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Re: [libvirt] [PATCH 4/3] Control LXC capabilities

On Tue, Jun 23, 2009 at 07:45:34PM -0700, Casey Schaufler wrote:
> Serge E. Hallyn wrote:
> > Quoting Daniel P. Berrange (berrange redhat com):
> >   
> >> This patch updates the LXC driver to make use of libcap-ng for managing
> >> process capabilities. Previously Ryota Ozaki had provided code to remove
> >> the CAP_BOOT  capabilities inside the container, preventing host reboots.
> >> In addition to that one, I believe we should be removing ability to
> >> load kernel modules, change the system clock and changing audit/MAC.
> >> So this patch also clears the following:
> >>
> >>      CAP_SYS_MODULE, /* No kernel module loading */
> >>      CAP_SYS_TIME, /* No changing the clock */
> >>      CAP_AUDIT_CONTROL, /* No messing with auditing */
> >>      CAP_AUDIT_WRITE, /* No messing with auditing */
> >>      CAP_MAC_ADMIN, /* No messing with LSM */
> >>      CAP_MAC_OVERRIDE, /* No messing with LSM */
> >>     
> What is going to run inside your container? Turning off the MAC
> capabilities can seriously limit the programs that can run inside
> it. If you can't drop CAP_DAC_OVERRIDE or CAP_KILL it's unlikely
> that it makes sense to drop CAP_MAC_OVERRIDE. Similarly, if you
> can't drop CAP_FOWNER or CAP_CHOWN you'll probably be ill advised
> to forgo CAP_MAC_ADMIN.

The containers are all run with 


and each has a private filesystem setup. Thus there is no need to 
restrict things like CAP_FOWNER/CHOWN, since the only files the
container process can access are those within its private FS.
Likewise CAP_KILL is ok, since CLONE_NEWPID ensures the container 
can only see its own processes, and none of those from the host.

Given those CLONE_* flags being set,  is it safe to allow a
container to have CAP_MAC_ADMIN/CAP_MAC_OVERRIDE capabilities ?
I was concerned that those capabilities may still allow the
container to perform changes that would impact MAC settings 
for the host as a hole, and not be confined. If that's not
the case, then I will change the patch to not clear those

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