Re: [PATCH] Define CAP_SYSLOG

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Matthew Helsley (matt.helsley@gmail.com):
> On Sat, Mar 13, 2010 at 10:35 PM, Serge E. Hallyn <serue@us.ibm.com> wrote:
> > Quoting Michael Kerrisk (mtk.manpages@googlemail.com):
> >> > There is one downside to this patch:  If some site or distro currently
> >> > has syslogd/whatever running as a non-root user with cap_sys_admin+pe,
> >> > then it will need to be changed to run with cap_syslog+pe.  I don't
> >> > know if there are such sites, or if that concern means we should take
> >> > a different approach to introducing this change, or simply refuse this
> >> > change.
> >>
> >> *If* this is a problem, would the way to address it not be to permit
> >> syslog if the caller has *either* CAP_SYS_ADMIN or CAP_SYSLOG? (The
> >> only weakness I see in this idea is that it fails to lighten the
> >> hugely overlaoded CAP_SYS_ADMIN.)
> >
> > Which becomes a very big weakness because it won't allow a
> > container to be started with cap_sys_admin but not cap_syslog
> > in its capability bounding set.
> >
> > So, if it is deemed a problem, then the alternative will be to
> > introduce a syslog namespace.  Container setup can then create
> > a new syslog namespace, and can no longer read or clear the
> > host's syslog.
> >
> > thanks,
> > -serge
> 
> Would it make sense to warn once when CAP_SYS_ADMIN permits what
> CAP_SYSLOG will be used for in the future? Something like:
> 
> -            type != SYSLOG_ACTION_SIZE_BUFFER) && !capable(CAP_SYS_ADMIN))
> +            type != SYSLOG_ACTION_SIZE_BUFFER) &&
> !(capable(CAP_SYSLOG)||capable(CAP_SYS_ADMIN))) {
> +             WARN_ONCE(capable(CAP_SYS_ADMIN) &&
> !capable(CAP_SYSLOG), "CAP_SYS_ADMIN will not permit syslog
> configuration in the near future. Please switch your code to
> CAP_SYSLOG\n");
>                return -EPERM;
> +        }
>        return 0;

Good idea - though I'd prefer to WARN_ONCE and then deny :)  If we log
and allow, the log msg will be ignored.

> After a period of time allowing userspace apps to transition to
> CAP_SYSLOG remove the CAP_SYS_ADMIN portions. Of course this won't fix
> containers for that transition period but it would avoid a sudden
> change of what CAP_SYS_ADMIN allows.
> 
> > So, if it is deemed a problem, then the alternative will be to
> > introduce a syslog namespace.  Container setup can then create
> > a new syslog namespace, and can no longer read or clear the
> > host's syslog.
> 
> Yup, this is also an option. Possibly better as it doesn't involved
> changing the meaning of a overly-[ab]used capability bit and wouldn't
> require a transition period.

Still I can definately see a case where you want the container to
be in the host's syslog for simplicity, but not be able to clear it.

-serge