Crash when passing empty json object to filterx for parsing

[mitzkia]

axosyslog version:

(dbld)micek@DESKTOP-0E9OKG3:/install/sbin$ ./syslog-ng -V
axosyslog 4 (4.8.0.217.g17b1fd8)
Config version: 4.2
Installer-Version: 4.8.0.217.g17b1fd8
Revision:
Compile-Date: Aug 26 2024 05:05:23

Reproduction:
Axosyslog got crahsed when started with the following configuration:

@version: 4.2

source genmsg {
    example-msg-generator(
        num(1)
        template("foobar")
        values(
            "values.json" => json(''),
        )
    );
};

destination dest_true {
        file (dest-true.log);
};

log {
    source(genmsg);
    if {
        filterx { 
            $olr = otel_logrecord();
            $olr.body = ${values.json};
            $MSG = format_json($olr.body);  
        };
        destination(dest_true);
    };
};

axosyslog start:

[2024-08-31T06:14:09.547009] syslog-ng starting up; version='4.8.0.217.g17b1fd8'
[2024-08-31T06:14:09.547009] Running application hooks; hook='2'
[2024-08-31T06:14:09.547009] Setting value; name='values.json', value='', type='json', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] Setting value; name='MESSAGE', value='-- Generated message. --', type='string', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] Setting value; name='MESSAGE', value='foobar', type='string', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] Incoming generated message; msg='foobar'
[2024-08-31T06:14:09.547009] >>>>>> Source side message processing begin; location='aaa.conf:5:5', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] Setting value; name='HOST_FROM', value='DESKTOP-0E9OKG3', type='string', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] Setting value; name='HOST', value='DESKTOP-0E9OKG3', type='string', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] Setting tag; name='.source.genmsg', value='1', msg='0x563bc7be50d0'
[2024-08-31T06:14:09.547009] Setting value; name='SOURCE', value='genmsg', type='string', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] >>>>>> filterx rule evaluation begin; rule='#anon-filter0', location='aaa.conf:21:16', msg='0x563bc7be50d0', rcptid='1199'
[2024-08-31T06:14:09.547009] FILTERX ESTEP; expr='aaa.conf:22:13|       $olr = otel_logrecord()', value='', truthy='1', type='otel_logrecord'
Segmentation fault

