Re: [net-next PATCH v3 4/8] net: Change return type of sk_busy_loop from bool to void

[Paolo Abeni]

Hi,

On Thu, 2019-03-21 at 23:05 -0400, Christoph Paasch wrote:
> On Thu, Mar 21, 2019 at 12:43 PM Alexander Duyck
> <alexander.duyck@xxxxxxxxx> wrote:
> > On Thu, Mar 21, 2019 at 2:45 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
> > > The following - completely untested - should avoid the unbounded loop,
> > > but it's not a complete fix, I *think* we should also change
> > > sk_busy_loop_end() in a similar way, but that is a little more complex
> > > due to the additional indirections.
> > 
> > As far as sk_busy_loop_end we could look at just forking sk_busy_loop
> > and writing a separate implementation for datagram sockets that uses a
> > different loop_end function. It shouldn't take much to change since
> > all we would need to do is pass a structure containing the sk and last
> > pointers instead of just passing the sk directly as the loop_end
> > argument.
> > 
> > > Could you please test it?
> > > 
> > > Any feedback welcome!
> > 
> > The change below looks good to me.
> 
> I just tried it out. Worked for me!
> 
> You can add my Tested-by if you do a formal patch-submission:
> 
> Tested-by: Christoph Paasch <cpaasch@xxxxxxxxx>

Thanks for testing!

I'm trying to reproduce the issue locally, but I'm unable. I think that
the current UDP implementation is not affected, as we always ensure
sk_receive_queue is empty before busy polling. Unix sockets should not
be affected, too, as busy polling should not have any effect there
(sk_napi_id should be never >= MIN_NAPI_ID). Can you reproduce the
issue on an unpatched, recent, upstream kernel?

Can you please provide the syzkaller repro?

Thanks,

Paolo