svn commit: r348509 - head/lib/libjail

[Kyle Evans]

(Resend to get the list address right- sorry Jamie!)

On Sun, Jun 2, 2019 at 9:04 AM Kyle Evans <kevans at freebsd.org> wrote:
>
> Author: kevans
> Date: Sun Jun  2 14:03:56 2019
> New Revision: 348509
> URL: https://svnweb.freebsd.org/changeset/base/348509
>
> Log:
>   jail_getid(3): add special-case immediate return for jid 0
>
>   As depicted in the comment: jid 0 always exists, but the lookup will fail as
>   it does not appear in the kernel's alljails list being a special jail. Some
>   callers will expect/rely on this, and we have no reason to lie because it
>   does always exist.
>
>   Reported by:  Stefan Hegnauer <stefan.hegnauer gmx ch>
>   MFC after:    soon (regression, breaks inspecting jail host bits, partial
>   revert)
>
> Modified:
>   head/lib/libjail/jail_getid.c
>
> Modified: head/lib/libjail/jail_getid.c
> ==============================================================================
> --- head/lib/libjail/jail_getid.c       Sun Jun  2 09:28:50 2019        (r348508)
> +++ head/lib/libjail/jail_getid.c       Sun Jun  2 14:03:56 2019        (r348509)
> @@ -54,6 +54,15 @@ jail_getid(const char *name)
>
>         jid = strtoul(name, &ep, 10);
>         if (*name && !*ep) {
> +               /*
> +                * jid == 0 is a special case; it will not appear in the
> +                * kernel's jail list, but naturally processes will be assigned
> +                * to it because it is prison 0.  Trivially return this one
> +                * without a trip to the kernel, because it always exists but
> +                * the lookup won't succeed.
> +                */
> +               if (jid == 0)
> +                       return jid;
>                 jiov[0].iov_base = __DECONST(char *, "jid");
>                 jiov[0].iov_len = sizeof("jid");
>                 jiov[1].iov_base = &jid;
>

On a related note- do we have a good reason for not exposing jid 0 via
jail_get(2) if that's what's requested and we're operating in prison0?
I have no historical context here, so it's not clear to me what issues
that might expose other than the issue of exposing a prison that's not
all that interesting.

Thanks,

Kyle Evans