From 3032fd443e32afd049682b8346872d534718b6ae Mon Sep 17 00:00:00 2001 From: John Naylor Date: Thu, 15 Oct 2026 08:54:43 +0700 Subject: [PATCH v1] 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. Discussion: https://postgr.es/m/ Reported-by: Evan Si 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 adbafd0ecd3..274ed9d3184 100644 --- a/src/backend/utils/adt/jsonfuncs.c +++ b/src/backend/utils/adt/jsonfuncs.c @@ -4934,9 +4934,11 @@ 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 82c31e2962b..615f6232b0d 100644 --- a/src/test/regress/expected/jsonb.out +++ b/src/test/regress/expected/jsonb.out @@ -4915,6 +4915,34 @@ 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 610ee28b97f..be766f4fe53 100644 --- a/src/test/regress/sql/jsonb.sql +++ b/src/test/regress/sql/jsonb.sql @@ -1283,6 +1283,16 @@ 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 -- 2.55.0