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Fix use-after-free in json_encode() of a JsonSerializable object #22470

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Fix use-after-free in json_encode() of a JsonSerializable object #22470

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5 changes: 5 additions & 0 deletions ext/json/json_encoder.c
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Original file line number Diff line number Diff line change
Expand Up @@ -598,6 +598,8 @@ static zend_result php_json_encode_serializable_object(smart_str *buf, zval *val

ZEND_GUARD_PROTECT_RECURSION(guard, JSON);

GC_ADDREF(obj);

ZVAL_STRING(&fname, "jsonSerialize");

if (FAILURE == call_user_function(NULL, val, &fname, &retval, 0, NULL) || Z_TYPE(retval) == IS_UNDEF) {
Expand All @@ -610,6 +612,7 @@ static zend_result php_json_encode_serializable_object(smart_str *buf, zval *val
smart_str_appendl(buf, "null", 4);
}
ZEND_GUARD_UNPROTECT_RECURSION(guard, JSON);
OBJ_RELEASE(obj);
return FAILURE;
}

Expand All @@ -622,6 +625,7 @@ static zend_result php_json_encode_serializable_object(smart_str *buf, zval *val
smart_str_appendl(buf, "null", 4);
}
ZEND_GUARD_UNPROTECT_RECURSION(guard, JSON);
OBJ_RELEASE(obj);
return FAILURE;
}

Expand All @@ -638,6 +642,7 @@ static zend_result php_json_encode_serializable_object(smart_str *buf, zval *val

zval_ptr_dtor(&retval);
zval_ptr_dtor(&fname);
OBJ_RELEASE(obj);

return return_code;
}
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21 changes: 21 additions & 0 deletions ext/json/tests/gh21024.phpt
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@@ -0,0 +1,21 @@
--TEST--
GH-21024 (UAF in json_encode() when jsonSerialize()'s error handler frees the object)
--EXTENSIONS--
json
--FILE--
<?php
class Bar implements JsonSerializable {
public function jsonSerialize(): mixed {
trigger_error("free me");
return ['k' => 1];
}
}
$arr = [new Bar];
$ref = &$arr[0];
set_error_handler(function () use (&$ref) { $ref = null; });
var_dump(json_encode($arr));
echo "survived\n";
?>
--EXPECT--
string(9) "[{"k":1}]"
survived
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