Re: Fix out-of-bounds array indexing in JsonValueList

On Mon Oct 5, 2026 at 2:37 PM UTC, Greg Burd wrote:
>
>> On Oct 5, 2026, at 7:51 AM, Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
>>
>> On 29.09.26 07:50, Peter Eisentraut wrote:
>>> On 29.09.26 06:04, Tristan Partin wrote:
>>>> When compiling Postgres with -fsanitize=bounds, I get the following
>>>> errors in the log:
>>>>
>>>> jsonpath_exec.c:3832:3: runtime error: index 3 out of bounds for
>>>> type 'JsonbValue[2]'
>>>> jsonpath_exec.c:3918:10: runtime error: index 3 out of bounds for
>>>> type 'JsonbValue[2]'
>>>
>>> I've run into this problem as well, but only when compiling with -
>>> fstrict-flex-arrays=1. Is that what you are using?
>>>
>>> I would like to get this fixed, because this site appears to be the only
>>> problem of this kind. I will check your proposal.
>>
>> I played around with this a bit more and came up with the attached
>> solution, which is much simpler but requires that we don't go higher
>> than -fstrict-flex-arrays=1 -- which we can't anyway for other reasons
>> shown in the patch.
>> <v1.5-0001-Add-compiler-option-fstrict-flex-arrays-1.patch>
>
> Thanks Peter.
>
> I took a look. It seems to make the right trade-offs for where we are
> and add value where we can. I like the use of the union, too bad that
> struct isn't at the end so we could use FLEXIBLE_ARRAY_MEMBER.

I concur with Greg that it looks fine. Attached is another potential
solution if we didn't want treewide -fstrict-flex-arrays=1. I saw that
GCC supports a strict_flex_array attribute, which Clang does not
currently support. Your solution is probably better for that reason, but
I figured that I would post this anyway.

--
Tristan Partin
PostgreSQL Contributors Team
AWS (https://aws.amazon.com)