Re: [PATCH] IB/IPoIB: Check the headroom size

[Paolo Abeni <pabeni-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Wed, 2017-04-26 at 20:52 +0800, Honggang LI wrote:
> On Wed, Apr 26, 2017 at 09:46:34AM +0200, Paolo Abeni wrote:
> > On Wed, 2017-04-26 at 00:50 +0300, Or Gerlitz wrote:
> > > so maybe @ least for the time being, we should be picking Hong's patch
> > > with proper change log and without the giant stack dump till we have
> > > something better. If you agree, can you do the re-write of the change
> > > log?
> > 
> > I think that Hong's patch is following the correct way to fix the
> > issue: ipoib_hard_header() can't assume that the skb headroom is at
> > least IPOIB_HARD_LEN bytes, as wrongly implied by commit fc791b633515
> > (my fault, I'm sorry).
> > 
> > Perhaps we can make the code a little more robust with something
> > alongside the following (only compile tested):
> > ---
> > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > index d1d3fb7..d53d2e1 100644
> > --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > @@ -1160,6 +1160,11 @@ static int ipoib_hard_header(struct sk_buff *skb,
> >                              const void *daddr, const void *saddr, unsigned len)
> >  {
> >         struct ipoib_header *header;
> > +       int ret;
> > +
> > +       ret = skb_cow_head(skb, IPOIB_HARD_LEN);
> 
> I don't think so. When this skb_under_panic arise, all slaves had been
> removed from a busy bonding interface, so it is better to immediately
> give up and return error.

I fear we can hit the same condition even with other, more convoluted,
setup (e.g. some kind of ip tunnel on top of ipoib) and the
skb_cow_head() check should be cheap, in the common case.

Anyway I'm fine even with the original fix, which has the advantage to 
minimize the side effects.

Paolo
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