Horton

Re: BUG #17858: ExecEvalArrayExpr() leaves uninitialised memory for multidim array with nulls

Alexander Law <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Richard Guo <guofenglinux@gmail.com>, pgsql-bugs@lists.postgresql.org
Date: 2023-03-21T13:00:00Z
Lists: pgsql-bugs 
Hi Richard,
21.03.2023 14:52, Richard Guo wrote:
> Nice catch.  This can also be seen on master.
>
> I searched the codes a little bit and found that in array_set_slice()
> and array_set_element() the 'newarray' is allocated with palloc0 and
> then the nulls bitmap is zeroed with
>
>  MemSet(nullbitmap, 0, (nitems + 7) / 8);
>
> if havenulls is true.  I wonder if we can do the same here.

I'm afraid that zeroing only bytes behind nitems bits is not enough, as outDatum() doesn't bother to calculate the exact 
size of nulls bitmap, it just outputs all bytes of a datum (40 bytes in that case):
    length = datumGetSize(value, typbyval, typlen);
...
             for (i = 0; i < length; i++)
                appendStringInfo(str, "%d ", (int) (s[i]));

Best regards,
Alexander

Commits

  1. Fix oversights in array manipulation.

  2. Fix array- and path-creating functions to ensure padding bytes are zeroes.