[Python-checkins] bpo-40020: Fix realloc leak on failure in growable_comment_array_add (GH-19083)

[Alexander Riccio]

https://github.com/python/cpython/commit/51e3e450fbed46198d9be92add1a5dee6a1f7f41
commit: 51e3e450fbed46198d9be92add1a5dee6a1f7f41
branch: master
author: Alexander Riccio <test35965 at gmail.com>
committer: GitHub <noreply at github.com>
date: 2020-03-30T23:15:59+02:00
summary:

bpo-40020: Fix realloc leak on failure in growable_comment_array_add (GH-19083)

Fix a leak and subsequent crash in parsetok.c caused by realloc misuse on a rare codepath. 

Realloc returns a null pointer on failure, and then growable_comment_array_deallocate crashes later when it dereferences it.

files:
A Misc/NEWS.d/next/Core and Builtins/2020-03-19-21-53-41.bpo-40020.n-26G7.rst
M Parser/parsetok.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-03-19-21-53-41.bpo-40020.n-26G7.rst b/Misc/NEWS.d/next/Core and Builtins/2020-03-19-21-53-41.bpo-40020.n-26G7.rst
new file mode 100644
index 0000000000000..948404baba288
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-03-19-21-53-41.bpo-40020.n-26G7.rst	
@@ -0,0 +1 @@
+Fix a leak and subsequent crash in parsetok.c caused by realloc misuse on a rare codepath.
diff --git a/Parser/parsetok.c b/Parser/parsetok.c
index 554455dbc2bad..cb9472150f2ca 100644
--- a/Parser/parsetok.c
+++ b/Parser/parsetok.c
@@ -37,11 +37,13 @@ growable_comment_array_init(growable_comment_array *arr, size_t initial_size) {
 static int
 growable_comment_array_add(growable_comment_array *arr, int lineno, char *comment) {
     if (arr->num_items >= arr->size) {
-        arr->size *= 2;
-        arr->items = realloc(arr->items, arr->size * sizeof(*arr->items));
-        if (!arr->items) {
+        size_t new_size = arr->size * 2;
+        void *new_items_array = realloc(arr->items, new_size * sizeof(*arr->items));
+        if (!new_items_array) {
             return 0;
         }
+        arr->items = new_items_array;
+        arr->size = new_size;
     }
 
     arr->items[arr->num_items].lineno = lineno;