Re: CAP_SYSLOG, 2.6.38 and user space

[david]

On Thu, 3 Feb 2011, Serge E. Hallyn wrote:

> Quoting Gergely Nagy (algernon@xxxxxxxxxx):
> > On Thu, 2011-02-03 at 15:32 +0000, Serge E. Hallyn wrote:
> > > > Back in november, a patch was merged into the kernel (in  commit
> > > > ce6ada35bdf710d16582cc4869c26722547e6f11), that splits CAP_SYSLOG out of
> > > > CAP_SYS_ADMIN.
> > > >
> > > > Sadly, this has an unwelcomed consequence, that any userspace syslogd
> > > > that formerly used CAP_SYS_ADMIN will stop working, unless upgraded, or
> > > > otherwise adapted to the change.
> > > >
> > > > However, updating userspace isn't that easy, either, if one wants to
> > > > support multiple kernels with the same userspace binary: pre-2.6.38, one
> > > > needs CAP_SYS_ADMIN, but later kernels will need CAP_SYS_ADMIN. It would
> > > > be trivial to keep both, but that kind of defeats the purpose of
> > > > CAP_SYSLOG,
> > >
> > > The idea would be to only use both when you detect a possibly older
> > > kernel.
> >
> > I was considering that, but... how do I reliably detect an older kernel?
> > So far, I didn't find a reliable way with which I can detect a kernel
> > version at run-time (apart from parsing utsname)
>
> ...  Why not parse utsname?

because the name may be different on different systems, a generic software 
package is not going to be able to interpret them all.

> > > However, you're right of course, I really should have provided some way
> > > for userspace to click 'ok, got the message, now continue anyway because
> > > I'm running older userspace for now,'  i.e. a sysctl perhaps.
> > >
> > > Sorry about the trouble.  Here is a patch to just warn for now, with
> > > the changelog showing what i intend to push next.
> > >
> > > sorry again,
> > > -serge
> > >
> > > From 2d7408541dd3a6e19a4265b028233789be6a40f4 Mon Sep 17 00:00:00 2001
> > > From: Serge Hallyn <serge@peq.(none)>
> > > Date: Thu, 3 Feb 2011 09:26:15 -0600
> > > Subject: [PATCH 1/1] cap_syslog: don't refuse cap_sys_admin for now
> > >
> > > At 2.6.39 or 2.6.40, let's add a sysctl which defaults to 0.  When
> > > 0, refuse if cap_sys_admin, if 1, then allow.  This will allow
> > > users to acknowledge (permanently, if they must, using /etc/sysctl.conf)
> > > that they've seen the syslog message about cap_sys_admin being
> > > deprecated for syslog.
> >
> > Could we have it the other way around, at least for a while? Otherwise,
>
> Sure.
>
> So long as there is a definite path toward eventually having syslog
> with CAP_SYS_ADMIN be denied.

I can see what you would want to allow for a syslog daemon to have 
CAP_SYSLOG without needing to have CAP_SYS_ADMIN, but why do you see it as 
important to deny the ability if someone has CAP_SYS_ADMIN?

David Lang

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