Re: puzzling JSON bug

Andrew Dunstan <andrew@dunslane.net> writes:
> David Wheeler has presented me with a nasty bug case.
> If I do this:

>     select '{"members": { "add": [3, 4]}}'::json #> '{members,add}';

> then I get a crash.

> If I comment out the pfree() at json.c:parse_object_field() lines 378-9 
> then I get back the right result but instead get a warning like this:

>     WARNING:  problem in alloc set ExprContext: bogus aset link in block
>     0x1efaa80, chunk 0x1efb1f0

> I'm not quite sure where I should go looking for what I've done wrong here.

Routine array-overrun memory stomp.  The chunk header data for "fname"'s
alloc chunk is being overwritten here:

Watchpoint 2: *(int *) 1075253088

Old value = 1074925616
New value = -1
0x50fe14 in get_array_start (state=0x40170e88) at jsonfuncs.c:688
688                     _state->array_level_index[lex_level] = -1;

It appears that lex_level is 2 but only enough room for 2 entries has
been allocated in array_level_index[].
        regards, tom lane