Re: [PATCH net-next v2 1/4] vm_sockets: Include flags field in the vsock address data structure

[Paraschiv, Andra-Irina]

On 09/12/2020 19:30, Jakub Kicinski wrote:
> 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 ;)

Thanks for the shared option, that could be one case to reuse the 
reserved field, with a two phase check logic.

I'll give it a try to the option of having a new field "svm_flags" and 
the "svm_zero" updated and then send out a new revision. Just let me 
know if there are other updates needed / questions in the meantime.


struct sockaddr_vm {
    __kernel_sa_family_t svm_family;
    unsigned short svm_reserved1;
    unsigned int svm_port;
    unsigned int svm_cid;
    unsigned short svm_flags;
    unsigned char svm_zero[sizeof(struct sockaddr) -
                   sizeof(sa_family_t) -
                   sizeof(unsigned short) -
                   sizeof(unsigned int) - sizeof(unsigned int) -
sizeof(unsigned short)];
};


Thanks,
Andra



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