jsonb iterator not fully initialized

I got this error message via -fsanitized=undefined:

jsonfuncs.c:5169:12: runtime error: load of value 127, which is not a
valid value for type '_Bool'

The query was

select ts_headline('{}'::jsonb, tsquery('aaa & bbb'));

This calls the C function ts_headline_jsonb_byid_opt(), which calls
transform_jsonb_string_values(), which calls

it = JsonbIteratorInit(&jsonb->root);
is_scalar = it->isScalar;

but it->isScalar is not always initialized by JsonbIteratorInit(). (So
the 127 is quite likely clobbered memory.)

It can be fixed this way:

--- a/src/backend/utils/adt/jsonb_util.c
+++ b/src/backend/utils/adt/jsonb_util.c
@@ -901,7 +901,7 @@ iteratorFromContainer(JsonbContainer *container,
JsonbIterator *parent)
{
JsonbIterator *it;

- it = palloc(sizeof(JsonbIterator));
+ it = palloc0(sizeof(JsonbIterator));
it->container = container;
it->parent = parent;
it->nElems = JsonContainerSize(container);

It's probably not a problem in practice, since the isScalar business is
apparently only used in the array case, but it's dubious to leave things
uninitialized like this nonetheless.

--
Peter Eisentraut http://www.2ndQuadrant.com/
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