On Mon, 2016-11-28 at 11:47 -0800, Eric Dumazet wrote:
> On Mon, 2016-11-28 at 20:34 +0100, Dmitry Vyukov wrote:
> > On Mon, Nov 28, 2016 at 8:04 PM, 'Andrey Konovalov' via syzkaller
>
> > > Hi Eric,
> > >
> > > As far as I can see, skb_network_offset() becomes negative after
> > > pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data) in nf_ct_frag6_queue().
> > > At least I'm able to detect that with a BUG_ON().
> > >
> > > Also it seems that the issue is only reproducible (at least with the
> > > poc I provided) for a short time after boot.
> >
> >
> > Eric,
> >
> > Is it enough to debug? Or maybe Andrey can trace some values for you.
>
> Well, now we are talking, if you tell me how many modules you load, it
> might help ;)
>
> nf_ct_frag6_queue is nowhere to be seen in my kernels, that might
> explain why I could not reproduce the bug.
>
> Let me try ;)
>
Might be a bug added in commit daaa7d647f81f3
("netfilter: ipv6: avoid nf_iterate recursion")
Florian, what do you think of dropping a packet that presumably was
mangled badly by nf_ct_frag6_queue() ?
(Like about 48 byte pulled :(, and/or skb->csum changed )
diff --git a/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
b/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
index f7aab5ab93a5..31aa947332d8 100644
--- a/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
+++ b/net/ipv6/netfilter/nf_defrag_ipv6_hooks.c
@@ -65,8 +65,8 @@ static unsigned int ipv6_defrag(void *priv,
err = nf_ct_frag6_gather(state->net, skb,
nf_ct6_defrag_user(state->hook, skb));
- /* queued */
- if (err == -EINPROGRESS)
+ /* queued or mangled ... */
+ if (err)
return NF_STOLEN;
return NF_ACCEPT;
