On Mon, 2017-07-17 at 14:30 -0700, Eric Dumazet wrote:
> On Mon, 2017-07-17 at 22:59 +0200, Paolo Abeni wrote:
> > Eric noticed that in udp_recvmsg() we still need to access
> > skb->dst while processing the IP options.
> > Since commit 0a463c78d25b ("udp: avoid a cache miss on dequeue")
> > skb->dst is no more available at recvmsg() time and bad things
> > will happen if we enter the relevant code path.
> >
> > This commit address the issue, avoid clearing skb->dst if
> > any IP options are present into the relevant skb.
> > Since the IP CB is contained in the first skb cacheline, we can
> > test it to decide to leverage the consume_stateless_skb()
> > optimization, without measurable additional cost in the faster
> > path.
>
> Also the problem was not skb->dst at all, but fact that
> skb->head can not be freed if IP options need later to be fetched.
>
> ( __ip_options_echo() ->
> sptr = skb_network_header(skb);
>
> ... -> use after free
Oh well, I read again the whole thing, and it seems you are right.
Acked-by: Eric Dumazet <[email protected]>
