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Date:   Wed, 9 Dec 2020 09:30:19 -0800
From:   Jakub Kicinski <>
To:     "Paraschiv, Andra-Irina" <>
Cc:     Stefano Garzarella <>,
        netdev <>,
        linux-kernel <>,
        "David S . Miller" <>,
        David Duncan <>,
        Dexuan Cui <>,
        Alexander Graf <>,
        Jorgen Hansen <>,
        Stefan Hajnoczi <>,
        Vitaly Kuznetsov <>
Subject: Re: [PATCH net-next v2 1/4] vm_sockets: Include flags field in the
 vsock address data structure

On Wed, 9 Dec 2020 17:17:56 +0200 Paraschiv, Andra-Irina wrote:
> > I agree that could be a problem, but here some considerations:
> > - I checked some applications (qemu-guest-agent, ncat, iperf-vsock) and
> >   all use the same pattern: allocate memory, initialize all the
> >   sockaddr_vm to zero (to be sure to initialize the svm_zero), set the
> >   cid and port fields.
> >   So we should be safe, but of course it may not always be true.
> >
> > - For now the issue could affect only nested VMs. We introduced this
> >   support one year ago, so it's something new and maybe we don't cause
> >   too many problems.
> >
> > As an alternative, what about using 1 or 2 bytes from svm_zero[]?
> > These must be set at zero, even if we only check the first byte in the
> > kernel.  
> Thanks for the follow-up info.
> We can also consider the "svm_zero" option and could use 2 bytes from 
> that field for "svm_flags", keeping the same "unsigned short" type.

Or use svm_zero as a gate for interpreting other fields?
If svm_zero[0]* == something start checking the value of reserved1?
* in practice the name can be unioned to something more palatable ;)

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