From cb98b23da3a687f842a559bcc0e577b2447f4ba4 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 97cc3d60340..d71c052cd5b 100644 --- a/src/backend/utils/adt/jsonfuncs.c +++ b/src/backend/utils/adt/jsonfuncs.c @@ -4935,9 +4935,11 @@ 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 fc27adb913b..5ef6f8e4a2f 100644 --- a/src/test/regress/expected/jsonb.out +++ b/src/test/regress/expected/jsonb.out @@ -4935,6 +4935,34 @@ 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 a13e904a9e2..a200cbf8642 100644 --- a/src/test/regress/sql/jsonb.sql +++ b/src/test/regress/sql/jsonb.sql @@ -1294,6 +1294,16 @@ 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