[PATCH] getlogin_r: return early when linux sentinel value is set

[Jesse Hathaway]

This is my first time submitting a patch, so any feedback would be
very much appreciated.

On Fri, Mar 16, 2018 at 11:18 AM, Jesse Hathaway <jesse@mbuki-mvuki.org> wrote:
> When there is no login uid Linux sets /proc/self/loginid to the sentinel
> value of 4294967295. If this is set we can return early and avoid
> needlessly looking up the sentinel value in any configured nss
> databases.
>
> diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c
> b/sysdeps/unix/sysv/linux/getlogin_r.c
> index 73ea14c8f9..43f55a2188 100644
> --- a/sysdeps/unix/sysv/linux/getlogin_r.c
> +++ b/sysdeps/unix/sysv/linux/getlogin_r.c
> @@ -55,6 +55,12 @@ __getlogin_r_loginuid (char *name, size_t namesize)
>     endp == uidbuf || *endp != '\0'))
>      return -1;
>
> +  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
> +     value of 4294967295, so check if the value is set and return early to
> +     avoid making unneeded nss lookups. */
> +  if (uid == 4294967295)
> +    return ENXIO;
> +
>    struct passwd pwd;
>    struct passwd *tpwd;
>    int result = 0;