Date: Fri, 7 Jan 2011 11:53:06 +0100 From: Gary Jennejohn <gljennjohn@googlemail.com> To: Garrett Cooper <gcooper@FreeBSD.org> Cc: FreeBSD Current <freebsd-current@freebsd.org>, Ed Schouten <ed@freebsd.org>, Craig Leres <leres@ee.lbl.gov> Subject: Re: xterm -C and TIOCCONS vs. PRIV_TTY_CONSOLE Message-ID: <20110107115306.2bfd15d8@ernst.jennejohn.org> In-Reply-To: <AANLkTi=gHW=ShE_p=LPj-k1FC1e2-SpAWxyAsD=2MF7o@mail.gmail.com> References: <4D268557.2090704@ee.lbl.gov> <AANLkTinWu9-ZP_D0ShfvAtDpbuRPWa81hLb3hw=OQoxX@mail.gmail.com> <4D268B98.3080906@ee.lbl.gov> <AANLkTinEG7SJ80Ljrecg%2Bq_TOGy8bicKVUPZRRpzieV%2B@mail.gmail.com> <4D269B72.4040709@ee.lbl.gov> <AANLkTi=gHW=ShE_p=LPj-k1FC1e2-SpAWxyAsD=2MF7o@mail.gmail.com>
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On Thu, 6 Jan 2011 21:09:05 -0800
Garrett Cooper <gcooper@FreeBSD.org> wrote:
> On Thu, Jan 6, 2011 at 8:49 PM, Craig Leres <leres@ee.lbl.gov> wrote:
> > On 01/06/11 20:05, Garrett Cooper wrote:
> >> Just to make sure we're both on the same page:
> >>
> >> $ grep xterm /etc/ttys
> >> ttyv0 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv1 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv2 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv3 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv4 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv5 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv6 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv7 "/usr/libexec/getty Pc" xterm on secure
> >> ttyv8 "/usr/local/bin/xdm -nodaemon" xterm off secure
> >
> > No, that's not what mine looks like. I changed it to match and rebooted
> > but it doesn't help with the TIOCCONS issue.
> >
> > When I run xinit, it starts up the xterm -C which does a TIOCCONS. The
> > 8.1 kernel checks for PRIV_TTY_CONSOLE which isn't set and denies the
> > request:
> >
> > case TIOCCONS:
> > /* Set terminal as console TTY. */
> > if (*(int *)data) {
> > error = priv_check(td, PRIV_TTY_CONSOLE);
> > if (error)
> > return (error);
> >
> > /*
> > * XXX: constty should really need to be locked!
> > * XXX: allow disconnected constty's to be stolen!
> > */
> >
> > if (constty == tp)
> > return (0);
> > if (constty != NULL)
> > return (EBUSY);
> >
> > tty_unlock(tp);
> > constty_set(tp);
> > tty_lock(tp);
> > } else if (constty == tp) {
> > constty_clear();
> > }
> > return (0);
> >
> >
> > There's nothing I see in all of /usr/src that turns on PRIV_TTY_CONSOLE
> > in any case. You could rewrite the above like this:
> >
> > case TIOCCONS:
> > /* Set terminal as console TTY. */
> > if (*(int *)data) {
> > return (EPERM)
> > } else if (constty == tp) {
> > constty_clear();
> > }
> > return (0);
> >
> > and it won't change any behavior.
>
> Ok -- figured I would ask about the obvious. I wish I could help
> you further right now, but unfortunately I have a lot on my plate.
> I've CCed ed@ and the list again so that someone else might be able to
> chime in and help you further.
>
I'd say there are a few factors which come into play here:
1) the setting of security.bsd.suser_enabled, default 1
2) kern_tty.c checking for a cred which is never set
3) whether xterm is setuid root
a) suser_enabled is almost guaranteed to be 1 on OP's system since just
about nothing works when it is set to 0 (tried that)
b) the kernel checking for the cred PRIV_TTY_CONSOLE is probably a bug
since it never gets set anywhere. However, this usually isn't noticed
because
c) xterm is generally setuid root and the logic in priv_check_cred() in
kern_priv.c doesn't even look at what cred is set to, except for a few
which can raise some limits, because cr_uid is 0 (super user)
So, the crux of the matter is whether OP's xterm is setuid root. My
xterm is and I can run 'xterm -C' without a problem.
--
Gary Jennejohn
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