Re: [PATCH v4 0/2] MR6021: nsiproxy.sys: Use pcblist64 sysctl to enumerate TCP & UDP connections on macOS.

[Brendan Shanks (＠bshanks)]

Brendan Shanks (@bshanks) commented about dlls/nsiproxy.sys/udp.c:
>  }
>
> #elif defined(HAVE_SYS_SYSCTL_H) && defined(UDPCTL_PCBLIST) && defined(HAVE_STRUCT_XINPGEN)
>      {
> -
>    int mib[] = { CTL_NET, PF_INET, IPPROTO_UDP, UDPCTL_PCBLIST };
>    size_t len = 0;
>    char *buf = NULL;
>    struct xinpgen *xig, *orig_xig;
>
> -
>    if (sysctl( mib, ARRAY_SIZE(mib), NULL, &len, NULL, 0 ) < 0)
>
> +#ifdef __APPLE__
> -
>    static int mib[CTL_MAXNAME];
> -
>    static size_t mib_len = 0;
> -
>    if (mib_len == 0)
> -
>    {
> -
>        mib_len = CTL_MAXNAME;

I'm not sure how likely it is, but if the first thread has set mib_len but sysctlnametomib() hasn't returned yet, another thread would call sysctl() with an invalid/empty mib.
Maybe use dispatch_once() or pthread_once() to fill the cache? Or don't cache at all?