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

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

On 10/24/2012 10:18 AM, Corey Bryant wrote:
>
>
> 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?  We only
> want to prevent execve() after main_loop() is entered.  In other words
> we want to allow execve() caused by a command line option (e.g. -net
> tap) but we want to prevent execve() when it is the result of a monitor
> command (e.g. netdev_add tap).
>

Or perhaps we could put the check in net_init_tap() and only prevent the 
command when runstate != RUN_STATE_PRELAUNCH?

Note that we plan to only prevent the hotplug of net devices in the 
cases when execve() would be called.  So libvirt will still be able to 
pass an fd.

>>> ---
>>>   hmp.c |  6 ++++++
>>>   net.c | 13 +++++++++++++
>>>   2 files changed, 19 insertions(+)
>>>
>>> diff --git a/hmp.c b/hmp.c
>>> index 70bdec2..f258338 100644
>>> --- a/hmp.c
>>> +++ b/hmp.c
>>> @@ -1091,6 +1091,12 @@ void hmp_netdev_add(Monitor *mon, const QDict
>>> *qdict)
>>>       Error *err = NULL;
>>>       QemuOpts *opts;
>>>
>>> +#ifdef CONFIG_SECCOMP
>>> +    error_set(&err, ERROR_CLASS_GENERIC_ERROR,
>>> +            "Cannot hotplug TAP device when -sandbox is in effect");
>>> +    goto out;
>>> +#endif
>>> +
>>>       opts = qemu_opts_from_qdict(qemu_find_opts("netdev"), qdict,
>>> &err);
>>>       if (error_is_set(&err)) {
>>>           goto out;
>>> diff --git a/net.c b/net.c
>>> index ae4bc0d..a652ee9 100644
>>> --- a/net.c
>>> +++ b/net.c
>>> @@ -752,6 +752,12 @@ void net_host_device_add(Monitor *mon, const
>>> QDict *qdict)
>>>       Error *local_err = NULL;
>>>       QemuOpts *opts;
>>>
>>> +#ifdef CONFIG_SECCOMP
>>> +    error_set(&local_err, ERROR_CLASS_GENERIC_ERROR,
>>> +            "Cannot hotplug TAP device when -sandbox is in effect");
>>> +    goto out;
>>> +#endif
>>> +
>>>       if (!net_host_check_device(device)) {
>>>           monitor_printf(mon, "invalid host network device %s\n",
>>> device);
>>>           return;
>>> @@ -765,6 +771,7 @@ void net_host_device_add(Monitor *mon, const
>>> QDict *qdict)
>>>       qemu_opt_set(opts, "type", device);
>>>
>>>       net_client_init(opts, 0, &local_err);
>>> +out:
>>>       if (error_is_set(&local_err)) {
>>>           qerror_report_err(local_err);
>>>           error_free(local_err);
>>> @@ -800,6 +807,12 @@ int qmp_netdev_add(Monitor *mon, const QDict
>>> *qdict, QObject **ret)
>>>       QemuOptsList *opts_list;
>>>       QemuOpts *opts;
>>>
>>> +#ifdef CONFIG_SECCOMP
>>> +    error_set(&local_err, ERROR_CLASS_GENERIC_ERROR,
>>> +            "Cannot hotplug TAP device when -sandbox is in effect");
>>> +    goto exit_err;
>>> +#endif
>>> +
>>>       opts_list = qemu_find_opts_err("netdev", &local_err);
>>>       if (error_is_set(&local_err)) {
>>>           goto exit_err;
>>>
>>
>>
>>
>>
>

-- 
Regards,
Corey Bryant