Re: [Qemu-devel] [PATCH 4/4] Warning messages on net devices hotplug

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

On 10/25/2012 03:40 AM, Paolo Bonzini wrote:
> Il 24/10/2012 19:30, Corey Bryant ha scritto:
>>
>>
>> On 10/24/2012 11:45 AM, Paolo Bonzini wrote:
>>> Il 24/10/2012 17:39, Corey Bryant ha scritto:
>>>>
>>>>
>>>> On 10/24/2012 11:21 AM, Paolo Bonzini wrote:
>>>>> Il 24/10/2012 16:18, Corey Bryant ha scritto:
>>>>>>
>>>>>>
>>>>>> On 10/18/2012 11:15 AM, Paolo Bonzini wrote:
>>>>>>> Il 17/10/2012 15:15, Eduardo Otubo ha scritto:
>>>>>>>> With the inclusion of the new "double whitelist" seccomp filter,
>>>>>>>> Qemu
>>>>>>>> won't be able to execve() in runtime, thus, no hotplug net devices
>>>>>>>> allowed.
>>>>>>>>
>>>>>>>> Signed-off-by: Eduardo Otubo <otubo@linux.vnet.ibm.com>
>>>>>>>
>>>>>>> Please check this in net_init_tap instead.  When using libvirt,
>>>>>>> hotplug
>>>>>>> is done with a completely different mechanism that involves
>>>>>>> file-descriptor passing and does not require executing a helper.
>>>>>>>
>>>>>>> Paolo
>>>>>>>
>>>>>>
>>>>>> Are you sure net_init_tap() is the right place for this check?
>>>>>
>>>>> Yes, assuming there is a global that says whether the seccomp
>>>>> sandbox is
>>>>> in effect.  Even something like "if (sandbox_active && !tap->has_fd)
>>>>> error(...)" can be enough.
>>>>>
>>>>> Paolo
>>>>>
>>>>
>>>> What do you think about this? It moves the checks into the functions
>>>> that actually cause execve() to be called, and it only prevents the
>>>> commands after QEMU is done with initialization in main().
>>>
>>> It doesn't do error reporting correctly because these functions do not
>>> get an Error **.  If you change that and use error_setg instead of
>>> error_report, it should be okay.
>>
>> I just wanted to follow up on a few things..
>>
>> All of the following functions currently use qerror_report().  I'm
>> thinking conversion of these and sub-functions to pass an Error **
>> parameter should be a separate undertaking.
>>
>> net_init_nic
>> net_init_slirp
>> net_init_tap
>> net_init_socket
>> net_init_vde
>> net_init_dump
>> net_init_bridge
>> net_init_hubport
>
> Ok, but it should not be hard considering that the immediate caller of
> all these functions (net_client_init1) takes an Error **.  Please
> consider this for 1.4 at least.
>
>>> However, I really think what your testing is not
>>> runstate_is_prelaunch(), it is seccomp_effective().  If you structure
>>> the test like that, it also lets you eliminate the #ifdef (which in
>>> general we prefer to avoid).
>>
>> The reason for testing runstate_is_prelaunch() is because seccomp will
>> be effective during and after prelaunch.  The only difference is that a
>> more restrictive syscall whitelist will be in effect after prelaunch. So
>> perhaps the tests can be similar to the following so that we can get rid
>> of the preprocessor #ifdef:
>>
>> if (seccomp_is_effective() && !runstate_is_prelaunch()) {
>>      error_report("Cannot execute network helper from QEMU monitor "
>>                   "when -sandbox is in effect");
>>      return -1;
>> }
>
> Then you can make the seccomp query return many levels or flags, like
> SECCOMP_SANDBOX_ENABLED | SECCOMP_CAN_EXECVE.
>
> Paolo
>

True, we can do that.  I'll take that approach.  Thanks for the suggestion.

-- 
Regards,
Corey Bryant