static char *gs_main_tempnames(gs_main_instance *minst)
{
    i_ctx_t *i_ctx_p = minst->i_ctx_p;
    ref *SAFETY;
    ref *tempfiles;
    ref keyval[2];      /* for key and value */
    char *tempnames = NULL;
    int i;
    int idict;
    int len = 0;
    const byte *data = NULL;
    uint size;
    if (minst->init_done >= 2) {
        if (dict_find_string(systemdict, "SAFETY", &SAFETY) <= 0 ||
            dict_find_string(SAFETY, "tempfiles", &tempfiles) <= 0)
            return NULL;
        /* get lengths of temporary filenames */
        idict = dict_first(tempfiles);
        while ((idict = dict_next(tempfiles, idict, &keyval[0])) >= 0) {
            if (obj_string_data(minst->heap, &keyval[0], &data, &size) >= 0)
                len += size + 1;
        }
        if (len != 0)
            tempnames = (char *)malloc(len+1);
        if (tempnames) {
            memset(tempnames, 0, len+1);
            /* copy temporary filenames */
            idict = dict_first(tempfiles);
            i = 0;
            while ((idict = dict_next(tempfiles, idict, &keyval[0])) >= 0) {
                if (obj_string_data(minst->heap, &keyval[0], &data, &size) >= 0) {
                    memcpy(tempnames+i, (const char *)data, size);
                    i+= size;
                    tempnames[i++] = '\0';
                }
            }
        }
    }
    return tempnames;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.