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

[Paolo Bonzini <pbonzini@redhat.com>]

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