Re: [RFC PATCH] udp: don't rereference dst_entry dev pointer on rcv

Eric Dumazet
2013-04-11T16:32:47Z

On Thu, 2013-03-14 at 16:29 +0100, Eric Dumazet wrote:
> On Thu, 2013-03-14 at 16:05 +0100, Eric Dumazet wrote:
> > On Thu, 2013-03-14 at 14:45 +0000, Tom Parkin wrote:
> > > On Thu, Mar 14, 2013 at 02:18:04AM +0100, Eric Dumazet wrote:
> > > > Ah thanks for this, as this definitely makes more sense ;)
> > > >
> > > > Could you try the following fix ?
> > > >
> > > > diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> > > > index b6d30ac..87f4ecb 100644
> > > > --- a/net/ipv4/ip_fragment.c
> > > > +++ b/net/ipv4/ip_fragment.c
> > > > @@ -529,6 +529,7 @@ found:
> > > > qp->q.meat == qp->q.len)
> > > > return ip_frag_reasm(qp, prev, dev);
> > > >
> > > > + skb_dst_force(skb);
> > > > inet_frag_lru_move(&qp->q);
> > > > return -EINPROGRESS;
> > > >
> > >
> > > Thanks Eric, with this patch I can no longer reproduce the oops :-)
> >
> > Thanks for testing.
> >
> > I am considering an alternative patch :
> >
> > We can drop the reference instead, and use the dst of the last skb.
> >
> > This would help to not dirty the dst refcount.
> >
> > I'll send an updated version.
> >
>
> OK, I tested the following one instead, please test it so that I can send an official patch.
>
> Thanks
>
> diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> index b6d30ac..2d23830 100644
> --- a/net/ipv4/ip_fragment.c
> +++ b/net/ipv4/ip_fragment.c
> @@ -529,6 +529,7 @@ found:
> qp->q.meat == qp->q.len)
> return ip_frag_reasm(qp, prev, dev);
>
> + skb_dst_drop(skb);
> inet_frag_lru_move(&qp->q);
> return -EINPROGRESS;
>
>

Short update : I do not understand yet why this patch is not working.

Normally, the reassembled packet should get the dst from the last skb
(the one completing the packet)...

I have to make more experiments.