agtype: fix substring() backend crash when start-offset is SQL NULL and length is supplied#2401
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MuhammadTahaNaveed merged 1 commit intoApr 20, 2026
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…nd length is supplied
age_substring() reads the null map produced by extract_variadic_args()
and rejects null offset/length with this guard:
if ((nargs == 2 && nulls[1]) ||
(nargs == 3 && nulls[2]))
{
ereport(ERROR, ..., errmsg("substring() offset or length cannot be null"));
}
The condition only checks nulls[1] in the 2-argument form. When the
caller passes `substring(str, null, len)` the function takes nargs = 3,
nulls[1] = true, but the guard above does not fire. Execution reaches
the numeric-parameter loop below, which reads args[1] through
DatumGetInt32 / DATUM_GET_AGTYPE_P without ever re-checking nulls[i].
The Datum in that slot is undefined, the dereference segfaults, and
the PostgreSQL backend terminates - not a query error but a
connection-level crash (apache#2386).
Widen the guard to nargs >= 2 && nulls[1] so it catches start-is-null
in both the 2-arg and 3-arg forms. nulls[2] is still only checked
when nargs == 3. No behaviour change on any non-null path; the
connection-crash case is now reported as a normal query error,
matching the intent the existing error message already implies.
Fixes apache#2386
MuhammadTahaNaveed
approved these changes
Apr 20, 2026
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Fixes #2386.
age_substring()reads the null map produced byextract_variadic_args()and rejects null offset/length with this guard:The condition only checks
nulls[1]in the 2-argument form. When the caller passessubstring(str, null, len)the function takesnargs = 3,nulls[1] = true, but the guard above does not fire. Execution reaches the numeric-parameter loop below, which readsargs[1]throughDatumGetInt32/DATUM_GET_AGTYPE_Pwithout ever re-checkingnulls[i]. The Datum in that slot is undefined, the dereference segfaults, and the PostgreSQL backend terminates — not a query error but a connection-level crash.This widens the guard to
nargs >= 2 && nulls[1]so it catches start-is-null in both the 2-arg and 3-arg forms.nulls[2]is still only checked whennargs == 3. No behaviour change on any non-null path; the connection-crash case is now reported as a normal query error, matching the intent the existing error message already implies.