From 52af12e9d908fd528bc347a0c01bb931d3c89010 Mon Sep 17 00:00:00 2001 From: John Naylor Date: Mon, 19 Oct 2026 11:29:41 +0700 Subject: [PATCH] Fix use-after-free in jsonb_set_lax for Const NULL new_value Commit a83586b5543 decided to scribble on the caller's fcinfo but failed to take into account that const arguments are written once at expression init and assumed never to change. The use_json_null branch overwrote fcinfo->args[2] with a jsonb null built in the per-tuple expression context. In later rows, args[2].isnull is still false and args[2].value still holds that pointer, but the per-tuple context has been reset. Later rows find args[2].isnull = false, short-circuit past the NULL handling at the top of the function, and jump straight to jsonb_set with the stale pointer regardless of their own null_value_treatment argument, which is never read. To fix, call jsonb_set through its own call frame instead. Arguments 0, 1 and 3 were already checked non-NULL above, so we can use DirectFunctionCall4. Add regression tests covering use_json_null followed by delete_key and return_target, and a multi-row default-treatment query. Reported-by: Evan Si Discussion: https://postgr.es/m/CANWCAZY-PS=ev8TiiV1j=NoR2xLopEL8fDq0fyQZahHiP5b+Pw@mail.gmail.com Backpatch-through: 14 --- src/backend/utils/adt/jsonfuncs.c | 8 +++++--- src/test/regress/expected/jsonb.out | 28 ++++++++++++++++++++++++++++ src/test/regress/sql/jsonb.sql | 10 ++++++++++ 3 files changed, 43 insertions(+), 3 deletions(-) diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c index 775da3c060d..3702c231d19 100644 --- a/src/backend/utils/adt/jsonfuncs.c +++ b/src/backend/utils/adt/jsonfuncs.c @@ -4954,9 +4954,11 @@ jsonb_set_lax(PG_FUNCTION_ARGS) newval = DirectFunctionCall1(jsonb_in, CStringGetDatum("null")); - fcinfo->args[2].value = newval; - fcinfo->args[2].isnull = false; - return jsonb_set(fcinfo); + return DirectFunctionCall4(jsonb_set, + PG_GETARG_DATUM(0), + PG_GETARG_DATUM(1), + newval, + PG_GETARG_DATUM(3)); } else if (strcmp(handle_val, "delete_key") == 0) { diff --git a/src/test/regress/expected/jsonb.out b/src/test/regress/expected/jsonb.out index 2332c5feba8..67952d64119 100644 --- a/src/test/regress/expected/jsonb.out +++ b/src/test/regress/expected/jsonb.out @@ -4883,6 +4883,34 @@ select jsonb_set_lax('{"a":1,"b":2}', '{b}', null, null_value_treatment => 'use_ {"a": 1, "b": null} (1 row) +-- multi-row cases with a constant NULL new_value +select jsonb_set_lax(j, '{a}', null, true, t) +from (values ('{"a":1}'::jsonb, 'use_json_null'), + ('{"a":1}'::jsonb, 'delete_key')) v(j, t); + jsonb_set_lax +--------------- + {"a": null} + {} +(2 rows) + +select jsonb_set_lax(j, '{a}', null, true, t) +from (values ('{"a":1}'::jsonb, 'use_json_null'), + ('{"a":1}'::jsonb, 'return_target')) v(j, t); + jsonb_set_lax +--------------- + {"a": null} + {"a": 1} +(2 rows) + +select jsonb_set_lax(j, '{a}', null) +from (values ('{"a":1}'::jsonb), ('{"a":2}'::jsonb), ('{"a":3}'::jsonb)) v(j); + jsonb_set_lax +--------------- + {"a": null} + {"a": null} + {"a": null} +(3 rows) + \pset null '' -- jsonb_insert select jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"'); diff --git a/src/test/regress/sql/jsonb.sql b/src/test/regress/sql/jsonb.sql index 30d34e2f71d..d96ab3dd7c9 100644 --- a/src/test/regress/sql/jsonb.sql +++ b/src/test/regress/sql/jsonb.sql @@ -1277,6 +1277,16 @@ select jsonb_set_lax('{"a":1,"b":2}', '{b}', null, null_value_treatment => 'retu select jsonb_set_lax('{"a":1,"b":2}', '{b}', null, null_value_treatment => 'delete_key') as delete_key; select jsonb_set_lax('{"a":1,"b":2}', '{b}', null, null_value_treatment => 'use_json_null') as use_json_null; +-- multi-row cases with a constant NULL new_value +select jsonb_set_lax(j, '{a}', null, true, t) +from (values ('{"a":1}'::jsonb, 'use_json_null'), + ('{"a":1}'::jsonb, 'delete_key')) v(j, t); +select jsonb_set_lax(j, '{a}', null, true, t) +from (values ('{"a":1}'::jsonb, 'use_json_null'), + ('{"a":1}'::jsonb, 'return_target')) v(j, t); +select jsonb_set_lax(j, '{a}', null) +from (values ('{"a":1}'::jsonb), ('{"a":2}'::jsonb), ('{"a":3}'::jsonb)) v(j); + \pset null '' -- jsonb_insert