[Bug]Heap-buffer-overflow read in JS_ReadFunctionBytecode atom-fixup loop (get_u32 past the bytecode buffer) (CWE-125)

/*
 * poc_driver.c - minimal PoC driver for QuickJS JS_ReadObject
 * deserialization bugs. Byte-for-byte mirrors the fuzz harness (harness.c):
 * the first byte of the input selects the JS_ReadObject flag combination,
 * the remaining bytes are the serialized bytecode/object stream.
 *
 * Build with AddressSanitizer against a QuickJS checkout:
 *   gcc -g -O1 -fsanitize=address -I. poc_driver.c quickjs.c libregexp.c \
 *       libunicode.c cutils.c dtoa.c quickjs-libc.c -lm -lpthread -ldl \
 *       -o poc_driver
 * Run:
 *   ./poc_driver <poc.bin>
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include "quickjs.h"
#include "quickjs-libc.h"
#include "cutils.h"     /* FALSE/TRUE */

static int nb_interrupts;

static int interrupt_handler(JSRuntime *rt, void *opaque)
{
    nb_interrupts++;
    return (nb_interrupts > 100);   /* abort runaway scripts */
}

int main(int argc, char **argv)
{
    FILE *f;
    long sz;
    uint8_t *buf;
    JSRuntime *rt;
    JSContext *ctx;
    JSValue obj, val;
    static const int flags_tbl[] = {
        0,                                          /* plain object      */
        JS_READ_OBJ_BYTECODE,                       /* bytecode function */
        JS_READ_OBJ_BYTECODE | JS_READ_OBJ_ROM_DATA,/* rom-data aliasing */
        JS_READ_OBJ_BYTECODE | JS_READ_OBJ_SAB,
        JS_READ_OBJ_BYTECODE | JS_READ_OBJ_REFERENCE,
        JS_READ_OBJ_BYTECODE | JS_READ_OBJ_ROM_DATA |
            JS_READ_OBJ_SAB | JS_READ_OBJ_REFERENCE,
    };

    if (argc < 2)
        return 1;
    f = fopen(argv[1], "rb");
    if (!f)
        return 1;
    fseek(f, 0, SEEK_END);
    sz = ftell(f);
    fseek(f, 0, SEEK_SET);
    buf = malloc((size_t)sz);
    if (fread(buf, 1, (size_t)sz, f) != (size_t)sz)
        return 1;
    fclose(f);

    rt = JS_NewRuntime();
    ctx = JS_NewContext(rt);
    JS_SetMemoryLimit(rt, 0x4000000);   /* 64 MB, same as fuzz harness */
    JS_SetMaxStackSize(rt, 0x10000);    /* 64 KB */
    JS_SetInterruptHandler(rt, interrupt_handler, NULL);

    /* First byte selects flags; the rest is the serialized stream. */
    obj = JS_ReadObject(ctx, buf + 1, (size_t)sz - 1, flags_tbl[buf[0] % 6]);
    if (JS_IsException(obj)) {
        JS_FreeValue(ctx, JS_GetException(ctx));
        return 0;
    }

    /* Execute the deserialized bytecode if it is a module/function. */
    if (JS_VALUE_GET_TAG(obj) == JS_TAG_MODULE) {
        if (JS_ResolveModule(ctx, obj) < 0) {
            JS_FreeValue(ctx, obj);
            JS_FreeValue(ctx, JS_GetException(ctx));
            return 0;
        }
        js_module_set_import_meta(ctx, obj, FALSE, TRUE);
    }
    val = JS_EvalFunction(ctx, obj);
    if (JS_IsException(val))
        JS_FreeValue(ctx, JS_GetException(ctx));
    else
        JS_FreeValue(ctx, val);
    return 0;
}