bpo-40412: Nullify inittab_copy during finalization (pythonGH-19746)

Otherwise we leave a dangling pointer to free'd memory. If we then initialize a new interpreter in the same process and call PyImport_ExtendInittab, we will (likely) crash when calling PyMem_RawRealloc(inittab_copy, ...) since the pointer address is bogus. Automerge-Triggered-By: @brettcannon
skrah · May 1, 2020 · 64224a4 · 64224a4
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diff --git a/Misc/NEWS.d/next/C API/2020-05-01-17-28-04.bpo-40412.dE0D8N.rst b/Misc/NEWS.d/next/C API/2020-05-01-17-28-04.bpo-40412.dE0D8N.rst
@@ -0,0 +1 @@
+Nullify inittab_copy during finalization, preventing future interpreter initializations in an embedded situation from crashing. Patch by Gregory Szorc.
diff --git a/Python/import.c b/Python/import.c
@@ -298,6 +298,7 @@ _PyImport_Fini2(void)
 
     /* Free memory allocated by PyImport_ExtendInittab() */
     PyMem_RawFree(inittab_copy);
+    inittab_copy = NULL;
 
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 }