Re: [Qemu-devel] virtio-rng and fd passing

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

On 03/04/2013 05:29 AM, Daniel P. Berrange wrote:
> On Fri, Mar 01, 2013 at 04:14:40PM -0700, Eric Blake wrote:
>>> I understand the reason that fdsets exist (because NFS is stupid and
>>> doesn't support labeling).  But we aren't doing dynamic labeling of
>>> /dev/random and I strongly suspect it's not on NFS anyway.
>>>
>>> So why are we trying to pass fds here?
>>
>> Consistency - how do you write a policy that allows open("/dev/random")
>> while forbidding open("/nfs/...")?  It's much simpler to forbid open(),
>> even if /dev/random doesn't have any labeling issues.
>
> IIUC, it is actually pretty straightforward from a policy POV. Every
> filesystem has a unique type, and SELinux can make rules scoped to that
> filesystem type. That's how we have the 'virt_use_nfs' tunable already
> which only affects NFS.
>
> Daniel
>

Yes it should be simple, at least for SELinux.  I think all we need to 
do is remove open permission from the qemu process (svirt_t) on NFS 
files (files labeled with nfs_t).

Here's what I see for base qemu permissions on NFS files on Fedora 18:
$ sesearch  -A -s svirt_t -t nfs_t | grep ": file" | grep open
    allow virt_domain nfs_t : file { ioctl read write create getattr 
setattr lock append unlink link rename open } ;

And I think 'setsebool -P virt_use_nfs 0' will remove the open 
permission, so this may already be covered.

I'm not sure how easy it is for other MAC implementations.  Last I 
checked AppArmor didn't have the granularity of preventing open and 
allowing read/write.

-- 
Regards,
Corey Bryant