Re: [Qemu-devel] [PATCH v3 3/3] seccomp: set the seccomp filter to all threads

[Marc-André Lureau]

Hi

On Wed, Aug 22, 2018 at 6:07 PM, Eric Blake <address@hidden> wrote:
> On 08/22/2018 10:58 AM, Marc-André Lureau wrote:
>
>>> At this point you might as well not bother using seccomp at all. The
>>> thread that is confined merely needs to scribble something into the
>>> stack of the unconfined thread and now it can do whatever it wants.
>>
>>
>> Actually, that message is incorrect, it should rather be "not all
>> threads will be filtered" (as described in commit message).
>>
>>> IMHO we need to find a way to get the policy to apply to those other
>>> threads.
>>
>>
>> That's what the patch is about ;)
>
>
> In other words, this patch is patching the gaping security hole that already
> exists, but...
>
>>>> +++ b/qemu-options.hx
>>>> @@ -3864,6 +3864,8 @@ Disable set*uid|gid system calls
>>>>   Disable *fork and execve
>>>>   @item address@hidden
>>>>   Disable process affinity and schedular priority
>>>> address@hidden address@hidden
>>>> +Apply seccomp filter to all threads (default is auto, and will warn if
>>>> fail)
>>>
>>>
>>> IMHO this should never exist, as setting "tsync" to anything other
>>> than "yes", is akin to just running without any sandbox.
>>
>>
>> Then we should just fail -sandbox on those systems.
>
>
> ...leaving the backdoor open.  Yes, we should instead fix things to hard
> fail when -sandbox cannot fully protect the process, rather than adding a
> tsync=off backdoor to permit execution in spite of the insecurity.

Ok, -sandbox will now require libseccomp 2.2.0 (not available in
Debian oldstable - so it will fail at configure time) and kernel >=
3.17 (error during start). If that sounds ok, I'll update the series.