pgsql: Fix integer overflow in array_agg(), when the array grows too la

Fix integer overflow in array_agg(), when the array grows too large

If you accumulate many arrays full of NULLs, you could overflow
'nitems', before reaching the MaxAllocSize limit on the allocations.
Add an explicit check that the number of items doesn't grow too large.
With more than MaxArraySize items, getting the final result with
makeArrayResultArr() would fail anyway, so better to error out early.

Reported-by: Xint Code
Author: Heikki Linnakangas <heikki(dot)linnakangas(at)iki(dot)fi>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Backpatch-through: 14
Security: CVE-2026-6473

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e49e9590d984d60bfd95b438e5c6c07d08e9d661
Author: Heikki Linnakangas <heikki(dot)linnakangas(at)iki(dot)fi>

Modified Files
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src/backend/utils/adt/arrayfuncs.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)