Re: [PATCH 2/2] exit_notify: kill the wrong capable(CAP_KILL) check

Serge E. Hallyn
2009-02-25T23:51:15Z

Quoting Oleg Nesterov (oleg@redhat.com):
> On 02/25, Serge E. Hallyn wrote:
> >
> > Quoting Oleg Nesterov (oleg@redhat.com):
> > > On 02/25, Serge E. Hallyn wrote:
> > > >
> > > > Quoting Oleg Nesterov (oleg@redhat.com):
> > > > > On 02/25, Serge E. Hallyn wrote:
> > > > > Can't understand... Why do you think CAP_KILL makes things better?
> > > > >
> > > > > Actually, how can it make any difference in this case?
> > > >
> > > > Well the check by itself isn't quite right - it seems to me it
> > > > should also check whether tsk->euid == parent->uid. But letting
> > > > an unprivileged task send SIGSTOP to a privileged one bc of
> > > > some fluke in the task hierarchy doesn't seem right.
> > >
> > > I think you misread this CAP_KILL check.
> > >
> > > It does not restrict the unprivileged task to send the signal. Instead,
> > > if the exiting task has CAP_KILL, we bypass other security checks.
> >
> > ? If the exiting task does not have CAP_KILL,
>
> _and_ (not "or") the execution domains for parent/chils are different,
>
> > we set the signal to
> > SIGCHILD (which is deemed safe).
>
> Yes. So why we should not set the signal to SIGCHLD if the task has
> CAP_KILL ?

Yeah, you're right, I wasn't thinking right.

> And again, the malicious application can exec the setuid binary before
> exit, in this case we never reset ->exit_signal (of course, unless
> that binary drops CAP_KILL).

Heh, thanks for taking the time to set me straight.

Acked-by: Serge Hallyn <serue@us.ibm.com>

Thanks.

-serge