src/freon.c mishandles 3rd arg to open functions (mode)

[vapier]

the open signature is:
int open(const char *pathname, int flags, ...);

and mode is only passed in for certain flags (O_CREAT and O_TMPFILE), so trying to extract it otherwise is undefined behavior. you might get garbage, or you might crash.

freon.c assumes it's always passed in:

int open(const char *pathname, int flags, ...) {
    if (!orig_open) preload_init();

    va_list argp;
    va_start(argp, flags);
    mode_t mode = va_arg(argp, mode_t);
    va_end(argp);

same for open64.

you can do something instead like:

int open(const char *pathname, int flags, ...) {
    if (!orig_open) preload_init();

    mode_t mode = 0;
    va_list argp;
    va_start(argp, flags);
    if (flags & (O_CREAT | O_TMPFILE))
        mode = va_arg(argp, mode_t);
    va_end(argp);