars;
+    Py_ssize_t i, n_cellvars, n_varnames, total_args;
 
     /* Check argument types */
     if (argcount < 0 || kwonlyargcount < 0 || nlocals < 0 ||
@@ -138,10 +138,22 @@ PyCode_New(int argcount, int kwonlyargcount,
         flags &= ~CO_NOFREE;
     }
 
+    n_varnames = PyTuple_GET_SIZE(varnames);
+    if (argcount <= n_varnames && kwonlyargcount <= n_varnames) {
+        /* Never overflows. */
+        total_args = (Py_ssize_t)argcount + (Py_ssize_t)kwonlyargcount +
+                ((flags & CO_VARARGS) != 0) + ((flags & CO_VARKEYWORDS) != 0);
+    }
+    else {
+        total_args = n_varnames + 1;
+    }
+    if (total_args > n_varnames) {
+        PyErr_SetString(PyExc_ValueError, "code: varnames is too small");
+        return NULL;
+    }
+
     /* Create mapping between cells and arguments if needed. */
     if (n_cellvars) {
-        Py_ssize_t total_args = argcount + kwonlyargcount +
-            ((flags & CO_VARARGS) != 0) + ((flags & CO_VARKEYWORDS) != 0);
         bool used_cell2arg = false;
         cell2arg = PyMem_NEW(Py_ssize_t, n_cellvars);
         if (cell2arg == NULL) {