gdb:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff62cd084 in filterx_object_is_type (object=0x0, type=0x7ffff7fba2e0 <filterx_type_dict>) at /source/lib/filterx/filterx-object.h:106
warning: Source file is more recent than executable.
106       FilterXType *self_type = object->type;
(gdb) bt
#0  0x00007ffff62cd084 in filterx_object_is_type (object=0x0, type=0x7ffff7fba2e0 <filterx_type_dict>) at /source/lib/filterx/filterx-object.h:106
#1  0x00007ffff62ceb3d in syslogng::grpc::otel::filterx::OtelKVListField::FilterXObjectSetter (this=0x7ffff630fb80 <syslogng::grpc::otel::filterx::otel_kvlist_converter>, message=0x555555621d10, reflectors=..., object=0x55555561e780,
    assoc_object=0x7fffffffdde8) at /source/modules/grpc/otel/filterx/object-otel-kvlist.cpp:515
#2  0x00007ffff62ca7bf in syslogng::grpc::otel::ProtobufField::Set (this=0x7ffff630fb80 <syslogng::grpc::otel::filterx::otel_kvlist_converter>, message=0x555555621d10, fieldName="kvlist_value", object=0x55555561e780, assoc_object=0x7fffffffdde8)
    at /source/modules/grpc/otel/filterx/protobuf-field.hpp:93
#3  0x00007ffff62d7166 in syslogng::grpc::otel::AnyField::FilterXObjectDirectSetter (this=0x7ffff630feb0 <syslogng::grpc::otel::any_field_converter>, anyValue=0x555555621d10, object=0x55555561e780, assoc_object=0x7fffffffdde8)
    at /source/modules/grpc/otel/filterx/otel-field.cpp:258
#4  0x00007ffff62d6985 in syslogng::grpc::otel::AnyField::FilterXObjectSetter (this=0x7ffff630feb0 <syslogng::grpc::otel::any_field_converter>, message=0x5555555e9f98, reflectors=..., object=0x55555561e780, assoc_object=0x7fffffffdde8)
    at /source/modules/grpc/otel/filterx/otel-field.cpp:124
#5  0x00007ffff62ca7bf in syslogng::grpc::otel::ProtobufField::Set (this=0x7ffff630feb0 <syslogng::grpc::otel::any_field_converter>, message=0x5555555e9f98, fieldName="body", object=0x55555561e780, assoc_object=0x7fffffffdde8)
    at /source/modules/grpc/otel/filterx/protobuf-field.hpp:93
#6  0x00007ffff62c9489 in syslogng::grpc::otel::filterx::LogRecord::set_subscript (this=0x5555555e9f90, key=0x555555567ed0, value=0x7fffffffdee8) at /source/modules/grpc/otel/filterx/object-otel-logrecord.cpp:85
#7  0x00007ffff62c9853 in _set_subscript (s=0x55555561e720, key=0x555555567ed0, new_value=0x7fffffffdee8) at /source/modules/grpc/otel/filterx/object-otel-logrecord.cpp:184
#8  0x00007ffff7edeec0 in _setattr (s=0x55555561e720, attr=0x555555567ed0, new_value=0x7fffffffdee8) at /source/lib/filterx/object-dict-interface.c:149
#9  0x00007ffff7ed2273 in filterx_object_setattr (self=0x55555561e720, attr=0x555555567ed0, new_value=0x7fffffffdee8) at /source/lib/filterx/filterx-object.h:230
#10 0x00007ffff7ed2413 in _eval (s=0x555555567f00) at /source/lib/filterx/expr-setattr.c:60
#11 0x00007ffff7ee2d1e in filterx_expr_eval (self=0x555555567f00) at /source/lib/filterx/filterx-expr.h:73
#12 0x00007ffff7ee2d49 in _eval_expr (expr=0x555555567f00, result=0x7fffffffdfe0) at /source/lib/filterx/expr-compound.c:43
#13 0x00007ffff7ee3006 in _eval_exprs (self=0x55555556ba90, result=0x7fffffffdfe0) at /source/lib/filterx/expr-compound.c:89
#14 0x00007ffff7ee3060 in _eval (s=0x55555556ba90) at /source/lib/filterx/expr-compound.c:102
#15 0x00007ffff7ed701b in filterx_expr_eval (self=0x55555556ba90) at /source/lib/filterx/filterx-expr.h:73
#16 0x00007ffff7ed7480 in filterx_eval_exec (context=0x7fffffffe0b0, expr=0x55555556ba90, msg=0x55555561e100) at /source/lib/filterx/filterx-eval.c:198
#17 0x00007ffff7edfa3f in log_filterx_pipe_queue (s=0x5555556135e0, msg=0x55555561e100, path_options=0x7fffffffe090) at /source/lib/filterx/filterx-pipe.c:65
#18 0x00007ffff7e685bb in log_pipe_queue (s=0x5555556135e0, msg=0x55555561e100, path_options=0x7fffffffe1f0) at /source/lib/logpipe.h:485
#19 0x00007ffff7e68820 in log_multiplexer_queue (s=0x55555561aec0, msg=0x55555561e100, path_options=0x7fffffffe3c0) at /source/lib/logmpx.c:115
#20 0x00007ffff7e685bb in log_pipe_queue (s=0x55555561aec0, msg=0x55555561e100, path_options=0x7fffffffe3c0) at /source/lib/logpipe.h:485
#21 0x00007ffff7e683f6 in log_pipe_forward_msg (self=0x55555561a260, msg=0x55555561e100, path_options=0x7fffffffe3c0) at /source/lib/logpipe.h:439
#22 0x00007ffff7e685d4 in log_pipe_queue (s=0x55555561a260, msg=0x55555561e100, path_options=0x7fffffffe3c0) at /source/lib/logpipe.h:489
#23 0x00007ffff7e683f6 in log_pipe_forward_msg (self=0x555555619dc0, msg=0x55555561e100, path_options=0x7fffffffe3c0) at /source/lib/logpipe.h:439
#24 0x00007ffff7e685d4 in log_pipe_queue (s=0x555555619dc0, msg=0x55555561e100, path_options=0x7fffffffe3c0) at /source/lib/logpipe.h:489
#25 0x00007ffff7e68820 in log_multiplexer_queue (s=0x555555619f80, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logmpx.c:115
#26 0x00007ffff7e5f050 in log_pipe_queue (s=0x555555619f80, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:485
#27 0x00007ffff7e5ee8b in log_pipe_forward_msg (self=0x555555619bf0, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:439
#28 0x00007ffff7e5f069 in log_pipe_queue (s=0x555555619bf0, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:489
#29 0x00007ffff7e5ee8b in log_pipe_forward_msg (self=0x555555619aa0, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:439
#30 0x00007ffff7e5f069 in log_pipe_queue (s=0x555555619aa0, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:489
#31 0x00007ffff7e5ee8b in log_pipe_forward_msg (self=0x5555555ee6e0, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:439
#32 0x00007ffff7e5f9e4 in log_src_driver_queue_method (s=0x5555555ee6e0, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/driver.c:238
#33 0x00007ffff7e6f7f9 in log_pipe_queue (s=0x5555555ee6e0, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:485
#34 0x00007ffff7e6f634 in log_pipe_forward_msg (self=0x55555561b870, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:439
#35 0x00007ffff7e7174e in log_source_queue (s=0x55555561b870, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logsource.c:674
#36 0x00007ffff7e6f7f9 in log_pipe_queue (s=0x55555561b870, msg=0x55555561e100, path_options=0x7fffffffe730) at /source/lib/logpipe.h:485
#37 0x00007ffff7e71391 in log_source_post (self=0x55555561b870, msg=0x55555561e100) at /source/lib/logsource.c:593
#38 0x00007ffff507d5e1 in _send_generated_message (self=0x55555561b870) at /source/modules/examples/sources/msg-generator/msg-generator-source.c:131
#39 0x00007ffff507d606 in _timer_expired (cookie=0x55555561b870) at /source/modules/examples/sources/msg-generator/msg-generator-source.c:139
#40 0x00007ffff7f34ec4 in iv_run_timers (st=0x555555561960) at /source/lib/ivykis/src/iv_timer.c:124
#41 0x00007ffff7f38266 in iv_main () at /source/lib/ivykis/src/iv_main_posix.c:98
#42 0x00007ffff7e7a500 in main_loop_run (self=0x7ffff7fbc460 <main_loop>) at /source/lib/mainloop.c:763
#43 0x0000555555556aac in main (argc=1, argv=0x7fffffffea18) at /source/syslog-ng/main.c:345